Machinery or structural joints aremostly riveted joints, screw
joints orwelded joints.With the development ofwelding technology,
welding is used to make most structural joints. As the
welding heats the base metal by generating high-temperature
heat of 5000–6000 ◦C in a short period of time, the thermal
expansion or cooling of the base metal results in thermoplastic
deformation such as local bending and twisting. Welding
structures usually fracture at the zones whose geometric
shapes change rapidly, such as the weld reinforcement, toe
area of the filletwelding and the fillet area of voids or an opening.
Fracture also occurs as the conditions and environment at
which the welding structure is used become worse along with
the appearance of larger but lighter machines and structures.