THE EFFECT OF STRAIN RATE ON DAMAGE MECHANISMS IN A GLASS POLYPROPYLENE COMPOSITE

Changes in damage accumulation and energy absorption were studied as a function of strain rate in a glass reinforced polypropylene composite during uniaxial tensile testing. The polypropylene matrix was reinforced with long discontinuous glass fibers, arid was manufactured using a du Pont proprietary wet-forming process. Acoustic emission monitoring was combined with mechanical testing and microscopic observation to study details of the damage accumulation process. Maximum stress, strain at maximum stress, arid energy absorption capability all increased with increasing strain rate. Mechanical response, acoustic emission signatures and micrographs of the fracture surfaces all showed a strain rate dependent transition in failure mechanism. Results show that the "apparent" fiber-matrix interface properties changed as a function of strain rate, and were closely coupled to the balance between the time scale of fiber pull-out and the characteristic time scale of resin deformation. Also, a systematic change in total energy absorption capability was used to demonstrate the competition between specific energy absorption (i.e., per unit volume) and the size of the damage zone.