1. The easiest way to modify the contact stiffness is via the scaling factors SFS and SFM on Card 3 of *CONTACT and if SOFT=1, the variable SOFSCL on Optional Card A. A factor of 10.0 greater than the default value for these variables would be a decent first guess. 2. If SOFT=1 or SOFT=2, lowering the time step will serve to increase the contact stiffness. Contact stiffness for these contacts are proportional to 1/(timestep^2). But without actually lowering the solution time step, the effect of time step on contact stiffness can be modified by using the variable DTSTIF on Opt. Card C. 3. For SOFT=2 only,the variables FNLSCL and DNLSCL allow for a nonlinear contact stiffness; see the Remarks on Opt. Card D of *CONTACT. There are different forms for this type of scaling, but the first form goes like this ... Scaling factor on stiffness = FNLSCL * sqrt(penetration/DNLSCL) so DNLSCL is the penetration at which the nonlinear scaling of stiffness begins. 4. For MORTAR contacts (strongly recommended for implicit analysis), see the variables IGAP and IGNORE on Optional Card C. The aforementioned SFS and SFM also affect MORTAR contact stiffness. Ticket#2016052710000071 But in the broad scheme of things, remember this... In an impact event, momentum conservation is of utmost importance. The contact type you're using is penalty-based. By changing the contact penalty stiffness, it is possible to change the shape of the force pulse, but the impulse should remain nearly constant. By softening the stiffness you will broaden the pulse and lessen the peak force. If the penalty is reduced too much you will begin to see gross overlap of the parts, and the interface may begin to break down. [If the penalty is too high, contact forces may be unrealistically high and cause instability of the solution.] You should be most concerned with momentum transfer and less so with the force magnitude. Ticket#2017112410000072 ___________________________________________- Internal Note: Ticket#2020050410000034 reports an unexpected nonlinearity of contact stiffness in automatic S2S. This was just a result of the two passes made by S2S contact. See ticket for details and test cases that clearly illustrate this phenomenon. jd