query regarding the analysis

[ankitsen2909]

Hi

Please tell me that while doing an analysis of a material for example steel , which components of stress should we take into account so that if does not fail i.e Von mises or Max principle stress or shear stresses etc. ?

Secondly if the yield strength of a material is 150 mpa and after the analysis the Von mises component of stress is under yield strength but shear stress is not under yield strength, then will the material fail?

 

[rb1957]

1) are you modelling with 2D elements (plates) or 3D (solids) ? if 3D, are you sure the thickness stress is valid ? what are the three (or two) principAL stresses being used to calc von Mises ?

2) failure theories ...
i understand max principAL stress compares easily with coupon test results (like your 150 MPa allowable), so it's easy to use.
von Mises combines together the two (or three) principAL stresses and so is "better" in accounting for multi-axial stresses when comparing to the coupon (uni-axial) allowable.
i believe von Mises is strictly an elastic failure theory, but i'll compare von Mises stress to material yield and ultimate allowables.
max shear stress is another failure model which should (i think) line up with max principal stress ... surprised it doesn't.
note, if your stress state is tension-tension, then von Mises will be lower than the max principal, tension-compression and von Mises is higher.

3) i'd've thought that, if you're dealing with a large chunk of metal, von Mises was a more relevant failure theory than max shear. Of course, if you're dealing with a thin wall strcuture, buckling will be your critical mode.