Computer aided fatigue design.

Today's competitive market requires engineers to produce reliable light weight products at low cost. This can be achieved by more effective use of computer aided engineering tools during early stages of the design process.A research programme has been undertaken to investigate the data requirements of integrating commercially available software packages (finite element analysis and fatigue life evaluation) to evaluate the integrity and durability of engineering components at the conceptual design stage.A real engineering component, in the form of a steering arm, supplied by a European truck manufacturer was used as a basis for the investigation. This is a typical vehicle component, in which, under service loading conditions, a multiaxial state of stress occurs.A geometric model of the component was created using the Prime "MEDUSA" software suite. The model was used to locate the boundary co-ordinates necessary for the development of a PAFEC Finite Element model. By imposing the conditions experienced during the service, the critical areas of the component were identified by analysing the F.E. model and a detailed description of the elastic stress/strain fields were also established. These were incorporated in an energy density approach and Neuber's uniaxial analysis to predict total local elastic/plastic strains at these critical- locations. These were compared with strain gauge measurements. The calculated results were used to plot a number of load/local strain calibration curves for the development of a load history, suitable for experimental fatigue life assessment.Fatigue crack initiation tests were performed on the steering arm using a computer controlled DARTEC multiaxial fatigue testing machine. Fatigue life assessment based on full service loading was carried out using a software package based on the critical location approach. A comparison of computerised, experimental and actual test circuit fatigue lives has been made.The work enabled a specification to be produced for the integration of the two items of software. This integrated software was developed by third parties and used to produce a computerised life map of the steering arm.