Nonlinear Effects in Unidirectional Elastic Memory Composite Material

The growing application of TEMBO Elastic Memory Composite (EMC) materials for deployable space structures has highlighted the need for an improved understanding of the material’s mechanical behavior. Recent mechanical testing has revealed significant nonlinearity in the stress-strain response of highly-aligned, unidirectional EMC materials. It is hypothesized that the nonlinearity in the material’s longitudinal modulus is due to a combination of nonlinear behavior inherent in the carbon fiber reinforcement and processinduced wavy fiber imperfections in EMC laminates. A model is developed accounting for fiber nonlinearity and process-induced wavy fibers and using this model, a data-analysis protocol is developed that allows the relative contribution of these effects to be separated out of the observed global nonlinear stress-strain response. In essence, this protocol provides an indirect method of measuring the effective magnitude of the wavy fiber imperfections, given an accurate knowledge of the nonlinear elastic response of the fibers, or vice-versa. The results for the test laminates considered indicate that the nonlinearity in the fiber reinforcement is predominately responsible for the nonlinear behavior of the composite material. However, effects due to process-induced wavy fibers on the longitudinal modulus can become significant at relatively high compression strains.

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