Evaluation of composites interphase mechanical properties considering CZM and FGM behaviors using single-fiber composite tensile tests.

The mechanical behavior of the matrix-fiber interphase plays a critical role in the performance of composite materials, as damage often initiates and propagates from this region. This study combines experimental and numerical approaches to investigate the interphase mechanical properties between glass fibers and epoxy matrix using specially designed single-fiber composite specimens. Tensile tests are performed at a low loading rate, and the obtained elastic responses are matched to those calculated from finite element analyses (FEA) of three-phase models by varying the interphase mechanical properties. Two modeling strategies were applied: (1) a functionally graded material (FGM) approach, in which Young's modulus varies across the interphase thickness, and (2) a cohesive zone model (CZM) representing the fiber-matrix interphase. The CZM parameters were calibrated to match the experimental elastic modulus. Results show that the cohesive zone model better reproduces the experimental elastic response than the FGM approach. This improvement is attributed to the CZM's capability to capture interphase softening near the composite's failure surface, effectively representing interphase damage initiated prior to the final failure of the fiber and matrix.