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The aim of this paper is to show a new geometrical specimen in fatigue to define the behavior of semi elliptical crack growth in thick-walled pressure vessels. This research emphasize on the importance of the behavior of fatigue crack in test specimen and real conditions in vessels .In other word, there must be more adaptations between stress intensity factor in new specimen and real vessel that includes crack along the wall, so, under Fatigue loadings, as a result, more adaptation will be obtained between growth speed and relative crack lifetime according to loading cycles. By introducing this new specimen we compare the results of fatigue loading on propositional new specimen with results of vessel fatigue loading and standard specimen. We estimate the behavior of fatigue crack growth in specimen and pressure vessel with (FEM) and experimental method. In order to comparing of limit component with experimented results, some piece of with new specimen made of steel (ck45) can be used and all of these must be under fatigue testing and results are obtained in these methods.

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Curved thin-walled structures are extensively used in many industrial applications including aviation industries. These parts have a specific role in manufacturing of helicopter main rotor blade. Fracture mechanics parameters are needed for life estimation and life extension of curved thin-walled structures. Standard methods of fracture mechanics testing are not applicable to these parts because of curvature and thinness of the specimens. So new test methods for these specimens is necessary to be investigated and developed. Vast trying has been done by scientists to overcome these problems and some theories and experimental methods such as the theory of fracture of thin-walled curved plates, the conventional burst test method and some new non-standard test methods has been initiated and developed. In the present paper, first of all, the theory of thin-walled curved plates has been briefly presented to link the behavior of curved specimens to the flat ones and the conventional burst test (BT) method has been accordingly introduced. Then, the newly developed non-standard test methods such as compact curved tension (CCT), pin loading tension (PLT), three points bending (TPB), double edge notched tension (DENT), internal conical mandrel (ICM) and X-specimen have been reviewed. Finally, a comparison between mentioned methods had been done to determine the most appropriate one.