CHAPTER 1INTRODUCTION

1.1 OBJECTIVE

The composite will be fabricated using Kevlar and leather at macroscopic level. Since Kevlar is very expensive fibre hence tried to replace it by few layers of leather in prepared specimen which provide strength to specimen and helps to increase the impact strength of Kevlar composite. To check impact strength of developed we also designed impact testing rig which capable of performing low and high impact velocity test on prepared specimen. And their strength on different layer combination is measured.

1.2 INTRODUCTION OF MATERIALS

Materials can be of natural origin or synthetically processed and manufactured. According to their chemical nature they are broadly grouped traditionally into inorganic and organic materials. Their physical structure can be crystalline, or amorphous. Composites are combinations of materials assembled together to obtain properties superior to those of their single constituents. Composites are classified according to the nature of their matrix: metal, ceramic or polymer composites, often designated MMCs, CMCs and PMCs, respectively.

1.3 Types of material

It has been estimated that there are between 40 000 and 80 000 materials which are used or can be used in todays technology. Figure 3.3 lists the main conventional families of materials together with examples of classes, members, and attributes. For the examples of attributes, sufficient characterization methods are named.

Table 1: Material and its Family1.3.1 Processing of material

For their use, materials have to be engineered by processing and manufacture in order to fulfil their purpose as the physical basis of products designed for the needs of the economy and society. There are the following main technologies to transform matter into engineered materials: Machining, i. e. shaping, cutting, drilling, etc. Of solids, Net forming of suitable matter, e.g. liquids, moulds, Nanotechnology assembly of atoms or molecules.In addition to these methods, there are also further technologies, like surfacing and joining, which are applied to process, shape and assemble materials and products. The design of materials may also be supported by computational methods. It has been estimated that there are at least 1000 different ways to produce materials.

1.3.2 Properties of material

According to their properties, materials can be broadly classified into the following groups: Structural materials: engineered materials with specific mechanical or thermal properties Functional materials: engineered materials with specific electrical, magnetic or optical properties Smart materials: engineered materials with intrinsic or embedded sensors and actuators which are able to react in response to external loading, aiming at optimising the materials behaviour according to given requirements for the materials performance

1.4 Classification of Materials Characterization Methods

From a realization concerning the application of all material, a classification of materials characterization methods can be outlined in a simplified manner: Whenever a material is being created, developed, or produced the properties or phenomena the material exhibits are of central concern. Experience shows that the properties and performance associated with a material are intimately related to its composition and structure at all levels, including which atoms are present and how the atoms are arranged in the material, and that this structure is the result of synthesis, processing and manufacture. The final material must perform a given task and must do so in an economical and socially acceptable manner. These main elements: Composition and structure, Properties, PerformanceAnd the interrelationship among them defines the main categories of materials characterization methods to be applied to these elements, the materials characterization methods comprise analysis, measurement, testing, modelling, and simulation. These methods are described in detail in the following parts of this book: Methods to analyze the composition and structure of materials with respect to chemical composition, nano-scopic architecture and microstructure, surfaces and interfaces are compiled in Part B. Methods to measure the mechanical, thermal, electrical, magnetic and optical material properties are described in Part C. Methods of testing material performance through the determination of mechanisms which are detrimental to materials integrity, like corrosion, wear, bio-deterioration, materials-environment interactions, are outlined in Part D , which also contains the description of methods for performance control and condition monitoring. Methods of modelling and simulation by mathematical and computational approaches ranging from Molecular Dynamics Modelling to Monte Carlo simulation are described in Part E . Supporting the presentation of the materials characterization methods, in the Appendix relevant International Standards of Materials Measurement Methods are compiled.

1.3.5 Application of materials

For the application of materials, their quality, safety and reliability as constituents of products and engineered components and systems are of special importance. This adds performance attributes to the characteristics to be determined by materials measurement and testing. In this context the materials cycle must be considered. Figure 1 illustrates that all materials (accompanied by the necessary flow of energy and information) move in cycles through the techno-economic system: from raw materials to engineering materials and technical products, and finally, after the termination of their task and performance, to deposition or recycling. From the materials cycle, which applies to all branches of technology, it is obvious that materials and their properties to be determined through measurement and testing are of crucial importance for the performance of technical products. This is illustrated in Table 1 for some examples of products and technical systems from the energy sector.

Fig 1: Material Cycle

Table 2: Application examples of materials and relevant materials properties

1.5 Composite Material

Generally speaking, composites are hybrid creations made of two or more materials that maintain their identities when combined. The materials are chosen so that the properties of one constituent enhance the deficient properties of the other. Usually, a given property of a composite lies between the values for each constituent, but not always. Sometimes, the property of a composite is clearly superior to those of either of the constituents. The potential for such a synergy is one reason for the interest in composites for high-performance applications. However, because manufacturing of composites involves many steps and is labour intensive, composites may be too expensive to compete with metals and polymers, even if their properties are superior. In high-tech applications of advanced composites it should also be borne in mind that they are usually difficult to recycle.Advanced composite fabrics are those materials which have been used for a number of years in aerospace applications, replacing standard fibreglass fabrics. Todays materials - Kevlar, graphite, S glass and ceramics - are now making the transition from aerospace to homebuilt aircraft.

Table 3 - Properties of Composite Fibres

Of course, these materials are not generally usable as fibres alone, and typically they areimpregnated by a matrix material that acts to transfer loads to the fibres. The matrix also protects the fibres from abrasion and environmental attack. The matrix dilutes the properties to some degree, but even so very high specific (weight-adjusted) properties are available from these materials. Metal and glass are available as matrix materials, but these are currently very expensive and largely restricted to R&D laboratories. Polymers are much more commonly used, with unsaturated styrene-hardened polyesters having the majority of low-to-medium performance applications and epoxy or more sophisticated thermo sets having the higher end of the market. Thermoplastic matrix composites are increasingly attractive materials, with processing difficulties being perhaps their principal limitation.

1.5.1 Classification of composite

Composite are classified broadly in three forms according to their formation of process: Particle Reinforced Fiber Reinforced Structural These composite are further classified according to their properties which are given in fig2:

Fig 2: Classification of composite

1.5.2 Advantages Lower density (20 to 40%) Higher directional mechanical properties (specific tensile strength ratio of material strength to density) 4 times greater than that of steel and aluminium. Higher Fatigue endurance. Higher toughness than ceramics and glasses. Versatility and tailoring by design. Easy to machine. Can combine other properties (damping, corrosion). Cost.

1.5.3. Disadvantages Not often environmentally friendly. Low recyclability. Cost can fluctuate. Can be damaged. Anisotropic properties. Matrix degrades. Low reusability.

1.6 Sandwich panels:

When design requirements demand superior strength to weight ratios, sandwich structure is indicated. In addition to its high strength, inherent rigidity and minimum weight, sandwich provides the desirable side benefits of thermal and acoustical insulation.Sandwich, by its very nature, is generally used as sheeting or flat panel form, applied to open framework as a transverse web to carry shear loading. In other applications, it acts as a support diaphragm. It serves as both a primary and secondary load member. And, it is capable of transmitting extremely high loads when properly attached to the framework.Other applications take advantage of its favourably low weight-to-area ratio. Typically, these include curtain walls for decoration or the baffling of sound and light. Such applications do not generally consider the inherent load capabilities of the structure. Initially sandwich was used only in flat panel applications-a logical step away from plywood and other sheet panels. Recent improvements, however, in fabrication techniques and growing industry awareness of sandwich potential have spurred bolder forms. Today these include compound curves, skeletonised sections and many complex shapes previously considered impossible.

1.6.1 Principle

Sandwich-structured composites are a special class of composite materials with the typical features of low weight, high stiffness and high strength. Sandwich is fabricated by attaching two thin, strong, and stiff skins to a lightweight and relatively thick core.

1.6.2 Sandwich Structure Details

The principal form of sandwich structure is the honeycomb configuration. This consists of top and bottom face sheets attached to an inner core material; the core is made of hexagonal cells having walls perpendicular to the face sheet planes (See Figure 1). Many materials have been used successfully in honeycomb sandwich including aluminium, steel, high-temperature alloys, paper, wood, fiber glass and plastics. In some applications honeycomb cells are filled with a foam-in-place expanding plastic.Other forms of sandwich consist of face sheets bonded to homogeneous cores such as foamed plastics or wood. The variety is limited only by the state of the art and the imagination of the designer.

