INTRODUCTIONThe mechanical properties of metals and foundries are influenced by the chemical composition, production of material, heat treatment, environmental conditions, heating and cooling rate, and especially the degree of resistance to deformation generated by forces external and internal to them that they should be constantly.You must have a high awareness of the extreme conditions in which they work materials, especially metals, as this is the material in which we capture our knowledge of design, maintenance, production and construction. This rest is the best way to understand the steels by tests on experimental specimens.In general, when undergoes a material to a set of forces occurs both Flex, such as shear or torque , these efforts involve the emergence of tensions both of traction as compression. Although engineering is distinguished between the effort of compression (axial) and compression stress.Trials practiced for measuring compressive stress are contrary to those applied to the traction, the direction of the applied force. It has several limitations: Difficulty of applying a load, concentric or axial, without appearing buckling. A test-piece of circular cross-section is preferable to other forms.The test is performed on materials: Hard. Semi-hard. Soft. Ceramic materials.

TEST OF COMPRESSION AND ITS PROPERTIES TO EVALUATECompressive stress is the result of tensions or pressures that exist within a deformable or medium continuous, solid characterized because it tends to body volume reduction and a shoulder of the body in particular direction (coefficient of Poisson).Compression test consists of determining the properties of a material with a negative axial situation. Solicitation that tries to compress the test specimen. This compression module will be attached to a press, which is a device used to compact. The term comes from the catalan press and linked to exert pressure or use a force. Hydraulic press, presents a mechanism with compartments that are implemented by the Pistons and that through different strengths of little and great intensity, allows other more intense compaction forcesTERMINOLOGYConcentric load: Load applied to a column or pile which is not symmetrical with respect to the core, producing a bending moment. Also called strength eccentric.Shear: Lateral deformation caused by an external force. Also called cutting, chiselling.Covalent bond: The covalent bonds are defined as the union that occurs between 2 atoms sharing of 2 or more electrons in its outer layer in order to form a stable molecule.Young's modulus: Relationship between unitary fatigue and corresponding unitary deformation in a material subjected to an effort that is below the limit of elasticity of the material. Also called coefficient of elasticity, modulus of elasticity, elastic modulus.Voltage: Force applied to an elastic body produces it or tends it to produce a voltage. Also called pulling force.Drive: Makes different particles that compose a piece, to separate each other, tending to extend it. For example, when a lamp hung from a string, the string is subject to a tractive effort, tending to increase their length.APPLICATIONSThis type of testing is important in applications such as packaging, design of bridges, buildings and other structures.By means of the compression test characteristics of the materials can be determined as modulus of elasticity, determining the supported load and deformation presented in the used probe. These properties are decisive for determining the quality of a material, are used as a basis to audit their characteristics and measurements in large projects.ASTM STANDARDSASTM-E9-89a: Test methods of compression testing of metallic materials at room temperature. These test methods cover the disruption, signs and the procedure for testing of axial compression, load of metallic materials at room temperature. ASTM C-773: Established for high strength ceramic.ASTM D-695: Test methods standard for compression of rigid plastics, established for polymers properties.ASTM C-39: Established for concrete.REQUIREMENTS AND CONDITIONS FOR PERFORMING THE TEST Determine the strength of the material: hard, medium-hard, soft and ceramic materials and deformation of each. In many cases the compression test is easy to spot depending on the metal, and therefore previous calculations, tables of results and graphs for satisfactory results should be done.

EXCEPTIONS AND CONSIDERATIONS WHEN PERFORMING THE TEST We must bear in mind that type of material is the specimen. The tests are performed in the machine universal AMSLER and hydraulic press. The friction between the bridges of trial machine or the support plates and surfaces of the ends of the test specimen due to lateral expansion of this. We see a remarkable difference between the theoretical results and practical. We detect that there are three types of dimensions suggested for the samples, for example: the short are for use in metal antifriction, medium-sized utility and the long test that determines the modulus of elasticity. As the length of the specimen is increased, is a growing trend towards the bending of the piece. Although many important mechanical properties of a material can be determined with this test, they are mainly used to determine the relationship between the average normal effort and unit normal deformation in many materials used in engineering, or metal, ceramic, polymer compounds.

MATERIALS AND EQUIPMENT USEDFigure 1: Micrometer ofOutdoor, 1 in.

Figure 2: 6 in Vernier.

Figure 3: Industrial safety equipment.

Figure 4: 20 ton hydraulic press force.

Figure 5: Hydraulic press plate.

Figure 6: Universal machine.

Figure 7: Plate of universal machine.

