Reliability prediction of the fatigue life of a crankshaft

Crankshaft, the core element of the engine of a vehicle, transforms the translational motion generated by combustion to rotational motion. Its failure will cause serious damage to the engine so its reliability verification must be performed. In this study, the S-N data of the bending fatigue limit of a crankshaft are derived. To evaluate the reliability of the crankshaft, reliability verification and analysis are performed. For the purpose of further evaluation, the bending test of the original crankshaft is carried out, and failure mode analysis is made. The appropriate number of samples, the applied load, and the test time are computed. On the basis of the test results, Weibull analysis for the shape and scale parameters of the crankshaft is estimated. Likewise, the B10 life under 50% of the confidence level and the MTTF are exactly calculated, and the groundwork for improving the reliability of the crankshaft is laid. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Do-Hyun Jung received his B.S. and M.S. degrees in Mechanical Engineering from Ajou University in 1988 and 1990, respectively. He then obtained his Ph.D. degree from Changwon National University in 2006. Dr. Jung is currently an Adjunct Professor at the School of Mechanical Engineering of Sunmoon University, Korea. He also manages the Reliability Application Research Center of the Reliability Division of KATECH. Dr. Jung’s fields of study include fatigue, reliability, and remanufacturing issues.     

转轴疲劳强度的可靠性设计

提出了采用复合应力法建立转轴的疲劳强度可靠性设计的理论,该方法与安全系数法相比计算简便,易于转轴工程可靠性设计与应用。     

Reliability design of preventive maintenance scheduling for cumulative fatigue damage

As the cumulative running times of a locomotive truck increases, degradation such as fatigue, wear, and deterioration occur. Particularly the container train and uncovered freight train, their maintenance cost during their lifetime is three times more than the manufacturing cost. Generally, for the freight train, corrective maintenance to repair a bad part after a breakdown is not adapted; however, preventive maintenance that fixes a bad part before a breakdown is. Therefore, it is important and necessary to establish a system of optimal preventive maintenance and exact maintenance period. This study attempts to propose a preventive maintenance procedure that predicts a repair period using reliability function and instantaneous failure rate based on fatigue test and load history data. Additionally, this method is applied to the end beam of an uncovered freight train, which is the brake part, and its usefulness is examined and analyzed. This paper was recommended for publication in revised form by Associate Editor Chongdu Cho Seok-Heum Baek received a B.S. and M.S. degree in Mechanical Engineering from the Dong-A University in 2001 and 2003, respectively. He is currently a Ph.D. student at the School of Mechanical Engineering at Dong-A University in Busan, Korea. Student Baek works on ceramic composite design and robust and reliability-based design, and his research interests are in the areas of trade-off analysis in multicriteria optimization, design under uncertainty with incomplete information, and probabilistic design optimization. Seok-Swoo Cho received a B.S. degree in Mechanical Engineering from Dong-A University in 1991. He then went on to receive his M.S. from Dong-A University in 1993 and Ph.D. degree from Dong-A University in 1997. Dr. Cho is currently a Professor at the Vehicle Engineering at Kangwon National University in Kangwon-do, Korea. Dr. Cho works on crack growth modeling and composite design and optimization, and his research interests are in the areas of structural optimization and inverse and identification problems, and X-ray diffraction, brittle collapse and crack propagation, fatigue fracture phenomena. Hyun-Su Kim received a B.S. degree in Mechanical Engineering from Seoul National University in 1978. He then went on to receive his M.S. from KAIST in 1980 and Ph.D. degree from University of Iowa in 1989. Dr. Kim is currently a Professor at the Mechanical Engineering at Dong-A University in Busan, Korea. His research interests are in the area of high temperature creep fatigue, bio-engineering, design using the finite element method, optimization, and MEMS. Won-Sik Joo received a B.S. degree in Mechanical Engineering from Dong-A University in 1968. He then went on to receive his M.S. from Dong-A University in 1978 and Ph.D. degree from Kookmin University in 1988. Dr. Joo is currently a Professor at the Mechanical Engineering at Dong-A University in Busan, Korea. His research interests are in the area of creep and fatigue in high temperature alloy, fatigue design, and strength evaluation.     

圆柱螺旋弹簧疲劳强度的可靠性设计

指出传统机械设计的缺陷,结合现代机械设计理论,并基于应力和强度干涉模型,介绍了圆柱螺旋弹簧疲劳强度的可靠性设计,同时利用实例,进一步阐明了设计步聚.对于重要或有可靠性要求的圆柱螺旋弹簧提供了可行的设计方法.     

Development of a design verification methodology including strength and fatigue life prediction for agricultural tractors

During the operations of an agricultural tractor, front axle and front axle support encounter the worst load conditions of the whole tractor. If the design of these components is not verified by systematic engineering approach, the operators of the tractor may face with sudden failures. This paper aims to develop a verification method, which involves testing an agricultural tractor on a special test track and agricultural field and together with the computer aided engineering analysis, in order to prevent such failures in the lifetime of the agricultural tractor. For this purpose, a strain gage data acquisition system has been designed to measure the strain values on the component in order to determine maximum principle stresses for the calculation of overload safety on the agricultural field and stress data for the prediction of fatigue life on a radial washboard test track. The cycle number of these stress data for the fatigue analysis has been established by rainflow cycle counting method. Total fatigue damage for the front axle support has been calculated considering damage accumulation hypothesis defined by Miner.     