1.6.3 Method for joining

Regardless of form, the methods for joining the two face skins and inner core into a rigid member are numerous. By far the most widely used is that of adhesives applied by any of several techniques, and activated chemically or thermally.1. One method consists of brushing or spraying the adhesive film over one surface, and subsequently mating with the second part pre-coated with activator.2. A second approach use prefabricated sheet adhesive. Adhesive, rolled into a thin sheet partially cured to retain form, is stored between temporary non-adhering film, ready for use.3. Another bonding technique consists of applying the adhesive with rollers to a scrim or grid cloth, which is then cut to size and applied between core and face skins.4. Still another method simply calls for an even coating of adhesive on the face skin, which is subsequently activated and applied before setup.

In all methods, development of optimum strength depends on proper preparation of face skins and controlled application of adhesive to form optimum fillets between mated ends or faces of the core structure. Such bonding optimization achieves even transmission of loads from face skins to core without bond rupture.

Other forms of sandwich structure which offer excellent high temperature strength performance are composed of all steel honey-comb and face skin. These are most often resistance welded or of brazed construction.

1.6.4 TYPICAL SANDWICH PANEL APPLICATIONS

AIRCRAFT INDUSTRY Floor Panels Interior Walls Food Handling Galley Assemblies Wing Control Surfaces Passenger Storage Racks Thrust Deflector AssembliesAEROSPACE INDUSTRY Capsule Panels Ablative Shields for Nose Cones Instrumentation Enclosures & Shelves Bulkhead Panels Space Satellites

ELECTRONICS INDUSTRY Electronic Redone Construction Large Antenna or Disk Reflectors Military Electronic Instrumentation Shelters

TRANSPORTATION INDUSTRY Cargo Pallets Shipping Containers Refrigeration Panels Rapid Transit Floor Panels Special Automobile Bodies

CONSTRUCTION INDUSTRY Architectural Curtain Walls Partitions & Divider Panels Expandable Hospital Shelters

1.7 Advantages of Composites over metals:

Composites bring many performance advantages to the designer of structural devices, among which we can list:

Composites have high stiffness, strength, and toughness, often comparable with structural metal alloys. Further, they usually provide these properties at substantially less weight than metals: their specific strength and modulus per unit weight is near five times that of steel or aluminium. This means the overall structure may be lighter ,and in weight - critical devices such as airplanes or spacecraft this weight savings might be a compelling advantage. Composites can be made anisotropic, i.e. have different properties in different directions, and this can be used to design a more efficient structure. In many Structures the stresses are also different in different directions; for instance in closed end pressure vessels such as a rocket motor case the circumferential stresses are twice the axial stresses. Using composites, such a vessel can be made twice as strong in the circumferential direction as in the axial. Many structures experience fatigue loading, in which the internal stresses vary with time. Axles on rolling stock are examples; here the stresses vary sinusoid ally from tension to compression as the axle turns. These fatigue stresses can eventually lead to failure, even when the maximum stress is much less than the failure strength of the material as measured in a static tension test. Composites of then have excellent fatigue resistance in comparison with metal alloys, and often show evidence of accumulating fatigue damage, so that the damage can be detected and the part replaced before a catastrophic failure occurs. Materials can exhibit damping, in which a certain fraction of the mechanical strain energy deposited in the material by a loading cycle is dissipated as heat. This can be advantageous, for instance in controlling mechanically-induced vibrations. Composites generally offer relatively high levels of damping, and furthermore the damping can often be tailored to desired levels by suitable formulation and processing. Composites can be excellent in applications involving sliding friction, with tribological (wear) properties approaching those of lubricated steel. Composites do not rust as do many ferrous alloys, and resistance to this common form of environmental degradation may offer better life-cycle cost even if the original structure is initially more costly. Many structural parts are assembled from a number of subassemblies, and the assembly process adds cost and complexity to the design. Composites offer a lot of flexibility in processing and property control, and this often leads to possibilities for part reduction and simpler manufacture.

Of course, composites are not perfect for all applications, and the designer needs to be aware of their drawbacks as well as their advantages. Among these cautionary notes we can list:

Not all applications are weight-critical. If weight-adjusted properties not relevant, steel and other traditional materials may work fine at lower cost. Anisotropy and other special features are advantageous in that they provide a great deal of design flexibility, but the flip side of this coin is that they also complicate the design. The well-known tools of stress analysis used in isotropic linear elastic design must be extended to include anisotropy, for instance, and not all designers are comfortable with these more advanced tools. Even after several years of touting composites as the material of the future, economies of scale are still not well developed. As a result, composites are almost always more expensive often much more expensive than traditional materials, so the designer must look to composites various advantages to offset the extra cost. During the energy-crisis period of the 1970s, automobile manufacturers were so anxious to reduce vehicle weight that they were willing to pay a premium for composites and their weight advantages. But as worry about energy efficiency diminished, the industry gradually returned to a strict lowest-cost approach in selecting materials. Hence the market for composites in automobiles returned to a more modest rate of growth. Although composites have been used extensively in demanding structural applications for a half-century, the long-term durability of these materials is much less certain than that of steel or other traditional structural materials. The well-publicized separation of the tail fin of an American Airlines A300-600 Airbus after takeoff from JFK airport on November 12, 2001 is a case in point. It is not clear that this accident was due to failure of the tails graphite - epoxy material, but NASA is looking very hard at this possibility. Certainly there have been media reports expressing concern about the material, and these points up the uncertainty designers must consider in employing composites.

1.8 Impact Strength:Impact strength of any material is decided according to limit of sudden load or force applied on that material which it can wear without failure. It is used to limit the sudden load applied to it. As the considered composite is used as armour shield in which impact is generated by bullet or projectile, so there should be high impact strength in that material to protect human body from that impact. Kevlar have high impact strength but it is costly due to which we can substitute it with some other layer of material along with it.1.8.1 Impact property of sandwich panelsIn sandwich panels impact strength of any prepared composite can be altered or manipulated according to the requirements, because by using layers of different composite having specific properties, when they combine with other properties of each composite combines and gives another specific property which can be regulated and manipulated. To improve impact strength composite should be attached with another composite having high impact strength and to improve another properties of any developed sandwich composite following table 4 options can be used.Almost any structural materials which are available in the form of thin sheet may be used to form the faces of a sandwich panel. The properties of primary interest for the faces are : High stiffness giving high flexural rigidity High tensile and compressive strength Impact Resistance Surface finish Environmental resistance Wear resistance