DIMENSIONS and shapes of the samples according to the standard ASTM E9-89a

Figure 8: Norm ASTM E9-89a.

Figure 9: ASTM E9-89a

Figure 10: Dimensions suggested for the samples

THE TEST IS PERFORMED1. Measures are taken early in the probe, length and diameter, if necessary take further images, so better to compare outcomes.2. Familiarization with the machine and test instruments and placed you attachments corresponding to hold the specimen. Proceed to lower the machine to place the test piece in the right place, to ensuring that this more focused as possible to base.3. Verify that this press holding the press enough, but without great pressure.4. Starts to the trial, putting pressure on the hydraulic press, taking values every certain period of time, to observe the longitudinal variations generated.

THEORETICAL BASISShortening (h): As the material is subjected to compression loads suffer deformation of shortening. The usually cylindrical specimens of flats, thus shortening are the variation of height.

Where h0 is the calibrated length and hf the length at the end of the trialNormal effort (): the effort is perpendicular to the area, therefore is called normal effort. The effort is defined as the intensity of force per unit area. Figure 20 shows the cross-section nn of a test tube, if the axial force acting on the central axis of the area (A) efforts is distributed uniformly; the following equation is used to determine the magnitude of the efforts:

When the material is compressed area tends to expand. If the area is used initial (ator) of the specimen in the ecuacion16 for the calculation of the effort, the effort is called nominal effort or conventional compression effort.

Figure 11: Normal efforts on the bar.

Unitary deformation (): in the same way which is determined in the tensile test, unitary deformation is determined directly by dividing the change in height (shortening) between the calibrated original height (ho). If it is assumed that unitary deformation is constant in the calibrated region (hor constant), defined nominal unitary deformation as:

Real efforts (): as defined in the tensile test, due to the change in the area of the test piece during the test, determines the actual or true effort considering the variable area into the equation for the calculation of the effort 16. Thus determines the real effort on compression:

Where P and Af are the load and actual area, respectively. The area is normally determined by conservation of volume and is greater than the initial area, because it is the crushed material.

The force-deflection diagrams unitary for compression and traction, frequently, have similar forms, but recent compression efforts are much greater than the traction: Unitary deflection curve: Curves differ deflection unit for materials in compression curves of traction. Ductile, like steel, aluminum and copper metals, are very close to the traction limits of proportionality in compression, and the initial regions of its tensile and compression unit deflection diagrams are more or less equal. However, once it begins the creep behaviour is very different. In a tensile test, the specimen is stretched, can have a necking and eventually fracture.

Figure 12: Bend stress - strain unit.When the material is compressed, expands to the sides and their shape becomes like barrel, because the fraction between the specimen and the plates at the ends avoids the lateral expansion. By increasing the load is flattened and offers a high resistance to greater contraction, which means that the curve deflection increases its descent. This characteristic is illustrated in Figure 22. Since in the area cross real of a specimen tested in compression is greater than the initial area, the actual effort in a compression test is lower than nominal effort.

Figure 13: Curves stress - strain nominal and real for the compression test.ADVANTAGES AND DISADVANTAGESThere are advantages and disadvantages of having knowledge about compressive stress, since considering it helps prevent future failures, delays in production and in severe cases large economic losses. To avoid these events it is important to have considered the properties of each material that is occupied in a process or in the manufacture of something. There are trials of compressive stress which may be considered the resistances and the calculations necessary to know in that parts is required each material according to its function. Among the advantages that can be mentioned about these types of trials are as follows:Advantages Prevent stoppages in production because certain material not resisted the effort of compression during the process. Having identified that material is suitable according to their characteristics for some function in which no effort of compression. The compression tests are not very costly to perform. Have safety as companies that have their materials standardized by the corresponding associations, there is a control with respect to compressive stress. You have the materials suitable for processes that involved compressive stress, produces less the possibility of a failure at these, consequently avoid stoppages, poor production and unplanned expenses.Disadvantages Having no knowledge of which may lead to compression in materials, creates the possibility of an unexpected failure during your time. Compressive stress generated expenses by changes of materials. Not controlled materials, compressive stress generate accidents because of it.CONCLUSIONS To put an end to this research it is important to have controlled the events that happen to the types of metals that are in use, in this case the compressive stress have controlled. The use of rules of associations dedicated to the study of the characteristics of the metals is a great way of testing with metals and using that have the understanding of what form is most appropriate for use. Finally, it is advisable to follow the procedures for the use of metals which can cause failures not be occupied properly and in cases more serious accidents in staff by low resistance that could have a material before an event such as compressive stress that occurs in an area where it is circled by people.