Study Of Ⅰ+Ⅱ Mixed Mode Crack Propagation In Ta2

As having excellent corrosion resistance and comprehensive mechanical properties, TA2 is one of the commonly used materials for pressure vessels. Crack defect is the major source for the failure of equipment and thus, the crack initiation and propagation are much concerned in engineering. In this thesis, crack transformation propagation and the overloading retardation effect in TA2 are studied experimentally and metallographic observation and fracture morphology analysis are also carried out to discuss Ⅰ+Ⅱ mixed mode crack propagation mechanism. The main conclusions are as follows:(1) Experiments were carried out on the Ⅰ+Ⅱ mixed mode notched-crack fatigue propagation in TA2 plate under constant amplitude loading. It is found that after initiation from the crack tip, the new formed crack propagates in a Mode I form. The fatigue crack growth rate is controlled by Mode I stress intensity range(2) Experiments under constant amplitude loading with overloading were also performed. It is found that overloading has no effect on the new crack growth path. However, the overloading has great influence on the crack growth rate. Owing to the residual compressive stress zone formed after overloading, crack initiation and propagation become much difficult, but the crack growth rate is recovered out of that zone.(3) Metallographic experiment shows that the crack growth path is transgranular without obvious branches. Macrofractgraphic observation found that the material has better plasticity. There exist beach lines after overloading and under the same magnitude of overloading, the longer the crack length, the wider the beach line, which means that the larger that effect of the overloading is. Micro fractgraphic analysis show that the striation density increases remarkable after overloading, which means the crack propagation is slowed or the overloading retardation effect occurs.