The hydrothermal treatment was applied to jute fibers and the destruction behavior of middle lamella that cements between the adjacent fibrous cells of jute was investigated. The destruction of middle lamella seems to be brought about by the decomposition of lignin-carbohydrate-complex through the hydrothermal treatment especially at a temperature higher than 160 °C.
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.
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.
