Fracture Toughness Characterization of Welds and HAZ at Various Loading Rates Using Differing Specimen Geometries

The characterization of the fracture toughness in weld and HAZ materials employed in nuclear power plant (NPP) piping is essential to assess the structural integrity of the piping systems under various loading conditions, when cracks/flaws are present in the weld/HAZ material regions. The current investigation was undertaken to determine the resistance to crack propagation using ASTM E1820 standard based compact tension, 1T-C(T), specimens with initial crack in the weld centerline (WCL) and adapted 1T-C(T) specimens with slanted cracks in the heat-affected-zone (HAZ) materials. The experiments were conducted at loading rates ranging from quasi-static to dynamic rates estimated for seismic loading at normal operating temperature. The fracture tests were also conducted at various loading rates to verify the occurrence of phenomena such as dynamic-strain-aging (DSA) that could potentially cause significant changes in the material toughness, J-R curves of the weld and HAZ materials. The investigation also compared the fracture toughness obtained from 1T-C(T) fracture tests with those obtained from impact loading on single-edge-notch-bend (SENB) specimens in a drop-weight-tear-test (DWTT) machine and others obtained from SEN(B) specimens tested at quasi-static loading rates. The range of crack growth resistance curves obtained from the various fracture tests and specimens were used to develop bounding JIc and J-R curves that are to be employed in computational finite element analysis (FEA) that are used determine crack propagation and stability in the weld/HAZ materials of NPP plant piping.© 2011 ASME