Coalescence criteria for coplanar multiple surface cracks

New criteria are proposed to predict the coalescence for coplanar multiple surface cracks under uniform tensile loading. The coalescence is assumed to occur when the internal plastic zones between cracks are attached, or the brittle fracture condition is satisfied. The plastic zone sizes for the coplanar surface cracks are approximated using the Dugdale solution for the coplanar through cracks by empirically modifying the effect of the three-dimensional profile. The stress intensity factor of the multiple surface cracks is calculated based upon the Newman-Raju equation by multiplying the finite width and mutual interaction factors. The applicability of the proposed criteria is verified by correlating with the constant amplitude fatigue growth data. It is shown that the proposed coalescence criteria are superior to the ASME design rule.