For the detailed analysis of welds, the section forces and moments must be available along the weld. These can easily be extracted from shell models, however, in case of solid models this is a rather complicated task. In literature different approaches can be found for the extraction of structural stresses from solid models. Often these methods need structured meshing with hexahedrons and a certain mesh size, see e.g. the recommendations of the International Institute for Welding (IIW). In large industrial projects such as bogie frames these constraints are difficult to meet.
LIMIT offers a unique solution for this problem, which is called Sensor technology. Sensors are placed all around the welds and calculate the section forces and moments including nominal or structural stress correction. Sensors use the displacement field from the finite element analyses, not the stress results. As the primary solution variable, the displacement fields are continuous throughout the elements. All solid element types can be used with Sensors. The only requirement is a sufficiently fine mesh in order to resolve the displacement field in areas with large stress or strain gradients.
The following pictures show the classical shell modelling approach on the left side and the Sensor technology on the right side. In case of the solid models nonconforming interfaces and tie or glue constraints known from FE analysis between the parts are also supported in LIMIT, again reducing the time to set up the numerical model.
In case of shell modelling the location of a weld is marked by a set of nodes and the attached elements. In case solid modelling the Sensors are generated in LIMIT CAE. Sensors are placed in the mid surface of parts with constant sheet thickness. Sensors detect membrane strains and changes in the curvature. This way section forces and section moments can be calculated.
The results are very similar in both methods. Here the degrees of utilization according to the FKM guideline are shown.