THRESHOLD CRACK GROWTH IN A36 STEEL

Objectives of the study were to investigate the regions of high cycle and threshold fatigue crack propagation and to correlate the findings with observed results from tests of welded structural details. The crack propagation phase focused on cycling plate specimens at low ranges of stress to determine levels of stress for which no crack extension appeared. Results indicated a definite trend towards a threshold for fatigue crack propagation. Through a fracture mechanics analysis this threshold region of cyclic stress was described in terms of the range of the stress intensity factor for the plate specimens. The crack growth and threshold value were used to predict stress ranges which would not cause failure at the weld toe of cover plates fillet-welded to beam flanges. A mathematical model was used to relate the stress conditions existing at the weld toe to the stress applied on the detail. Using the threshold value of the stress intensity factor range found in the crack growth studies, a runout stress range was derived which agreed well with results of coverplated beam studies.