Transcript
Page 1: New Engineering Works

NEW ENGINEERING WORKS.,located in Patna,India,was established in

1990 and is specialized in Manufacturing quality spare parts for projectile

looms. We are the largest and most well-known manufacturer of Sulzer

Projectile Weaving Machines Replacement Parts for Model PU, TW-11, P-

7100,P-7200 & P-7300. Our main profile is the manufacturing and export in

spare parts for Sulzer Projectile Weaving Machines Which includes Picking

Shoes, Picking lever, Projectile Returners, R.H slide piece, and many

more. 

Over 23 years of Experience in this field we can offer a product range of

Unique and Patented manufacture to give textile manufactures reliable

quality components at a cost effective price. Whether through continuous

improvement in product quality or management, our motto is

to "Continuously Strive to Be the Best." 

We Have Been Adhering To The Principle Of “Continuously Strive To Be

The Best”

Our Parts Have Been Marketed to india as well as Exported To Global

Markets like South africa, Indonesia,Sri lanka, Bangladesh, Nepal, Europe,

Middel - east etc. 

We have built long term, good relationship with many customers From India

and Abroad and We Get The Reputation For Our Top Quality and adhering

to promises and reasonable after sale service as well. As A Result, Our

Sales Volumes Have Steadily Risen Over The Past Several Years . Our

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Parts Are Equilant to Original Parts and a real alternative to expensive

original parts.

New Engineering Works Prides Itself For Having Experienced Employees

Who Manage The Design And Manufacturing Process Of The Highest

Quality Spare Parts.

Uniqueness Of Our Company Is That We Are Manufacturing Most Critical

Parts Of Sulzer Projectile Looms. And We Are Using High Grade Materials

and Best Metal treatments To Achieve Quality Differences Among The

Other Suppliers. We Rely On Sufficient Techincal Force, Advace

Production Technology.

Our philosophy is to strive continuously for innovation and therefore the

company today can manufacture any mechanical component according to

technical details / sample.

We Are Looking Forward To Cooperating With You, It Would Be

Appreceiated To Hear From You. 

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Our Engineering Division was established to provide custom designed

products for industrial applications, service and maintenance of products,

and supply parts for all our products.

ASW is capable of developing ad hoc solutions to meet individual customer

requirements. Our technical experts are experienced in designing and

manufacturingtailor-made products, and proposing innovative

improvements and solutions for all applications. We work with you to

develop the optimum solution.

In addition, we will assist in the commissioning of your plant equipment,

and continue to provide top class service and support, whenever you need

it. All our projects are completed professionally, timeously, and within

budget.

Machining Workshop

Turning

Milling

Surface Grinding

Small Quantity Machining

Production Run Machining

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Precision Machining

Mechanical and Electrical Workshops

We repair various types of pumps including the following:

Centrifugal Pumps

Dosing Pumps

Peristaltic Pumps

Canned Motor Pumps

Progressive Cavity Pumps

Magnetic Drive Pumps

Compressors Gearboxes

Hydrostatic Drives

We also Repair Hydraulic Equipment Including:

Cylinders

Valves

Pumps

Lubrication Equipment

Motors

Hydraulic Control Stations

Power-Packs

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Our Service Department:

On Site Installations

On Site Repairs

Service Contracts

Refurbishments

Upgrades

Commissioning

Fabrication Workshop

All welding done according to API 1104

Workshop Facilities

Machine Shop floor area 300sq.m 

Fitting Shop floor area 180sq.m 

Stockholding floor area 260sq.m 

Welding Bay 60sq.m

Fabrication Shop 260sq.m

APPLIED MECHANICS

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Applied mechanics is a branch of the physical sciences and the practical

application of mechanics. Applied mechanics describes the response of

bodies (solids and fluids) or systems of bodies to external forces. Some

examples of mechanical systems include the flow of

a liquid under pressure, the fracture of a solid from an applied force, or the

vibration of an ear in response to sound. A practitioner of the discipline is

known as a mechanician.

Engineering mechanics may be defined as branch of science that

describes the behavior of a body, in either a beginning state of rest or of

motion, subjected to the action of forces.

