Constitutive modeling of polymeric composites under various loading conditions

Changming Zhu, Purdue University

Abstract

The plastic behavior of AS4/PEEK composite under monotonic loading was first investigated using a finite element micromechanical approach. The boundary conditions for off-axis loading were discussed, and various unit cells were analyzed. The finite element results were used to establish and verify the one parameter plasticity model. The predicted responses of the composite were also compared with the experimental results. In the second part of the research, uniaxial cyclic tests were performed on unidirectional composite IM7/5260 and matrix Narmco 5260 specimens at various temperatures. Based on the test results, a constitutive model was obtained to describe matrix cyclic plasticity. By assuming linear elastic behavior for fiber IM7, an analytical micromechanical model was used to predict the cyclic plasticity in the composite. In the third part, an overstress viscoplasticity model was proposed to describe the behavior of IM7/5260 and IM7/K3B composites under both loading and unloading conditions. In the model, a three-parameter function was used to describe viscoplastic strain rate. Based on two assumptions regarding the unloading behavior, equilibrium stress was determined using multistep relaxation tests for both loading and unloading. Satisfactory results were obtained using this model. Finally, the behavior of IM7/5260 and AS4/PEEK composite laminates were predicted using the above viscoplasticity model and a rate-dependent one parameter model. It was found that for certain situations, deformation-induced fiber orientation change significantly affects predicting the nonlinear behavior of the laminates, while processing-induced thermal stress played a more important role for other cases.

Degree

Ph.D.

Advisors

Sun, Purdue University.

Subject Area

Aerospace materials|Mechanical engineering

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