Tensile Stress and shear stress

[giri]

Suppose, a mild steel bar is being pulled from both ends.The stress acting on it will be tensile in nature.There is no compressive stress on material in this situation.When the pull exceeds material's yield strength,plastic deformation and strain hardening will occur.If pulling force is increased, neck may form on middle portion of material, which may lead to material failure.Here can I consider necking process is a form of shear failure and the stress lead to necking is shear stress?

 

[timthereaper]

No I don't think you can because in tension nothing's shearing. As you said, necking is a product of Poisson's effect and strain hardening.

 

[Dr.D]

For your tensile test specimen, look at Mohr's circle. A stress block oriented parallel and perpendicular to the specimen long axis shows max normal stress on the transverse sides and zero normal stress on the axial sides. This means that there is a max shear stress equal to half the max normal stress acting at 45 deg to the long axis. As the specimen necks down, there is definitely shearing action happening along a 45 deg line; this should be visible in an actual test in the latter stages.