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A method of fatigue life prediction of spot welded joint under multi-axial loads has been developed by fatigue life estimation working groups in the committee on fatigue strength and structural reliability of JSAE. This method is based on the concept of nominal structural stress ( σ ns) proposed by Radaj and Rupp, and improved so that D value is not involved in stress calculation. The result of fatigue life estimation of actual vehicle with nominal structural stress which was calculated through newly developed method had very good correlation with the result of multi-axial loads fatigue test carried out with test piece including high strength steel.

In this paper the fatigue life of welded steel sheet structures is predicted by using FE-Fatigue, which is one of fatigue analysis software tools on the market, and these predicted results are evaluated by reference to corresponding experimental results. Also, we try to predict these structures by using two fatigue life prediction theories established by the JSAE fatigue and reliability committee to compare prediction results. It was confirmed that spot welds fatigue life predictions agree qualitatively with corresponding experimental results and arc welds fatigue life predictions are in good agreement with corresponding experimental results in cases where the SN curve database is modified appropriately.

In order to quantitatively evaluate mechanical durability of metal substrates for catalytic converters under heat cycles, thermal stresses and strains were simulated by FEM elastic-plastic analysis. Flat and corrugated sheets constituting honeycomb structures were directly modeled by thick-shell elements without replacing the structures with equivalent solid elements. It was reported that an asymmetric joint structure with “Strengthened Outer Layer” could provide metal substrates with high mechanical durability against heat cycles and the results of analysis in this study could show their high durability. It is important for improvement of mechanical durability to control the location of initial cracks generation and the direction of their propagation.

A metal support for use in an automotive catalyst is exposed to the severe heat cycle brought about by the intermittent flow of a high temperature exhaust gas. Accordingly, the metal support must have high beat resistance(ex. oxidation resistance) and a rigid structure. Therefore, 20% chromium-5% aluminum ferritic stainless steel(containing small quantities of rare earth metals and titanium) is used as a highly beat resistant honeycomb foil in addition to a highly mechanical durable brazing honeycomb structure. This study examined the durability of a metal honeycomb installed in a gasoline engine. Both an engine bench durability test of a manifold converter type metal support which is connected directly to the exhaust manifold of the gasoline engine and a vehicle durability test of an under the floor type metal support were carried out to evaluate oxidation damage of the metal honeycomb as well as its mechanical durability.