Relations between intralaminar micromechanisms and translaminar fracture behavior of unidirectional FRP supported by experimental micromechanics

Abstract

The translaminar fracture behaviors of partially different unidirectional composite systems, constituted by the same carbon fibers but different (thermoset vs. thermoplastic) matrices, were characterized by means of compact tension fracture tests. The resulting crack resistance curves (R-curves) and fracture surfaces, were studied in detail and found to be rather different between those material systems, in spite of the same reinforcing fibers at similar volume fractions. In the attempt to justify this difference, the effects of the underlying micromechanisms were evaluated by employing experimental micromechanical measurements of the fracture characteristics of fibers, matrices and fiber/matrix interfaces. By means of a thorough analysis and quantification of the micromechanisms that contribute to the work of fracture, it was possible to decompose the translaminar fracture toughness of the composites into different contributions. Independently of the material considered, fibre bundle pull-out was found to be the mechanism that dissipates the highest amount of energy. Different patterns of bundle pull-out in different material systems were found to be the result of different outcomes from the competition of fracture micromechanims, and to be responsible for the differences between the translaminar fracture energies of both material systems. Moreover, it was realized that the energy dissipated in bundle pull-out, hence also the overall measured translaminar fracture toughness are strongly governed by in-situ effects, i.e. effects of specimen lamination features.

An Assessment of ASTM E1922 for Measuring the Translaminar Fracture Toughness of Laminated Polymer Matrix Composite Materials

“…It was found that the major characteristics describing the fracture surfaces in the laminates comprised a mixture of the failure mechanisms, ply splitting, fibers bridging, and fiber pull-out. Haldar et al [ 6 ] showed that the fiber bundle pull-out was the process that dissipates the most energy. Furthermore, Souza et al [ 7 ] modified the ASTM E399 test method to account for the orthotropy of the composite materials and specimen geometry effects using a correction function based on a numerical evaluation of the strain energy release rate.…”

Effect of temperature on the mixed mode I/II translaminar fracture of laminated composites reinforced with natural fibers

“…Based on the direction of loading, mode I, mode II, and mode III translaminar fracture or any combination of them may occur in the laminated composites [10]. Most of researchers have studied the translaminar fracture behavior of laminated composites under mode I loading condition [11][12][13][14][15][16]. For example, Underwood and Kortschot [11], Gigliotti and Pinho [12] measured the translaminar fracture toughness (TFT) of the laminated composites reinforced by carbon bers.…”

“…These researchers obtained the mode I translaminar fracture toughness of ax/epoxy laminated composites under compressive and tensile loading states. The in uence of matrix type on the translaminar fracture toughness of laminated composites was evaluated by Haldar et al [15]. These researchers used unidirectional carbon bers to reinforce the laminated composites.…”