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How can I obtain weld stresses between two surfaces?
To determine the correct stresses, it is necessary to know the local coordinate system of the surface. You can activate it in the Display navigator under “Model” -> “Surfaces” -> “Surface Axis Systems x, y, z.” All stresses with an “+” in the index indicate the stress at the top surface, that is, the side of the positive local z-axis. When showing the surface moments, notice that there is a fundamental difference between surface and member internal forces: While the member moment My about the local member axis y “rotates,” a surface moment my is acting in the direction of the local surface axis y, that is, about the axis x of this surface.
For the given example, this means that the bending moment of the lap joint is acting in the direction of the global y-axis and therefore has to have a value of 2 kNm/m as result. The average in the depicted diagram confirms this assumption by a value of 1.95 kNm/m (deviations can be reduced by a finer FE mesh). The average of the shear flow is 100 kN/m and therefore corresponds to the applied load.
The stress sigma-y,+ thus represents the compressive stress of the lap joint at the top surface and tau-xy,x represents the shear stress in the interface on the same side.
weld, weld stress, internal forces in surfaces