Stress‐transfer micromechanics for fiber length with a photocure vinyl ester composite

Abstract The objective was to test how increasing fiber length above the critical length would influence mechanical properties and fracture crack propagation. Micromechanics considering fiber/matrix stress‐transfer was used to evaluate the results in addition to a shear debonding volume percent correction term necessary for the final analysis. Fiber lengths of 0.5, 1.0, 2.0, 3.0, and 6.0 mm with 9 μm diameters were added into a photocure vinyl ester particulate‐filled composite at a uniform 28.2 vol%. Mechanical flexural testing was performed using four‐point fully articulated fixtures for samples measuring 2 × 2 × 50 mm ³ across a 40 mm span. Fiber length correlated with improved mechanical properties for flexural strength, modulus, yield strength, strain, work of fracture, and strain energy release, p < 0.001. In addition, sample fracture depth significantly decreased with increasing fiber lengths, p < 0.00001. All mechanical properties correlated significantly as predictors for fracture failure, p < 0.000001, and as estimators for each other, p < 0.0001. The stress‐transfer micromechanics for fiber length were improved upon for strength by including a simple correction factor to account for loss of fiber volume percent related to cracks deflecting around debonded fiber ends. In turn, the elastic property of modulus was shown to exhibit a tendency to follow stress‐transfer micromechanics. Polym. Compos. 27:153–169, 2006. © 2006 Society of Plastics Engineers.