Table 4: Properties of sandwich layers

CHAPTER 2LITERATURW REVIEW

Currently, Kevlar has many applications, ranging from bicycle tires and racing sails to body armor because of its high tensile strength-to-weight ratio; by this measure it is 5 times stronger than steel on equal weight basis .it is also used to make modern drumheads that hold up withstanding high impact. When used as woven material, it is suitable for mooring and underwater applications.We have gone through the previous papers and research works and those are in short:Body armor history at early stage:One of the earliest forms of soft body armor was animal skin. These offered more protection than other forms of armor with the advantage of light-weight. While this armor was quite effective for the threats of the time ,it was extremely heavy in weighing about 60 lbs.Body made of flak jacket:During World War II, the next step toward the soft body armor was when the military began using the flak jacket which was constructed of ballistic polyamides. This flak jacket helped shield personnel against munitions fragment but could not protect against most rifles and pistols.Today , nonwoven materials are being used in ballistic protection application because of their light weight and flexibility. The use of nonwoven fabrics in market began in the late 1960s. In a study by US Department of Defence, needle-punched nonwoven structure containing fibres was produced at one third the weight of woven fabric while retaining 80%of its ballistic resistance.[1]Fibrous materials for ballistic protection were significantly improved in the last few decades. Nylon fibers were leading the industry prior to 1970s. These fibres showed considerable non-linearity in stress-strain behaviour, with relatively high strain values to failure.[2]The current state-of the art body armor system being fielded by the US army is Interceptor, consisting of an outer tactial vest made of Kevlar KM2 weave that is able to stop high-powered handgun ammunition. The interceptor body armor system weighs 16.4 lbs. Where the previous body armor the flak jacket, weighted 25.1 lbs[5]. These polymers include aramids(e.g. Kevlar, Tawron, Technora ), highly oriented polythene (e.g. Spectra , Dyneema) and PBO(e.g. Zylon).[3]Experimental and numerical studies were carried out to determine the ballistic response of laminated Kevlars 29 and 129 composite panels, commonly used in protective body armor. These panels were impacted at velocities between 130 to 250m/s, which were below the penetration limit of panels. Experimental testing showed that kevlars 29 exhibited a lower BFS than Kevlar 129 at low velocities; however this changed for higher velocity impacts.[4]Carbon fibre sandwich composites have relatively low impact properties. In an attempt to improve upon the impact properties while maintaining the high stiffness, lightweight nature of the carbon fibre, Kevlar or hybrid were added to the face sheet. The impact and compression after impact data characterized how adding Kevlar or hybrid to the face sheet improved the sandwich composite performance during and after impact. The elastic modulidata helped characterize the loss in stiffness resulting from the addition of Kevlar or hybrid to the face sheet.[5]The test configuration described here was designed to be somewhat representative of fabric containment systems used in jet engines, while maintaining repeatability and simplicity in the test. The results show that under the conditions of this test, KEVLAR is able to absorb over twice as much energy as ZYLON when compared on an overall weight basis. The normalized energy absorbed is relatively insensitive to the number of layers of material. These results are consistent with results of those of an earlier study (Pereira and Revilock, 2004). This allows for a fairly simple design procedure if the assumption is made that the amount of energy absorbed per unit weight is independent of the number of layers of material. Except in cases where the yaw angle was high, the heavier weight Zylon material performed better than the lighter material, for the same overall weight. The energy absorbed by the fabric when normalized by the overall areal weight of the fabric ring is approximately linearly related to the presented area of the projectile at impact and, within the parameters of this study, is independent of the actual shape of the projectile. The limited testing performed under conditions of no fabric tension indicate that there is no significant difference in energy absorption between the two tested conditions. However, this should be validated by additional testing [6]A numerical model that describes the ballistic impact of a fragment - simulating projectile with fabric armor can be developed and it will more helpful for predicting the behavior of composite during impact test it also include that Kevlar having really best impact strength compared to other composite. The model predicts the residual velocity curve and the ballistic limit for ballistic impact of a single layer of fabric and also for woven fabric with the help of residual velocity we can easily calculate the energy absorbed lamina. The model accurately indicates the effect of changing the projectile kinetic energy and impact area as well as the effect on the impact process of changing the size of the panel boundary .[7]The proposed correlation on the energy absorption for Kevlar-29/polyester materials is well to predict the behaviour of energy impact for the composite material. The results inferred from the work presented described formulation of the energy absorption for composite material plate target against 7.62 mm of conical nose projectiles are suitable to compute accurate result within an error of maximum 3.6% of experimental work. The energy absorption of the composites were increased as the initial velocity increases and the numerical simulation was developed and combined with academic AUTODYN-software by explicit mesh to calculate time vs. velocity curves and energy absorption of kevlar29/polyester composite laminated plates. The impact energy absorptions of numerical simulation compared with experimental work which it was calculated by using equation. The good agreements of the comparisons with maximum errors were 3.6% .The increasing of thickness of plate affected on the behaviour of energy absorption and ballistic limit for the projectile that the structure obtained of 20mm thickness was optimum structure to resist the impact loading under 320m/s impact velocity as armour application [8].Kevlar-29, of various thread thicknesses (44, 66, 88 and 132 tex), was used as the through-thickness stitch fibre in the Interlaminar tension test (ITT) experiments. ITT loaddisplacement curves show similar features and could be characterised into various force and displacement parameters[9]Impact of a rigid sphere onto a high-strength plain-weave Kevlar KM2 fabric was modeled using LSDYNa. Results indicate that ballistic performance depends upon friction, elastic modulus and strength of the yarns. While friction improves ballistic performance by maintaining the integrity of the weave pattern, material properties of the yarns have a significant influence on the effect of friction. It is shown that fabrics comprised of yarns characterized by higher stiffness and strength relative to the baseline Kevlar KM2, exhibited a stronger influence on ballistic performance.[10]

The impact of three different projectiles (0.357 Magnum, 9-mm FMJ and 0.30 cal FSP) onto Kevlar was modeled using a commercial finite-element program. For one-layer and multiple-layer targets validation consisted on matching experimental data of pyramid formation recorded by an ultra-high-speed camera. This paper shows that the main features of the impact physics are well reproduced by the finite-element model. Prediction of ballistic limits for the 9-mm FMJ and FSP projectiles were within the scatter of the tests, while for the 0.357 projectile the difference was only 15%[11].The following conclusions were drawn from this study [12]: 1. The addition of Kevlar to the face sheet improved the maximum absorbed energy and average maximum impact force of the 1Kevlar4Kevlar samples by approximately 10% compared to the Carbon Fibre samples.2. The addition of hybrid to the face sheet improved the maximum absorbed energy of the 1K4K samples by approximately 5% and the average maximum impact force by approximately 14% compared to the CF samples.3. The addition of Kevlar or hybrid minimized the reduction in compression after impact strength when considering non-impacted samples and those that experienced complete striker penetration. However, the compression strength of the non-impacted samples was the highest for the CF samples. 4. The elastic moduli, E1 and E2, were reduced when Kevlar or hybrid were added to the facesheet. However, the reduction can be minimized to around 9% by replacing only one layer of carbon fiber with Kevlar or hybrid.5. The advantages and disadvantages of using 1K samples over CF are: Advantage:(a) 12.5% higher average absorbed energy (3545 J),(b) 11.9% higher average maximum force. Disadvantage(c) 12.7% lower non-impacted compressive strength,(d) reduction in stiffness .It was also mentioned that the Kevlar is best suited for aerospace it with stand up-to high temperature and its strength of impact is also high which is beneficial to protect it from unwanted condition it also help full in war condition to protect it from normal injury condition it can resist up-to 600m/s normally with metal impregmentation [13].The predicted damages by Autodyn-3D v12.1 software of the composite Kevlar29/epoxy-Al2O3 laminated plates perforating in with different (4, 8 and 12mm) thicknesses at range of (160 - 400 m/s) strike velocities of steel 4340 bullet, an example of (100 x 100 x 4mm) target under 240 m/s is much accurate and by which we can say that Kevlar have high impact strength compared to other composite material.[14]

The study presented here shows the significant effects of boundary conditions on the energy absorption mechanisms, and subsequent ballistic performance of fabric structures. Fixed boundaries promote a more rapid development of strain energy within the fabric and an increase in strain localisation, with relatively small panel deformation prior to complete impact energy absorption or failure. Free-free boundaries are more likely to promote gross translation of impact energy into kinetic energy of the panel with relatively little strain localisation and failure. The current version of the numerical model accurately predicts the trends and instantaneous values of the projectile velocity and energy absorption by the panel. However, the predictive capability of this model needs to be further enhanced by incorporation of realistic failure criteria that account for conditions that lead to the failure (perforation) of the fabric during impact.[15]The current and also new perspective ballistic materials can be evaluated with use of results of free fall test carried out with falling weight of suitable mass and shape, especially from the point of view of their stiffness that is one of the components of ballistic resistance against small arms projectiles, or its capability to eliminate deformation of rear side of Kevlar adjoined to the body. The deformation behaviour of the Kevlar is the essential criterion for the assessment of the ballistic resistance against small arms projectiles.[17]In the experimental field, studying the various failure modes and their mechanisms in woven fabrics is of interest as these results could be useful to design better performing armor systems. The failure modes for fabrics are numerous, coupled and dependent on many factors internal and external to the fabric. The progress of deformation for these fabrics in an in-service condition occurs at a very high speed and capturing all the details of interest requires the use of new technologies and equipment. The next general personal armors will incorporate sensors, micro-fluidic and micro-electronic devices embedded in them. The effect of these devices on the overall performance of the system presents interesting challenges. As armor systems become more and more complex with the use of novel materials and processes, modelling these new innovations become a challenge. With the advent of new computational tools it would be possible to simulate complex failure mechanisms and propagation of defects in fabric impact scenarios. The use of new materials and processes to augment the performance of existing aramid fabrics is a field which will see a sustained focus in the near future. The history of armor design amply demonstrates that it has always kept pace with the progress in weapons design and the aim has always been to remain one step ahead in both fields.[18]It can be seen that 40 plies of Kevlar-49 are enough to stop both types of bullets, while 45 plies (M-16) and 48 plies (AK-47) of Kevlar-49 are required for this. On the right vertical axis, N* p , the volume of penetrated plies (trauma) is pointed in the case when the bullet is stopped by the target.[19]