Applied mechanics, as its name suggests, bridges the gap between

physical theory and its application to technology. As such, applied

mechanics is used in many fields of engineering, especially mechanical

engineering. In this context, it is commonly referred to as engineering

mechanics. Much of modern engineering mechanics is based on Isaac

Newton's laws of motion while the modern practice of their application can

be traced back to Stephen Timoshenko, who is said to be the father of

modern engineering mechanics.

Within the theoretical sciences, applied mechanics is useful in formulating

new ideas and theories, discovering and interpreting phenomena, and

developing experimental and computational tools. In the application of

the natural sciences, mechanics was said to be complemented

by thermodynamics, the study of heat and more generally energy,

andelectromechanics, the study of electricity and magnetism

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The advances and research in Applied Mechanics has wide application in

many fields of study. Some of the specialties that put the subject into

practice are Civil Engineering, Mechanical Engineering, Construction

Engineering, Materials Science and Engineering, Aerospace

Engineering, Chemical Engineering, Electrical Engineering, Nuclear

Engineering, Structural engineering and Bioengineering Prof. S. Marichamy

said that "Mechanics is the study of bodies which are in motion or rest

condition under the action of Forces"

Major Topics of applied mechanics

Acoustics

Analytical mechanics

Computational mechanics

Contact mechanics

Continuum mechanics

Dynamics (mechanics)

Elasticity (physics)

Experimental mechanics

Fatigue (material)

Finite element method

Fluid mechanics

Fracture mechanics

Mechanics of materials

Mechanics of structures

Rotordynamics

Solid mechanics

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Soil mechanics

Stress waves

Viscoelasticity

Examples of applications

Civil engineering

Mechanical Engineering

THERMAL ENGINEERING

Thermal engineering deals with the conversion of heat energy between

mediums and into other usable forms of energy. Most of the energy from

thermal sources is converted into chemical, mechanical or electrical

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energy. In order to achieve this, thermal engineers are experts in heat

transfer. Some areas a thermal engineer may specialise in include solar

heating, boiler design or HVAC (heating, ventilation and air conditioning).

Common industries that employ thermal engineers include power

companies, the automotive industry and commercial construction. Travel is

usually involved to factory locations or to the site of their current projects.

Heating or cooling of processes, equipment, or enclosed environments are

within the purview of thermal engineering.

One or more of the following disciplines may be involved in solving a

particular thermal engineering problem:

Thermodynamics

Fluid mechanics

Heat transfer

Mass transfer

Thermal engineering may be practiced by mechanical

engineers and chemical engineers.

One branch of knowledge used frequently in thermal engineering is that

of thermofluids.

Application

Engineering : HVAC

Cooling of computer chips

Boiler design

Solar heating

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In design of combustion engines

Thermal power plants

Thermodynamics:  The branch of science that deals with the study of

different forms of energy and the quantitative relationships between them.

System:  Quantity of matter or a region of space which is under

consideration in the analysis of a problem.

Surroundings:  Anything outside the thermodynamic system is called the

surroundings. The system is separated from the surroundings by the

boundary. The boundary may be either fixed or moving.

Closed system:  There is no mass transfer across the system boundary.

Energy transfer may be there.

Open system:  There may be both matter and energy transfer across the

boundary of the system.

Isolated system:  There is neither matter nor energy transfer across the

boundary of the system.

State of the system and state variable:  The state of a system means the

conditions of the system. It is described in terms of certain observable

properties which are called the state variables, for example, temperature

(t), pressure (p), and volume (v).

State function:  A physical quantity is a state function in the change in its

value during the process depends only upon the initial state and final state

of the system and does not depend on the path by which the change has

been brought about.

Macroscopic system and its properties:  If as system contains a large

number of chemical species such as atoms, ions, and molecules, it is

called macroscopic system. Extensive properties: These properties depend

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upon the quantity of matter contained in the system. Examples are; mass,

volume, heat capacity, internal energy, enthalpy, entropy, Gibb's free

energy. Intensive properties:  These properties depend only upon the

amount of the substance present in the system, for example, temperature,

refractive index, density, surface tension, specific heat, freezing point, and

boiling point.

