In situ interfacial evaluation of aramid/epoxy composites by interfacial stress transfer characteristics

Interfacial bonding between aramid fibers and epoxy resin is crucial for the mechanical properties of fiber-reinforced epoxy composites. Interfacial stress transfer between resin and fibers bridges microscopic and macroscopic properties. Using micro-Raman spectroscopy for in situ stress measurement offers insights into interface bonding through assessment of interfacial stress transfer characteristics. This study measures stress distribution on loaded microdroplet sample surfaces, analyzes stress transfer at the interface, and proposes an evaluation method using finite element analysis (FEA). The results show that interfacial stress along the fiber decreases from the droplet's edge to center, indicating stress transfer between the fiber and matrix, as evidenced by the stress-dependent Raman shift of aramid fiber. The interface modulus (E-if), derived from the FEA model, effectively reflects interface bonding, with droplet shape influence removed in evaluations. The agreement between the proposed method and the transverse fiber bundle test confirms its applicability. The method offers a direct, non-destructive, and shape-independent way to evaluate the interface of aramid/epoxy composites.