Showing 8 results for Fatigue
M. Azadi, M. Baloo, G. H. Farrahi, S. M. Mirsalim,
Volume 3, Issue 1 (3-2013)
Abstract
In the present paper, a complete literatures review of thermal barrier coating applications in diesel engines
is performed to select a proper type and to find coating effects. The coating system has effects on the fuel
consumption, the power and the combustion efficiency, pollution contents and the fatigue lifetime of engine
components. Usually there are several beneficial influences by applying ceramic layers on the combustion
chamber, including the piston, the cylinder head, the cylinder block, intake and exhaust valves by using a
plasma thermal spray method. Several disadvantages such as producing nitrogen oxides also exist when a
coating system is used. In this article, all effects, advantages and disadvantages of thermal barrier coatings
are investigated based on presented articles.
E. Honarvar Gheysari, A. Babakhani, A. Haerian,
Volume 4, Issue 1 (3-2014)
Abstract
Shot peening applies a residual compressive stress field (RCSF) on the surface of parts. It also shifts “crack nucleation sites” to sub-surface locations. A nondestructive method of measuring the stresses, Sin2ψ was utilized here and the stress values introduced to Ansys software. For this purpose, uniform stress in all directions was applied on the con rod. Loading on the rod in Ansys had three steps: RCSF caused by shot peening (measured by XRD), and tensile and compressive stresses caused by inertial and gas forces, respectively (calculated). Fatigue Macro of Ansys was resumed carrying out the cyclic loading and thereby, improvement of powder forged connecting rods' fatigue life, caused by shot peening was obtained.
H. Saeidi Googarchin, S. M. Hossein Sharifi ,
Volume 5, Issue 1 (3-2015)
Abstract
The reason of this study is low cycle failure of cast iron cylinder head during the E5 standard durability test. The goal of the present investigation is durability test simulation and low cycle fatigue life evaluation of cast iron cylinder head. With uncouple structural analysis, preloads, thermal and mechanical load and boundary conditions are prescribed to finite element model of the cylinder head. To cover the durability test, the analysis steps repeated at five crack speed, 750, 1650, 2075, 2350 and 2600 rpm. The cylinder head is subjected to cyclic multi-axial non-proportional variable amplitude loads. In fatigue analysis, critical plane model with cumulative damage theory is applied to predict fatigue life. A general scripting is developed and validated to calculate fatigue life. The results show that the failure of critical cylinder head is the type of low cycle fatigue. The valve bridge region, where high temperature exists during operation of the engine, is the critical area in cast iron cylinder head in fatigue analysis approach. The simulation results are in accordance with the results of durability test.
H. Ashuri,
Volume 5, Issue 2 (6-2015)
Abstract
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 viscoelasticity model. 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 correspond with the experimental tests, carried out by researchers, and illustrated the cylinder heads cracked in this region. The results of the thermo-mechanical analysis showed that when the engine is running the stress in the region is compressive caused by the thermal loading and combustion pressure. When the engine shut off the compressive stress turned into the tensile stress because of assembly loads. The valves bridge was under the cyclic tensile and compressive stress and then is under low cycle fatigue. After several cycles the fatigue cracks will appear in this region. The lifetime of this part can be determined through finite element analysis instead of experimental tests. Viscous strain was more than the plastic strain which is not negligible.
Sepehr Beigzadeh, Javad Marzbanrad,
Volume 8, Issue 3 (9-2018)
Abstract
Nowadays, lightweight automotive component design, regarding fuel consumption, environmental pollutants and manufacturing costs, is one of the main issues in the automotive societies. In addition, considering safety reasons, the durability of the automotive components, as one of the most important design requirements should be guaranteed. In this paper, a two-step optimization process including topology and shape optimization of an automotive wheel, as one of the most significant chassis components, is studied. At first, topology optimization method with volume and fatigue life constraints is used to obtain the optimal initial lightweight design, followed by shape optimization technique to improve the fatigue life. The results show 31.841% weight and 33.047% compliance reduction by topology and also 652.33% average minimum fatigue life enhancement, by the shape optimization. Therefore, the proposed two-step optimization method is qualified in designing the lightweight automotive wheel. The method used in this study can be a reference for optimization of other mechanical components.
Hojjat Ashouri,
Volume 11, Issue 2 (6-2021)
Abstract
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.
Adel Basiri, Ebrahim Amini,
Volume 12, Issue 1 (3-2022)
Abstract
The objective of the present paper is to assess the capability of several classical damage models in prediction of service lifetime of engine components subjected to Thermo-mechanical Fatigue (TMF) loading. The focus of the present study is based on efficient and robust predictive tools which are suitable in industrial development process, thus the classical fatigue damage models are selected to perform such a tsk. In the classical framework, three strain-based models including Manson-Coffin, Smith-Watson-Topper and Ostergren models and one plastic strain energy-based model are examined. Besides, some correction factors are added to the Manson-Coffin, Ostergren and plastic strain energy models regarding the mean stress and temperature effects. The statistical analysis of the models is carried out utilizing the Low-cycle fatigue and Thermo-mechanical Fatigue tests on standard specimens of A356 aluminum alloy. The analysis indicated that modified Ostergren model is the most reliable model in fatigue lifetime description of the A356 alloy among the others. The studied engine component is a passenger-car diesel engine cylinder head made of A356 aluminum alloy. The temperature, stress and strain distribution fields of the component are considered as the given boundary conditions from our previous work as they are not in the scope of the present investigation. The selected damage models based on the best accuracy identified during statistical analysis are introduced into the ABAQUS software. The modified Ostergren model presented the most accurate and realistic results based on empirical observations of fatigue crack area in diesel engine cylinder heads studied in the literature.
Hojjat Ashouri,
Volume 12, Issue 4 (12-2022)
Abstract
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.
