Application of Verity Method to Predict Bushing Fatigue Life and Load Limit 2009-01-0813

Durability performance is one of the most important aspects of exhaust system design. Great effort has been expended to develop the ability to accurately and quickly predict the durability of the system in the early development stages.

Welded joints in an exhaust system are the most prone to failure; however, the fatigue life of a welded joint is usually much more difficult to predict than that of a base material. The difficulty of predicting the fatigue life of a welded structure lies primarily in the variability associated with the elements of a weldment, including differing material and gap requirements, notch generation, residual stresses, and imprecise application, among others. The experts at the Battelle Center for Welded Structures Research have developed an approach to predict the fatigue life of a welded structure known as the Verity method. The Verity method has thus far been successfully used to predict the fatigue life of welded joints across a wide array of applications and industries.

The purpose of this paper is to describe the successful application of the Verity method to exhaust system bushing and flange weld joints at Tenneco Automotive. Two methods of applying the Verity method are introduced: the first is to predict the fatigue life for a component under a given load and system of constraints; the second is to predict a component’s load capability by developing a series of load limit curves specific to that joint. The successful application of the Verity Method at Tenneco Automotive will significantly decrease the number of testing and number of testing samples on fatigue bench testing, which, in turn, drives down the cost of system development. More importantly, this also reduces development cycle. Especially, the use of load limit curves for a component will guide optimized designs early in the development process.