Test Proof Of Studying On Space Tank's Crack Enlargement Effects Under Over-Loading

In our country's development process of aerospace industry, we widely use 37SiMnCrNiMoV super high strength steel for high pressure gas cylinders manufacturing materials, but as 37SiMnCrNiMoV super high strength steel has environmental sensitivity, so that most of the problems are stress corrosion crackings, stress corrosion cracking threshold value becomes the main of the research.This article using the improvement of the method for calculating stress intensity factors of crack and considering the front and the rear surfaces on crack common effect of the high oxygenic pressure vessels, it is divided into three parts, separately for each part of the fracture assessment, the stress peak value maximum area, is not necessarily the cylinder portion of the overall fracture easily occur in the most dangerous area, because of the cylinder body thickness direction stress gradient and local reinforcement effect, it makes that the gas bottle mouth transition section into fracture is the most prone to the danger area, After using MSC.MARC2010 finite element based crack model, and the model of different crack areas using different mesh method, on crack tip singularity by degradation of the 20 node unit division, it gets stabilized the J integral values, and then the value obtained for the crack front stress intensity factor calculation, and the calculation results are very close to the result calculating by formula, that is precise, complete simulation of cracked plate drawing process, and through the overload simulation in the course of loading crack first initiation site, an overload indeed improves the residual stress value of the crack tip at the same time, undertook to the model two loading, see two times overload cycle after the end of the crack tip residual stress value increases, illustrate the overload can improve the crack resistance ability of brittle fracture, then the method is verified by experiment, the overload does in improving the residual stress, improve the crack tip plastic deformation has certain beneficial effect, but when the overload number reaches a certain value, the beneficial effects without significantly increasing, it will lead to certain material hardening and the adverse phenomenon, so blind to increase load not only for experimental material and process is a waste, but also may bring adverse effect, should be integrated into the overload times is advantageous with adverse effect, needs more reasonable overload times.Finally, according to the actual situation, small sample dispersion coefficient method is introduced, because space cylinders relative stress corrosion threshold, in small characters capacity conditions often deviates from the actual statistical value, the paper presents the small sample dispersion coefficient is introduced into the space cylinders relative stress corrosion threshold value, consider the reliability, confidence level and the number of experimental overload factor influence, it is closer to the actual statistical value, for stress corrosion threshold relative coefficient theory value and overload times rationality offered new thinking, has the certain experimental reference value, so it is suitable for identifying the appropriate relative stress corrosion threshold value and overload times provides statistical support, has the certain instruction significance.