41 Weld Stress

Weld stresses may be increased or concentrated in a specific area by discontinuities. Weld stresses are magnified when discontinuities reduce the cross-sectional area of the weld that is available to support the load. The average stress on a weld is in direct proportion to the reduction of the load-bearing cross-sectional area caused by the discontinuity. The lower the load-bearing cross-sectional area, the higher the stress.

If the load-bearing cross-sectional area of a weld is reduced sufficiently, structural failure may occur under load. Concentrated weld stresses occur at discontinuities that create abrupt changes of geometry, resulting in a notch effect. A notch effect is a stress-concentrating condition caused by an abrupt change in section thickness or in continuity of the structure. The sharper the change of geometry, the greater the stress concentration.

Tensile stresses perpendicular to the notch and shear stresses parallel to the notch are concentrated at the tip of the notch. Extremely high stress concentrations can develop at extremely sharp notches created by planar-type discontinuities such as cracks, laminations, or incomplete fusion. Such discontinuities may lead to catastrophic fracture in service. Discontinuities that concentrate stress can be extremely harmful.