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Traditionally, fatigue calculations are based on the time domain approach. Acceleration time history inputs are used to excite the system. Through the element stress time history output and rainflow cycle count algorithm, fatigue damage can be calculated through the Palmgren-Miner cumulative damage rule. Nevertheless, it can be a daunting process for CAE analysts as it requires iteration for each individual event in the schedule before calculating the fatigue life. The alternative approach is frequency domain fatigue calculation. In this approach, both the dynamic loading and response are expressed in terms of Power Spectral Density (PSD) functions and the dynamic structure is treated as a linear transfer function. The stress PSD is then obtained by multiplying the transfer function with the PSD load. The objective of this paper is to present a CAE based virtual shaker table procedure for an automotive exhaust component and subjecting it to PSD for fatigue life prediction.

A variety of parameters influence the durability of a converter to pipe joint of an automotive exhaust system. Some of the parameters are design variables and some factors are related to manufacturing. The design parameters include the thickness of the components, diameter of the pipe, sleeve length of the cone etc. While the variables like the weld penetration and the fit-up of the joint are related to manufacturing. Traditional durability simulations utilizing computer aided engineering (CAE) methods are conducted using nominal values of the design and manufacturing variables. In reality scatter and randomness in parameters are present due to the tolerance in components and limitations of the manufacturing process. In this paper a CAE based stochastic approach to determine the life distribution for a converter joint of an automotive exhaust system is presented.

Virtual validation of the dynamic performance of exhaust systems with measured vehicle loads is being used increasingly by many OEM's and exhaust system suppliers. The loads induced due to power train roll motion, the vibration characteristic from the ground and power train system are collected during the RLDA (Road Load Data Acquisition). Modal transient dynamic analysis is carried out using FEA with input loading from the full event RLDA to predict the behavior of the system. The key performance measures that are studied in this work are the force transmitted by the exhaust system to the vehicle body and the damage at the critical joints. There are many design variables that could impact the dynamic response of the system like the choice of the isolator, the thickness of the parts, the weld characteristics of joints etc. Inherent variability in the vibration data obtained during RLDA could also influence the behavior of the exhaust system.

Canning is a very important aspect in the catalyst converter design, especially with the current trend of using more thin wall and ultra-thin wall substrates. This paper systematically investigated canning issues at different stages of converter manufacturing processes and operations. Commonly used converter canning processes, which include traditional clamshell style and tourniquet wrap, are included in the studies. Using a previously developed mat material model, visco-elastic behavior, as well as the unique expansion characteristic of the intumescent mat under high temperature, are included in the simulations. Lab testing of the mat material at different loading speeds was conducted to obtain the visco-elastic properties. These will allow the studies of the effect of closing speed on the peak pressures during canning processes, as well as the pressures during heating and cooling.

This paper discusses many aspects of the structural analysis of catalytic converters on automotive exhaust systems. The analysis covers a canning process, where a substrate is wrapped with a mat material and canned with a steel shell; and a heating process, where high temperature exhaust gas passes through the substrate. In designing a catalytic converter, the maximum pressure on the substrate should not exceed the minimum isostatic strength of a chosen cell geometry of that substrate. At the same time, sufficient pressure is required to maintain a minimum retention force to hold the substrate in place. Also, lack of compression in the mat material, where the mat is in contact with exhaust gas, will cause mat erosion. Therefore, a careful investigation is needed to have the right amount of pressure on the substrate, both during canning and operation conditions, and at room and elevated temperatures.

This paper deals with the dynamic simulation of an automotive exhaust system. Selection of dynamic loads, processing of test data, determination of damping ratio and nonlinear stiffness are explained in detail. Validation of CAE model to test data is also included. It will be shown that the failure location was successfully predicted using modal analysis, and the dynamic stresses were correlated with the dynamic analysis at the failure location.