滚子输送链联接牢固度的可靠性优化设计

根据过盈联接设计和可靠性优化的基本理论，以联接可靠度最高为目标，对滚子输送链联接牢固度的可靠性进行了优化分析，通过实例进行了设计验证。分析结果可为选择链节合理的过盈配合精度提供理论依据。     

Investigation of the fatigue behaviour of butt-welded joints treated by ultrasonic peening process and compared with fatigue life assessment standards

Ultrasonic peening is a technique to be used for improving the fatigue life of welded structures. The technique makes use of an ultrasonically vibrated pin which is pressed against the toe regions of the weld. The beneficial effect is mainly due to the introduction of favourable compressive stresses on weld toe regions, causing local plastic deformation and reducing stress concentration effect. This paper deals with the influence of ultrasonic peening treatment on fatigue life improvement in butt-welded plates. Fatigue life is predicted for the welded plate as per BS 7608 standard, AWS D 1.1 structural welding code and IIW-XIII-1539-96 standard, and they are compared with the experimental results. The ultrasonic peening technique is applied on a plain carbon steel plate weldment, and specimens conforming to ASTM E 466 standard are prepared and tested in a servohydraulic static dynamic testing machine at three different stress levels. Afterwards their fatigue lives are obtained. The comparison of the fatigue life in unpeened and peened specimens brings out the beneficial influence of the treatment. It is found that the improvement in fatigue life is up to 35% at 250 MPa of applied stress. But at higher stress levels, the benefit is less. At 350 MPa of applied stress, peening results in lower fatigue life. A comparison of the predicted fatigue lives from various standards with the experimental results shows that it is very close to the life at 50% probability of survival as predicted by the BS 7608 standard. The details of the experiments conducted and the results obtained are furnished in this paper.     

Die fatigue life design and assessment via CAE simulation

In die design process, the design and prediction of die fatigue life is a non-trivial issue. Many factors in die life cycle from design, fabrication to service all affect die life. The die life in cold forging processes is basically determined by die fatigue failure. The design and assessment of die fatigue life needs to consider all the affecting factors including die structure and component design, materials selection and properties configuration, die fabrication and service conditions. Currently, there is no efficient approach to providing complete solutions by considering all of these factors. CAE simulation technology, however, presents a promising approach to addressing the issue. In this paper, a simulation-based approach for die life design and assessment is presented. The approach employs both stress-life and strain-life fatigue analysis methods to conduct the die fatigue life design and analysis based on the stress and strain revealed by CAE simulation. As the die stress and strain in forming process vary dynamically, the integrated simulation of forming process and die deformation is conducted in such a way that the dynamic die stress and strain can be identified and determined. To implement this idea, a realization framework is orchestrated and the processes and procedure under the framework are succinctly articulated. The implementation with case studies is finally used to test and verify the validity, robustness, and efficiency of the developed approach. The approach is proven to be able to provide satisfactory solutions for die life design and assessment in the early stage of die design.     

Reliability estimation of solder joints under thermal fatigue with varying parameters by using FORM and MCS

One of major reasons for the failure of solder joints is thermal fatigue. Also, the failure of solder joints under thermal fatigue loading is influenced by varying boundary conditions such as the material of the solder joint, the materials of substrates(related to the difference in CTE), the height of solder, the distance of the solder joint from the neutral point (DNP), the temperature variation and the dwell time. In this paper, first, the experimental results obtained from thermal fatigue test are compared to the outcomes from theoretical thermal fatigue life equations. Second, the effects of varying boundary conditions on the failure probability of the solder joint are studied by using probabilistic methods such as the first order reliability method (FORM) and Monte Carlo simulation (MCS).     

轮盘低循环疲劳寿命可靠性分析方法

疲劳寿命呈现异方差特性,其标准差随弹性应变幅和塑性应变幅的减小而增大,因此在Manson-Coffin公式中引入标准正态变量斗和线性标准差σe、σp,将ε-N曲线参数表示为随机变量μ的函数,建立了低循环疲劳寿命的概率模型。在低循环疲劳试验数据的基础上应用异方差回归分析方法获得了该模型的参数,通过蒙特卡洛模拟验证了模型的精度。应用该模型进行等厚空心轮盘的低循环疲劳寿命可靠性分析,得到了轮盘中心孔危险点的疲劳寿命分布。由于没有事先假设疲劳性能参数的分布特性,参数均由试验数据分析得到,并且采用异方差回归分析能够充分利用数据信息,在提高分析精度的同时能够节约疲劳试件,因此该分析方法具有较好的工程应用前景。     

Stress analysis and design for a structural fatigue testing machine

A closed loop servo-hydraulic structural fatigue testing machine was developed. It can apply fatigue loads on actual engineering parts or components for their fatigue strength evaluation. The testing machine consists of a structural bending load frame, a structural torsion load frame, a hydraulic system, and a control system. Stress analysis and design for the crosshead, columns and test bed for the structural bending test frame are described. Finite element analysis was performed for the structural torsion load frame. Evaluation of the structural load frames and application of the test machine are briefly given.     