CHAPTER 3RAW MATERIAL AND EQUIPMENTS3.1 Raw materialThe composite is prepared which having high impact strength; a sandwich composite is to be prepared to prepare that composite we require three materials one is Kevlar, leather and one adhesive material (araldite).3.2 Kevlar

Kevlaris the registeredtrademark for apara-aramidsynthetic fiber, related to otheraramidssuch asNomexandTechnora. Developed atDuPontin 1965,this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires. Typically it is spun into ropes orfabricsheets that can be used as such or as an ingredient incomposite materialcomponents.Currently, Kevlar has many applications, ranging from bicycletiresandracing sailstobody armourbecause of its hightensile strength-to-weight ratio; by this measure it is 5 times stronger than steel on an equal weight basis.[2]It is also used to make moderndrumheadsthat hold up withstanding high impact. When used as a woven material, it is suitable for mooring lines and other underwater applications.A similar fiber calledTwaronwith roughly the same chemical structure was developed byAkzoin the 1970s; commercial production started in 1986, and Twaron is now manufactured byTeijin.

3.1.1 Fabrication Process:As explained earlier, Kevlar is a polymer. A polymer is comprised of monomers, or simply individual molecules. The monomers are attached in a series of chains that creates the polymer. A polymer is synthetic or man-made, which means it is prepared in a lab.Kevlar is also a carbon-basedaramid. The name aramid is an abbreviation foraromaticpolyamide.

Fig 3: Monomers of Kevlar

Kevlar does not start out as a polymer. Like all other synthetic substances, it has to undergo a fabrication process. A condensation reaction with a diamine, a terephthalic acid and sulphuric acid create the substance that will become the final product. A diamine is any organic compound containing two amino groups (NH2) while a terephthalic is a carboxylic acid that consists of abenzenering in its molecule.

Fig 4: Molecular structure of KevlarThe substance that the condensation reaction has created is called the intermediate. In order to make the Kevlar, it must be drawn. Drawing is essentially stretching the product at a set temperature to strengthen the product. Once the intermediate has been drawn, poly-para-phenylene terephthalamide is created, or simply, Kevlar 29. In order to become a stronger product, Kevlar 29 must be hot-drawn at 400C. Hot drawing allows higher degrees of strength and crystallinity and this creates Kevlar 49, the strongest type of Kevlar. Fig 5: Fiber of KevlarOnce the Kevlar has been drawn it must be spun to produce the filaments. In order to do so, it is extruded though a spinneret. After this, it is washed and neutralized and then taken to be dried. The final step of the manufacturing process is winding the Kevlar into spools. This creates a more flexible approach for the buyers so that they can use the threads for their needs instead of buying the Kevlar in sheets.3.1.2 Properties:

Kevlar is such a successful material due to its tremendous tensile strength (the amount of stretching it can withstand before breaking). The reason why it is so strong is mainly due to the straight fibres that it possesses. In order to fully understand this concept, crystallinity must be taken in to account.

Cristallinity is a property of polymers. When a polymer is not arranged in an orderly manner it is called amorphous. Amorphous polymers are polymer chains that are tangled up and do not follow a strict pattern. They give the polymer the ability to bend without breaking, an important part in Kevlar. If a polymer is arranged in a neat, orderly manner the polymer is considered crystalline. Crystallinity gives the polymer strength, but crystallinity tends to make the polymer extremely brittle. For instance, Plexiglas is easily susceptible to shattering due to its high crystallinity and weak amorphousness. Yet Lexan is much more shatter resistant due to its lower crystallinity and higher amorphousness. By mixing the two characteristics, sacrificing strength for flexibility or flexibility for strength, an ideal substance can be created. When scientists look for high tensile strength fibres, they search for a polymer with trans- conformations and try to avoid ones with cis- conformations. Cis- conformations can be a problem due to the fact that they have a tendency to cause unwanted bends in the polymer chain. Bends are a problem due to the fact that they weaken the fibres and lower the strength and crystallinity. Trans- conformations are wanted and useful thanks to the fact that they create a fully stretched out and straight polymer chains. With many polymers, even the slightest amount of energy can change the conformations. Kevlar is an exception. It tends to keep its trans- conformations and rarely form cis- conformations. This is due to the shape of the aromatic rings that Kevlar possesses. When Kevlar attempts to bend into the cis- conformation, the hydrogens on the aromatic rings cannot be manipulated to fit in the gap, they take up too much space. This is why Kevlar tends to remain in the trans- conformation. The aromatic hydrogens have plenty of room and with this trans- conformation and the molecule tend to stay in a nice and long fibre.

Fig 6: Polymer structure of KevlarAnother important characteristic about Kevlar is that it can make strong types of intermolecular forces, hydrogen bonds. Hydrogen bonds are responsible for keeping multiple fibre strands "glued together". The polar amide groups on adjacent chains bond together with magnetic charges. The oxygen atom can be considered negative and the hydrogen atom positive. The negative atom attracts the positive atom and a hydrogen bond is created.

Fig 7: Cis and Trans view of Kevlar molecule

All these properties give Kevlar many advantages over other polymers. It has a tremendously high tensile strength and is five times stronger than steel. Underwater, Kevlar is up to 20 times stronger than steel! Temperature-wise, Kevlar exceeds the performance of many other materials. It can withstand temperatures up to 300C while retaining its strength properties. Even at -196C Kevlar shows no signs of embrittlement or loss of strength. Almost all solvents are ineffective at degrading Kevlar except the few powerful acids.However, Kevlar is not indestructible. One of the factors that can impede and degrade its performance is ultraviolet light. The degradation is small though, only the outside layer is affected and not the inside one. Even the performance is not affected too much; the Kevlar retains most of its strength and rigidity.3.1.3 Properties and advantages Very high tensile strength- tensile strengthof about 3,620 MPa. Low density- relative densityof 1.44 Highly impact resistant Resistant to wear and abrasion Thermally stable: Kevlar maintains its strength and resilience down to cryogenic temperatures (196 C); in fact, it is slightly stronger at low temperatures. At higher temperatures the tensile strength is immediately reduced by about 1020%, and after some hours the strength progressively reduces further. For example at 160 C (320 F) about 10% reduction in strength occurs after 500 hours. At 260 C (500 F) 50% strength reduction occurs after 70 hours. No affect of water or moisture- Kevlar remained "virtually unchanged" after exposure to hot water for more than 200 days and its super-strong properties are "virtually unaffected" by moisture. Can sustain high temperatures- Kevlar does not melt. It decomposes at relatively high temperatures of about 450 0C. No shrinkage- Kevlar does not shrink like other organic fibers when exposed to hot air or hot water.

