Numerical investigation of the interfacial behavior of short carbon fiber/SBR composite using a multiscale finite element method: Effect of fiber/matrix interface stiffness

The mechanical performance of short carbon fiber (CF)-reinforced styrene–butadiene rubber (SBR) composites is strongly governed by stress transfer across the fiber–matrix interphase. In this study, a multiscale finite element framework was developed to investigate the interfacial behavior of surface-modified short CF/SBR composites containing randomly distributed fibers. The carbon fibers were modified through oxidation, TESPT grafting, and rubber sizing treatment to enhance interfacial adhesion with the rubber matrix. Two interfacial modeling approaches, namely the continuum interphase model and cohesive zone modeling (CZM), were employed to describe the mechanical response of the fiber–matrix interface. The effects of interphase stiffness, representative volume element (RVE) size, and interfacial damage evolution on stress transfer, strain localization, and the effective mechanical response were systematically investigated. Numerical predictions were assessed through comparison with experimental mechanical properties and scanning electron microscopy (SEM) observations. The results demonstrated that the interfacial characteristics significantly influence local stress–strain fields, damage evolution, and the predicted effective stiffness of the composite. The developed multiscale framework provides valuable insights into the role of the fiber–matrix interphase in governing the mechanical behavior of short fiber-reinforced elastomer composites and offers an effective methodology for the design and optimization of rubber-based structural materials.