| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 87 === The pressure vessels are important structural components in industry. Small cracks, due to the unappropriate manufacturing process of long-term exposition to bad environment such as high temperature or internal pressure, may be induced in these structural components. Those cracks will grow up to the critical size and finally to cause catastrophic damage. Among the factors that affect the growth and propagation of cracks, the effects of hydraulic pressure applied on the fracture surface can not be ignored. The main purpose of this paper is to evaluate the safety of the integrity structure with cracks by using stress intensity factors and strain energy density theory.
Five cases which are the circumferential, the longitudinal and inclined (α＝30o、45o、60o) internal semi-elliptic cracks are considered. In the first two cases, the variations of the stress intensity factors along the elliptic crack front (2ψ/π) are obtained and plotted with or without considering the hydraulic pressure applied on the crack surfaces. Since the last three cases is a kind of mixed mode crack problem, its fracture behavior has to be evaluated via the use of strain energy density theory. All the results, including the Smin’s and the angles of crack extension, have been computed. It is shown that the hydraulic pressure plays an important role in the consideration of the safety of pressurized vessels. Also, it have been proved that the poisson’s ration makes the caseα＝30o more dangerous than the others.
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