FEA Simulation Based Thermo-mechanical Analysis of Tractor Exhaust Manifold

Abstract

The main objective of this research work is thermo-mechanical analysis of tractor exhaust manifold. Present study analysed the response of exhaust manifold under higher temperature. Thermal effect was considered to evaluate the FEA simulation results. Free vibration based modal analysis was performed to find the fundamental frequencies. The solid model of exhaust manifold was designed using Pro-E. Finite element analysis was performed using Ansys 14.5. The parameter used for the FEA simulation is constant exhaust gas temperature of 800 °C which was applied to the exhaust manifold. The natural frequency and vibration mode of the exhaust manifold was obtained in modal analysis and vibration characteristics of exhaust manifold was analysed. The analysis show that the natural frequency of vibration varies from 53.2 to 466.68 Hz.

1 Introduction

There are significant research works (ANSYS 2011; David Rathnaraj 2004; Deger et al. 2004; Gopaal et al. 2014; Kumar et al. 2014; Mavropoulos 2011; Sonekar 2011) proposing, for exhaust manifold designs, new geometries, materials and manufacturing techniques, and this evolution has undergone with a continuous improvement over the past decades and required thorough examination of the smallest details. The exhaust system of a vehicle is subjected to thermo-mechanical fatigue. Exhaust manifolds are sensitive and prone to crack damage. The new material like cast alloys are also subjected to high deformation at relatively high operational temperatures. The methodology for analyzing the Exhaust Manifold is a uniformly distributed temperature of 800 °C is applied to the 321-Austenitic Stainless steel exhaust manifold for the transient thermal Analysis. The thermal deformations and stresses (Figs. 6, 7 and 8) are calculated for one complete working cycle of 1 s. For vibration analysis the first 05 order vibration mode (Fig. 11) of exhaust manifold is obtain. The natural frequency of vibration varies from 53.2 to 466.68 Hz.

In present research work FEA simulation method was used for the Thermal, Structural and Modal analysis of 321-Austenitic Stainless steel exhaust manifold. For thermal analysis a uniform temperature of 800 °C is applied and various results were calculated. The natural frequency and mode shape of the exhaust manifold was obtained using modal analysis. The main objective of the vibration analysis is to identify natural frequencies and vibration modes of the exhaust manifold.

2 Material Properties

Austenitic Stainless steel-321 is stabilized steel consisting of carbon, nickel and titanium. This titanium addition prevents carbide precipitation at high temperature (427–816 °C) and improves the elevated temperature properties of the alloy. Austenitic Stainless steel-321 provides excellent resistance to oxidation, corrosion and possesses good creep strength at higher temperature. Its mechanical properties are as following:

Density: 9.01 g/cc; Hardness, Rockwell B: 80; Ultimate Tensile Strength: 621 MPa; Yield Tensile Strength: 276 MPa; Modulus of Elasticity: 193 GPa; Poisson’s Ratio: 0.24; Shear Modulus: 78 GPa; Thermal Conductivity: 22 W/m - k @ Temperature 500 °C; Specific heat: 500 J kg⁻¹ K⁻¹; Maximum service temperature: 870 °C; Melting Point: 1371–1399 °C.

3 FEA Simulation

In present research work for thermal analysis a constant temperature of 800 °C is applied on exhaust manifold (Figs. 1 and 2) for complete cycle of 1 s. The result of thermal analysis was imported for static structural analysis. Static structural analysis evaluates the deformation, strain and various stresses. Pro-E software was used for design the cad modal. FEA based Ansys 14.5 was used for the thermal, structural and modal analysis. For FEA the geometry is divided into elements. These elements are interconnected to each other at a point known as Node. Element size can be kept as per our requirements. Very small element size increases the calculation time. The total no of Nodes is 27,398 and elements are 13,798. Wall thickness of exhaust manifold is 2 mm and the internal diameter is 46 mm.

Fig. 1

CAD model of the exhaust manifold

Fig. 2

Meshing of exhaust manifolds

4 Computation of Results

The Thermo-mechanical analysis of Austenitic Stainless steel-321 Exhaust Manifold is important from different prospective. First, the temperature distribution leads to thermal deformations and thermal stresses. Thermal deformation has an important role in Exhaust Manifold design. In this analysis the thermal stresses and maximum temperature distribution is calculated (Figs. 3 and 4) for one complete cycle of 1 s for Exhaust Manifold temperature to remain constant at 800 °C throughout a working cycle. To exhaust manifold a temperature of 800 °C is applied and thermal analysis result is obtained. During static structural analysis of exhaust manifold the thermal results of exhaust manifold was considered.

Fig. 3

Boundary conditions applied

Fig. 4

Constant temperature applied

Figure 5 shows the maximum temperature variation in 1 s. The applied temperature is 800 °C which is increased by 51.3 °C in 1 s cycle. In all places the deformation (Fig. 6) is within prescribed limit showing the safe design conditions.

Fig. 5

Maximum temperature variations in 1 s

Fig. 6

Total deformation in exhaust manifold

4.1 Static Structural Analysis

In this analysis (Figs. 7, 8, 9 and 10) the temperature value obtain from the thermal analysis was imported for structural analysis.

Fig. 7

Maximum principal stress

Fig. 8

Equivalent stress

Fig. 9

Maximum principal elastic strain

Fig. 10

Equivalent elastic strain

5 Modal Analysis

In modal analysis the load is applied by program automatically, by applying the suitable boundary conditions. The fixed supported boundary condition and material properties was applied. The exhaust manifold of tractor is subjected to external excitation. The reason for the fracture is matching of external excitation frequency to natural frequency of the exhaust manifold. The natural frequency of exhaust manifold vibration varies from 53.24 to 466.68 Hz. The modal frequency results are free vibration result if exhaust manifold is subjected to forced vibration the chances of fracture will be maximum. In order to prevent fracture during external loading the design should be modified so that the excitation frequency does not match, to the natural frequency. All five vibration mode of exhaust manifold is shows in Fig. 11, to find out the fracture location during the external loading condition. Figure 12 Natural frequency variations for exhaust manifold.

Fig. 11

Five mode shape and corresponding natural frequencies

Fig. 12

Natural frequency variations for exhaust manifold

6 Conclusion

In Austenitic Stainless steel-321 Exhaust Manifold, titanium addition prevents carbide precipitation at high temperature which reduces environmental damages and can maintain its properties at that temperature. It is observed that thermo-mechanical fatigue is the main reason for exhaust manifold failure. In form of thermo mechanical fatigue an exhaust manifold is subjected to vibration and thermal stresses. The first 5 order natural frequency of the exhaust manifold and its vibration mode were obtained. The results of this study show that stresses which are produced during the operations for 321-Austenitic Stainless steel exhaust manifold are in the safe region. This study also provides the way for a developer to deal with thermal, structural analysis of different exhaust manifold of different materials.