The fatigue and fracture performance of a cracked plate can be substantially improved by providing patches as reinforcements.
The effectiveness of the patches is related to the reduction they cause in the stress intensity factor (SIF) of the crack. So, for reliable design, one needs an accurate evaluation of the SIF in terms of crack, patch and adhesive parameters. In this investigation a finite element technique to compute the SIF through the J-integral for patched cracked plates is presented. TRIM6 and TRUMPL elements of ASKA are employed to model cracked sheet and cracked sheet-adhesives-patch regions, respectively. Path independency of J-integral for unpatched plates is shown by considering many contours. For patched plates, the contours chosen do not enclose the patch-cracked sheet region. The values of SIF's are obtained for unpatched edgecracked, unpatched centre-cracked and patched centre-cracked plates. These values are compared with the analytical and numerical results existing in the literature. This study shows that conventional finite elements can be used to model patched cracks and reasonable estimate of SIF can be made via the J-integral. NOTATION J-integral Contour surrounding the crack tip Traction vector defined according to the outward normal along I-, Fig. 1 Displacement vector at a point on contour, 1 = iu+jv Arc length along the contour Crack length and semi crack length for edge crack and centre-crack plates respectively Width and semi width for edge-crack and centre-crack plates respectively Length of plates State of stress at a point (x. y) State of strain at a point (x, v) Young's modulus of the cracked plate Strain energy density, l/2 (CT~E, + o,.&~ + CT&,) Directions perpendicular and parallel to crack line Stress Intensity Factor (SIF) Reference value of SIF SIF for patched plate SIF for unpatched plate Applied stress Thickness of patch Thickness of sheet