In reference to eqn for stiffness shown in Theory Manual under subsection "Soft Constraint Penalty Formulation" m*=min(m_master_nodes, m_slave_node). Ticket#2020012310000069 ____________________________________________________________ R10.1.0 release note: Add command line option "soft=" for switching value of SOFT in contacts: - "soft=2to1" converts all SOFT=2 contacts to SOFT=1; - "soft=1to2" converts SURFACE_TO_SURFACE and SINGLE_SURFACE contacts with SOFT=1 to SOFT=2. This option does not set other variables related to SOFT=2, e.g., SBOPT and DEPTH. __________________________________________________________________________ The contact formulation invoked by setting SOFT=1 on optional card A of *contact is not so radical a departure from the default penalty contact formulation (SOFT=0) as the SOFT=2 contact formulation. SOFT=1 is more or less the same as SOFT=0 EXCEPT in the way the contact stiffness is determined. SOFT=1 calculates contact stiffness based on stability considerations taking into account the timestep. In other words, you can liken SOFT=1 contact to a group of simple spring-mass systems, each with a Courant timestep matched to the actual timestep used in the simulation. SOFT=1 will generally be more effective than SOFT=0 for SOFT materials contacting stiff materials or where the mesh densities of the two contacting surfaces are dissimilar. When SOFT=1, contact stiffness is calculated as follows: k = max(SLSFAC*SFi*k0, SOFSCL*k1) where k is the penalty stiffness SLSFAC is user input on *CONTROL_CONTACT SFi is either SFS or SFM on *CONTACT card 3 SOFSCL is user input on *CONTACT optional card A k0 is the stiffness calculated from material bulk modulus and element dimensions. This is the stiffness used when SOFT=0. See the section "Standard Penalty Formulation" in the LS-DYNA Theory Manual. k1 is the stiffness calculated from nodal masses and the solution time step (analogous to how Courrant time step is determined based on mass and stiffness). DTSTIF on Opt. Card C will override the solution time step in this regard. PENOPT in *CONTROL_CONTACT may additionally affect the contact stiffness. If you must quantity the contact stiffness beyond a shadow of a doubt in any given situation, I encourage you to prescribe motion in a 2-element problem to develop a known penetration and then get the contact force for rcforc. It's possible for the solution to become unstable when the SOFT=0 method generates a higher (and unstable) stiffness than the second method. Since the second method is based on stability, it doesn't make a lot of sense to use a larger value but that's what can happen. One way to avoid this potential stability problem is to reduce the stiffness scale factor for the first method to a very small number such the the second method is always used. This is possible because the two methods use different scale factors. The SOFT=0 method uses SFS and SFM on card 3. The second method uses SOFSCL on card A. So setting SFS and SFM to a tiny number like 1.e-6 make SOFT=1 more stable, however a reasonable value of SOFSCL must be used. Regarding contact time step: SOFT=1 contact calculates the maximum frequency of the SOFT=0 stiffness and warns users not to exceed the stable timestep for that frequency, but SOFT=2 does not do this. Therefore, SOFT=1 reports a reasonable timestep (like 1 msec or something) but SOFT=2 reports a really big number like... slave surface of interface # 1 type= 13 surface timestep= 0.100E+17 current minimum= 0.100E+17 The LS-DYNA time step size should not exceed 0.100E+17 I suppose you could read this message as meaning that the contact interfaces are not placing any constraint on the solution timestep since the solution timestep will never be that large. However, the printing of this message does seem to cause confusion. lpb, jpd