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Tensile coupon test

Tensile coupon test

Tensile coupon test

(OP)
I have carried out several coupon tests (rectangular coupons similar to those of ASTM E8). Some of these tests have kind of weird behavior. The problem arises when I simulate results with ABAQUS. It goes pretty well until a few steps after necking. Test and ABAQUS results match exactly until several steps before fracture. After this point, there is a discrepancy between results and my attempts in capturing the observed behavior was unsuccessful. (around 10% or more plastic strain).
The FORCE-DISPLACEMENT curve from experimental result show a more plateau type curve after necking, with a sharp decrease in force right before fracture. I am unable to capture this part. I think it can be attributed to the fact that stress, in experimental test, remains uniform and no stress concentration or necking takes place until a sudden necking followed by fracture.
In my models, I either have necking take place, say right on time, or no such necking takes place and strain remains uniform and entire length of the specimen takes part in elongation.


Recently I applied a virtual load around the center of the coupon where we should expect necking in ABAQUS. I used second order accuracy and incompatible modes. All of these enabled me to come up with the right deformation (necking at centre instead of somewhere else or having multiple necking along the length of the coupon).


I would appreciate any suggestion.

Thanks.
Ron, PhD  

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