Table 5: Properties of Kevlar

3.1.4 Applications of KevlarKevlar is used in a number of applications, be it in industry, law enforcement or in general consumer products. The products made with Kevlar are part of daily life.Another use for this material is in the production of sporting goods. Some components of Kevlar are used in an array of rackets, such as tennis, badminton and squash rackets. Canoes and kayaks were also improved when Kevlar technology was applied there. They are now more durable during impacts. Kevlar is also used in a variety of skis, snowboards, skateboards, gloves, helmets and shoes.3.1.5 Some other application CryogenicsKevlar is often used in the field of Cryogenics for its low thermal conductivity and high strength relative to other materials for suspension purposes. Most often used to suspend a paramagnetic salt enclosure from a superconducting magnet mandrel in order to minimize any heat leaks to the paramagnetic material. It is also used a thermal standoff or structural support where low heat leaks are desired. ArmorKevlar is a well-known component ofpersonal armorsuch ascombat helmets,ballistic face masks, andballistic vests. ThePASGT helmet and vestused by United Statesmilitary forces from the 1980s into 2005 both have Kevlar as a key component, as do their replacements. Other military uses include bulletproof facemasks used by sentries andspall linersused to protect the crews ofarmored fighting vehicles. EvenNimitz-class aircraft carriersinclude Kevlar armor around vital spaces. Related civilian applications include Emergency Service's protection gear if it involves high heat (e.g., tackling a fire), and Kevlar body armor such as vests for police officers, security, andSWAT. Personal protectionKevlar is used to manufacture gloves, sleeves, jackets, chaps and other articles of clothingdesigned to protect users from cuts, abrasions and heat. Kevlar based protective gear is often considerably lighter and thinner than equivalent gear made of more traditional materials. Sports equipmentIt is used as an inner lining for somebicycle tiresto prevent punctures, and due to its excellent heat resistance, is used forfire poiwicks. In table tennis, plies of Kevlar are added to custom ply blades, or paddles, in order to increase bounce and reduce weight. It is used formotorcycle safety clothing, especially in the areas featuring padding such as shoulders and elbows. It was also used as speed control patches for certainSoap Shoesmodels. Audio equipmentKevlar has also been found to have useful acoustic properties for loudspeaker cones, specifically for bass and midrange drive units.]Additionally, Kevlar has been used as a strength member in fiber optic cables such as the ones used for audio data transmissions. StringsKevlar can be used as an acoustic core on bows forstring instruments.Kevlar's physical properties provide strength, flexibility, and stability for the bow's user. To date, the only manufacturer of this type of bow isCoda Bow. DrumheadsKevlar is sometimes used as a material on marching snare drums. It allows for an extremely high amount of tension, resulting in a cleaner sound. There is usually a resin poured onto the Kevlar to make the head airtight, and a nylon top layer to provide a flat striking surface. Woodwind reedsKevlar is used in the woodwind reeds of Fibracell. The material of these reeds is a composite of aerospace materials designed to duplicate the way nature constructs cane reed. Very stiff but sound absorbing Kevlar fibers are suspended in a lightweight resin formulation. Frying pansKevlar is sometimes used as a substitute forTeflonin some non-stick frying pans. Rope, cable, sheathThe fiber is used in woven rope and in cable, where the fibers are kept parallel within apolyethylenesleeve. The cables have been used insuspension bridges such as the bridge atAberfeldyinScotland. They have also been used to stabilize cracking concrete cooling towers by circumferential application followed by tensioning to close the cracks. Electricity generationKevlar was used by scientists atGeorgia Institute of Technologyas a base textile for an experiment in electricity-producing clothing.. Building constructionA retractable roof of over 60,000 square feet (5,575 square meters) of Kevlar was a key part of the design ofMontreal's Olympic stadiumfor the1976 Summer Olympics. It was spectacularly unsuccessful, as it was completed ten years late and replaced just ten years later in May 1998 after a series of problems. BrakesThe chopped fiber has been used as a replacement for asbestos inbrake pads. Dust produced from asbestos brakes is toxic, while aramids are a benign substitute. Expansion joints and hosesKevlar can be found as a reinforcing layer inrubberbellowsexpansion jointsand rubberhoses, for use in high temperature applications, and for its high strength. It is also found as a braid layer used on the outside of hose assemblies, to add protection against sharp objects. Particle physics experimentA thin Kevlar window has been used by theNA48 experimentatCERNto separate a vacuum vessel from a vessel at nearly atmospheric pressure, both 192cm in diameter. The window has provided vacuum tightness combined with reasonably small amount of material (only 0.3% to 0.4% ofradiation length). Smart phonesTheMotorola Droid RAZRhas a Kevlar back plate, chosen over other materials such as carbon fiber due to its resilience and lack of interference with signal transmission.

3.1.6 Bulletproof VestsOne of the most popular applications for Kevlar is with bulletproof vests. Over the years, bulletproof vests have saved countless lives of military personnel, other law enforcement officers and civilians alike. To date it has saved more than 2,749 police officers. Thanks to the invention of Kevlar, bulletproof vests will continue to do so for years to come.

Fig 8: Kevlar application as bulletproof vests

Bulletproof vests are very simple. They consist of a carrier, plastic film and Kevlar. In order to be successful at stopping projectiles, there must be layers of material. These layers are made of Kevlar and plastic film. The plastic film surrounds the woven Kevlar to aid in the energy transmission and absorption. The layers are then placed between the outer shells, also called the carrier. The carrier is what you would see if you saw someone wearing the vest.When a projectile makes contact with the vest, the kinetic energy is dispersed along the woven Kevlar layers. The first layer softens the impact by using the woven pattern's horizontal and vertical tethers. When the projectile hits a vertical tether, every horizontal tether is pulled. This distributes some of the projectile's energy along its tightly woven tethers before the layer breaks. The next layer then absorbs the energy and the process continues until the kinetic energy is zero. Since most non-armour piercing bullets are lead and lead is a soft metal, the bullets that come into contact with the vest deform further reducing the bullet's energy. This is called "mushrooming". 3.3 LEATHERLeatheris an extraordinarily differently durable and very flexible material created by thetanningofputrescibleanimalrawhideandskin, basically primarilycattle hide. Leather is inherently flexible, extremely durable, does not tear easily, is lightweight and can resist being punctured.3.3.1 TypesIn general, leather is sold in four forms:Full-grainleather refers to hides that have not been sanded, buffed, or snuffed (as opposed to top-grain or corrected leather) to remove imperfections (or natural marks) on the surface of the hide. The grain remains allowing the fiber strength and durability. The grain also has breathability, resulting in less moisture from prolonged contact. Rather than wearing out, it will develop apatinaover time. High quality leather furniture and footwear are often made from full-grain leather. Full-grain leathers are typically available in two finish types:anilineand semi-aniline.Top-grain(Most common type used in upper end leather products)leather is the second-highest quality. It's had the "split" layer separated away, making it thinner and more pliable than full-grain. Its surface has been sanded and a finish coat added to the surface which results in a colder, plastic feel with less breathability, and will not develop a natural patina. It is typically less expensive and has greater resistance to stains than full-grain leather, so long as the finish remains unbroken.Corrected-grainleather is any leather that has had an artificial grain applied to its surface. The hides used to create corrected leather do not meet the standards for use in creating vegetable-tanned or aniline leather. The imperfections are corrected or sanded off, and an artificial grain impressed into the surface and dressed with stain or dyes. Most corrected-grain leather is used to make pigmented leather as the solid pigment helps hide the corrections or imperfections. Corrected grain leathers can mainly be bought as two finish types: semi-aniline and pigmented.Splitleather is leather created from the fibrous part of the hide left once the top-grain of therawhidehas been separated from the hide. During the splitting operation, the top grain and drop split are separated. The drop split can be further split (thickness allowing) into a middle split and a flesh split. In very thick hides, the middle split can be separated into multiple layers until the thickness prevents further splitting. Split leather then has an artificial layer applied to the surface of the split and is embossed with a leather grain(bycast leather). Splits are also used to createsuede.3.3.2 Production processesThe leather manufacturing process is divided into three fundamental sub-processes:preparatory stages,tanning, andcrusting. All true leathers will undergo these sub-processes. A further sub-process, surface coating can be added into the leather process sequence, but not all leathers receive surface treatment. Since many types of leather exist, it is difficult to create a list of operations that all leathers must undergo.Thepreparatory stagesare when the hide/skin is prepared for tanning. Preparatory stages slay include: preservation, soaking, liming, unhairing, fleshing, splitting, relining,deleing,bating,degreasing, frizzing,bleaching,pickling, and depickling.Tanningis the process which converts theproteinof the raw hide or skin into a stable material which will not putrefy and is suitable for a wide variety of end applications. The principal difference between raw hides and tanned hides is that raw hides dry out to form a hard inflexible material that when re-wetted (or wetted back) putrefy, while tanned material dries out to a flexible form that does not become putrid when wetted back. Many different tanning methods and materials can be used; the choice is ultimately dependent on the end application of the leather. The most commonly used tanning material ischromium, which leaves the leather, once tanned, a pale blue color (due to the chromium); this product is commonly called "wet blue". The hides once they have finished pickling will typically be betweenpH2.8 and 3.2.At this point, the hides would be loaded in a drum and immersed in a float containing the tanning liquor. The hides are allowed to soak (while thedrumslowly rotates about itsaxle) and the tanning liquor slowly penetrates through the full substance of the hide. Regular checks will be made to see the penetration by cutting the cross-section of a hide and observing the degree of penetration. Once an even degree of penetration exists, the pH of the float is slowly raised in a process called basification. This basification process fixes the tanning material to the leather and the more tanning material fixed, the higher the hydrothermal stability and increasedshrinkagetemperature resistance of the leather. The pH of the leather when chrome tanned would typically finish somewhere between 3.8 and 4.2.Crustingis the process by which the hide/skin is thinned, retanned, and lubricated. Often a coloring operation is included in the crusting subprocess. The chemicals added during crusting must be fixed in place. The culmination of the crusting subprocess is the drying and softening operations. Crusting may include the following operations:wetting back, sammying, splitting, shaving, rechroming,neutralization, retanning,dyeing, fatliquoring, filling, stuffing, stripping,whitening, fixating, setting, drying, conditioning, milling, staking, and buffing.

