Abstract
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, effects of emergency control for fatigue crack tip are reported based on experimental results. The specimen material SCM440 has higher yield stress, therefore some fatigue troubles are reported in the SCM440 structures. Under cyclic tensile loading, fatigue crack re-growth from stop hole are observed. Stress intensity factor is measured from the tensile loading density. Parameter about fatigue crack growth (Paris low) are estimated from approximation based on experimental data. Dependence of crack re-growth on tighten torque are also discussed. Retardation of crack re-growth are distinguished by increase of tighten torque.
