Responses of cracked stiffened plates to low-cycle fatigue loads

Abstract Low cycle fatigue (LCF) crack propagation experiments are conducted on 12 stiffened plate specimens with centrally located through cracks using MTS Dynamic Test System. The a-N curves of the specimens are obtained via crack propagation videos recorded by an electron microscope. Accumulated maximum crack opening displacement (AMCOD) is measured by an extensometer. Accumulated mean strain (AMS) is calculated from the loading rod displacement data recorded by the computer that controls the test machine. The effects of LCF loading on crack propagation, AMCOD and AMS are analyzed based on the experimental results. The parameter values in the general constitutive relation for fatigue crack growth are derived through curve fitting the da/dN-a results. Comparisons of AMCOD and elongation of the 12 specimens show that the two parameters are almost equal at all times; correlation between AMCOD and elongation is almost 1 for all 12 specimens. AMCOD is the main cause of elongation. The three responses (crack propagation, AMCOD and AMS) of the specimen to LCF loading occur simultaneously. Evaluating crack propagation length, AMCOD and AMS together can increase the accuracy of the evaluation of the ultimate strength of cracked structural elements in a ship.