Papers by Keyword: Crack Arrest

Abstract: Modern pipeline steel has high toughness and ductility, which can effectively prevent long-distance crack propagation. The full-scale blasting test is the most effective method to verify and evaluate the crack propagation and arrest behavior in high-grade pipeline steel pipes. This article investigates the crack propagation and crack arrest behavior of X90 grade natural gas pipeline steel pipes through full-scale blasting tests. The test results show that once the X90 grade natural gas pipeline steel pipe cracks and propagation under a pressure of 12MPa, as long as the Charpy impact toughness CVN of the steel pipe is greater than 286J, it can ensure effective crack arrest of the pipeline, providing technical support for the application of X90 high-grade pipeline steel pipe in high-pressure transmission pipelines.

Abstract: The detour effect and Joule heating of electropulsing is employed on crack arrest. With respect to Inconel 625 alloy, the relationship between discharge parameters and the area of fusion zone, microstructure around the crack tip and mechanical properties are studied. The experimental results indicate that the area of molten hole is directly proportional to the electric energy input. The microstructure ahead of the crack tip is refined and uniform with the increase of electric energy input. The optimum discharge parameter range, which contributes to the improvement of comprehensive mechanical properties, can be obtained.

Abstract: Hamiltonian of the solid body with a crack inside in field of tensile stresses was derived. Hamiltonian equations describe process of crack propagation. A crack propagation was considered in heterogeneous material when in ground matrix present inclusions with work-of-fracture per unit surface significantly greater than in the matrix. Condition of cracks arrest in such system was found and length of path, passed until crack’s stop, was calculated.

Abstract: Our purpose is to propose a methodology for assessing dynamic crack propagation laws under mixed-mode loading. Dynamic brittle fracture experiments are performed on polymethylmethacrylate (PMMA) in which mode combination changes and crack arrest phases occur. Then, these experiments are numerically reproduced by using the eXtended Finite Element Method (X-FEM) in order to validate the algorithms and the criteria assumed.

Abstract: In this study, the effect of thickness on the fracture toughness of the steel plate with the thickness of 80mm has been investigated by the wide plate tensile test and ESSO test. The fracture toughness for crack initiation and propagation was evaluated quantitatively for the full thickness specimen. It was found that EH-36 grade steel with the thickness of 80mmt showed the KIC value of 164kgf/mm1.5 at -145°C. Also, large-scale ESSO test result showed that the steel with the thickness of 80mm had 520kgf/mm1.5 at -10°C. Although it was known that the fracture toughness decreases with the increase of the plate thickness, EH-36 grade steel with the thickness of 80mm had enough values of fracture toughness to prevent the crack initiation and arrest the brittle crack propagation.

Abstract: When a suitable pulse current is introduced into a metal die containing a crack, the current concentration effect is immediately apparent, small welded joints are formed at a small sphere near the crack tip inside the metal die by metal melting as a result of the heat concentration effect. An axial symmetric metal die with a half–embedded crack on the top face is the object studied. The high intensity pulse current is switched on and flows from the outer to the inner surface of the hollow metal die. The complex function method is used to solve for the temperature field around the crack tip at the moment when the pulse current is switched on. The expression for the temperature field provides the basis for determining the current density and current direction. The experiment surveys show that the temperature around the crack tip grows up instantly above the melting point of the metal, the round crack tip is melted.

Abstract: As a retardation of fatigue crack propagation occur under two step loading such as high to low loading, it is difficult to predictt the fatigue life in variable loading conditions. Therefore, the mechanism of retardation was investigated by changing the ratio of two step-loading in some materials in this paper. It is found in this study that when the ratio of low loading to high loading is less than 50 %, crack arrest occur in agreement with Elber’s formula about crack closure. We believe that crack closure phenomenon is the main problem in considering mechanism of crack propagation in the second stage. In this paper it is estimated that crack closure phenomenon arises because tensile plastic zone at crack tip is compressed by surrounding elastic zone. On the basis of the crack closure phenomenon, the mechanism of crack propagation in the second stage is proposed.