3.3.3 Properties of Leather High tensile strength Resistance to tear High resistance to flexing High resistance to puncture Good heat insulation Resistance to fire 3.4 Cow Leather

Cow leather known for its strength and durability. It is the most abundantly available leather. This aniline cow leather maintains its integrity and also takes the shape of the wearer. Also known as aniline leather, this cow leather gives extra comfort with everyday use. Cow leather is easy to care and is resistant to water and dirt.

3.4.1 Top Grain CowhideThis is a layer, which is on the outside of the animal with hair growing out of it. It has beautiful smooth surface with strength and flexibility. It is a premium product for applications where durability and dexterity, both are essential.

3.4.2 Split CowhideThis is a layer below the top grain. It can be used as suede as well as grain leather. The finished product has a soft feel to it.

3.4.3 Characteristics of Cowhide Leather It is strong and tough. It is durable. It is easy to maintain. It is resistant to water and dirt. It takes the shape of the wearer. It is comfortable to wear.3.4.4 Uses of Cowhide Leather

This Leather is commonly used as Shoe Upper leather. It is also used as garments, ladies bags, upholstery, belts, etc.

3.5 Goat Leather

Goatskin leather is very soft and supple. Soft goat leather is comfortable as well as durable. The soft goat leather contains a pleasing pebble grain which adds to its beauty. It colours beautifully and is identified by a distinctive texture of ridges and furrows in the grain.Usually there are two types of goatskin leather such as straight grained and crushed. Straight-grained goatskin leather is produced by rolling a damp skin, so that all the grains run in the same direction. Crushed goatskin leather is produced by flattening the ridges with ironing, rolling or plating.

3.5.1 Characteristics of Goatskin Leather It is soft and supple It is lightweight and flexible It is comfortable It is durable It is water-resistant

3.5.2 Uses of Goatskin Leather Goatskin leather is widely used as a shoe upper leather and in providing other soft goat products Goatskin leather is also used for garments, gloves, wallets, brief case, bags, etc.

3.6 Buffalo Leather

Buffalo hide is strong and tough and has an interesting texture with a rubbery feel and pebbly features to its leather. Buffalo leather is very thick and can be sliced into 2 to 3 layers before tanning it into leather. The main characteristic of the hide is the originality in its grain. Buffalo Leather is also known as nubuck buffalo leather and glazed buffalo leather is used as shoe upper leather for high end products. It is widely used for Institutional Shoes such as for Army, Police, Factory workers etc.

Fig 9: Goat leather3.6.1 Characteristics of Buffalo Hide It is strong and tough It is thicker than cow leather It looks attractive It is soft and has pebbly features It has rubbery feel

3.6.3 Uses of Buffalo Hide Shoe uppers. Institutional Shoes for Army, Police, Factory workers etc Furniture Belts Wristwatch strap Bookbinding and casing

3.7 AralditeAraldite is a multipurpose, two components, room temperature curing, paste adhesive of high strength and toughness. It is suitable for bonding a wide variety of metals, ceramics, glass, rubber, rigid plastics and most other materials in common use. It is a versatile adhesive for the craftsman as well as most industrial applications.

Fig 10: Araldite 3.7.1 Key properties

High shears and peel strength Tough and resilient Good resistance to dynamic loading Bonds a wide variety of materials in common use3.7.2 Product data

MixedBATable 6: Product details of araldite

CHAPTER 4

MATERIALS AND METHODS

4.1 Method of Development

To develop sandwich composite there are lots of method in which one of them is wet lay-up method which is most effective and cheap process to develop sandwich composite.

4.2 Wet Lay-up Method

This is one of the oldest but still one of the most commonly used methods to manufacture sandwich components with composite faces. This method is very flexible yet labour-intensive and thus best suited for short production series of especially large structures. The wet-layup may perform either by hand lay-up or spray-up. The process uses a single-sided mould, male or female, which is treated with the mould release agent. Normally, a neat resin layer, a gel coat, is deposited directly onto the mould which is allowed to gel before the lamination starts. The gel-coat resin usually is of high -quality and has good environmental resistance, thus allowing the use of a lower-quality, cheaper resin within the actual laminate. The gel-coat also produces, a smooth cosmetically appealing surface that hides the reinforcement structure, which otherwise may be visible on the composite surface.

In case of vacuum assisted wet layup the core is placed on top of the laminated but not cross-linked laminate whereupon the vacuum is applied and the laminate is cross-linked. the "top" laminate is then laminated directly onto the core and vacuum preferentially drawn to improve compaction. Alternatively the core and the top laminate may be applied concurrently before applying vacuum. Rolling on top of the vacuum bags is common in order to work out voids and remove excess resin.The wet lay-up methods Require small capital investments Typically use resins that cross-link at room temperature with little or not applied pressure and that are tolerant to variations in processing temperature Use simple tooling due to modest cross-linking requirements Are labour intensive Are cost - effective for short production series and prototype production Are suitable for any size structures, notably very large. Bring on work health concerns due to the active chemistry of the resin.

Applications of wet lay-up methods include: Motor and sailing yachts Mine-sweepers and high-speed passenger ships Refrigerated truck and railroad containers Storage tanksThe main difference between hand laid-up and sprayed-up composites are due to the differences in labour costs and mechanical properties. The lower labour cost of spray-up implies that longer series are economically feasible and the inferior mechanical properties achieved mean that commodity-type products are more common. Sprayed-up sandwich components include small pleasure boats and storage containers and tanks.

4.2.1 Hand lay-up methodThe hand (wet) lay-up is one of the oldest and most commonly used methods for manufacture of composite parts. Hand lay-up composites are a case of continuous fibre reinforced composites. Layers of unidirectional or woven composites are combined to result in a material exhibiting desirable properties in one or more directions. Each layer is oriented to achieve the maximum utilisation of its properties. Layers of different materials (different fibres in different directions) can be combined to further enhance the overall performance of the laminated composite material. Resins are impregnated by hand into fibres, which are in the form of woven, knitted, stitched or bonded fabrics. This is usually accomplished by rollers or brushes, with an increasing use of nip-roller type impregnators for forcing resin into the fabrics by means of rotating rollers and a bath of resin. Laminates are left to cure under standard atmospheric conditions. A typical hand lay-up method is shown in Fig.

Fig 11: Wet Hand Lay-up Process

Some of the advantages and disadvantages of hand lay-up of composite structures are as follows:

4.2.2 Advantages Design flexibility. Large and complex items can be produced. Tooling cost is low. Design changes are easily effected. Sandwich constructions are possible. Semi-skilled workers are needed. Higher fibre content and longer fibres than with spray lay-up.

