The objective of this research effort has been to gain a better understanding of energy absorption behavior in composite laminates. Crush tests of nine flat plate specimens with three different lay-ups of T650-35/F584 graphite/epoxy fabric were performed to evaluate the mechanisms that contribute to the energy absorption process. A nonlinear finite element approach was used to model the sustained crushing of the flat plate, and a progressive failure model was implemented as part of the finite element analysis to enable modeling of the fundamental mechanisms involved in the crushing behavior. The progressive failure model was based on linear elastic fracture mechanics for prediction of crack growth and a set of failure criteria for predicting fiber/matrix failures that occurred as a result of large deformations. Friction between the specimen and the crushing surface was included in the model. Predicted values of sustained crushing stress agreed with experimental results for the flat plate specimens within nine percent.
An analytical methodology for predicting energy absorption capability of composite open-section stiffeners is oresenled. The methodoloev is based a n comnosite laminate and elastic stahilitv theories and on ... nundintensional crippling dalu. Applicalions of lhi\ mrlhudology lo gmphitelcpoxy rhan~nrl and ha1 stiffenrn are pre~enlcd. 'rhc ynphil~~l./~po~y \liffencr dr\igns tltal ,"err. qtudicd ulilircd ply drop-nlTs 11, inilidtc crushing andfa maintain ela;iestabil&. The analytical ;esults for the energy-absorbing capability of the stiffeners are compared with test results. The energy absorption characteristics associated with different laminate designs are identified, and their significance to the design of energy-absorbing stneners is discussed.
Notation
A;Element cross-sectional area (in2) and crippling of metallic stiffeners (Refs. 1-3). Consequently, . , b Element width (in.) there are-reliable design methods available that are routinely used . . Dij Laminate flexural stiffness (Ib-in.) for conventional metallic structural elements. With respect to E Stiffener average elastic modulus (IbIin.2) local buckling and crippling of composite stiffeners, several research efforts have been directed at generating experimental Ei Element elastic modulus (lblin.2) databases, and some design support testing has been conducted I Element thickness (in.) v, v, Laminate Poisson's ratios P Minimum radius of gyration of stiffener cross section (in.)
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