Effect of elastic and thermal mismatch on push-in mechanism and shear strength measurement of fiber/matrix interface

The effect of elastic and thermal mismatches between fiber and matrix on the push-in mechanism and interfacial shear strength (τ0) measurement of typical polymer and ceramic matrix composites was studied in this work by comprehensive finite element modeling of push-in response, using carbon fiber-reinforced epoxy and SiC matrix (Cf/epoxy and Cf/SiC) as model materials. The results highlight a strong effect of fiber-localized environment on the push-in response, especially for the Cf/epoxy with large elastic mismatch. This led to errors to estimate τ0 if applying directly the standard shear-lag model to calculate τ0 according to the push-in response. Calibrations of the shear-lag model were thus performed in both Cf/epoxy and Cf/SiC, and the results suggest a negligible effect of the elastic mismatch in the Cf/SiC due to the comparable elastic properties between fiber and matrix. The shear-lag model can thus well estimate τ0 based on the push-in force–displacement curves. If the residual thermal stress was considered, the push-in deformation was altered by increasing evidently the critical load leading to interfacial fracture, which led to overestimation of τ0. This is a consequence of the large shear stress level concentrated mainly at the fiber/matrix interface. Detailed parametric push-in simulations were afterwards performed to incorporate the effect of interfacial shear stress in the standard shear-lag model, and a more proper shear-lag model calibrated by incorporating both elastic and thermal mismatches was finally proposed.