4.2.3 Disadvantages Only one moulded surface is obtained. Quality is related to the skill of the operator. Low volume process. Longer cure times required. Resins need to be low in viscosity to be workable by hand. This generally compromises their mechanical/thermal properties. The waste factor can be high. 4.3 Specimen development4.3.1Procurement of the materials Kevlar From GSP SUPERB TECHNOLOGY R-10 B, STREET No.11, Industrial Area Anand parbat, New delhi-110005 Leather and binding solution From Zakir bhai leathers Phool wali gali, mool gunj, kanpur4.4 Specification of materials4.4.1 Kevlar: Grade: Kevlar 49;Thickness: 0.02mmChemical name: poly-para-phenylene terephthalamide

Fig 12: Kevlar 49Colour: Golden;Elastic modulus: 131 GPa;Density: 1.44 Areal density: 0.2275 g/cm2Ultimate stress: 3620 Pa;Passion ratio: 0.44;

4.4.2 Leathers:Type (Grain)Goat (Top Grain )Buffalo (Top Grain)Cow (Top Grain)

Elastic modulus GPa454847

Tensile strength Mpa504538

Poisson ratio 0.560.890.78

Density g/cm36.787.897.85

Areal density g/cm20.4890.7860.783

Thickness mm11.021.03

Table 7: Leathers and its Properties

Fig 13: Goat leather (top and bottom view)

Fig 14: Buffalo leather (top and bottom view)

Fig 15: Cow leather (top view)

4.5 Equipment required: Fig 16: Clamping deviceHammer Measuring scale Clamping plates (fig 18) cutter scissors Pressing machine (fig19 ) Adhesive material (araldite) Weighing Machine

Fig 17: Pressing machine

4.6 WORK PIECE FABRICATIONS STEP 1. Using a cutter and a plier, prepare the individual component required for the specimen .i.e. cut out leather(cow, goat, buffalo) and Kevlar according to the required dimensions(120x120mm2) (fig 20).

Fig 18: Cut pieces of Kevlar and Leather. STEP 2. After cleaning the bonding surfaces, apply the araldite to individual layers of Kevlar and leather. Now wait for these layers to soak the adhesive araldite. STEP 3. Now, place alternate layers each of Kevlar, and leather to form a composite of these constituents.

Fig 19: Sandwiched layers of Kevlar and leather STEP 4. After completing one specimen, put it under a clamp and apply pressure on it with the help of pressing machine (fig 20) to provide better support between the individual layers of the specimen otherwise it will bend. STEP 5. Using a plier and a cutter, cut out, further, the pieces of Kevlar, and leather to complete the alternate layering of the constituents to form more number of specimen.

Fig 20: Different Specimens

Kevlar fiber

Araldite

SandwichingClamping force

Testing of w/pLeather

Work piece inspection

Fig 21: Process of fabrication

Different composition of composite is prepared by using alternate layer sandwich method; In this method we are using Kevlar and leather layer alternatively in different numbers.

4.7 Specimens specifications:The entire specimens have same dimensions: Length 120 mm, Width 120 mmSpecimen 1:- 1 layers of Kevlar + 4 layer of Goat leather (fig 22)Specimen 2:- 3 layers of Kevlar + 4 layers of Goat leather (fig 23)Specimen 3:- 1 layers of Kevlar + 4 layers of Buffalo leather (fig 24)Specimen 4:- 3 layers of Kevlar + 4 layers of Buffalo leather (fig 25)Specimen 5:- 1 layers of Kevlar + 4 layers of Cow leather (fig 26)Specimen 6:- 3 of Kevlar + 4 layers of Cow leather (fig 27)Figures of specimen:

Fig 22 Specimen 1:- 1 layers of Kevlar + 4 layer of Goat leather

Fig 23 Specimen 2:- 3 layers of Kevlar + 4 layers of Goat leather

Fig 24 Specimen 3:- 1 layers of Kevlar + 4 layers of Buffalo leather

Fig 25 Specimen 4: 3 layers of Kevlar + 4 layers of Buffalo leather Fig 26 Specimen 5: 1 layers of Kevlar + 4 layers of Cow leather

Fig 27 Specimen 5: 3 layers of Kevlar + 4 layers of Cow leather

CHAPTER 5DESIGN AND FABRICATION OF IMPACT TETSING RIG 5.1 INTRODUCTIONThere are lots of impact testing machines are available in market by which impact strength of any metals can be easily determined such as; Izod Impact test , Charpy Impact test, Drop test Ballistic impact test. Above three test provides better result in metals, last one can be used for both composite and metals in ballistic impact testing we have to find out impact strength of material by performing Low impact velocity test and High impact velocity test.

Ballistics testing is a form of high speed testing that is used to test the ultimate impact strength of composites. High velocity testing is characterized by an impactor travelling in the range of 150-800 m/s. For high velocity impact conditions, structural response is less important than in a low velocity case, and the damage area is more localized; therefore the geometrical considerations are less important. Ballistics testing consists of firing a high speed projectile at an object and determining after the impact how localized the damage is. This is a good method for testing impact resistance of composites, and has been used for testing products such as composite armour.

5.2 Ballistic testing set-up

To perform ballistic impact testing there are lots of conventional methods are used in which a projectile or impactor is projected at a velocity which directly strikes to target after travelling through thickness of target when projectile comes out it have some reduction in velocity it implies that lost in energy in form of decrease in velocity is stored in target which is equivalent to the impact strength of target.This type of impact testing is performed by following methods:

By use of conventional gun. By use of air compressed gun. By mechanical set-up.

In first method by direct use of gun which is used in war to perform high impact testing. Gun is loaded with bullet is directly projected on target. After impact testing residual velocity is calculated and kinetic energy corresponding to residual velocity is subtracted from initial energy. Reduction in energy is considered as absorbed energy which is impact strength of target material. Which is not convenient at college level and use of it is considered as illegal.In second setup air is used which act as medium to provide energy to bullet or impactor that impactor strikes to the target and remaining calculation is same as in previous setup. In this set up projectile is moving with the help of air which provide force or impulse to projectile.Firstly air is compressed in compressor that compressed air is blown into the piston cylinder arrangement in which a spring is attached to it which is compressed up-to a level according to the required velocity. After releasing spring a plunger attached to it strikes to the bullet or impactor that impactor gets motion and started toward target. This set-up in convenient at college level but it requires more time and more expensive.

Third set-up is more reliable and convenient at college level in which we can directly change velocity as required with replacement of spring according to the calculated stiffness spring. In it whole spring is designed according to designed spring design of gun case and barrel is designed according to calculated diameter of spring with gap between inner diameter of case due to which there is reduction in friction. It consist mainly three parts: Design of spring. Design of casing. Design of striker.Calculation of design of each part is given below:

5.2.1 Design of spring: In design of spring we have to calculate spring constant of spring according to desired velocity;Assume we require velocity V to impact projectile on target, then according to conservation of energy spring energy is transferred to impactor:

Where; K=stiffness of spring; x= deflection (fixed 10~20cm);m=mass of impactor (8~10 gm);v=velocity of projectile; Since velocity of projectile is fixed and deflection is also fixed; mass of projectile is also considered according to standard. Spring material is also considered according to availability in market.

Fig 28: details view of springWe have considered stainless steel as material and 150mm deflection; now if we required velocity 250 m/s with mass of 8.8 gm:Hence;

K=24444.44 N/mmAfter calculating spring constant now we have to proceed for cal calculation of spring:Modulus of rigidity of spring Es= 80~90 GN/m2 (stainless spring)Working stress of stainless steel is 500 N/mm2Now load applied on it is follows following calculation:Assume spring index(S) = 12Stress factor (K) =

K=

K=1.2525

The static load applied can be obtained by use of following equation:fs=K

From standard table relation between wire diameter and allowable shear stress as given below we find appropriate diameter of wire:

Table 8: wire diameter and allowable stress in N/mm2According to average life we have considered wire diameter approx 2.00mmNow proceed to for calculation on load and diameter and its validation:Spring index(S) = Hence; D=d*S;D= 22mm;500=Where : D= mean diameter of spring (mm); d= diameter of wire (mm); P=static load (N);

Hence; P=44.45 NNow deflection produced by spring is as follows and with the help of given formula we can easily calculate number of active coil;

As given above deflection of spring:x=150mm

After calculation we will get number of active coil: 64:Solid length of spring: (z+2)*d= (64+2)*2 = 206mm;Free length of spring= solid length +deflection under load+ clash allowance = 136+ 150+ 0.25*150 = 409mmPitch of coil can be obtained by relation:

p=4.98mmHence all required data for design of spring is calculated.

