Analysis of a diesel generator crankshaft failure

This paper analyses a catastrophic crankshaft failure of a four-stroke 18 V diesel engine of a power plant for electrical generation when running at a nominal speed of 1500 rpm. The rated power of the engine was 1.5 MW, and before failure it had accumulated 20,000 h in service operating mainly at full load. The fracture occurred in the web between the 2nd journal and the 2nd crankpin. The mechanical properties of the crankshaft including tensile properties and surface hardness (HV₁) were evaluated. Fractographic studies show that fatigue is the dominant mechanism of crankshaft failure, where the beach marks can be clearly identified. A thin and very hard zone was discovered in the template surface close to the fracture initiation point, which suggests that this was the origin of the fatigue fracture. A finite element model of the crankshaft has predicted that the most heavily loaded areas match the fractured zone.     

Failure analysis of a cylinder sleeve from a turbocharged diesel engine

This work presents the conclusions of a failure analysis performed on a V12 Turbo Charged diesel engine cylinder sleeve. The failure analysis carried out established the most relevant factors that caused damage to the cylinder sleeve. An examination of the internal surface of the cylinder sleeve revealed an elevated number of cavities close to the top center area, which acted as stress concentrators reducing the resistance of the component, creating crack nucleation spots. Additionally there were internal differences in the microstructure of the component, which indicate that different cooling conditions occurred during its manufacture, providing a secondary failure mechanism, due to material fragility.     

Analysis of the error in measuring the specific fuel consumption of a dc diesel generator

Translated from Izmeritel'naya Tekhnika, No. 2, pp. 41–43, February, 1992.     

柴油发电机控制箱振动故障诊断

利用实验测试与数值分析对柴油发电机控制箱内电子元器件振动故障进行研究。测试结果表明机组正常运转阶段控制箱关键点产生的振动较为平稳,无振动过载现象。据此推测控制箱内仪表故障的强烈振动主要发生于启动、停机阶段。利用Ansys有限元分析对机组0Hz～50Hz范围振型进行计算。结果表明机组多阶振型频率处于0Hz～50Hz范围,其中三个振型给控制箱造成较大的振动位移,相应的振动加速度远大于重力加速度,可能造成了严重的过载。过载力完全可能导致控制箱内仪器、仪表引脚连接失效。最后指出动力机械控制元件抗过载能力必须加以考虑。     

Fracture failure of a diesel engine piston-pin

Longitudinal cracking and transverse fracture took place on a diesel engine piston-pin used in a truck during service. The banded texture throughout the whole length of the longitudinal fracture is presented in the middle region of the longitudinal fracture. The longitudinal crack originated from the banded texture and propagated toward the internal hole surface and the external circle surface of the piston-pin. Metallographic and chemical inspections of the piston-pin material away from the crack origin reveal all the parameters to be acceptable. Subsequent metallographic examinations were performed on the smoothed longitudinal fracture surface. These reveal the presence of the longitudinal inclusion clusters of 25 mm long mainly consisting of calcium aluminate, associated with the banded texture on the longitudinal fracture. Under the integrated action of structure stress and service stress, the crack propagated along the longitudinal first, and then propagating along the transverse by fatigue under the alternative service load. The appearance of longitudinal inclusion clusters of excess size in the crack origin zone is mainly responsible for the failure of piston-pin.     

Failures of single cylinder diesel engines crank shafts

The single cylinder diesel engines are extensively used in agricultural areas for several purposes such as water pumping. In some cases, these engines are also used for driving some auxiliary agricultural vehicles. This imposes unexpected loads on the components of the engines resulting in the premature failures. In this study, two different failure cases of crankshafts of these engines are analyzed. Some characterization studies and fractographic analyses are carried out to asses the failure reason. However, the cranks have some miner design differences, both failures are occurred after a fatigue process. One of the failed cranks has important heat treatment error.     

Crankshaft failure analysis of a boxer diesel motor

This paper reports a failure mode analysis of a boxer diesel engine crankshaft. Crankshafts are components which experiment severe and complex dynamic loadings due to rotating bending combined with torsion on main journals and alternating bending on crankpins. High level stresses appear on critical areas like web fillets, as well as the effect of centrifugal forces and vibrations. Since the fatigue fracture near the crankpin-web fillet regions is one of the primary failure mechanisms of automotive crankshafts, designers and researchers have done the best for improving its fatigue strength. The present failure has occurred at approximately 2000 manufactured engines, and after about 95,000 km in service. The aim of this work is to investigate the damage root cause and understand the mechanism which led to the catastrophic failure. Recommendations for improving the engine design are also presented.     

Failure mode analysis of two crankshafts of a single cylinder diesel engine

This paper reports an investigation carried out on two damaged crankshafts of single cylinder diesel engines used in agricultural services for several purposes. Recurrent damages of these crankshafts type have happened after approximately 100 h in service. The root cause never was imputed to the manufacturer. The fatigue design and an accurate prediction of fatigue life are of primordial importance to insure the safety of these components and its reliability. This study firstly presents a short review on fatigue power shafts for supporting the failure mode analysis, which can lead to determine the root cause of failure. The material of these damaged crankshafts has the same chemical composition to others found where the same type of fracture occurred at least ten years ago. A finite element analysis was also carried out in order to find the critical zones where high stress concentrations are present. Results showed a clear failure by fatigue under low stress and high cyclic fatigue on crankpins.     

