Fracture Mechanism Study of Flake Glass Filled RIM Urethane Systems

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Abstract
Impact resistance in reaction injection molding (RIM) polyurethanes is desired in automotive applications such as fascia and exterior body panels. In these applications, flake glass is usually added to control thermal expansion and contraction, which adversely affects the impact damage resistance of the composite. It is, therefore, important to investigate and understand the impact failure modes involved in the loss of this damage resistance. The present study examines the major mechanisms of fracture initiation under a variety of loading conditions. Four distinct modes of crack initiation, namely: (1) debonding at the glass/matrix interface, (2) tensile cracking in the matrix, (3) multiple glass breakages in the central region of glass flake, and (4) matrix cracking and fibrillation at the edge surface of glass flake, have been identified. These fracture modes are discussed with respect to existing elastic stress analysis theory involving short glass fiber. This fracture mechanism study is carried out with the aid of a model glass filled system. The failure modes in the model system are followed by optical microscopy. The results are then compared to a real system which is impact tested and studied by scanning electron microscopy.

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