Side-groove influenced parameters for determining fracture toughness of self-healing composites using a tapered double cantilever beam specimen

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© 2014 Elsevier Ltd. The influence of side grooving on the parameters, m and β, in the calculation of fracture toughness for self-healing composites is investigated with 3D tapered double cantilever beam models. The impact of side grooving is elucidated through investigation of both specimen compliance and stress intensity factors along the crack front for models differing in crack length and groove ratio, the ratio of specimen thickness to crack width. The models exhibit a linear change in compliance (C) with crack length (a), allowing for a crack-length-independent determination of fracture toughness owing to a constant m value. However, dC/da increases by ~20% as the groove ratio changes from 1 to 6 showing that the parameter m is groove ratio dependent. This influence on m has not been accounted for in previous studies on self-healing composite fracture toughness. Stress intensity factors were also found to depend on groove ratio. Those at the specimen mid-plane were exponentially fitted as a function of groove ratio and the determined exponent agrees with the analytical form of β that is suggested by ASTM. Stress intensity factors at the intersection of the crack front with the side groove give a higher exponent due to the local stress concentration. Exponents from both simulation and experimentation fall within the theoretical bounds set forth by Freed and Krafft while the value currently used in self-healing literature falls outside these bounds. In the light of these findings, an alteration to the current method of calculating fracture toughness for self-healing material is suggested.

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Theoretical and Applied Fracture Mechanics