脆性破壊伝播停止特性に関する小型試験法の検討

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Robertson type test method such as double tension test or ESSO test is very popular for the assessment of propagating and arresting properties of brittle fracture of steel plates with fracture mechanics approach. This is a so-called large scale test, requiring large amount of material, the test pieces being very expensive. Thus it is not suitable as a material test method. Recently, double cantilever beam (DCB) test has been proposed as a small scale fracture mechanics test for this purpose. However, it is necessary to machine very sharp grooves on the specimen surfaces in order to guide the crack path on the symmetric axis of specimen. Because of grooves, specimens tend to be expensive, and full thickness properties of plates can not be obtained. Therefore, it is required to develop a new test method which has following advantages ; (1) Specimen is small and not expensive. (2) Test method is simple and convenient. (3) Full thickness properties can be obtained ; i.e, crack propagates straightly on the symmetric axis without any surface grooves. (4) Test result can be evaluated with the fracture mechanics. In this paper, triangle specimens which were subjected to three point bending load were examined. Then, it was found that full thickness properties of crack arresting can be determined with the~ triangle bend specimens which have a pressed notch and gradient temperature distribution. Furthermore, using: finite element method, crack paths of DCB specimen and triangle bend specimen were analyzed with a criterion of maximum strain energy release rate. As a result, it was found that the crack path of DCB specimen is unstable. Namely, in case of ideally symmetric specimen, the crack would propagate along the symmetric axis. However, if any small disturbances exist, the crack deviates from the symmetric axis. On the other hand, the crack path of triangle bend specimen is stable, the crack propagating along the axis even if small disturbances exist.
社団法人日本船舶海洋工学会の論文

脆性破壊伝播停止特性に関する小型試験法の検討

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