Case Studies

TRAILER DESIGN

Trailers featuring a swivel table made under sub-contract were being used by a major motor manufacturer to transport components around the factory. The trailers had suffered a number of failures, ranging in severity from loosening bolts, leading to wheels becoming detached through to the failure of the swivel ring attachment and dropping a pallet. A combination of a visit to the factory, a general inspection of some of the trailers, a detailed inspection of the drawings and stress analysis of one of the most highly loaded components established the conclusion that the trailers were poorly designed with little thought having been given to dynamic loading, poorly fabricated and poorly inspected before release. Despite these serious deficiencies, the trailers could be refurbished to produce a very rugged and reliable design if the recommendations by DCW&P were implemented.

The design requirement was for a loading of 1500 kg uniformly distributed over the full surface of the table. In fact the pallets could only apply their loading along two sides at their skids. To check the effects of this loading a finite element model was prepared to look at the two forms of loading. The adjacent model represents a quarter of the table, using symmetry boundary conditions to represent the other sections. Contours of imposed stress are shown with a peak of 259 N/m2, 60% higher than the upper allowable figure. This stress occurs in the edge strips which span between the skids. If the dynamic effect is included, the peak stress is of the order of 2.25 times the yield of the material, clearly unacceptable.