Types of thermodynamic processes:  We say that a thermodynamic

process has occurred when the system changes from one state (initial) to

another state (final).

Isothermal process:  When the temperature of a system remains constant

during a process, we call it isothermal. Heat may flow in or out of the

system during an isothermal process.

Adiabatic process:  No heat can flow from the system to the surroundings

or vice versa.

Isochoric process:  It is a process during which the volume of the system

is kept constant.

Isobaric process:  It is a process during which the pressure of the system

is kept constant.

Reversible processes:  A process which is carried out infinitesimally

slowly so that all changes occurring in the direct process can be exactly

reversed and the system remains almost in a state of equilibrium with the

surroundings at every stage of the process.

STUDY OF TWO STROKE I.C.ENGINES

In this engine, the working cycle is completed in two strokes of the piston or

one revolution of the crank shaft.

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In case of two strokes engine, the valves are replaced by ports. Two rows

of ports at different levels are cut in the cylinder walls as shown in fig.

These are known as exhaust ports and transfer ports. In the case of single

cylinder engines, a third row of ports is provided below the first two and

these are known as inlet ports.

A specific shape is given to the piston crown as shown in fig Which helps to

prevent loss of incoming fresh charge entering into the engine cylinder

through the transfer port and helps in exhausting only burnt gases.

The charging of cylinder with air fuel mixture in case of petrol engine or with

air in case of diesel engine, compression of the mixture or air, expansion of

gases and exhausting of the burnt gases from the cylinder are carried out

in two strokes. This can be done by using the following two methods.

By using closed crank case compression. In this method crank case works

as an air pump as the piston moves up and down. The charge or air to be

admitted in the cylinder is compressed in crank case, by the pumping

action of underside of piston. This method is known as three channel

system & used for single cylinder small power engines like scooters &

motorcycles.

A separate pump outside the cylinder is provided to compress the charge

or air before forcing it into the cylinder. This pump is an integral part of an

engine & driven by engine it self. This method of charging is used for large

capacity multi-cylinder engines.

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WORKING OF TWO STROKE PETROL ENGINE:

It will be easier to describe the cycle beginning at the point when the piston

has reached to TDC completing the compression stroke.

The position of the piston at the end of compression as shown in fig.( ). The

spark is produced by spark plug as the piston reaches the TDC (Top Dead

Centre). The pressure and temperature of the gases increases and the

gases push the piston downwards producing power stroke, when the piston

downwards producing power stroke. When the piston uncovers (opens) the

exhaust port as shown in fig ( ) during downward stroke, the expanded

burnt gases leave the cylinder through the exhaust port. A little later, the

piston uncovers (opens) the transfer port also as shown in (a). In this

condition the crank case is directly connected to cylinder through port.

During the downward stroke of piston, the charge in crank case is

compressed by the underside of the piston to a pressure of 1-4bar. At this

position, as shown in fig.( ), the compressed charge (fuel & air) is

transferred through the transfer port to the upper port of the cylinder. The

exhaust gases are swept out with the help of fresh charge (scavenging).

The piston crown shape helps in this sweeping action as well as it prevents

the loss of fresh charge carried with the exhaust gases. This is continued

until the piston reaches BDC position. During this stroke of piston

(downward stroke) the following processes are completed.

Power is developed by the downward movement of piston.

The exhaust gases are removed completely from the cylinder by

scavenging.

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The charge is compressed in the crank case with the help of

underside of the piston.

As the piston moves upward, it covers transfer ports stopping flow of fresh

charge into the cylinder. A little later, the piston covers exhaust ports and

actual compression of charge begins. This position of piston is shown in fig.

The upward motion of the piston during this stroke lowers the pressure in

the crank case below atmosphere, therefore, a fresh charge is

admitted/induced in the crank case through the inlet port as they are

uncovered by the piston.

The compression of charge is continued until the piston reaches its original

position (TDC) and the cycle is completed.

In this stroke of the piston, the following processes are completed.