船用柴油发电机组非线性隔振系统动态特性分析

以计算多体动力学理论为指导,以船舶柴油发电机组的抗冲击研究为背景,建立了柴油发电机组的多体动力学以及线性隔振系统模型,并通过实验验证模型的正确性;在此基础上构建机组的非线性隔振系统,并对机组额定工况以及冲击条件下隔振系统的动态特性进行分析,结果表明非线性隔振系统较线性隔振系统有良好的隔振效果。文中的建模与求解方法较数学建模与求解简单易行,对隔振器选型与安装、非线性隔振器的参数化设计与优化、其它船用机械的抗冲击研究奠定了一定的工程应用基础。     

Catastrophic failure of a fan in a diesel engine cooler

The fan used to cool a diesel engine fractured catastrophically after approximately 100 h of operation. The fan failed at a spider, which was resistance spot welded to a shim placed between two circular spiders of 3 mm thickness. The detailed analysis of the fracture indicated that the premature failure of the fan was due to inadequate bonding between the sheets at the weld nugget. The fracture was initiated from the nugget-plate interface. The inadequate penetration and lack of fusion between the steel sheets during resistance spot welding led to poor weld strength and the fracture during operation. The propensity to crack initiation and failure was accentuated by improper cleaning of the surfaces prior to welding and to inadequate nugget-to-sheet edge distance.     

Failure analysis of cylinder clamping rods in diesel engines

This article discusses the failure of cylinder clamping rods in single cylinder diesel engines. The AISI 4140 hardened and tempered steel clamping rods were failing after 200–250 h of operation. The fatigue failures initiated at the root of the last thread on the clamping rod that was engaged in a blind hole in the cylinder block. The failures were caused by loose tolerances on the threads that resulted in a non-uniform distribution of load. The load was concentrated on the last threads to engage, thus causing fatigue crack nucleation at the thread root and propagation until the rod broke by overload. Changing the tolerance on the threads virtually eliminated the fatigue problem.     

Failure analysis of a diesel engine cylinder head based on finite element method

Macro fatigue cracks are expected to occur in valve bridges of cylinder head when engine is operating in normal working condition. In order to determine the causes of these failures, stress analysis is carried out using finite element method with a concern of temperature dependency of material properties. Mechanical and thermal properties of material tested at high temperatures are applied to the finite element analysis. Furthermore, temperatures of the cylinder head in actual working condition are measured to validate the simulation results of finite element analysis. After that, stress computation is performed and the regions of stress concentration on the flame deck surface are obtained. The analysis results of stress show that the regions of stress concentration are in agreement with the actual failure regions of the cylinder head. When analyzing the failures on the flame deck surface of a cylinder head by evaluating stress concentration, temperature’s effect on mechanical strength of material should not be ignored. The methodology of failure analysis proposed in this paper is time-saving and also relatively accurate and predictive in actual engineering practice.     

柴油机缸盖振动加速度信号影响因素分析

改变195柴油机的转矩、转速及供油时刻,测量分析各工况的缸盖振动加速度信号,分析结果表明,同样转速时,缸盖振动加速度时域最大波动量及2kHz以下各频带能量与缸内燃烧状况相对应;当转速发生改变时,加速度信号时域最大波动量及各频带能量与缸内燃烧状况间无对应关系。建立有限元分析模型,研究缸盖联接螺栓预紧力及材料刚度对缸盖振动加速度信号的影响规律,结果表明当材料的杨氏模量或联接螺栓预紧力减小时,系统的固有频率降低,使得缸盖振动加速度信号时域最大波动量及2kHz以下各频带能量呈增大的趋势。     

船用柴油机气缸套几何误差在线测量技术研究

设计一套船用柴油机气缸套几何误差在线测量系统,分析机床定位误差、传感器安装及测量误差对缸套表面各被测点坐标计算准确度的影响,建立测量误差计算数学模型。基于非线性规划方法建立缸套直线度误差、圆度误差、圆柱度误差的评定数学模型,通过与现有测量数据及误差评定模型的对比分析,表明该模型评定准确度较高。搭建在线测量原型系统,并进行测量实验,实验数据表明该系统具有结构简单、检测准确度及检测效率高等特点。     

Analysis of a crack in a disclinated cylinder

In this paper, the stress intensity factors and the opening displacement of a crack loaded by a negative wedge disclination in an isotropic cylinder are numerically determined. The disclination axis coincides with the long axis of the cylinder, and one end of the crack coincides with the disclination location. The cylinder may also be subjected to equal and opposite line loads on its surface. An exact formulation leads to a pair of decoupled singular integral equations of the Cauchy type. Numerical solutions show that if the cylinder represents a grain in a polycrystal, (i) unstable submicroscopic cracks 10^-5 to 10^-1 times the grain size and stable microscopic cracks of the order of the grain size, are predicted, (ii) the submicroscopic crack length to grain size ratio decreases, while the microscopic crack length to grain size ratio increases, as the grain size increases, (iii) significant differences exist, even in the case of the submicroscopic cracks, between the predictions of the exact theory and the approximate theory which ignores stress redistribution, and (iv) the opening displacement is independent of the elastic constants and the crack profile is wedge-shaped.