Compression Test On Metals

Compression test may be regarded as opposite to the tensile test in so far as the un axial load applied is compressive rather than tensile. The compression is rarely used as an acceptance test for structural materials. Since Brittle materials are unsuitable for the tension test these are usually used in compression to evaluate the strength properties of such materials. Brittle materials such as cast iron , concrete , mortar, brick, ceramics are commonly tested in compression.

Specimens are usually plain right cylinders or prisms whose ends are made as nearly flat and parallel as possible to avoid eccentric loading. Occasionally specimens have enlarged ends to add to their lateral stability.

A Universal Testing machine, fitted with compression plates, is usually used to apply the load, and the specimen should be measured in accordance with standard procedure before it is placed in the machine. After the specimen is properly placed and aligned, a small initial load is usually applied to hold it firmly while the strainometer is being attached. A strainometer especially made of use in compression is often referred to as a compressometer. From this point on, the conduct of the compression test is almost identical with that of the tension test.

In Commercial tests, the only property ordinarily determined is the compressive strength. For brittle materials with which fracture occurs, the ultimate strength is definitely and easily determined. For materials where there is no unique phenomenon to mark ultimate strength , arbitrary limits of deformation are taken as the criteria of strength.

In tests to determine the modulus of the elasticity, Poisson's ratio , proportional limit stress , and modulus of resilience, exactly the same procedure is followed as in tension.

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