penalty stiffness using penalty method

[dogbural82]

Dear all,

I've had experimental results and tried to get FE results to be as close to the tests as possible. However,it was found that FE over-predicted over the tests especially contact force and strain with shorter impact duration. So i've been thinking of ways to reduce the contact force in FE. Having tried many things, i lastly tried changing the penalty stiffness (k). With significant amount of stiffness dropping, the contact force was droped as expected according to the equation F=k*x. However, i have a big doubt on such method in a way that a large penetration was allowed to be happened; thus, i would like to confirm if such way to reduce the contact force is reasonable.

By the way, the impactor is considered to be rigid (2d shell) and the target (a composite using 2d shell) to be elastic behaviour , i.e. no failure.

Lastly, Im wondering how to plot the penetration over the time graph like a Figure 1.6.23-6 in an example 1.6.23 in abaqus verification manual.

Any advice will be appreciated.

Regards,
Minki

 

[xerf]

Have tried to use Lagrange multiplier approach for constraint enforcement? This should enforce the contact constraints exactly.

In order to plot the penetration you have to request
*CONTACT OUTPUT
CDISP,

This will output a quantity called COPEN that you can plot on the slave surface.

COPEN <0 means penetration, COPEN>0 means clearance.

You should be able to create XYData for COPEN=function (time) at specific nodes.

Best.

 

[dogbural82]

Hi xerf,

Thank you for your help.

However, im able to output CPRESS and CSHEAR but COPEN using ODB field output even though i requested in inp file as per below:

*CONTACT PAIR, INTERACTION=NO_FRI,mechanical constraint=penalty, cpset=Int-1
M_CONTACT, S_CONTACT
*CONTACT CONTROLS,CPSET=Int-1,SCALE PENALTY=10.
*SURFACE INTERACTION,NAME=NO_FRI
*Output, field,time interval=3e-5
*Contact Output
CSTRESS,CDISP,PPRESS
*Output, history, time interval=1.78e-5
*Contact Output, cpset=Int-1
CFS, CFT, CMN, CMS, CMT


Currently im using nonlinear explicit method for this impact analysis. If im right, Lagrange multiplier approach is supported only for implicit.

Regards,
Minki