Contact analysis and experiment of delaminated cantilever composite beam

Cantilever composite beam with strip-type delamination under transverse loa ding was investigated analytically and experimentally. A two-dimensional (2 D) nonlinear finite element code based on updated Lagrangian formulation wa s extended to analyze the behavior of the laminated beams under transverse loading and the local buckling phenomenon of the sublaminate in the delamin ated region. The contact problem between the upper and the lower delaminate d surfaces was dealt with the transformation matrix method, which satisfies the compatibility of displacements and can reduce the number of system unk nowns. The resulting nonlinear system equation was solved by the modified N ewton-Raphson method with a load-controlled scheme in the incremental solut ion procedure. This process was updated for the next increment when the con tact condition was satisfied by iteration. The analytical results are impro ved when compared with the results without contact analysis. A tensile-test machine was modified with a set of fixture to record the load-displacement response of the delaminated cantilever beam; the response was in good agre ement with the analytical ones. The results show that the size of the delam inated region had no significant influence on the stiffness of the laminate d beams with or without local buckling. The stiffness of the delaminated be ams reduced as the delaminated region located further deeper in the thickne ss direction. The normal and tangential contact forces on the surface of th e delaminated region varied along the delaminated length with maximum value s at the point most close to the fixed end. (C) 1999 Elsevier Science Ltd. All rights reserved.