Element Size Recommendations
Element Size Recommendations At Welds For DVS 1612
The DVS 1612 makes use of the nominal stress concept when assessing welds for fatigue. The increase in stress caused by the shape of the construction and the weld seam itself is taken into account by notch case dependent fatigue strength values, which can be found in the tables from the appendix B (DVS 1612:2014-08).
In FEAs the nominal stresses should be gathered at a specific evaluation distance in order to make sure, stress increases resulting from the shape of construction are not taken into account. The DVS 1612 recommends an evaluation distance of 1 to 1,5 times the sheet thickness from the weld seam transition.
WeldFEM calculates the evaluation distance for the assessment standard DVS 1612 by 1,5 times the sheet thickness from the weld seam transition.
To make sure that WeldFEM gathers mainly nominal stresses out of the plate-elements, it is recommended to set up at least one row of elements at the weld junction, where the element edge lengths perpendicular to the weld are equal to the size of its sheet thickness.
By doing that it is ensured that at least two rows of elements are taken into account for the weld assessment.
The following picture shows the element edge lengths at the weld junction and the evaluation distances, which are illustrated by the red curves.
Element Size Recommendations At Welds For DVS 1608
The DVS 1608 makes use of the nominal stress concept when assessing welds for fatigue. The increase in stress caused by the shape of the construction and the weld seam itself is taken into account by notch case dependent fatigue strength values, which can be found in the tables from the appendix B (DVS 1608:2011-09).
In FEAs the nominal stresses should be gathered at a specific evaluation distance in order to make sure, stress increases resulting from the shape of construction are not taken into account. The DVS 1608 recommends an evaluation distance of 5 mm plus half the length of the strain gauge from the weld seam transition. In this case, half the length of the strain gauge is equal to 5 mm.
WeldFEM calculates the evaluation distance for the assessment standard DVS 1608 as follows: 10 mm from the weld seam transition. To make sure that WeldFEM gathers mainly nominal stresses out of the plate-elements, it is recommended to set up at least one row of elements at the weld junction, where the element edge lengths perpendicular to the weld are maximum 10 mm long.
By doing that it is ensured that at least two rows of elements are taken into account for the weld assessment.
The following picture shows the element edge lengths at the weld junction and the evaluation distances, which are illustrated by the red curves.
Element Size Recommendations At Welds For DIN EN 13001-3-1
The DIN EN 13001-3-1 makes use of the nominal stress concept when assessing welds for static and fatigue. The increase in stress caused by the shape of the construction and the weld seam itself is taken into account by notch case dependent fatigue strength values, which can be found in the table D.3 from the appendix D (DIN EN 13001-3-1:2012-09).
In FEAs the nominal stresses should be gathered at a specific evaluation distance in order to make sure, stress increases resulting from the shape of construction are not taken into account. The DIN EN 13001-3-1 gives no recommendations regarding an evaluation distance. Since the DVS 1612 is also based on the nominal stress concept, the recommendation for estimating the evaluation distance can be adopted.
WeldFEM calculates the evaluation distance for the assessment standard DIN EN 13001-3-1 as follows: 1,5 times the sheet thickness from the weld seam transition. To make sure that WeldFEM gathers mainly nominal stresses out of the plate-elements, it is recommended to set up at least one row of elements at the weld junction, where the element edge lengths perpendicular to the weld are equal to the size of its sheet thickness.
By doing that it is ensured that at least two rows of elements are taken into account for the weld assessment.
The following picture shows the element edge lengths at the weld junction and the evaluation distances, which are illustrated by the red curves.
Element Size Recommendations At Welds For Eurocode 3
The Eurocode 3 makes use of the structural stress concept when assessing welds for static and fatigue. Accordingly, for fatigue assessments the notch case dependent fatigue strength values are taken into account, which can be found in table B.1 of appendix B (DIN EN 1993-1-9:2010-12).
In FEAs the structural stress should be determined by extrapolating stresses at the surface. For that, stresses at two extrapolation points at specified distances to the weld junction are being used. These extrapolation points are at a perpendicular distance of 0,5 times and 1,5 times the sheet thickness from the intersection of the mid-planes. Typically these distances are specified in relation to the weld seam transition, but for in general more coarse meshing it is conservative to use these distances in relation to the mid-planes.
To make sure WeldFEM has 2 different stress values for each extrapolation point, it is recommended to set up at least two rows of elements at the weld junction, where the element edge lengths perpendicular to the weld are equal to the size of its sheet thickness. By doing so, it is ensured that for each extrapolation point at 0,5 and 1,5 times the sheet thickness a stress value from a different element is used.