ESTIMATION OF STRESS INTENSITY FACTORS IN PARTIALLY PATCHED CRACKED COMPOSITE LAMINATES BY MULTILAYER HYBRID-STRESS FINITE-ELEMENT METHOD

A multilayer hybrid-stress finite element model together with two types of composite multilayer elements (MLTUP and MLTPH) which have been developed to analyze patched crack is employed to evaluate the influence of various patch parameters (position, length, thickness and fiber orientation) on the estimation of stress intensity factors in partially patched cracked composite: laminates. Three-dimensional stresses of the laminated panel, adhesive and patch are accounted for. The assumed stress field satisfies the equilibrium conditions within each layer, the interlaminar traction reciprocity conditions at interlaminar boundaries and traction-free boundary conditions on the bottom surface of the laminate. Once the traction boundary conditions on the top surface of the laminate are free, the conditions can be enforced by employing a Lagrangian multiplier technique. The interelement traction reciprocity condition at interelement boundaries is then satisfied through the introduction of other Lagrangian multipliers which are physically the interelement boundary displacements. The stress parameters assumed and the number of nodes taken are independent of the number of layers. The multilayer elements devised are therefore applicable to deal with the patched cracked laminate with a large number of layers. In addition, the technique developed also has the potentiality to treat general patched cracked laminates even with unknown stress singularities. The double and single patch configurations for both of the cracked (0 degrees/90 degrees)(s) and (-45 degrees/+45 degrees)(s) laminates under uniaxial tension are considered as examples. The patch made of composite material is a strip and covers only a part of the crack flanks. Excellent correlations between the present computed results with the referenced solutions show the versatility of the technique employed.