Partly scavenging takes place as the piston moves.

The fresh charge is sucked in the crank case through the Carburettor.

Compression of charge is completed as the piston moves.

The cycle of engine is completed within two strokes of the piston.

WORKING OF TWO STROKE DIESEL ENGINE:

As the piston moves down on the power stroke, it first uncovers the

exhaust port, and the cylinder pressure drops to atmospheric pressure as

the products of combustion come out from the cylinder. Further downward

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movement of the piston uncovers the transfer port (TP) and slightly

compressed air enters the engine cylinder from the crank case. Due to

deflector on the top of the piston, the air will move up to the top of the

cylinder and expels out the remaining exhaust gases through the exhaust

port (EP).

During the upward movement of the piston, first the transfer port and then

the exhaust port closes. As soon as the exhaust port closes the

compression of the air starts. As the piston moves up, the pressure in the

crank case decreases so that the fresh air is drawn into the crank case

through the open inlet port as shown in fig. Just before the end of

compression stroke the fuel is forced under pressure in the form of fine

spray into the engine cylinder through the nozzle into this hot air. At this

moment the temperature of the compressed air is high enough to ignite the

fuel. It suddenly increases the pressure and temperature of the products of

combustion. The rate of fuel injection is such as to maintain the gas

pressure constant during the combustion period. Due to increased pressure

the piston is pushed down with a great force. Then the hot products of

combustion expand. During expansion some of the heat energy produced

is transformed into mechanical work. When the piston is near the bottom of

the stroke it uncovers exhaust port which permits the gases to flow out of

the cylinder. This completes the cycle and the engine cylinder is ready to

suck the air once again.

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SPHERE LAB

building your own VMware vSphere lab

Part 1: Lab Overview (TechHead) and vinf,net Lab Series Overview

Part 2: Lab Hardware Configuration (TechHead) – Coming Soon!

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Part 3: ESXi Installation & Configuration (TechHead) – Coming Soon!

Part 4: Shared Storage Installation & Configuration

            – EMC Celerra (TechHead) – Coming Soon!

            – HP LefHand (TechHead) – Coming Soon!

            – StarWind iSCSI SAN (TechHead) – Coming Soon!

Part 5: Networking Configuration: VLAN’ing & Jumbo Frames (TechHead)

– Coming Soon!

Part 6: VM’ed ESXi (vinf.net) – Coming Soon!

Part 7: VM’d vCenter; auto start-up of VMs (vinf.net) – Coming Soon!

Part 8: VM’d FT and FT’ing vCenter VMs (vinf.net) – Coming Soon!

Part 9: FT on the ML115 series – benchmarking Exchange VMs (vinf.net) –

Coming Soon!

Part 10: VM’d Lab Manager farm environment on a pair of ML’s (vinf.net) –

Coming Soon!

Part 11: VM’d View 4 farm environment on a pair on ML’s (vinf.net) –

Coming Soon!

Part 12: Backing up your ESXi lab (Both) – Coming Soon!

 

Why build a virtualization lab?

Building your own virtualization lab either for home or work can serve many

purposes from providing an ideal test bed for those of you training for an

exam, wanting to test a new application or utility or just wanting to become

more familiar with building and running your own mini server infrastructure.

Gone are the days where running a multiple server lab environment meant

having a number of physical server whirring away creating costly electricity

bills, taking up plenty of space and not evening mentioning the noise and

heat generated.  As you no doubt know the beauty of server virtualization is

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that you can now run multiple VM server instances on a single piece of

server hardware greatly reducing many of the negative points mentioned

above.

From this single server you are able to run multiple operating systems

(OS), virtual appliance (VA) firewalls and network switches and even

nested instances of the hypervisor itself (ie: VMware ESX).

With the significant processing power found in modern processors and the

reduced cost of high capacity memory there has never been a better time

to build your own lab with as little as one server or decent desktop PC.

 

On with the show…

So hopefully I’ve now sold you on the virtues of running your own

virtualized server lab and have sparked your interest to find out how to

create your own. 

