Numerical modeling on scratch and mar induced damages in polymeric systems

Abstract

The barrel mar behavior, scratch induced delamination, and temperature-dependent scratch behavior were investigated in this dissertation via FEM modeling. The experimental tests were carried out according to ASTM/ISO standard to validate the FEM model.

Three amorphous polymers PMMA, PC, and PS were employed to study the barrel mar behavior. By comparison to experimental results, the numerical analysis showed that the maximum plastic principal strain and total dissipated plastic energy can be considered for evaluating mar visibility resistance. Higher mar visibility resistance corresponds to lower maximum plastic principal strain and dissipated plastic energy values. Based on these two criteria, the parametric analysis shows that mar visibility resistance increases with lower modulus, higher yield stress, higher hardening slope, and lower softening slope.

The FEA analysis to compare the delamination resistance of two semi-rigid PET-based laminates was conducted. The results show that the maximum principal stress distribution at the interface correlates well with the scratch-induced delamination behavior. A followed study was performed to validate the semi-quantitative FEM modeling approach with the double-layer epoxy-based polymeric coatings. The parametric yield stress study in both top and base layers revealed the delamination at the interface could initiate either from the scratch shoulder or behind the scratch tip.

A FEM modeling methodology to quantitatively predict the temperature-dependent scratch behavior of amorphous polymers was proposed with the following theories. The Arruda-Boyce viscoplastic model is utilized to account for temperature and strain rate dependent strain-softening and strain-hardening behaviors. The post-yield behavior predicted in this model is calibrated using the yield point determined by the Richeton cooperative model. The pressure dependent Drucker-Prager model with calibrated post-yield experimental data at various strain rates is chosen as the plastic constitutive relationship of the polymeric systems for FEM simulation. Furthermore, temperature and pressure dependent frictional behavior is input into an ABAQUS contact model to simulate the variation of the adhesion coefficient of friction. The FEM simulation findings show a good agreement with the experimentally determined scratch depth and scratch coefficient of friction (SCOF) measured using the scratch test.