Is thermal stress considered in equivalent stress? 4

[HaoZ]

I am analyzing a truss structure in ANSYS Workbench. It looks like uploaded figure.

I checked the strain after thermal load. The equivalent strain or equivalent total strain is much smaller than thermal strain.

But for stress, there's no choice for thermal stress. So is it included in equivalent stress? I am not sure because the equivalent stress is not large at all.

Thanks.

 

[flash3780]

Fundamentally, stress is an infinitesimal force over an infinitesimal area within a material. Strain, on the other hand, is the ratio of change in length over initial length for an infinitesimal segment of material.

For linear-elastic materials in the elastic regime, mechanical strains (i.e. those caused by internal and external forces in a material) are related to mechanical strains by a factor called Young's modulus.

However, all strains (see the definition) are not necessarily related to stress. Thermal growth, for example, can result in strain in a material, however if the material is otherwise unrestrained, there is no associated stress (remember, stress comes from forces). If you think of a square bar of steel which is simply heated in an oven, it will surely increase in length due to the temperature change, however since there is nothing restraining the bar, it will have no stress.

So, ANSYS does not isolate thermal stress because there's really no such thing. There are stresses caused by differential thermal growth, but that's a function of internal and external reaction forces, not necessarily of the thermal strain. If you're interested in isolating the effect of temperature changes on stress, I'd recommend running your model at room temperature and then again with temperatures applied and determining the differential.