Effects Of Assembly Stress And Residual Stress On Scratch Behaviors Of Polycarbonate Surface

As a thermoplastic engineering plastic,polycarbonate(PC),due to its excellent mechanical properties,optical properties,and impact resistance,has been widely used in the field of construction automobile,packaging,and aerospace industry.The residual stress and assembly stress caused by the manufacturing and usage process will influence its performance.Moreover,polycarbonate is inevitably affected by the scratch behavior from hard objects during its preparation,transportation,and service,which will seriously affect the polycarbonate surface in aesthetics and function.Understanding the effects of assembly stress and residual stress on the scratch performance could provide the guidance for an effective way to adjusting the surface scratch resistance.For the purpose of investigating the effects of the assembly stress and residual stress on the surface scratch behaviors of polycarbonate,the following research works have been carried out in this paper:(1)The polycarbonate scratch tests have been carried out with various assembly stress levels by using the house-designed scratch test equipment and the assembly stress fixture.Based on the selected scratch geometry and visual parameters,the scratch performance of polycarbonate and its mechanisms are evaluated and analyzed respectively.According to the experimental results,it is concluded that the scratch resistance of polycarbonate becomes worse with the change of the assembly stress from the compressive state to the tensile state which is introduced in the direction perpendicular to the scratch;(2)The numerical simulations on the polycarbonate scratch process with the consideration of the assembly stress and the distribution of the true residual stress have been performed with the finite element software ABAQUS.As shown from the numerical results,the scratch resistance of polycarbonate was significantly improved after introducing the assembly compressive stress perpendicular to the scratch,while the scratch resistance was slightly enhanced by the introduction of the residual stress distribution;(3)The differences between the effects of assembly stress and residual stress on the surface scratch behaviors of polycarbonate have been discussed.Since the introduced residual compressive stress diminishes with the increase of the sample thickness,the extent of possible improvement on the scratch performance brought from the residual stress is insignificant.The assembly stress generally keeps constant through the thickness and does not change with the increase of sample thickness.Therefore,its influence on the scratch resistance of polycarbonate surface is more obvious than that of residual stress.This conclusion has practical engineering significance,such as the scratch resistance of polymer materials can be improved by introducing the pre-assembly compressive stress or manufacturing residual stress distribution perpendicular to the scratch direction of polymer.