I have used Bilinear Kinematic Hardening Model for my problem of Swage Autofrettage but reviewers are asking why not and I am unable to identify the main difference
Viscoplasticity (http://en.wikipedia.org/wiki/Viscoplasticity)
There are physical rules for kinemtaic and isotropic hardeninghttp://inside.mines.edu/~apetrell/ENME442/Labs/1301_ENME442_lab7.pdf
If is not possible to say that the strain is small then:
Strain-rate dependent plasticity models is needed.
Flow stress model is required. "The quantity f(sigma,q) represents the evolution of the yield surface". The yield function "f" is then required in FEA calculation.
sigma is the Cauchy stress, and q is a set of internal variables (such as the plastic strain ), relaxation time.
Johnson–Cook flow stress model based on 5 material constants that can be calculated from plastcity curves.
best regards
Because the reviewer likes JC model more than this :). Just kidding!!
I know that, bilinear kinematic model assumes a fixed slope in the plastic regime which may not be exactly similar to your problem condition. Even possibility of over predicting the stress in the plastic domain. Can you elaborate a bit regarding your problem so that i can get a fair idea on what you are solving. Not all conditions you need to use JC model. It is a pure empirical fit based on lot of experiments done @ different strain rate (medium to very high). In your problem, is the strain rate too high, or the solution is largely based on time dependent behaviour. if so, the bilinear model may not work due to a constant strain increment which is associated with the flow rule.
Hi guys, Thanks for your response for my problem.
Autofrettage is a means of pre-stressing thick-walled tubes to better distribute the tensile hoop stress throughout the tube wall, so reducing the magnitude of the hoop stresses found at the ID when the tube is re-pressurized subsequent to pre-stressing.
In case of Swage autofrettage , an enforcing oversized mandrel is passed through the ID of the tube, causing a moving, axially localized outward radial displacement at the bore of the tube.
So the strain rate is at lower level but the process is for longer period because inorder to achieve the desired effect, process is done repeatedly and continuosly.
Dear Mithilesh
Thanks for your clarification. In your case, the JC model is not needed, as far as I am concerned. Since, looks like your process is quasistatic and has a time independent behavior! Can i know y u did not try Von mises or J2 plasticity behavior.
I don't understand why your reviewer needs to be worried about you using the bilinear kinematic model. The plastic regime is totally going to be unaffected as, from your description, the plastic strain has to be too small. It won't go to a large deformation in the plastic zone!
If possible share some of your plot results pertinent to plastic strain etc.. which can show whether it varies a lot between the time steps. You can convince them by stating that this regime is not extremely needed for the analysis.
Thanks Karthic for your response.
Well answer for not using VON MISES or J2 plasticity is that the process of Autofrettge includes the Bauschinger Effect which slowly increases its strength by causing the material flow in the ID of the Thick walled Tubes. so its necessary to include some plasticity hardening modela and BKIN is one the optimum because it will reduces the simulation time as compared to other plasticity models( Cabuchy or Hill plasticity)
Hey mithilesh
Oh, I understand your problem better now. You can convince the reviewers by stating these reasons also. You can even state that, Bauschinger effect (physics wise) is not captured in JC model and that is the reason why you don't want to use it. As far as i know, the only problem with reviewers now a days are, if they love a certain material model, irrespective of the problem, they keep on bugging the authors by showing that they are loyal to that :). Is there any rationale on their part for this query?? Do not worry and just defend your case.
All the best
- Badges
- Science topic
- Similar topics
- Engineering
- Mechanical Engineering