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An L16 orthogonal array parameter Design of Experiment (DOE) evaluated six design parameters of the mating thread interface between the exhaust manifold outlet flange and jointing stainless steel fastener. The objective of this study was to identify optimal parameters for the redesign the thread interface by ensuring 100% seating of the fastener into the manifold flange (here after referred to as stud seating). Since the current fastener and manifold outlet flange interface threads do not always achieve the design objectives, due in part to a form of abrasive wear, consideration was given to develop a testing strategy that would quantify the amount of remaining thread engagement for a given stud length. This testing strategy ensured that the control parameters considered in this experiment would reveal main effects and interactions between the stud and tapped hole threads thus providing the necessary parameters for the redesign on the joint threads.

An Automotive Exhaust System Structural Key Life Test has been successfully developed, in part, due to investigations into the boundary conditions of powertrain input. The powertrain (engine and trans-mission) degree-of-freedom study (here after referred to as engine) was investigated in order to determine the sensitivity of the exhaust system to engine motion. Understanding engine motion was necessary in order to establish proper control strategy in the laboratory simulation process. Accurate reproduction of exhaust system response to input road load events was crucial to reproducing known exhaust system fracture modes in early life wear-out conditions. A method multiple coherence analysis has been used to analytically measure the degree of severity between engine input motion and exhaust system output response by analyzing dynamic strain and acceleration. Removing one engine control input at a time, a multiple coherence function was calculated and the exhaust response computed.