An in-cylinder combustion analysis and a computational fluid dynamics (CFD) coolant flow analysis were performed using AVL FIRE software, which provided the heat transfer boundary conditions (HTBCs) ...to the temperature field calculation of the cylinder head. Based on the measured material performance parameters such as stress-strain curve under different temperatures and E-N curve, creep, and oxidation data material performance, the cylinder head-gasket-cylinder block finite element analysis (FEA) was performed. According to the temperature field calculation results, the maximum temperature of the cylinder head is 200°C that is within the limit of ALU material. The temperature of the water is more than 21.1°C below the critical burnout point temperature. The high-cycle fatigue (HCF) and thermal-mechanical fatigue (TMF) analysis of the cylinder head were performed by Finite Element Method FATigue (FEMFAT) software. The HCF safety coefficient and TMF life cycle of the cylinder head were calculated, which provided an important guidance for cylinder head structure design of a gasoline engine and diesel engine. The present article establishes a complete simulation and analysis process of cylinder head TMF. The fatigue assessment technology presented in this study is universal that is not only applicable to a cylinder head but also to exhaust manifold, piston, etc. The method has been successfully applied to the diesel engine platform and gasoline engine platform of Jiangling Motors with remarkable impacts.
•Tensile strength and S-N curve of the aluminum alloy 242.0 were determined.•Numerical thermomechanical analysis of the cylinder assembly was performed.•The cylinder assembly locations with the ...highest stress values were determined.•An integrity assessment of the cylinder assembly has been carried out.•The cylinder head failure is due to material fatigue caused by presence of porosity.•The further research will be related to the cylinder head with a crack analysis.
Failures of aircraft piston engine components are a common occurrence in practice. During operation, cylinder heads are components that are exposed to multiaxial thermomechanical loads leading to fatigue. Therefore, predicting the lifetime of the cylinder heads exposed to such loads is one of the most important tasks to ensure engine quality, durability and safety. This paper is the continuation of a comprehensive research of the Lycoming IO-360-B1F aircraft engine cylinder head failure. The failure of this type has already occurred during flight and about 50 failures like this have been registered from around the world, some of them with a fatal outcome and therefore require detailed research. This research includes the numerical stress and fatigue analysis of the cylinder assembly exposed to high cycle mechanical and thermal loads that failed due to a crack appearance on the cylinder head. A 3D cylinder assembly model was created. The locations with the highest stress values, both mechanical and thermal, were determined using numerical analysis. Also, the lifetime of the cylinder assembly has been determined, i.e. an integrity assessment has been carried out which will contribute to the consideration of the crack appearance problem. Defining the coupled thermomechanical load of the cylinder assembly in the numerical analysis gives special significance to this paper. The results obtained will serve to analyze the crack propagation in the cylinder head which is going to be the subject of further research.
Nowadays, the cylinder heads are subjected to higher thermal stress due to the increasing engine power output, fuel consumption and gas emission. Thus, simulation and analysis of fatigue cracks is ...essential. In this paper, the high cycle fatigue (HCF) life analysis of the cylinder head considering the stress gradient, is performed using the finite element method and ANSYS software to predict the temperature and stresses, and then, HCF life using Goodman theory and nCode Design Life software. Mechanical properties of cylinder head obtained by tensile tests at different temperatures. Tensile tests were simulated by ANSYS software, and very good agreement was shown between the experimental and simulation results of tensile tests. The results of finite element analysis (FEA) showed that the maximum temperature and stress values occur at the valve bridge between exhaust valves. The distribution of the HCF safety factor demonstrated no critical point in the cylinder head, and the minimum safety factor of 1.4 occurred in the exhaust port. The simulation results compared with the engine durability test. 800-hour durability test showed no rupture in different parts of the cylinder head.
After about seven years in service, four cylinder head studs, which tight the block and cylinder heads of a marine main engine, have fractured. Meantime, they were changed for new ones without to ...determine the root cause of failure. The aim of this research work is to carry out a failure analysis in order to avoid recurrent damages in that engine. The fracture morphology and thread roots of fractured studs were carefully observed by optical devices. Thread material defects and corrosion were not found. However, the thread roots, where the stress concentration are higher, can be pointed as the local of fatigue crack initiation. As is well-known, all cylinder head stud bolts are pre-tensioned in order to increase the mean stress σm and reduce the stress amplitude σa. The steel alloy quality and design are of primordial importance for improving the lifetime of studs, and this is supervised by the Classification Societies (CS), as is indicated by an engraved stamp on each stud end, that certifies each one of them. The pre-tightening of the studs was calculated, and results point as root cause of failure a significant high stress concentration mainly at the second thread root of the studs, close to the bottom side of the nut, which are critical stress zones.
