The scratch resistance of polymeric materials is generally known to deteriorate with increasing temperature of testing. The present study focuses on quantitatively predicting the effect of temperature on the scratch behavior of amorphous polymers. 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 (μ_a) during the ASTM standardized linearly increasing load scratch test. 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. Usefulness of the present study for design of scratch resistant polymers at elevated temperatures is discussed.

Mar is a type of subtle surface damage caused by a sliding object barely visible to human eyes. This minor damage phenomenon has rarely been systematically studied. Significant research efforts for the fundamental understanding of mar behavior in polymers are still needed. In this study, the mar behavior of a series of model amorphous polymers, i.e., polymethylmethacrylate (PMMA), polycarbonate (PC), and polystyrene (PS), were investigated based on a modified ASTM/ISO scratch testing methodology and a corresponding finite element method (FEM) modeling. Furthermore, the mar-induced visibility and material parameter relationships were established through a systematic FEM parametric study. Experimental results show that PMMA has the highest mar visibility resistance, indicated by lower surface roughness variation and low contrast between marred region and the background. The numerical analysis showed that the maximum principal plastic strain (ε₁^p) and total dissipated plastic energy (E_p) can be considered for evaluating mar visibility resistance. Higher mar visibility resistance corresponds to lower ε₁^p and E_p 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 usefulness of the present study for the preparation of mar resistant polymers is discussed.

Mar damage on polymer surfaces has become a significant concern over a wide range of engineering applications. To gain insight into the strategies for improving mar damage resistance of polymers, it is necessary to learn about why and how mar damage is formed and how it is related to constitutive parameters such as Young's modulus and yield stress, etc. In this study, three model amorphous polymers, i.e., PMMA, PC, and PS, were investigated using a well-established ASTM/ISO scratch testing in combination with finite element method (FEM) parametric study to gain the fundamental structure-property relationships to furtherly understand mar damage. It is found that the total plastic energy dissipation during mar process correlates well with mar damage formation and can possibly be chosen as the criterion for mar damage formation. Three-dimensional FEM parametric study was further performed based on the verified mar damage criterion.