Buttweld Under Axial and Transverse Loading formulas |
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\( \sigma_{butt} \;=\; \dfrac{ T }{ l \cdot d }\) \( \tau_{butt} \;=\; \dfrac{ V }{ l \cdot d }\) \( \sigma_{avg} \;=\; \dfrac{ \sigma_{butt} }{ 2 }\) \( \tau_{max} \;=\; \sqrt{ \sigma_{avg}^2 + \tau_{butt}^2 } \) \( \sigma \;=\; \sigma_{avg} + \tau_{max} \) |
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| Symbol | English | Metric |
| \( \sigma_{avg} \) (Greek symbol sigma) = Average Weld Stress | \(lbf\;/\;in^2\) | \(Pa\) |
| \( l \) = Weld Length | \(in\) | \(mm\) |
| \( \tau_{max} \) (Greek symbol tau) = Maximum Shear Stress | \(lbf\;/\;in^2\) | \(Pa\) |
| \( \sigma_{butt} \) (Greek symbol sigma) = Normal Weld Stress | \(lbf\;/\;in^2\) | \(Pa\) |
| \( V \) = Shear Force | \(lbf\;/\;in^2\) | \(Pa\) |
| \( \tau_{butt} \) (Greek symbol tau) = Weld Shear Stress | \(lbf\;/\;in^2\) | \(Pa\) |
| \( \sigma \) (Greek symbol sigma) = Principle Stress | \(lbf\;/\;in^2\) | \(Pa\) |
| \( T \) = Tensile Force | \(lbf\) | \(N\) |
| \( d \) = Weld Throat Depth | \(in\) | \(mm\) |
Buttweld Under Axial Loading
Axial loading is the forces applied along the longitudinal axis of the welded components, either in tension (pulling apart) or compression (pushing together). In tension, the weld experiences normal stress, which is the tensile force divided by the weld's area cross-sectional. The weld's throat depth and length determine the effective area. In compression, the weld may resist buckling or crushing, depending on the geometry and material properties.
Strength, the weld’s ability to withstand axial loads depends on the material’s yield strength, the quality of the weld (no defects like undercut or porosity), and the throat depth. Limitations of the butt welds are strong in axial loading but may be prone to fatigue failure under cyclic loads or if there are imperfections like cracks or incomplete penetration.
Buttweld Under Transverse Loading
Transverse loading is the forces applied perpendicular to the longitudinal axis of the weld, causing shear and/or bending stresses. Transverse forces induce shear stress in the weld. The maximum shear stress may occur at specific points and is often considered the principal stress. Bending moments may develop if the transverse load causes the welded structure to deform, leading to tensile and compressive stresses across the weld. The weld may also experience combined stresses (shear and normal) depending on the load direction and component geometry.
Strength, the weld’s resistance to transverse loading depends on its shear strength, which is typically lower than its tensile strength. Workmanship, such as avoiding excessive undercut, is critical to maintaining strength. Limitations of the butt welds under transverse loading are susceptible to failure if the weld is near the edge of a plate or if subjected to bending about the weld’s longitudinal axis. Cracks may initiate at the weld root under flexural stresses, especially in poorly fitted joints.
Combined Loading
Combined loading in real-world applications, butt welds often experience both axial and transverse loads simultaneously, leading to complex stress states. Theories like the maximum shear stress theory or maximum distortion energy theory are used to predict failure under combined loading. Butt welds are common in pipelines, pressure vessels, and structural components. However, they have limitations in scenarios involving plastic deformation or bending, where the weld may not accommodate large strains.
