Research on the thickness effect and micro-fracture mechanism of graphite sheets with layered structures

Size effect refers to alterations in material properties as their size varies, garnering significant attention as a cutting-edge issue. Graphite sheets, known for their exceptional thermal and electrical conductivity, the thickness effect on their mechanical properties is a notable gap in research. In this paper, the tensile strength, damage rate, and micro-fracture mechanism of graphite sheets with different thicknesses were studied through uniaxial tensile, digital image correlation (DIC) tests, and scanning electron microscope (SEM). The results reveal a significant thickness effect on the tensile strength of graphite sheets: thinner graphite sheets exhibit higher tensile strength and greater resistance to tensile fracture. Additionally, the thickness effect on the tensile strength was elucidated through the modified Weibull scaling law and Bažant size effect law. The thickness effect on the damage rate was revealed through strain evolution measured by DIC and the damage model. Thicker graphite sheets exhibit a more accelerated damage rate. It is noteworthy that the different fracture modes of layered structures are a crucial factor affecting the thickness effect of graphite sheets. Thinner graphite sheets exhibit more layers of stepped-like fracture, longer crack length, and a higher critical energy release rate. This study provides valuable insights for choosing the appropriate thickness of graphite sheets in practical applications and has the potential to enhance the safety performance of devices employing graphite sheets.