| The influence of the stop hole on the fatigue life of sheet metal is complex and changeable.In this paper,the industrial pure iron DT4 C is taken as the object,and the influence rule of the shape and position of the stop hole on the fatigue crack propagation performance and fracture mechanism of the plate specimen is studied.The main research contents are as follows:1.Using a 4 mm diameter circular/a 4mm long diameter and a 2mm short diameter elliptical stop hole,removal length of crack tip(0.3 mm,0.6 mm,and 0.9 mm,respectively)were investigated for the fatigue cracks of the sheet metal expanded compact tensile specimen(E-CT specimen).The effect of the expansion rate and life time was investigated.The results of the experiment showed that the elliptical stop hole with a cut-off amount of 0.6 mm had the largest increase in fatigue life and about 400% more fatigue life than the conventional sample.The microstructure and micro-Vickers hardness of crack tip specimens were observed and measured respectively.The position and size of plastic zone at the crack tip were analyzed.The influence of plastic zone and crack tip on fatigue crack growth life and regularity was explored.2.The effect of the crack line on the fatigue crack growth rate and life of the sheet metal expanded compact tensile specimen(E-CT specimen)was studied by using the line of 5mm and the circular arc with the radius of 3mm and the diameter of the circular hole of 1.2mm.The metallographic structure and the micro Vivtorinox were carried out on the tip specimens of the forthcoming instant crack.The hardness was observed and measured,the position and size of the plastic zone at the crack tip were analyzed,and the metallographic structure and microhardness of the crack tip specimens were measured,and the fracture mechanism of fatigue specimens was analyzed by scanning electron microscope.3.The ANSYS simulates the crack tip plastic zone and the crack tip stress field.When the crack lengths are different,the stress analysis of the crack tip forward expansion path is performed;simultaneously,the stress analysis of the crack propagation path along the trailing crack tip of the stop crack is simulated to assist the crack.Effect of tip passivation on crack tip stress,crack tip plastic region and crack growth rate. |
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