Is anyone here familiar with finite element analysis/solid mechanics modeling? I'm trying to get my feet wet and have a problem regarding the implementation of a contact problem. I posted it in an engineering forum, but it gets about zero traffic so I thought I'd try it here.
I'm currently trying to model an indenter device that I plan on building in the very near future. I've gone through several FE iterations thus far to figure out how the contact problem works in the software I'm using (StressCheck). It solves contact problems using an augmented Lagrangian method with normal spring displacements along the contact surfaces, where the spring stiffness is characterized by some stiffness related to the modulus of the softer material in the contact pair.
I'm currently modeling the solid as an elastic half-space with two layers of different thicknesses. The surface layer is very thin (t~15 microns) but has a relatively high modulus (E ~ 1 MPa), while the layer underneath is thicker (t>1000 microns) and softer (E ~ 1kPa). The indenter probe I'm considering is essentially rigid and will probably be constructed of steel. It's a cylinder that I'm modeling as a flat edge with fillets along the exterior circle to avoid singularities.
The output data that I'm interested in is determining the force required to displace the indenter probe a given distance. By varying the moduli of the materials in the FEA and comparing the F curve with experiments, I hope to be able to ascertain the modulus of a soft tissue having similar characteristics.
So, I can see several ways in which this problem might be modeled and I'm not really sure which one is conceptually correct.
1. Declare the contact zone as the entire probe surface that will come into contact with the elastic half-space.
2. Declare the contact zone as only the fillet edge and those edges of the half-space that will contact the fillet
3. Neglect the contact problem altogether and model it as a single piece with different material properties, where a displacement is applied to the indenter probe
Any advice would be greatly appreciated.
I'm currently trying to model an indenter device that I plan on building in the very near future. I've gone through several FE iterations thus far to figure out how the contact problem works in the software I'm using (StressCheck). It solves contact problems using an augmented Lagrangian method with normal spring displacements along the contact surfaces, where the spring stiffness is characterized by some stiffness related to the modulus of the softer material in the contact pair.
I'm currently modeling the solid as an elastic half-space with two layers of different thicknesses. The surface layer is very thin (t~15 microns) but has a relatively high modulus (E ~ 1 MPa), while the layer underneath is thicker (t>1000 microns) and softer (E ~ 1kPa). The indenter probe I'm considering is essentially rigid and will probably be constructed of steel. It's a cylinder that I'm modeling as a flat edge with fillets along the exterior circle to avoid singularities.
The output data that I'm interested in is determining the force required to displace the indenter probe a given distance. By varying the moduli of the materials in the FEA and comparing the F curve with experiments, I hope to be able to ascertain the modulus of a soft tissue having similar characteristics.
So, I can see several ways in which this problem might be modeled and I'm not really sure which one is conceptually correct.
1. Declare the contact zone as the entire probe surface that will come into contact with the elastic half-space.
2. Declare the contact zone as only the fillet edge and those edges of the half-space that will contact the fillet
3. Neglect the contact problem altogether and model it as a single piece with different material properties, where a displacement is applied to the indenter probe
Any advice would be greatly appreciated.
I've never had much luck finding any real advice... I've never had FEA and probably won't because I'm pursuing EE. It's kind of too bad though, because the guy who teaches it here is basically the guy who pioneered its use at GM.
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