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.
Resistance spot welding of MS1200 martensitic advanced high strength steel: Microstructure-properties relationship
Abstract This paper addresses the microstructure and tensile-shear mechanical performance of MS1200 Giga-grade martensitic advanced high strength steel resistance spot welds. The key phase transformations in MS1200 welds were lath martensite formation in the fusion zone (FZ) and upper-critical heat affected zone (HAZ), new ferrite formation in the inter-critical HAZ and martensite tempering in the sub-critical HAZ. The MS1200 welds were featured by a near matching hardness in the fusion zone and under-matching hardness in the heat affected zone (HAZ) compared to the base metal. At certain process window a complete nugget pullout and separation was observed with high post-necking tearing energy. The interfacial to pullout failure mode transition was explained in the light of FZ hardness as well as the HAZ softening associated with martensite tempering in the sub-critical HAZ. The load bearing capacity of MS1200 welds failed at interfacial mode was strongly depends on the FZ size as well as the FZ hardness. However, the peak load of welds failed at pullout mode was a function of HAZ softening as well as the plastic constraint in the HAZ associated with the hard upper-critical HAZ/FZ and martensitic BM.
Fascism in Britain: A History, 1918-1985
Tracing its origins from shortly after the World War I, this book presents a portrait of fascism in the 1930s. It reassesses Mosley's career, describes the reasons for internment in 1940 and the effect it had on leading fascists, exposes the famous Britons who subscribed to fascism, reveals the ominous re-emergence of the tradition after 1945, and explains its remarkable persistence into the l980s.