Reduction of Durability Evaluation Time for Automotive Components by Development of Generic Solutions 2003-32-0068

In the recent years, reduction of new product development time is the major challenge for all auto manufacturers to sustain in the stiff competition. Durability evaluation is one of the most time consuming element in New Product Development (NPD) process. Finding a generic solution for commonly faced design issues is a key factor for dramatic reduction in evaluation time. Testing time reduction can be achieved by breaking down the evaluation into subsystem level and component level instead of complete vehicle. But the maximum time reduction can be achieved only through durability evaluation at material / process level. This type of evaluation yields a generic solution, which results in establishing all-purpose design and material selection criteria during initial stage of development. By adopting this technique, separate evaluation of vehicles/ subsystems for improvements in material, welding, process etc. can be avoided. Basic design criteria for most of the automotive structural components can thus be established.

This paper describes the efforts made to arrive at a generic solution for some of the common structural design related issues. A dedicated test facility was developed for assessment of fatigue life for such generic requirements. The key parameters considered for this experiment were type of material (cold rolled, hot rolled, high tensile hot rolled, etc) and welding parameters (optimum weld bead size, effect of welding on sheet metals/ tubes, etc). A robust reliable test procedure was developed for these issues. Durability of different type of materials was evaluated for fatigue strength. Effect of welding on each material with different weld bead size was also evaluated. Fatigue life evaluation was also carried out at different stress levels considering the fact that materials can have different behavior at different stress levels. The fatigue life results were analyzed using Design of Experiments (a statistical technique). The results of ANOVA (Analysis of Variance) are discussed in detail in this paper.

By arriving at generic solutions, it was possible to reduce the testing time drastically. With this the generic issues like material change, welding related changes were evaluated in short span of time at component level instead of conducting all structural durability tests on a complete vehicle. The results obtained from this work showed a good correlation with other structural evaluation tests.

The paper also discusses correlation of experimental results with software based fatigue life prediction analysis. The generic solutions so obtained for material change and weld bead size were used for taking decisions. The technique is also applicable for evaluation of many other material/ process changes such as heat treatment, forming, drawing, flaring, joining process etc. Thus the technique of developing generic solutions to improve structural durability was effectively used for overall reduction in durability evaluation time.