Finite strain viscoplastic modeling of polymer glasses: application to contact phenomena

There are several techniques to probe local mech. properties of polymer systems. Two frequently used techniques are indentation and scratching, also known as sliding friction. The first is used to det. material parameters such as Young's modulus and yield strength, the later to resolve issues concerning friction and wear properties. Both techniques are based on contact of a specimen with a well-defined indentation/scratching geometry. If we take a closer look at an indentation expt., an indenter is pressed into the material and a force, the so called normal force, and penetration into the surface are measured. For the scratching expt. an extra sliding dimension is added and besides the normal force and penetration depth, a lateral force and sliding distance are measured. The first step of a scratching expt. is indentation; this implies that before we can start with investigation of sliding phenomena, all the phenomena governing indentation have to be captured. For polymers this technique should be used with great care, this because of the strong non-linearity and rate dependence of polymer systems. To understand both contact phenomena a combination of expts. and numerical techniques are used. To comprehend macroscopic polymer deformation a polymers' intrinsic deformation should be captured accurately. This deformation behavior is used as input for our constitutive model and subsequently the model is used for finite element calcns. (c) 2008 American Institute of Physics. [on SciFinder (R)]