Propagation rate of large cracks in stiffened panels under tension loading

Cyclic tension fatigue tests were conducted on approximately half-scale welded stiffened panels to study propagation of large cracks as they interact with the stiffeners. A linear elastic fracture mechanics analysis was used, to simulate the crack propagation, and gave reasonable agreement with the experiments. The range in stress intensity factor (Δ K) was determined with either a finite-element (FE) analysis or an analytical model at increments of crack length. Analytical and FE models included an idealized residual stress distribution similar to what was measured in the panels. Crack propagation rate as a function of Δ K was estimated using the Paris law with upper-bound coefficients. The experiments and analyses show little sensitivity to stiffener type. The models developed in this project can be easily reproduced and can be used to assess the remaining life of ships with large cracks, leading to more accurate assessment of safety and more efficient scheduling of repairs.