Transient Fatigue Analysis of Exhaust System Mounting Brackets for Commercial Vehicle - Correlation

In commercial vehicles, exhaust system is normally mounted on frame side members (FSM) using hanger brackets. These exhaust system hanger brackets are tested either as part of full vehicle durability testing or as a subsystem in a rig testing. During initial phases of product development cycle, the hanger brackets are validated for their durability in rig level testing using time domain signals acquired from mule vehicle. These signals are then used in uni-axial, bi-axial or tri-axial rig facilities based on their severity and the availability of test rigs. This paper depicts the simulation method employed to replicate the bi-directional rig testing through modal transient analysis. Finite Element Method (FEM) is applied for numerical analysis of exhaust system assembly using MSC/Nastran software with the inclusion of rubber isolator modeling, meshing guidelines etc. Finite Element Analysis (FEA) results are in good agreement with rig level test results. This paper also explains a method for identifying root cause for high stresses in critical locations and predominant mode causing failures using FEA. Effective design modifications can be done if root cause is clearly identified. Also, the type of test-rig to be used during physical testing can be identified using this procedure.