Behaviour of Failure in Fillet Welded Joints at Various Temperatures

Abstract

Behaviour of failure in fillet welded joints at low temperature has been seldom inspected, and the fillet welded joint of anti-corrosive steel including a comparatively high P content is thought to be under the condition that brittle fracture is apt to be caused at low temperature. The behaviour of failure in various fillet welded joints at various temperatures is, therefore, investigated in connection with the investigation of resistance to weathering, weldability, workability etc. of arc welded joints.
In the temperature range -120°C-120°C, fracture characteristics of various fillet welded joints under tension are classified in Table 4. The fracture of fillet is classified into two types, i.e. ductile fracture and brittle fracture ; and fracture transition temperatures are obtained rather distinctly. In the case of front fillet weld, the angle of ductile fracture is between 15°and 30°, and on the other hand, that of brittle fracture is almost invariably over 45°, increasing with decreasing temperature and reaching 70°-80° at about -110°C.
In the case of side fillet weld, shear fracture does not occur at the throat section which is minimum section under -60°C, and brittle fracture occurs at the end of fillet in the base metal. The above-mentioned behaviour is thought to be attributable to the fact that the fracture stress of side fillet weld is mostly a shearing stress ; therefore, as at such a low temperature the material becomes very brittle and slip deformation is restrained, the shear strength of fillet exceeds the cohesive strength of base metal remarkably.
The strength of double T fillet welded joint rapidly decreases under -80°C. This behaviour is thought to be caused by the fact that at such a low temperature, the material becomes very brittle, slip deformation being restrained, and stress concentration rapidly increases.
If general condition of ductile fracture and brittle fracture due to combined stresses is assumed as follows : R=τ/σ><t/N, the ratio of shear strength to cohesive strength (t/N) will be about 1-1.6, and very larger than the ratio of shear strength to tensile strength (t/n), at -60°C-20°C.