Here’s an overview of the hardware and software that will be used in this

vSphere lab series:

 

Hypervisor

For these postings we will be using the latest

version of VMware ESX available at the time of

writing, this being ESXi 4.0 Update 1 (U1) along

with other components of the VMware vSphere

suite.  One of the reasons ESXi was chosen over the full-fat ESX version

was that only ESXi can be installed onto a USB pen drive allowing us to

use 100% of the internal disk space of the servers as shared storage for

the VMs.  Also as the service console portion of ESX is going to be

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replaced in a future version of ESX now is a good time to familiarise

yourself with the remote command line (RCL).

Server:

For those of you that have read TechHead before already know that I

favour the HP Proliant ML110 and/or ML115 entry level servers for use in

my own virtualization test lab.  My reasons for this are:

Reliability: I like HP kit as it has proven to be very reliable in

my years of being in IT.  I have been running two ML110’s

and two ML115’s over the last 18 months both of which

have never had a hardware failure despite me working

them hard at times.  I have only heard of one, what I’d call

serious hardware failure on them this being on Simon

Gallagher’s ML115 where he had a motherboard failure – though this was

resolved after HP had shipped him a new replacement board.

Cost: This is probably the most important factor for many in the server

selection process.  The ML110 and ML115’s have fluctuated in price, at

least here in the UK, from a low bargain price of £80 each about 18 months

ago through to their current price of around £190 – which offers pretty good

value for money when you look at the specification of the server.  I’ve found

that the prices from the various online vendors are usually pretty much the

same though have warmed to using ServersPlus as they have consistently

proven to provide the most competitive pricing and good pre and after sales

support.  As a result I recommend them to others and have arranged a free

delivery deal for TechHead readers – as any savings in this current climate

has got to be a good thing.  Check out my‘Hot Deals’ section for decent

offers that I am told about or see – I try and keep this updated regularly.

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The HP ML115 has also proven to be cheap to run with an average load

consuming between 80-95 Watts of power – at least it does in my current

VMware lab.

 

Compatibility: On the whole the ML110/ML115 although never being on

the VMware ESX hardware compatibility list (HCL) has proven to be on the

whole almost fully compatible with VMware ESX.  In the early ESX 3.5 days

there were issues with some of the onboard network controllers though in

later 3.5 releases this was no longer an issue.  The largest bug-bear, as

you’d likely expect, has been around the storage controller compatibility

though across both models of server things have been pretty stable since

the ESX 3.5 U4 release. With the release of VMware vSphere and ESX 4.0

both G5 models of the ML110 and ML115 now work 100%  – although they

are not officially on the HCL which may be a consideration from a VMware

support perspective if you were thinking of putting these servers into a live

production environment.

Here’s a video I put together that gives you a brief overview of the HP

ML115 G5:

 

 

 

Portability? Just add wheels!

Also with the relatively small form factor of the ML115 you can also

transport it much easier than a full sized enterprise level server.  An

example of which can be seen with vinf’s vTARDIS.

 

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Other options:  Another popular method is to build your own ESX white

box.  You can actually end up building quite a powerful and cheap ESX

host if you can put together the correct ESX compatible parts.  There are

some good sources out on the web that maintain active lists of what

motherboards, disk controllers and network cards have been proven to

work with the different versions of ESX.  Here are some of these sites that

you may want to take a look at if considering building an ESX white box

solution.

Ultimate ESX WhiteBox

VMware Communities Maintained List

VM-Help WhiteBox Compatibility List

Others such as vinf.net have looked towards a desktop white box solution

such as the HP D530 for hosting their ESX environment.

 

Networking:

 

For my networking hardware in my virtualization home

lab I use a pair of eight port Linksys SLM2008 gigabit

switches.  The reason I use two is that I need this many

ports if running most of my ML110 and ML115’s with

shared iSCSI storage and wanting to have dedicated network connections

for vMotion and FT traffic, etc.  I also have a main PC from which I manage

my environment which also requires a port or two. As I postedhere I have

found the Linksys SLM2008 switches to offer great bang for buck for use in

a lab type environment.  It has the necessary features such as VLAN

tagging and Jumbo Frames which do come in useful when you start

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wanting to implement the more enterprise level features with your

ESX/ESXi hosts.

