Elastic-plastic finite element analysis of thermoplastic composite plates and shells

Abstract

A quadrilateral Mindlin-type plate finite element is developed for the elastic-plastic analysis of laminated composite plates and shells. A simple one-parameter plasticity model is used for characterizing the plastic behavior of the AS4/PEEK thermoplastic composite. A facet representation of the general shell geometry is adopted for the shell structural analysis. Numerical examples illustrate the effect of plasticity on the residual stresses in AS4/PEEK thermoplastic composite plates and shells after they are subjected to lateral pressures. NLIKE thermosetting composites, advanced thermo- plastic composites can be used to form structures by using conventional high-speed, hot-forming techniques and can be reformed under certain pressure and at certain tem- perature without losing their integrity and strength. However, understanding their forming behavior presents a challenge to manufacturing engineers; In forming fiber reinforced ther- moplastic composites, conventional trial and error method may prove costly or even futile because of the many param- eters that may affect the quality of the final product. High- speed computers combined with finite element technique pro- vide us with powerful tools in simulating the forming process and optimizing various parameters, thereby saving much time and expense during the design stage. The forming process of laminated thermoplastic composites often involves plastic bending deformations. Thus, an under- standing of the elastic-plastic response of laminated ther- moplastic composite plates and shells is very important. Although considerable progress has been made in the elastic- plastic analysis of isotropic plate/shell structures, work on laminated composite plate/shell structures is limited. Whang1 considered the elastoplastic finite element analysis of small deformation orthotropic plates and shells with strain hard- ening parameters. Owen and Figueiras2-3 used the semiloof element and thick shell element to study the problem. Their nonlinear material models were based on Hill's modified von Mises yield function and the associated flow rule;47 In the present study, the four-noded Mindlin-type T-element8'9 is chosen for its good performance in overcoming the lock- ing difficulty without introducing the reduced integration technique, allowing the inclusion of bending-transverse shear coupling in plastic deformation. The one-parameter plastic constitutive model developed by Sun and Chen10 is used be- cause of its simplicity j which is even more attractive when cost becomes the overriding consideration in the nonlinear analysis. The facet approximation of general shell geometry11-12 is adopted. The temperature-dependent material properties of AS4/PEEK advanced thermoplastic composites13 are used in the numerical examples.