# Discussion Forum

## Plasticity - Cyclic Hardening

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Matthew Malkin

April 3, 2013 4:54pm UTC

Plasticity - Cyclic Hardening

Hi all,

I am modelling a process where a steel plate is subject to cyclic forces that cause plastic deformation.

As the process is cyclic I am inclined to use the kinematic hardening option - I am however slightly confused by the description in the COMSOL documentation.

Am i correct in thinking that the kinematic hardening model uses Pragers rule and is therefore a bi-linear model?

Within the isotropic hardening module there is an option to input a user defined hardening function. Clearly this can be non linear however I presume this can never recreate the kinematic model i.e moving the yield surface as opposed to extending it?

Does anyone have any experience implementing a kinematic hardening model in comsol other than the default?

Also as an aside, I am running a simulation of cyclic loading. Currently I have the load described as a variable of time and am running a time dependent solution over a number of cycles. Is there a more efficient way to do this? possibly using the stationary solver?

Any help would be appreciated,

Thanks

Nagi Elabbasi
Certified Consultant
Veryst Engineering

April 3, 2013 7:05pm UTC in response to Matthew Malkin

Re: Plasticity - Cyclic Hardening

Hi Matthew,

Yes the only option for kinematic hardening plasticity is the linear hardening model (Prager’s rule) which is a good approximation for many problems. I think you can relatively easily circumvent that and make the back stress take any function of plastic strain, but that usually does not produce results that agree with experimental cyclic plastic behavior. You can implement a “mixed” or “combined” hardening model developed explicitly for cyclic plasticity.

Regarding the solver, you should use a stationary solver with a parametric sweep and setup the load to be a function of the parametric variable.

Nagi Elabbasi
Veryst Engineering

Chaney Long

June 5, 2013 3:06pm UTC in response to Nagi Elabbasi

Re: Plasticity - Cyclic Hardening

Hi Matthew,

Yes the only option for kinematic hardening plasticity is the linear hardening model (Prager’s rule) which is a good approximation for many problems. I think you can relatively easily circumvent that and make the back stress take any function of plastic strain, but that usually does not produce results that agree with experimental cyclic plastic behavior. You can implement a “mixed” or “combined” hardening model developed explicitly for cyclic plasticity.

Regarding the solver, you should use a stationary solver with a parametric sweep and setup the load to be a function of the parametric variable.

Nagi Elabbasi
Veryst Engineering

Hi Nagi

Could you give more information about the mixed or combined hardening model. I found in comsol that I can just choose one of kinematic and isotropic hardening rule.

btw: can user define the flow rule in comsol?

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