Investigating Cumulative Damage in a Highly Filled Polymeric Material

Abstract

Abstract : When a highly filled polymeric material consisting of many fine particles is stretched, the sizes and distribution of the filler particles, the crosslinking density of the polymer chains, and the variation of the bond strength between the particles and binder can produce highly nonhomogeneous local stress and strength fields. Because of the particle's high rigidity relative to the binder, the local stress is significantly higher than the applied stress, especially when the particles are close to each other. Since local stress and strength vary in a random fashion, the failure site in the material also varies randomly and does not necessarily coincide with the maximum stress location. The damage may appear in the form of microcracks and microvoids in the binder, or in the form of particle binder separation known as dewetting. With time, additional particle binder separation and vacuole formation takes place. In this study, a damage parameter based on linear cumulative theory was used to determine the damage state in a highly filled polymeric material under constant strain rate and dual-strain rate loading conditions. During the tests, volume dilatations were measured. Relationships among the damage parameter, volume dilatation, and the constitutive behavior of the material were investigated. In addition, ultrasonic techniques were used to measure the relative ultrasonic attenuation coefficient, alpha, as a function of the applied strain under constant strain rates and cyclic loading conditions. The characteristics of internal damage, measured in terms of alpha, were determined. Also, a time-dependent cumulative damage model under constant strain rate condition was developed and the applicability of using this model to predict damage was discussed.