A new forming-limit criterion for fracture prediction in a powder forging application

This research investigates the forging limit of sintered compacts by taking into particular consideration the effects of void evolution in the process. A new fracture criterion for a porous medium, which is based on the first principal strain energy density (FPSED), is developed as well. The experiment and the finite element analysis (FEA) have been conducted to examine the process. The material properties of porous compacts are measured by both the uni-axial tension and the compression tests. The finite element model is first verified with the upsetting experiment under different frictional conditions. By applying this new criterion, the fracture upsetting simulation demonstrates much better accuracy than the results derived from the equations proposed by other researchers. The fracture prediction in forging the gear blank is also presented as a practical application to reinforce the reliability of this model. Besides the degradation of the strength, this study specifically shows that voids in the sintered preform exponentially reduce the forging limit.     

一种USB加密狗的可靠性分析与设计

讨论了使用单片机和USBN9603芯片所设计的USB加密狗.分析了破解技术、反破解技术,并提出了反软件模拟、反静态分析和反动态跟踪等方法;最后考虑将USB加密狗与CAD应用软件相结合,提出了保证数据交互的完整性的可靠措施以及固件程序设计的可靠性方案,并给出了实验结果.     

抗疲劳断裂的可靠度计算

根据断裂力学的理论和应力-强度模型，给出了在变载荷作用下，裂纹不扩展，给定寿命时不断裂的概率计算公式和给定可靠度时可靠寿命的计算方法。     

概率疲劳设计方法与设计数据

:对正态分布下的无限寿命概率疲劳设计方法进行了研究 ,推导出了其设计计算公式 ,并提供了各种影响系数的变异系数试验数据     

腐蚀疲劳设计方法与设计数据

论述了腐蚀疲劳设计方法及其设计参数的确定方法,给出了钢和铸铁的腐蚀系数数据,并提供了解决腐蚀疲劳频率影响问题的普遍方法。     

Numerical analysis for prediction of fatigue crack opening level

Finite element analysis (FEA) is the most popular numerical method to simulate plasticity-induced fatigue crack closure and can predict fatigue crack closure behavior. Finite element analysis under plane stress state using 4-node isoparametric elements is performed to investigate the detailed closure behavior of fatigue cracks and the numerical results are compared with experimental results. The mesh of constant size elements on the crack surface can not correctly predict the opening level for fatigue crack as shown in the previous works. The crack opening behavior for the size mesh with a linear change shows almost flat stress level after a crack tip has passed by the monotonic plastic zone. The prediction of crack opening level presents a good agreement with published experimental data regardless of stress ratios, which are using the mesh of the elements that are in proportion to the reversed plastic zone size considering the opening stress intensity factors. Numerical interpolation results of finite element analysis can precisely predict the crack opening level. This method shows a good agreement with the experimental data regardless of the stress ratios and kinds of materials.     

Reliability and fatigue life evaluation of railway axles

The axle is one of the most important components of a rail vehicle which transmits the weight of the vehicle to the wheels, meets the vertical and horizontal loads formed during static and dynamic moving, and carries the driving moment and braking moment. The prediction of fatigue failure of axles plays an important role in preventing fatigue fractures. Varying loads on components lead to cumulative failure in the mechanism. In this study, failures in axles of rail vehicles serving the Istanbul Transportation Co. have been investigated. Statistical evaluation of real life values has been performed by taking into account the kilometer and load cycle. Equivalent stresses have been used to derive life equations and diagrams by using one of the cumulative life theories known as the Palmgren-Miner method. Finally, theoretical and practical Wohler diagrams S-N (σ-N: stress-life) have been plotted to reveal error calculation.     

On the application of Dang Van criterion to rolling contact fatigue

In this note, the problem of the calibration of the Dang Van multiaxial fatigue criterion is addressed. The discussion is based on uniaxial fatigue tests performed with different stress ratios. Results show that the usual technique for calibrating the constants of the Dang Van criterion does not agree with experimental evidence, especially for negative stress ratios. For this reason, a different fatigue failure locus made of two straight line segments is proposed and typical three-dimensional rolling contact stress histories are analyzed using the traditional and proposed methods. Results show that the conventional technique does not agree with knowledge coming from shakedown approaches of rolling contact while the proposed method seems to constitute a more appropriate limit.     

双圆弧齿轮传动弯曲疲劳强度可靠性分析

运用机械零件可靠度的计算方法 ,对双圆弧齿轮弯曲疲劳强度的可靠性进行计算 ,并给出了一实际算例。