Identification of critical factors governing the failure behavior of fiber-reinforced composites: Proposal of a weakness parameter

초록

While carbon fiber reinforced polymer (CFRP) exhibits high specific strength and stiffness, its adoption in safetycritical structures remains constrained by multi-mode fracture and the resulting uncertainty in reliability and lifetime prediction. However, a unified approach to objectively compare the vulnerability of the fiber-matrix interface with that of other constituents remains limited. This study identifies the key factors governing the tensile fracture behavior of CFRP by systematically evaluating the fiber, matrix, and interface. A single fiber tensile test was performed to characterize the statistical strength of carbon fibers. The neat epoxy matrix was tested in tension to obtain strength, modulus, and strain at break. Interfacial properties were determined by the microdroplet pull-out test to extract interfacial shear strength and apparent interfacial shear modulus. The Weibull distribution was fitted to each constituent and to the tow-composite to estimate scale and shape parameters, enabling consistent comparison across hierarchy levels. A novel weakness parameter (omega) was established as an objective indicator that integrates the magnitude of the property and its statistical scatter. Fracture surfaces were observed using scanning electron microscopy, and the observations were correlated with failure modes including fiber pull-out, matrix cracking, and interfacial debonding. This comparative analysis provides evidence that the fiber-matrix can act as a dominant contributor to tensile reliability within the present CFRP system. A reliability-based metric grounded in these mechanistic insights is provided to guide material selection, interface tailoring, and lifetime assessment of CFRP structures.

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