ON PROPAGATION OF SHEAR CRIPPLING (KINKBAND) INSTABILITY IN A LONG IMPERFECT LAMINATED COMPOSITE CYLINDRICAL-SHELL UNDER EXTERNAL-PRESSURE

A fully nonlinear analysis for prediction of shear crippling (kinkband ) type propagating instability in long thick laminated composite cylin drical shells is presented. The primary accomplishment of the present investigation is prediction of equilibrium paths, which are often unst able, in the presence of interlaminar shear deformation, and which usu ally deviate from the classical lamination theory (CLT)-based equilibr ium paths, representing global or structural level stability. A nonlin ear finite element methodology, based on a three-dimensional hypothesi s, known as layerwise linear displacement distribution theory (LLDT) a nd the total Lagrangian formulation,is developed to predict the aforem entioned instability behavior of long laminated thick cylindrical shel l type structures and evaluate failure modes when radial/hydrostatic c ompressive loads are applied. The most important computational feature is the successful implementation of an incremental displacement contr ol scheme beyond the limit point to compute the unstable postbuckling path. A long (plane strain) thick laminated composite [90/0/90] imperf ect cylinder is investigated with the objective of analytically studyi ng its premature compressive failure behavior. Thickness effect (i.e. interlaminar shear/normal deformation) is clearly responsible for caus ing the appearance of limit point on the postbuckling equilibrium path , thus lowering the load carrying capability of the long composite cyl inder, and localizing the failure pattern, which is associated with sp ontaneous breaking of the periodicity of classical or modal buckling p atterns. In analogy to the phase transition phenomena, Maxwell constru ction is employed to (a) correct the unphysical negative slope of the computed equilibrium paths encountered in the case of thicker cylinder s modeled by the finite elements methods that Call to include micro-st ructural defects, such as fiber waviness or misalignments, and (b) to compute the propagating pressure responsible for interlaminar shear cr ippling or kinkband type propagating instability. This type of instabi lity triggered by the combined effect of interlaminar shear/normal def ormation and geometric imperfections, such as fiber misalignment, appe ars to be one of the dominant compressive failure modes for moderately thick and thick cylinders with radius-to-thickness ratio below the co rresponding critical value. A three-dimensional theory, such as the LL DT; is essential for capturing the interlaminar shear crippling type p ropagating instability. (C) 1997 Elsevier Science Ltd.