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# Convert to Cyclic Plastic Strain ?

## Convert to Cyclic Plastic Strain ?

(OP)
Hi all,

I'm trying to analyse a specimen in Abaqus using kinematic hardening models, the way I understand it is that I need to get the material parameters from curve fitting a stabilized stress-strain curve. All I have is an engineering stress-strain curve but am I correct in assuming I need a Stress - Plastic Strain curve? How do I go about calculating this as if I simply get the tensile plastic component I lose symmetry so I must be doing something wrong.

Hope someone can help!!

### RE: Convert to Cyclic Plastic Strain ?

Hi bm92,

Under cyclic loads, many materials harden or soften so their stress-strain curve deviates from that obtained under static loads. But after a sufficiently high number of cycles, the hysteresis loop typically assumes a constant shape or in other words it becomes stable. By loading a set of specimens at different strain/stress amplitudes and measuring their stress/strain response once the initial work hardening or softening stage is consumed, a stabilised stress-strain curve can be constructed.

You will now understand that the stabilised stress-strain curve is definitely not a static stress-strain curve missing the elastic part.

### RE: Convert to Cyclic Plastic Strain ?

(OP)
Apologies maybe I wasn't clear or maybe I am misunderstanding it. I'm aware of the softening/hardening and I've taken a mid-cycle as the stabilized one. I now need to take that cycle I determine the material constants for the chaboche model, however for this I believe I need to remove the elastic part of the curve and deal only with plastic strain. The picture below shows the test data I have, and the other picture shows an example from literature on how to get the parameters, and it shows plastic strain. If I simply take off the linear elastic strain then the tensile and compressive don't match up at all. Thanks for replying, hope you can provide some further help !!

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