Monday, 11 October 2004 - 4:20 PM

This presentation is part of : Graduate Student Competition

Microplane Model for Strength, Fracture and Softening Damage in Fiber Composites

Alessandro Beghini and Zdenek P. Bazant. Northwestern University, Department of Civil and Environmental Engineering, 2145 Sheridan Rd., Evanston, IL 60208

Deformation and failure of fiber composites have been extensively studied experimentally and analytically in the linear range of material behavior and, for metal-matrix composites, also in the hardening nonlinear range. However, a mathematical model for postpeak softening damage, particularly the progressive fracturing, of quasibrittle polymer matrix composite is not yet available. To predict the size effect in static failures and the energy absorption capability under dynamic loading (e.g.: impact, blast or shock), a micromechanical model for progressive failure, caused by softening damage of the laminate, is required. It is shown that the microplane constitutive model, already successfully applied for concrete, rocks, ceramics and soils, is able to describe the distributed progressive fracturing, with the associated softening related to a certain material characteristic length, and can do so not only in the direction transverse to the fiber but also in the longitudinal direction. The model calibration has so far been based only on uniaxial tensile loading experiments, but extension to multi-axial loading is also discussed. Further discussed are questions of applicability of Dvorak's transformation field analysis, stemming from the Mori-Tanaka model, to the distribution of strain between the components, fiber and matrix, on a generic microplane. Experiments aimed at calibrating the softening parameters and material characteristic length are under way.

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