Changes in friction having no effect?

[rmettier]

I'm experiencing some very weird behaviour in ABAQUS Explicit 6.7 (+CAE)

I'm running a 2D model with quite complex geometry; 19 parts moving slightly against each other. Basically, push on one part and see how that moves the others. You'd expect the friction between the parts to have some effect on how the whole thing moves. All parts are modeled as purely elastic materials, each surface-to-surface contact is defined in the Interactions block with the same Contact Property definiton (SLIP). SLIP's normal behaviour is a simple hard contact with not re-seperation after contact.
For tangential behaviour, I've been using either 'penalty' or 'static-kinetic exponential decay'. For penalty, I've tried friction coefficients between 1e-4 and 1, and for static-kinetic exponential, I've tried similar spans of parameters, with decay coefficient of 1. I've tried with elastic slip stiffness at infinite and at zero, 0.1, 1 and 100.

While I see a difference in node motions between a totally frictionless scenario and those with friction, there seems to be no difference at all between those with varying coefficients of friction. I've compared the XY data from the history outputs, and they're identical, even down to the individual pixel level.

I'm running the models with double precision and with full nodal output precision.

Any suggestions towards what I'm missing here?

 

[rmettier]

I've set up a simple 2D test model to see if I could isolate the problem, and here's what I've observed:

The test model consists of only two parts, one part (ramp) is a simple ramp shaped object, with purely elastic material definitions. The second part (block) is a wedge shaped object laying on top of the ramp, also purely elastic.
Gravity is applied only to block, causing it to 'sink in' slightly on top of ramp. The bottom and side edges of ramp are fixed to prevent the whole model from moving.

First step allows for gravity to increase and the model to settle under it's own weight.
Second step: A velocity BC is applied to the lower edge of block, causing it to slowly move up the ramp.

The attached jpg shows the vertical displacement of a selected node at the surface of the block. The purple line is for a frictionless contact, the darker line is all the other settings (identical curves). The parameters that I tried for the friction definition are:

static coefficient: 0.4 0.8 8 800 8e5 and 8e10
kinetic coefficient: 0.2 0.4 4 400 4e5 4e10
elastic slip stiffness: infinite 0 0.1 1 10 1000 1e10

As you can see, apparently it doesn't matter what parameters are chosen to define the friction, the result is always the same. Can anyone give me a hint as to what I'm missing here?

 

[xerf]

I do not fully understand what you are trying, but if you prescribe the motion of the body, I do not see why you would get different kinematic results. Maybe just the forces should be different.

What do you mean by elastic slip stiffness? Could you post the friction definition from the input file ? Or attach the input file ?