Automotive Science and Engineering

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Loading conditions and complex geometry have led the cylinder heads to become the most challenging parts of diesel engines. One of the most important durability problems in diesel engines is due to the cracks valves bridge area. The purpose of this study is a thermo-mechanical analysis of cylinder heads of diesel engines using a two-layer viscoplasticity model. In this article, mechanical properties of A356.0 alloy, obtained by tensile tests at 25 and 200°C. The results of the thermo-mechanical analysis indicated that the maximum temperature and stress occurred in the valves bridge. The results of the finite element analysis of cylinder heads correspond with the simulation results, carried out by researchers.

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This paper presents low cycle fatigue (LCF) life prediction of an engine exhaust manifold. First Solidworks software was used to model the exhaust manifolds. Then Ansys Workbench software was used to determine stress and fatigue life based on Morrow and Smith-Watson-Topper (SWT) approaches. Thermal fatigue (TMF) of the engine components easily happens due to excessive temperature gradient and thermal stress. Modern exhaust systems must withstand severe cyclic mechanical and thermal loads throughout the whole life cycle. The numerical results showed that the temperature and thermal stresses have the most critical values at the confluence region of the exhaust manifolds. This area was under low cycle fatigue. After several cycles the fatigue cracks will appear in this region. The results of the finite element analysis (FEA) correspond with the experimental tests, carried out in references, and illustrate the exhaust manifolds cracked in this region. Finite element (FE) simulation proved a close correlation between Morrow and SWT criterions results. The lifetime of this part can be determined through finite element analysis instead of experimental tests.
 

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The confluence area cracks is most important durability problems in internal combustion engines. The aim of this article is a thermo-mechanical analysis for exhaust manifold using elasto-viscoplastic chaboche model. The Chaboche model was selected for the elasto-viscoplastic model including a kinematic hardening plastic law coupled with the Norton creep equation. The modeling, meshing and analyzing was performed on a finite element model of the exhaust manifold in ABAQUS software. In order to increase the accuracy of finite element analysis (FEA) results, temperature-dependent of material parameters was considered. The results of mechanical-thermal analysis showed that the temperature maximum and stress is visible in the confluence area. Obtained FEA results proved the manifold gasket leak is another region of critical that has to sustain the expanding and contracting of the heated exhaust manifold metal. The results of the modal analysis proved that the maximum strain energy density and total strain energy exist in the confluence area. The results of the thermo-mechanical analysis are compared with the real sample of the damaged exhaust manifold to evaluate the properly results, and it has been shown that serious identified zones correspond to the failure areas of the real sample.

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Loading conditions and complex geometry have led the cylinder heads to become the most challenging parts of diesel engines. The aim of this study is to compare the distribution of temperature and stress in the aluminum and magnesium cylinder heads under thermo-mechanical loads. The three-dimensional model of the cylinder heads was simulated in abaqus software and a two-layer viscoplasticity model was utilized to investigate the elastic, plastic and viscous behavior of the cylinder heads. The temperature and stress results of magnesium alloy was compared to aluminum alloy results. The results of finite element analysis (FEA) showed that surface temperature of the magnesium cylinder heads is about 23°C lower than the aluminum cylinder heads. As a result, the fatigue lifetime of the magnesium cylinder heads can be improved in comparison to the aluminum cylinder heads. The thermo-mechanical analysis showed that the magnesium cylinder heads tolerate less tensile and compressive cyclic stress compared to the aluminum cylinder heads. The stress reduction value in the magnesium cylinder heads was about 10 MPa which can lead to higher fatigue lifetimes in comparison to the aluminum cylinder heads.
 

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Due to the complex geometry and thermos-mechanical loading, cylinder heads are the most challenging parts among all parts engines. They must endure cyclic thermal and mechanical loading throughout their lifetime. Cast aluminum alloys are normally quenched after solution treatment process to improve aging responses. Rapid quenching can lead to high residual stress. Residual stress is one of the main reasons for failure of cylinder heads. The effect of residual stress on the thermal stress and low cycle fatigue life (LCF) of cylinder heads was studied. For this goal, Solidworks software was used to model the cylinder heads. Then the thermo-mechanical analysis was performed to determine the temperature and stress field in ANSYS software.  Finally, the fatigue life analysis that considers residual stress effect was done. The results of finite element analysis (FEA) proved that the effect of residual stress in LCF is significant which is not negligible. Thus, residual stress must be considered in the thermo-mechanical fatigue analysis of the engines cylinder heads. The numerical results showed that the area where the maximum temperature and stress is occurred is where the least LCF is predicted.