Prediction Between Instrumented Impact Test And Three-Point Bending Fracture Toughness Using Local Approach

Prediction and assessment of welded structure based on fitness for purpose are often considered in the engineering. They have large value in theory and praxis. Critical value of J integration JIC or critical value of crack tip opening displacement δC are used as fracture parameter at present defect assessment criterion. JR or δR resistivity curve are used as fracture parameter when ductile crack extension are considered. The failure of structure can be determined by comparison of fracture diving force and fracture resisting force. But recent research indicates that JIC or δC are not material constants like yield point, which are affected by thickness of sample and depth of crack and so on. JR or δR resitivity curve severely are affected by specimen pattern. It indicates that present fracture assessment and predict methods of defect structure based on traditional fracture parameters can not predict structure safe scientifically. It is the sixty-four-dollar question of present elasto-plastio fracture theory that using which fracture parameter which can unify fracture behavior of specimen and actual structure. Two methods are used to analyze the question from various viewpoints. One is the two-parameter characterization of crack-tip stress and deformation fields, such as the J-T and J-Q approaches. The other is local approach.COD and instrumented impact tests are usual fracture toughness tests and various fracture mechanics parameters such as J integration and δC can be transferred in some cases. It is very important that predicting some experimental results from another experimental tests using local approach. Uniaxial tension test, Charpy-type test, instrumented impact test and COD test of X65 pipeline steel are made and material mechanical properties are analyzed. Statistical analysis indicates that crack tip opening displacement of fracture parameter eigenvalue at -78?C obey three parametric Weibull distribution; Program of solving local fracture parameters and prediction program between COD and instrumented impact test are made and proved true through experiments. Local fracture parameters are calculated through instrumented impact test. Companion between finite element analysis results and experimental results prove that finite element analyses are true. Stress fields are analyzed on the basis of finite element analyses. Prediction results indicate that prediction between instrumented impact test and COD test using local approach without obvious ductile crack propagation is reasonable.