Welding Residual Stress and Distortion
The panels, subassemblies and assemblies being welded are subjected to thermal cycles of heating followed by cooling. It causes shrinkage forces to develop in the welded panels. The shrinkage forces tend to cause different degrees of distortion. Non unifo
- PDF / 789,459 Bytes
- 27 Pages / 439.37 x 666.142 pts Page_size
- 15 Downloads / 269 Views
Welding Residual Stress and Distortion
Abstract The panels, subassemblies and assemblies being welded are subjected to thermal cycles of heating followed by cooling. It causes shrinkage forces to develop in the welded panels. The shrinkage forces tend to cause different degrees of distortion. Non uniform shrinkage forces across thickness may lead to angular deformation, whereas the inplane compressive forces in plate panels made of thinner plates tend to buckle. In a welded joint, the base metal away from the weld zone remains at room temperature throughout the welding operation and is not subjected to any expansion or contraction. This ‘cold’ part of the base metal restrains the welded zone and the adjacent heated base metal from free expansion and contraction. This leads to stresses of near yield point magnitude in the weld. Under this stress the weld deposit and the adjacent heated base metal yields resulting in plastic strains. As the weld metal and the base metal cool down to the room temperature residual stresses are formed. If some of the external restraints such as clamps or welded lugs are removed, the residual stresses may find partial relief by causing the base metal to further deform.
Shipbuilding is primarily an assembling industry. The panels, subassemblies and assemblies being welded are subjected to thermal cycles of heating followed by cooling. Because of the phenomenon of thermal expansion and nonuniform heating and cooling cycle, it causes shrinkage forces to develop in the welded panels. The shrinkage forces tend to cause different degrees of distortion. Non uniform shrinkage forces across thickness may lead to angular deformation, whereas the inplane compressive forces in plate panels made of thinner plates tend to buckle. In a welded joint, the base metal away from the weld zone remains at room temperature throughout the welding operation and is not subjected to any expansion or contraction. This ‘cold’ part of the base metal restrains the welded zone and the adjacent heated base metal from free expansion and contraction. As a result as the weld metal cools down and solidifies, it attempts to contract to the volume it would normally occupy at the lower temperature. But because of the restraints from the
© Springer Nature Singapore Pte Ltd. 2017 N.R. Mandal, Ship Construction and Welding, Springer Series on Naval Architecture, Marine Engineering, Shipbuilding and Shipping 2, DOI 10.1007/978-981-10-2955-4_17
235
236
17
Welding Residual Stress and Distortion
adjacent cold metal, it cannot do so. This leads to stresses of near yield point magnitude at the prevailing temperature in the weld. Under this stress the weld deposit and the adjacent heated base metal yields resulting in plastic strains. The stresses which exceed the yield point only get relieved by this phenomenon. As the weld metal and the base metal cool down to the room temperature residual stresses are formed. If some of the external restraints such as clamps or welded lugs are removed, the residual stresses may find partial rel
Data Loading...
