Complex Structure

VrDesigner enables the designer to estimate the stresses, displacements and fatigue life generated by in-service loads in a given structure. VrDesigner takes as input CAD files that the define the geometry of the parts in a structure or assembly. The designer assigns a material type to each part. The type of adjacency relationship is specified, e.g., fixed, welded, bolted or contact. Displacements and loads are prescribed for each load case of in-service loads. Some parts may import state from manufacturing, e.g., distortion, residual stress and microstructure for welded, heat treated or cast parts. Then the parts are meshed largely automatically and the solver computes the displacement, stress and strain for all load cases.

An analysis of a structure with 108 parts with 500K elements and three load cases took less than three hours computing time on a single Intel Core 2 processor. More important, the user time to set up an analysis is usually about one hour.

Along lines normal to weld toes and normal to the surface of the part, the solver computes the stress profile. From this stress profile, the fatigue life can be estimated at each point along each weld toe path. This can be done for just in-service loads, just residual stresses or in-service loads combined with residual stresses. If the fatigue life is too short, the designer has the opportunity to redesign the structure early in the design process when the cost of design changes are minimal.

The maximum stress in all welds is computed. From this information, the designer can see which welds are over-designed and which welds are under-designed. This gives the designer the opportunity to optimize cost and performance early in the development process where the cost of design changes are minimal.

The following video is part of a large tractor; it is a structure which has 108 parts. The `arms’ protruding on the lower left and upper right approximate the tractor wheels. The displacement on the nodes where the `wheels’ touch the ground are fixed to zero. The displacement for some nodes in the articulating joint on the right side are also fixed to zero. Then the drawbar, which is on the left center of the image, is subjected to in-service loads for downward, upward and side forces. The displacement for these three load cases are shown. Some parts of the tractor are cast; some are welded sub-assemblies and some are as-machined or flame cut. VrDesigner can do this analysis with the residual stresses and deformation from the up-stream manufacturing stream.