 

Storage:

      

To use many of the useful features within VMware ESX such

as DRS, HA and FT you’ll need shared storage.  For the purposes of this

series I have decided to walk onto the storage vendor parking lot and kick a

few tyres.  The three vendors (EMC, HP and StarWind) I have chosen all

have storage products suitable for virtualised environments that I have

wanted to take a more in depth look at for sometime now.

All three of these storage vendors offer products that can be run as a virtual

appliance which will either pool and share the local disk of the ML115’s or

share out the local disk to ESX and then replicate it between both of the

ESX nodes (ie: ML115’s).  These are a couple of different methods for

presenting shared storage so it’s going to be fun to go into more depth with

them in the lab.

Here’s a summary of the storage virtual appliances I will be reviewing and

using:

EMC Celerra VSA

HP LeftHand VSA

StarWind iSCSI SAN Virtual Appliance

The good news is that if you are following this ‘build your own vSphere lab’

series by constructing your own home or work lab you can download fully

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working evaluation copies of all of these products to which I will be

providing the links.

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Strength of materials, also called mechanics of materials, is a subject which

deals with the behavior of solid objects subject to stresses and strains. The

complete theory began with the consideration of the behavior of one and

two dimensional members of structures, whose states of stress can be

approximated as two dimensional, and was then generalized to three

dimensions to develop a more complete theory of the elastic and plastic

behavior of materials. An important founding pioneer in mechanics of

materials was Stephen Timoshenko.

The study of strength of materials often refers to various methods of

calculating the stresses and strains in structural members, such as beams,

columns, and shafts. The methods employed to predict the response of a

structure under loading and its susceptibility to various failure modes takes

into account the properties of the materials such as its yield

strength, ultimate strength, Young's modulus, andPoisson's ratio; in

addition the mechanical element's macroscopic properties (geometric

properties), such as its length, width, thickness, boundary constraints and

abrupt changes in geometry such as holes are considered.

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Types of loadings

Transverse loading - Forces applied perpendicular to the longitudinal axis

of a member. Transverse loading causes the member to bend and deflect

from its original position, with internal tensile and compressive strains

accompanying the change in curvature of the member.[1] Transverse

loading also induces shear forces that cause shear deformation of the

material and increase the transverse deflection of the member.

Axial loading - The applied forces are collinear with the longitudinal axis of

the member. The forces cause the member to either stretch or shorten.[2]

Torsional loading - Twisting action caused by a pair of externally applied

equal and oppositely directed force couples acting on parallel planes or by

a single external couple applied to a member that has one end fixed

against rotation.

Design Terms

Ultimate strength is an attribute related to a material, rather than just a

specific specimen made of the material, and as such it is quoted as the

force per unit of cross section area (N/m2). The ultimate strength is the

maximum stress that a material can withstand before it breaks or weakens.

[12] For example, the ultimate tensile strength (UTS) of AISI 1018 Steel is

440MN/m2. In general, the SI unit of stress is the pascal, where 1 Pa = 1

N/m2. In Imperial units, the unit of stress is given as lbf/in² or pounds-force

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per square inch. This unit is often abbreviated as psi. One thousand psi is

abbreviated ksi.

A Factor of safety is a design criteria that an engineered component or

structure must achieve.  , where FS: the factor of safety, R: The

applied stress, and UTS: ultimate stress (psi or N/m2) [13]

Margin of Safety is also sometimes used to as design criteria. It is defined

MS = Failure Load/(Factor of Safety * Predicted Load) - 1

For example to achieve a factor of safety of 4, the allowable stress in an

AISI 1018 steel component can be calculated to be   = 440/4 = 110

MPa, or   = 110×106 N/m2. Such allowable stresses are also known

as "design stresses" or "working stresses."