•A detailed failure analysis of cylinder head studs of a four stroke marine diesel engine was performed.•The importance of the preload on studs and bolts, being pointed as the main root cause of the premature failure.•Fatigue process was initiated at the second thread root, which is a critical thread zone.•When studs and bolts should be changed by new ones.
The mechanical properties were evaluated on specimens of AlSi9Cu3–T6 (333-T6) gravity casting (GC) alloy at room temperature. The GC 333-T6 alloy showed higher yield strength (YS), ultimate tensile ...strength (UTS) and quality Index but lower hardening capacity than GC 333 aluminum alloy without heat treatment. In addition, the GC 333-T6 aluminum alloy offered a five-fold higher hardening capacity in the cyclic deformation than in the monotonic deformation. Cyclic deformation characteristics of GC 333-T6 aluminum alloy were obtained from the LCF test. The alloy exhibited cyclic stabilization at low strain amplitudes (0.2%) and cyclic hardening at higher strain amplitudes (0.25–0.35%). The extent of cyclic hardening increased with increasing strain amplitude. The Basquin' s equation and Coffin–Manson relationships could be used to describe the fatigue lifetime of this alloy. Additionally, micro-cracks initiated at pores would preferentially pass through the elongated Si particles at lower strain amplitudes. The fatigue crack propagation was mainly characterized by the formation of dimples or fatigue striations at different strain amplitudes. Meanwhile, the larger fatigue crack propagation zone and smaller spacing of fatigue striations at the lower total strain amplitude (0.2%) gave rise to a longer fatigue life. Furthermore, final fast fracture tended to preferentially occur from the larger defects in the fast-fracture region, such as large voids, small pits and inclusions.
In order to improve the identification rate of fuel supply fault in diesel engine by using the vibration acceleration signal, a method of using the orthogonal vibration signals at the top and side of ...the cylinder head is proposed. Vibration sensors are installed at the top and side of the diesel engine to synchronously acquire the vibration acceleration signals at the two places perpendicular to each other. The fault identification of diesel engine fuel supply is achieved by extracting 17 domain time eigenvalues together with the peak value and peak-to-peak value of cross-correlation function of the orthogonal vibration signals and by using Generalized Regression Neural Network (GRNN) for classification and identification. The experimental results show that the recognition rate of fuel supply fault in diesel engine can be improved greatly by using orthogonal vibration signal, which has great engineering application value.
•Unifying damage processes of Al–Si cast alloys in high and low plastictiy regimes.•Novel in-situ microstructural test system links HCF and LCF by crack growth behaviour.•Correlation of fatigue ...lifetime and the in-situ damaging process.•Mathematical approach based on in-situ damaging improves with higher correlation.
In this publication, ambient condition fatigue investigations with different types of Al–Si–Cu and Al–Si–Mg cast alloys in rotating-bending high-cycle fatigue (HCF) and push–pull low-cycle fatigue (LCF) regimes have been performed with varying Si, Cu, Fe and Sr contents. The cast alloys investigated here are common used in cylinder heads for automotive application. Because the cylinder head is one of the most fatigued parts in combustion chamber engines, the microstructural knowledge of the damage process provides a tool of construction and its material selection. The investigations were also supported with an in-situ microstructural crack observation in high plasticity rotating-bending regimes. The specimens were directly processed out of serial produced T79 heat-treated cylinder heads to provide the equal microstructure for testing as under operational conditions.
The observations clearly identified the effects of the individual alloying elements both under low- and high-cycle fatigue. The crack propagation speed and the crack paths were majorly influenced by the eutectic silicon. Additional, the precipitation hardening due to copper affected significantly the fatigue endurance, too. In high plasticities the silicon’s influence got almost lost and only the matrix strength was crucial. Thus, increased fatigue strength in high loaded LCF regimes was observed for alloys with less copper content, thus higher ductility. By contrast, improved HCF and low loaded LCF endurance was only achieved when the matrix strength was increased by copper’s precipitation hardening. Crack branching and deflections strongly influenced the microstructural damage of the ductile AlSi7Mg(Sr) and hence, gained its fatigue strength. Iron phases could not identified as harmful inclusions, since the phases were similar in size of other hard phase elements like the other primary intermetallic phases like Al2Cu and β-Si phases under notch stress aspects, by the well defined solidification process in the test section. Because the crack nucleation mainly occurred on Si particles, strontium as a refinement agent influenced the early crack onset and accordingly the fatigue in total. Thus, the AlSi6Cu4(Sr) had increased lifetimes compared to AlSi6Cu4 both in HCF and LCF. Further, the presented results provide a modification of the Manson–Coffin approach to describe the relationship between plastic strain and lifetime, valid for all proposed alloys with only one set of parameters. Thus, it was possible to perform the fatigue calculation with a reduced range of scatter.
