Static and dynamic large deflection flexural response of graphite- epoxy beams

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Virginia Tech

In support of crashworthiness studies of composite airframes, the present study was undertaken to understand the large deflection flexural response and failure of graphite-epoxy laminated beams. The beam specimens were subjected to eccentric axial impact loads and to static eccentric axial loads, in order to assess the damage caused by impact.

A geometrically and materially nonlinear analysis of the response and failure of the static test specimens is presented. The analysis employed an incremental, noniterative finite element model based on the Kantrovich method and a corotational solution technique. Width-wise effects are included by assuming specific forms of the displacements across the width, with length-wise variation introduced as a degree of freedom. This one-dimensional, 22 degree of freedom finite element accurately predicted the load-deflection and strain-deflection responses of the static test specimens.

Inclusion of nonlinear material behavior was found to be important in correctly predicting load-deflection response of uniaxial materials, while inclusion of width-wise effects was determined to be more important for laminates with off-axis plies due to the existence of coupling between bending and twisting curvatures (D16and D26). Once material nonlinearity begins to occur in flexure, even symmetric laminates exhibit bending-stretching coupling due to different material response in tension and compression.