Reply To: Negative eroding contact energy in impact testing

[Reno Genest]

Hello,

Which value did you use for SLSFAC? By increasing SLSFAC (contact stiffness), the timestep will change as well. Here is more information from the LS-DYNA User Manual Vol I:

"Time Step Scale Factor TSSFAC. During the solution we loop through the
elements and determine a new time step size by taking the minimum value over
all elements:
ΔW +T = TSSFAC × min{ΔWT, ΔW,, . . . , ΔWà}
where N is the number of elements. The time step size roughly corresponds to
the transient time of an acoustic wave through an element using the shortest
characteristic distance. For stability reasons the scale factor TSSFAC should be
set to a value less than 1.0. The default value of TSSFAC is as follows:
a) If contacts are present, and SLSFAC is specified in CONTROL_CONTACT,
then
TSSFAC = }
0.333 for SLSFAC ≥ 9.
0.667 for 1.≤ SLSFAC < 9."

So, if you used SLSFAC between 1 and 9, then TSSFAC will be equal to 0.667. So, this would have a similar effect to setting TSSFAC=0.66. Now, maybe the contact stiffness has an impact here.

I would try with SLSFAC set as before and set TSSFAC=0.667 and see  if it also fix the problem. If not, then the contact stiffness plays a role.

 

I don't understand what you mean by red and green lines in the RCFORC. Could you post the graph?

 

Reno.