Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : October 07, 2017 - October 09, 2017
Occurrence of fatigue crack cannot be prevented in industrial structures under various severe conditions. In maintenance of these structures, early detect of fatigue crack on material surface and are required. “Making of stop hole” and “tighten around crack tip” are introduced as one of emergency control of fatigue crack in sheet metal. Stress concentration around defect is reduced by making of stop hole. Bolt, nut and washer are used to tight sheet metal. "Compressive stress working" and "contribution of stiffness for bolt, nut and washer" are increased with tighten torque. However, these effects are not clarified based on fracture mechanics. In this study, stress concentration density of defect are discussed from 2D numerical simulation results. Finite element analyses are demonstrated based on the condition of fatigue crack growth of previous experimental study. Fatigue crack re-growth process are also simulated in the finite element analyses. J integral and stress intensity factor are measured from stress singular field around fatigue crack tip. Tighten effects are introduced as “additional compressive stress” and “virtual thickness change of numerical model”. The effects of stop hole making and tighten are appeared in histories of stress intensity factor. By working of higher tighten torque, stick condition is caused between the washer and the sheet metal. Washer, bolt and nut are also deformed by cyclic tensile load under stick conditions. Because sheet metal loading is decreased by the tighten, stress concentration is also decreased.
