Scratch behaviors of polyacrylate-based hard coatings on alternating multi-layered PMMA+PC substrates

In our previous work [1], the scratch behaviors of alternating multi-layered polymethyl methacrylate (PMMA)/polycarbonate (PC) laminates were studied. Generally, a hard coating layer must be introduced to the surface of PMMA + PC laminate to further enhance its hardness and scratch resistance. In this work, the same laminates used in our previous work were coated by a UV-cured polyacrylate hard layer, and the scratch behaviors and relating mechanisms of hard coating (HC) systems were investigated via both progressive normal load scratch test and pencil hardness test. Sliding counterfaces of two tests were stainless steel ball with a diameter of 1 mm and cylinder made of pencil core with a diameter of 2 mm, respectively. Length, width and thickness of test specimen were 150 mm, 33 mm and 1.6 mm, respectively. The effects of HC's thickness and substrate's hardness on scratch behaviors of HC systems were also included. In both scratch tests, experimental results demonstrated that scratch damages of HC systems were featured with dense periodic cracks. Finite element modeling (FEM) revealed that the formation of such crack types was attributed to the maximum principal stress perpendicular to crack propagation direction. Furthermore, it was found that the scratch resistances of HC systems were enhanced as thickness of HC or hardness of substrate increased, the mechanism behind which were found to be decreasing of the maximum principal stress and consequent delaying of crack formation as revealed through FEM.