Application of bridging-law concepts to short-fibre composites - Part 1: DCB test procedures for bridging law and fracture energy

This is the first paper in a series of four where notch sensitivities, frac ture energies and bridging laws of short-fibre polymer composites are inves tigated. In the context of crack-bridging, the bridging law is an important material parameter. The bridging law can be used in combination with a str ess analysis to address failure problems, for instance large-scale bridging , where linear elastic fracture mechanics is not valid. The bridging law of the material is sensitive to material composition and fibre architecture. Owing to the lack of established procedures, it is of interest to develop e xperimental and analytical methods for determination of the bridging law an d fracture energy of short-fibre polymer composites. A method based on a la rge DCB specimen loaded by pure bending moments is used. Commercial GMT and SMC materials are investigated in addition to chopped-strand-mat laminates based on glass fibres of two different lengths and two thermoset matrices of different ductility. Fracture energies and bridging law data are success fully determined. All materials demonstrate softening bridging laws and thi s is discussed on the basis of observed mechanisms of failure and existing micromechanical models. (C) 2000 Elsevier Science Ltd. All rights reserved.