Fracture toughness of the molten zone of resistance spot welds
A methodology for measuring the fracture toughness at crack initiation and the crack extension resistance of the molten zone of resistance spot welds under Mode I loading has been developed. The cross tensile test of U-shaped specimens was modified by crack growth monitoring and stress intensity factor determination. The resulting values of fracture toughness at crack initiation are independent of the nugget diameter and of the base material mechanical properties. The crack extension resistance seems to depend on base material mechanical properties and nugget diameter. Mixed cleavage + ductile mode associated to medium values of fracture toughness (54–90 $$\text{ MPa }\,\text{ m }^{0.5}$$) suggested a ductile to brittle transition behaviour. The relatively low fracture toughness (55–59 $$\text{ MPa } \,\text{ m }^{0.5}$$) associated to full interfacial ductile failure was quantitatively related to the high number density of small particles in the molten zone. This study opens the possibility to apply the local approach to fracture under monotonic loading to interfacial failure of resistance spot welds.
Effects of micro resistance spot welding parameters on the quality of weld joints on aluminum thin plate AA 1100
Resistance spot welding (RSW) is widely used in industries such as the aerospace, automotive, and electrical application industries. RSW is very useful for joining aluminum and its welding parameters lead to good quality joints. This research studied the influence of the welding parameters, such as welding current, welding time, and the electrode force, of micro resistance spot welding (MRSW) on the mechanical properties and fracture of a nugget of aluminum alloy (AA) 1100. AA 1100 plate with a thickness of 0.4 mm was used in this experiment. An alternating current (AC) RSW machine and electrode were used in this study. The welding parameters used in this study are welding current, welding time, and electrode force. Holding time is assumed to be constant. The welding time values of 6 CT, 8 CT, and 10 CT were combined with a welding current of 8 kV, and electrode forces of 32 kg, 42 kg, and 52 kg. The results showed that by increasing the electrode force, the load rate decreases, and the elongation distance tends to decrease, except for the electrode force of 52 Kg. The effect of the electrode force on the diameter and thickness of the weld nugget was not significant.
Using Small Cracked Round Bars to Measure the Fracture Toughness of a Pressure Vessel Steel Weldment: A Feasibility Study
The research objectives were to demonstrate the feasibility of using small fatigue pre-cracked round bars to measure the initiation fracture toughness of ductile nuclear pressure vessel steels and weldments and to refine and validate experiment and analysis procedures. Initiation fracture toughness values were measured for a duplicate of HSSI Weld 72W, unirradiated, in the temperature range -150° to 50°C, using small cracked round bar (CRB) specimens. The results were compared with the values obtained with 1T-CT specimens. The good agreement between the toughness values measured with CRB and 1T-CT specimens indicates that using small CRB specimens (possibly cut from Charpy bars) to measure fracture toughness is feasible. A relationship between J and the displacement due to the crack δ c r , where δ c r is obtained from extensometer measurements, was established experimentally. Fracture initiation in CRBs of the size investigated here occurred at or near maximum load, with the crack growth prior to maximum load being less than 200 μm. This observation, together with the unique relationship between J and δ c r , open the possibility of greatly simplified testing and data reduction procedures for fracture experiments with CRB.