Abstract
Fracture surface morphology in relation with toughening of thermosets modified with hollow microspheres was studied. Two different toughening methods were employedโone was with (MEH) and the other without (ME) compressive residual stresses around microspheres, respectively. The compressive residual stresses were to increase effective stress intensity factor. Various conditions arising from toughening method, properties of constituent materials, bonding between matrix and microspheres, relativity between bonding and microsphere strengths, and plane stress/strain were derived for part of generalization of fracture surface morphology. Mohr circle representations were employed for relative stress components analysis. New deformation mechanisms contributing to toughening were proposed. A major difference in toughening mechanism between ME and MEH methods was found to be in the location of plastic deformation under plane strain. The plastic deformation of ME was dominantly in matrix and appeared in the form of matrix cavitation. In the case of MEH, it was dominantly in microspheres. It was suggested that compressive residual stress promotes plastic deformation of microspheres caused by โextrusionโ effect. The microsphere deformation in MEH was found also under plane stress although it was not as much as under plane strain. Matrix cavitation in ME under plane stress, however, was not found. ยฉ 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007