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ANSYS Modelling 3D Surface-to-surface Contact, need help

I am fairly new to ANSYS and have been trying to model the interaction between glass micro-spheres and silicone polymer micro-structures for my dissertation research.  I've been working through the online manual, but have been getting very odd results when running the simulation.  Any help at all would be appreciated.  The summary of my problem is as follows:

 Modelling:

It may help to first refernce the first two images at : http://bdml.stanford.edu/twiki/bin/view/Main/AnsysModelling

I have a single, thin wedge shape modelled with SOLID95 elements.  The body of the wedge (everything but the round tip) is comprised of 20-node bricks.  The rounded top of the wedge is modelled with 10-node tetrahedron, with pyramidal interface eelements between the tets and the bricks.  The material model for the wedge is a linear isotropic one with ballpark values of: E=1e6 and PR=0.49.  I also gave it a friction coefficient of 1.

 Contact Elements: 

The contact surface is showin the third picture in the above link. 

I set the type to CONTA174 and, using the meshing tool, meshed the shown areas with triangular elements on the round top of the wedge, and quad elements on the front face.  I then set the R1 value in the real constant set to the desired radius of my sphere, which is the rigid target.  Using the same real constant set, I set the type to TARGE170 and created a pilot node element where I wanted the center of the sphere and then created a sphere element on top of the pilot node.  The sphere was the appropriate size, so I believe the shared real constant set is correctly set up.  

 Simulation:

I constrained the bottom of the wedge in all DOF, and put a simple displacement load on to the pilot node of the sphere.  I want the sphere to move straight down a certain distance, and observe how the wedge deforms.  I didn't change much in the way of thesolution controls.  I set it up as a large displacement static problem with a 250 set as the number of substeps and 150 as the minimum number of substeps.  The simulation fails each time, however, due to an error in element formulation.  It's easy to see why there is an error when I plot the deformed shape of the last solution set.  The elements become highly distorted almost as soon as the target comes in to contact with the contact surface.  This can be seen in the last image in the link above. 

As I said before, I'm a bit new to contact simulation in ANSYS.  Maybe I've made a silly, rookie error.  Any guidance at all would be greatly appreciated. 

Paul

 

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