The Safety Evaluation Technology Research On The Flaw Of Hoop-wrapped Composite Cylinder With Steel Liner

Hoop-wrapped composite cylinder with steel liner, which owns many merits aslight weight, high strength, excellent air tightness, corrosion resistance and lowproduction cost, etc. is widely applied in automobile industry. However, in the courseof its use, there are various defects in the cylinder, which surely affects its safety.These defects can be categorized into two types mainly: One is the defects on the liner,which primarily come from corrosive defects caused by the unconformity with relatedprescript during gassing and fatigue defects caused by repeating loading. The other iswinding layer defects, which mostly results from external factors as friction andscoring. This thesis studies the defect of liner and winding layer, mainly focusing onthe three position defects (middle liner, middle winding layer and the end part ofwinding layer) and two crack sizes (depth and length): firstly, considering the casethat defects occur only on the inside wall of middle liner, then, taking into account thedefects which happen on winding layers, based on which the three different defectivemodel (middle liner defective model/middle liner and winding layer defective model/middle liner and the end part of winding layer defective model) is built.This article builds the defective and indefective3D models of cylinder andresearches their stress distribution under working conditions respectively by ANSYSsoftware, which acquires the distribution of actual stress, intensity of stress,equivalent and interfacial stress of defective cylinder by using the path componentsuperposition method which is unable to get through commercial software, andanalyzes the influence of different defect locations, residual pressure, depth and lengthof crack on strength character.Fatigue life of cylinder under different residual pressure and defective size canbe calculated by reference to the fatigue analysis method in analysis and designstandard, analyzing the influence of different defect locations, residual pressure, depthand length of crack on fatigue life. That is, under the same residual pressure, withdefect in the middle of cylinder body, fatigue life of cylinder, at certain range, hasnothing to do with the depth of crack. When the depth of crack surpasses that certain value, the defective part will directly determine fatigue life of cylinder. On the otherhand, fatigue life of cylinder with defects in the end part of the winding layer shows atotally different tendency, compared with those with defects in the middle of cylinderbody. Under such circumstance, fatigue life decreases with increasing depth of crack.Explosion and fatigue experiment, the simulation result and fatigue analyzing methodare tested to be reasonable and accurate. Finally, this paper analyzes the change law ofrelationship between the maximum circumferential stress, fatigue life and residualpressure, defective size of different positions, and compares the influence of differentdefect model on fatigue life of cylinder. With respect to defective cylinder, the thesisexecutes the fitting to the relationship between the maximum circumferential stressand residual pressure, the depth of crack, which would provide an evaluation methodof predicting cylinder life.