I wanted to see how different geometries of the test specimens for a hot compression test affect the flow curve. Afterwards a statistical analysis based on linear regression was performed.
The specimens were made of austenitic steel ASTM 316L. Depending on the geometry there were 5 types of tests made. At a constant diameter, at a constant height, at different thicknesses of the Ta foil, at different roughness of the contact surface and with specimens whose contact surfaces were not plane-parallel.
We found that yield stress is a material property and depends only on temperature, strain and strain rate. The thickness of the Ta foil has direct proportional effect on the stress as the frictional conditions display great importance. Also the surface roughness affects stress albeit only at lower deformations, which can be attributed to the fact that the contact surface between the test piece and the tool is smaller.
Linear regression is not ideal for this type of curve. You would get more accurate results if you used, say, an inverse function.
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