Which among the two,Tension or Compression, requires high capacity machine?
Before answering this question i want to just brief out on the two tests:-
1. Tensile Test-
Tensile strength is defined as the ability of a material to support axial load without rupture and is determined through the tensile test. When equal and opposite forces are applied simultaneously at both the ends that pulls the material, it tries to elongate it and the diameter reduces.
Due to the stretching of the specimen in tensile test, the initial test specimen length L0 is increased to L and area A0 is reduced to A.
The tensile testis carried out at a constant cross head speed and extensometers of required gauge length are used to capture the elongation depending on the requirement.
In this process the material first elongates, then necking occurs & the fracture is produced. The necking phenomenon is observed mostly in tensile test and it also mainly depends upon the material that isused for test. If the material is brittle there is no chance of necking.
2. Compressive Test-
Compressive test is performed to determine the compressive strength of the material.
The material is applied equal and opposite compressive load.
Engineering stress is defined as
s=F /Ao
Where Ao= Original area of cross section, mm2
Engineering strain is defined as -
e=ℎ−ℎo/ℎo
Where h= height of the specimen at a particular moment into the test, mm
ho= starting height, mm
The strain will be negative. Usually the negative sign of the strain are ignored.
The stress strain curve shown above for compression test is different in the plastic region of stress strain curve for tensile test for same material. The reason of this variation is compression helps in increase in the cross section. The load rises more quickly than the tensile test.
In compression operation, due to friction between the surfaces there is an increase in area of the middle of the specimen than at the ends. This effect is called barreling effect in a compression test.
Compression operations are used mostly in metal forming than stretching operations. Generally forging, rolling etc. are the compression operation used in industry.
Now coming back to the question:-
The above explanation slightly gives a hint about which test will require a higher capacity machine.
The compression test requires higher capacity of the machine as the cross sectional area of the specimen, under the test, increases, which is just the opposite of tension test. The increase in area requires a load higher than that for the tension test to achieve the same stress level.
Furthermore, note that compression-test specimens generally have a larger original cross-sectional area than those for tension tests, thus requiring higher forces.