5.2.2 Design of casing:

Casing is designed in such a way that it will not in contact with spring and also provide support to it and prevent it by buckling hence mean diameter of spring is main consideration in designing of casing, it should be like that it will not provide any friction losses Hence inner diameter of casing:Di=mean diameter of spring +2*spring wire diameter + allowances (5~10mm)Di= 22+2*2+ 6Di=31mmThe material selected for casing is IS3074 alloy of steel and iron having properties according to the requirement. Thickness of pipe or casing is calculated on applying stress in pipes equations:Circumferential stress:

Longitudinal stress:

Where: P= static pressure applied (N);d=inner diameter of pipe (mm);t=thickness of pipe(mm);Having stress as follows:Circumferential stress: 569N/mm2Longitudinal stress: 461 N/mm2Hence thickness of pipe is:According to circumferential stress:

t=2.04mmAccording to longitudinal stress:

t=2.45mmHence optimum thickness of pipe is: 2.45mmOuter diameter of pipe is = 31 + 2*2.45=35.9mmLength of casing is determined according to volume of spring:Volume of spring= free length* area of spring=L* D2=406* *28*28 mm3Volume of pipe= volume of spring+ allowancesVp = inner area of pipe *lengthHence length of pipe=450mm;

5.2.3 Design of striker

Striker design data is taken from standard projectile which are used in gun or other papers to perform impact test: Striker 1:First striker having following detailsMaterial: stainless steel

Fig 29: striker design on CATIA

Striker 2:Material: stainless steel

Fig 30: design of striker on CATIA

Fig 31: Striker with stainless steelStriker 3:Material: stainless steel

Fig 32: Striker on CATIA Fig 33: striker of steel on CATIA

Fig 34: IMPACTOR OR PROJECTILE USED TO PERFORM TEST

5.2.4 DESIGN OF FRAMEDesign of frame is prepared according to the prepared specimen. This is made of iron stripes in which a finite space is given up-to which sample is tested and experimentation is done. Frame is of dimension 130 x 130mm2 and specimen is of dimension 120 x120mm2 which is covered by 10 mm of frame stripes.

Fig 35: Frame to Clamp Work Piece

5.3 Fabrication of set upIn whole main part of set-up is gun in which spring and plunger are attached on the tip of plunger striker or impactor is bolted with the help of nut and bolt arrangement in which plunger having internal thread of M6 and striker have outer thread of M6. According to the requirement each projectile and impactor is attached and tested. Impcator strikes to the target which is at a distance from gun and pierce it.Details of each component are listed below along with their sketch diagram, arrangement and materials are given below:

5.3.1 Spring:

Fig 36: Designed spring

Spring details along with all details are givenSpring 123

MaterialSpring steelSpring steelSpring steel

Wire diameter2 mm1.8mm2.2mm

Mean diameter24mm23mm20mm

Free length409mm430mm440mm

Solid length206mm158mm189mm

Spring constant24444.45 N/m14444 N/m10000 N/m

Table 9: Details of spring usedThese springs are inserted inside the casing and plunger is attached to it.

Fig 37: Design of complete spring set-up to perform impact test

5.3.2 Casing: Material: IS3074 (pipe) Length of pipe: 450 mm Inner diameter of pipe = 32mm Thickness of pipe = 2.45mm5.3.3 Striker: Material: stainless steel Coating: Nickel-chrome Mass: 8~10 gm Length: 40~50mm5.3.4 Equipment required for fabrication: Nut and bolt: - M10 (4) Drill machine (Hand drill/ Motor drill) Hammer Plier Wooden board Iron frameAfter fabrication whole set-up sketch is as follows:

Fig 38: Design of complete set-up to perform impact test

CHAPTER 6MATLAB ANALYSIS6.1 Introduction We are using the popular computer package MATLAB as a matrix calculator for doing the numerical calculations needed in mechanics of composite materials. In particular, the steps of the mechanical calculations will be emphasized in this chapter. Instead step-by-step solutions of composite material mechanics problems are examined in detail using MATLAB. All the problems in this chapter assume linear elastic behaviour in structural mechanics. The emphasis is not on mass computations or programming, but rather on learning the composite material mechanics computations and understanding of the underlying concepts.The basic aspects of the mechanics of fiber-reinforced composite materials are covered in this chapter. This includes lamina analysis in the local and global coordinate systems, laminate analysis, and energy absorption of a lamina due to impact.

6.2 MATLAB (Matrix laboratory)

MATLAB is laboratory of matrix in which all calculations are solved with the help of matrix which is more convenient. MATLAB is package in which all calculation is followed by accuracy and prediction of result easily with the help of both numerical data and graphical representation with the help of MATLAB all data arranged in proper way for finite element.6.3 Mathematical modellingA mathematical model is presented to compute the total energy absorbed and its components from the knowledge of the projectiles position in time. The model uses the basics of single yarn impact and extends it to a fabric via simple assumptions.Based on theory of single yarn impact an analytical model is proposed to approximate the energy absorption of fabric, knowing the displacement- time record of projectile. This model calculates the fabrics total absorbed energy in terms of strain and kinetic energy componentsIt is assumed that upon impact, longitudinal strain wave is generated in the strained yarns. The propagation velocity of this wave, C, for weaves and yarn crossovers. C=Where E and are elastic modulus of the yarns and mass density respectively. The elastic modulus is divided by a constant factor of 2,in order to account for reduction wave speed due to account for reduction of wave speed due to the fabric yarn crossovers, and the crimp, which exist in a fabric system.The longitudinal wave is then followed by transverse wave, which causes the material to move in direction perpendicular to the fabrics plane. The transverse displacement of the material within this wave forms a pyramid (deformation pyramid or cone) with the material within all the material move out-of-plane with the speed of the projectile. The propagation velocity of the transverse wave in the Lagrangian co-ordinate system, , can be derived as

= 64+0.74 VWhere V is velocity of impactor; there is relation in longitudinal strain wave, transverse strain wave and strain generated due to impact in fibers:=Simplification of the above relation results in laboratory co-ordinate

U=

The strain, s, is assumed to be constant along each yarn and is calculated using the yarn length within the longitudinal wave fronts. This assumption implies that only the yarns, which go through the deformation cone, are strained due to their transverse displacement Thus, it can easily be concluded that the strain wave travels only in those individual yams that go through the deformation cone in two directions.

The model predicts the absorbed energy and its components in time, for the duration before the first reflected longitudinal strain wave returns to the impact point. Analysis is divided into two phases; phase-I corresponding to the time when the longitudinal strain wave travels outwards to the boundaries, and phase-II corresponding to the period when the wave has reflected from the boundaries (either partially or fully) and is coming back to the impact point. This analytical model is established for panels with two different boundary conditions, fixed all-around, and free all-around. The approach is explained separately for each of these two cases.

The panels discussed here are considered to be square targets with clamped edges, meaning that all the degrees of freedom of the nodes on the boundary are restrained. Two time periods are considered: phase-I starting from the impact time and ending just as the longitudinal strain wave front reflects from the boundaries, and phase-II, which immediately follows phase-I and ends when the reflected strain wave returns to the impact point. Formulation of these two phases is presented below.

6.3.1 Phase-I

As mentioned above, phase-I starts from t = 0 to t = T1, where T1 is the termination time for phase-I and is calculated as follows:

Where L is the panel size. The total absorbed energy of the target is broken down into three components, strain energy of the yarns, transverse kinetic energy of the cone, and in-plane kinetic energy outside the cone.

6.3.2 Strain energyStrain is determined using the deformed length of a yarn. Figure 42(b) shows the deformed shape of a yarn going through the impact point (i.e. central yarn), for which, the deformed length, l, is equal to:

Where d is the projectile displacement and b is the cone size in the global co-ordinate system, calculated from the transverse wave velocity, U, as follow:

Considering the undeformed length of the yarn covered by the longitudinal strain wave, 2Ct, the strain in the central yarn, 0, can be calculated as follows:0In general, the same approach can be used to determine strain of yarn in the Y direction at a distance X from the impact point

Finally, from the above equations, the strain energy of the system can be calculated as follows:strainWhere v is the volume of the yarn; Due to the existing symmetry in the fabric, the strain energy is calculated for half-width of all the v-running yarns and then is multiplied by four to get the total strain energy: (t