Cast Al-Si alloy is widely used in cylinder head structures and long-term service in 200–250 °C elevated temperature environments, which is easy to cause the deterioration of alloy properties. In ...this study, the thermal stability of the alloy during thermal exposure at 200 °C and 250 °C is investigated through the microstructure characterization and the mechanical properties test. The results show that the thermal exposure leads to the damage evolution of the precipitates in the microstructure. With the coarsening of the precipitates, the dislocation changes from cutting precipitates to bypassing precipitates, resulting in a weakening of the precipitation strengthening effect. The T6 alloy is in the insufficient peak aging state, and the alloy first reaches the peak aging state and then enters the over aging stage during the thermal exposure. Overall, with the increase in thermal exposure time and temperature, the Al matrix hardness, ultimate tensile strength (UTS), and yield strength (YS) decrease gradually and finally tend to be stable. As the thermal exposure progresses, the alloy fracture characteristic transitions from brittle fracture to ductile fracture, and the elongation of the alloy increases. In addition, the coarsening process of the thermal exposure alloy is described based on the Lifshitz-Slyozov-Wagner (LSW) theory, and the modified coarsening kinetic model can be divided into the rapid roughening stage and the stable roughening stage. Further, the damage parameter is defined as the relative change of precipitation strengthening to describe the deterioration degree of the mechanical properties for thermal exposure alloy.
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•The thermal exposure results in a weakening of precipitation strengthening effect.•The alloy through the T6 heat treatment is in the insufficient peak aging state.•Alloy mechanical properties degrade with an increase in exposure time and temperature.•The coarsening process of precipitates is divided into rapid stage and stable stage.•The decline degree of the mechanical property is described by the damage parameter.
To meet several marketing demands, development of new aluminum alloys which can be used for future high-efficiency diesel engines has been widely pursued. Especially, cylinder heads (hereafter ...referred to as “head(s)”) are used at high combustion pressure and very high temperature, which makes it difficult to achieve a structure with light weight and high rigidity. In this study, aluminum alloy A356 (Al-Si-Mg series) which is a major head material, were conducted the thermal fatigue tests. Thus, the authors focused on the changing of material characteristics (hardness and stress-strain curves as for macroscopic characteristic and microstructure as for microscopic characteristic) during the test. This paper deals with the effects of artificial aging on two aluminum alloys A356, which have been often used for engine cylinder heads. The aluminum alloys were artificially aged under several different conditions after T6 heat treatment. The alloys were tested for fatigue characteristics as thermo-mechanical fatigue failure. The microstructure was observed by TEM to see the effects on microstructure in terms of fatigue failure. In addition, we examined the microstructure of an actual head after a durability test, and tried to find out whether material test conditions above mentioned were reasonable. Finally, the relationship between the microstructure changes and the low cycle thermal fatigue is discussed.
To satisfy the high-load bearing and high-temperature resistance requirements put forward by the increased power density of the cast iron cylinder head, the cast iron/GH4169 bimetal was manufactured ...by Powder Bed Fusion (PBF) in forward design. The performance of bimetals is simultaneously affected by different properties in several regions. Thus, a more comprehensive approach to evaluating bimetallic performance is urgently needed. This paper uses the Multi-Attribute-Decision-Making (MADM) method to evaluate the bondability and thermal fatigue resistance of the cast iron/GH4169 bimetal under different process parameters. Meanwhile, the shear test was used to verify the evaluation results of the bimetallic bondability. Furthermore, the matching relationship between process parameters and performance evaluation scores was established by combining the BP neural network to achieve the prediction of bimetallic thermal fatigue resistance. The results show that the evaluation results using the combination weighting method based on Game Theory (GT) were more accurate than those of the Analytic hierarchy process (AHP), Entropy method (EM), and combination weighting method based on average. The evaluation results of the interfacial bondability had a relatively high degree of congruence with the shear test results. It is feasible to use MADM to comprehensively evaluate the performance of the cast iron/GH4169 bimetal. Finally, the prediction model based on the BP neural network demonstrates good prediction capability. This study can provide research methods for evaluating and predicting the performance of bimetals to meet engineering needs in forward design.
•A comprehensive evaluation of multiple properties in various regions of the bimetal was performed.•The comprehensive performance of bimetals is evaluated using MADM for the first time.•The Game Theory shows a greater advantage in the comprehensive evaluation of bimetals.•The BP neural network predicts the performance of bimetal well.
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