Design stresses that have been determined from the ultimate or yield point

values of the materials give safe and reliable results only for the case of

static loading. Many machine parts fail when subjected to a non steady and

continuously varying loads even though the developed stresses are below

the yield point. Such failures are called fatigue failure. The failure is by a

fracture that appears to be brittle with little or no visible evidence of

yielding. However, when the stress is kept below "fatigue stress" or

"endurance limit stress", the part will endure indefinitely. A purely reversing

or cyclic stress is one that alternates between equal positive and negative

peak stresses during each cycle of operation. In a purely cyclic stress, the

average stress is zero. When a part is subjected to a cyclic stress, also

known as stress range (Sr), it has been observed that the failure of the part

occurs after a number of stress reversals (N) even if the magnitude of the

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stress range is below the material’s yield strength. Generally, higher the

range stress, the fewer the number of reversals needed for failure.

Failure theories

here are four important failure theories: maximum shear stress theory,

maximum normal stress theory, maximum strain energy theory, and

maximum distortion energy theory. Out of these four theories of failure, the

maximum normal stress theory is only applicable for brittle materials, and

the remaining three theories are applicable for ductile materials. Of the

latter three, the distortion energy theory provides most accurate results in

majority of the stress conditions. The strain energy theory needs the value

of Poisson’s ratio of the part material, which is often not readily available.

The maximum shear stress theory is conservative. For simple unidirectional

normal stresses all theories are equivalent, which means all theories will

give the same result.

Maximum Shear stress Theory- This theory postulates that failure will occur

if the magnitude of the maximum shear stress in the part exceeds the shear

strength of the material determined from uniaxial testing.

Maximum normal stress theory - This theory postulates that failure will

occur if the maximum normal stress in the part exceeds the ultimate tensile

stress of the material as determined from uniaxial testing. This theory deals

with brittle materials only. The maximum tensile stress should be less than

or equal to ultimate tensile stress divided by factor of safety. The

magnitude of the maximum compressive stress should be less than

ultimate compressive stress divided by factor of safety.

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Maximum strain energy theory - This theory postulates that failure will

occur when the strain energy per unit volume due to the applied stresses in

a part equals the strain energy per unit volume at the yield point in uniaxial

testing.

Maximum distortion energy theory - This theory is also known as shear

energy theory or von Mises-Hencky theory. This theory postulates that

failure will occur when the distortion energy per unit volume due to the

applied stresses in a part equals the distortion energy per unit volume at

the yield point in uniaxial testing. The total elastic energy due to strain can

be divided into two parts: one part causes change in volume, and the other

part causes change in shape. Distortion energy is the amount of energy

that is needed to change the shape.

Fracture mechanics was established by Alan Arnold Griffith and George

Rankine Irwin. This important theory is also known as numeric conversion

of toughness of material in the case of crack existence.

Fractology was proposed by Takeo Yokobori because each fracture laws

including creep rupture criterion must be combined nonlinearly.

Microstructure

A material's strength is dependent on its microstructure. The engineering

processes to which a material is subjected can alter this microstructure.

The variety of strengthening mechanisms that alter the strength of a

material includes work hardening, solid solution strengthening, precipitation

hardening and grain boundary strengthening and can be quantitatively and

qualitatively explained. Strengthening mechanisms are accompanied by the

caveat that some other mechanical properties of the material may

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degenerate in an attempt to make the material stronger. For example, in

grain boundary strengthening, although yield strength is maximized with

decreasing grain size, ultimately, very small grain sizes make the material

brittle. In general, the yield strength of a material is an adequate indicator of

the material's mechanical strength. Considered in tandem with the fact that

the yield strength is the parameter that predicts plastic deformation in the

material, one can make informed decisions on how to increase the strength

of a material depending its microstructural properties and the desired end

effect. Strength is expressed in terms of the limiting values of

the compressive stress, tensile stress, andshear stresses that would cause

failure. The effects of dynamic loading are probably the most important

practical consideration of the strength of materials, especially the problem

of fatigue. Repeated loading often initiates brittle cracks, which grow until

failure occurs. The cracks always start at stress concentrations, especially

changes in cross-section of the product, near holes and corners at nominal

stress levels far lower than those quoted for the strength of the material.

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