Mechanical Tests for Engineering Materials

There are a large number of tests for materials, the most important of which 

are: mechanical testing, thermal properties tests, electrical properties tests, radiation tests, biological damage and non-destructive tests. Standardized test methods have been developed by national and international bodies such as the Geneva-based International Organization for Standardization (ISO).

1 - Tensile and Compressive Test (Tensile and Compressive Test): Tensile test is considered one of the most important mechanical tests where each material elongates when exposed to tensile (strain) and collapses if this process continues. A simple static tension test determines the point of breakdown of the material after elongation. This test requires a cylindrical or rectangular test specimen or the middle part of which is smaller in diameter than the end, a test machine that applies different loads, measures and records them, and an appropriate set of handles (grips) to hold the test sample. The test machine pulls a small part of the sample, usually called a test section, and uses an extensometer to measure the length of the test part called the gauge length at different weights in order to calculate the tension, drawing a diagram representing the relationship between stress and strain. Testing:

Modulus of Elasticity: A constant value for each material that is a measure of the material's longitudinal deformity.

B) Yield Strength or Yield Point, a value that represents the beginning of the permanent deformation of the model measured under the influence of the projected load and is used as the maximum value in the design of ductile materials.

C) Ultimate Strength: The highest value of the stress on the model under examination before the failure.

The compression tests determine the response of the material to a crushing load or a pre-load as in the case of the house supports. The samples have a cylindrical shape and the standard length in the compression test is equal to the length of the sample.

It should be noted in these tests that the test pieces should be kept short and heavy to prevent bending during the test.

2. Torsional Test: The tests of shear in planar indicate the value of deformation in the material due to the forces applied tangentially, and are applied initially to thin-sheet materials, whether metal or composite, such as plastics reinforced with fiberglass. In the stress test, tension is generated on both sides of the element exposed to me and corresponding pressure stresses are generated on the other.

This test can be used to measure the tensile strength of materials for which it is difficult to perform a tensile test directly as the deformation of the material on the sides of the tested element varies depending on its resistance to tensile and compression, so you can know the value of the material's tensile strength.

3. Ductibility test: Ductibility is a characteristic of the material that shows the deformity of a permanent deformation due to the application of stress on it, and the material is usually deformed in the beginning, a flexible deformation that disappears after local stress is removed and then becomes permanent. If the deformation always does not return the cylinder to its previous shape, the ability of the cylinder to be pulled by pulling and shrinking space in one area or durability (Toughness), which is the amount of power needed to cause permanent deformation in the material.

4 - Hardness Test: Hardness test is tested for hardness of a steel ball (Brinell test or cone of steel or diamonds) Rockwell test or the diamond pyramid (Vickers test) on the surface of the piece being tested. Machines that record optional values ​​that are inversely proportional to the depth of penetration of the ball or cone in the piece It should be noted that the hardness test of rubber and plastics, according to this method, does not give meaningful results because the deformation, as a result of penetration of the ball or cone, may be temporary.

Figure 2 - Hardness tester

Some tests are performed dynamically by dropping a weight of known value from a specified height, usually in tests designed to measure the friction effect.

Impact Test: The most common impact tests use heavy-duty oscillating oscillators, hitting a rod with grooves made from the material tested. The height of the pelvis is used before and after the impact to calculate the ability to crack the penis and thus to calculate the strength of the shock. Some materials vary in their impact resistance with varying ambient temperatures as they become highly breakable at very low temperatures. Some tests have shown that the low elasticity and resistance of the material is often sudden at a certain temperature called the transition temperature of the material.

6. Fracture Test The stringent requirements imposed on materials used in space programs led to fundamental changes in the design philosophy. Designers asked materials engineering specialists to develop quantitative tests capable of measuring a material's tendency to crack and retain traditional methods. Failure is the sudden tendency to crack rather than to fracture. Tests have shown that cracks are determined by splitting, as two pieces of material are separated, located in one vertical plane, one of which moves upwards and upwards. Ri down, and sliding edges, as it split the material in a flat Ofiqitottagh piece of them towards the left and the other to the right, and rupture, as it splits article Vtaathrkqtah diagonally to the top left and the other moving diagonally down Nhawwahlmyn.

7 - Dimensional change test: (Creep Test) Dimensional change is the slow change in the dimensions of the material as a result of long-term stress. Less weight is applied to the material in the dimensional change test than to cause a simultaneous crack.