[ A s s i g n m e n t ]

Towing brackets are manufactured by using a cold-forging process. This production process introduced residual stresses, which can lead to an early failure of the product (fatigue). One method to reduce these residual stresses is heat treatment of the towing bracket, which tempers the residual stresses and increases the product’s life span. However, this treatment is not only very expensive, but there are also environmental arguments for avoiding tempering of the stresses. Femto Engineering determined the residual stresses of a towing bracket and the effect these stresses had on the product’s life span (fatigue strength).

[ S o l u t i o n ]

First, the production method of the towing bracket was analysed to determine the residual stresses. The steel pipe is deformable and has a prescribed plastic behaviour (material non-linearity). Rigid contact bodies simulate the forging tools. With these bodies, the bottom section of the pipe is flattened, which enables the bracket fixing to be bolted to a car. The steel bar is subsequently bent into the desired shape. When towing a trailer or caravan, forces will act upon the towing bracket. To determine the life span (fatigue strength), these forces are put on the finite element model (combined with the residual stresses). By knowing the exact fatigue strength, the design can be checked to see if it meets the prescribed standards.

[ R e s u l t s ]

By analysing the residual stresses, a design can be improved and tempering avoided. Furthermore, it is possible to determine whether the design’s fatigue strength meets the prescribed standards.