Advanced Materials Research Vols. 44-46

Abstract: An accelerated life model is an important factor affecting the evaluation of test data. Avoiding the existent difficulties of treating mixed data and based on the grey theory with composite GM(1,1) model, approach is presented for treating fatigue data under constant stress amplitude accelerated life tests. Availability of the approach has indicated by an example.

Abstract: As an important means to improve the reliability of complex manufacturing systems and to ensure that they can function better, condition monitoring systems (CMS) are usually designed and used in manufacture industries. And reliability is one of the most important characteristics of CMS. Fuzzy set theory based on reliability modeling and analysis methods for CMS are proposed in this paper. The methods include a fuzzy graph modeling technique for analyzing the system reliability of CMS, and fuzzy reliability computing methods to quantify uncertainties in function decomposition of CMS and compute system reliability of CMS by invoking Fuzzy-set theory and approaches. On the other hand, the fuzzy reliability of CMS based on fuzzy failure subset and confidence level is defined, and system reliability indexes of CMS are set up to compute the system reliability of CMS. A case of application is used to illustrate the procedure.

Abstract: This paper outlines a new technique to address the paucity of data in determining fatigue life and performance based on reliability concepts. Two new randomized models are presented for estimating the safe life and pS-N curve, by using the standard procedure for statistical analysis and dealing with small sample numbers of incomplete data. The confidence level formulations for the safe and p-S-N curve are also given. The concepts are then applied for the determination of the safe life and p-S-N curve. Two sets of fatigue tests for the safe life and p-S-N curve are conducted to validate the presented method, demonstrating the practical use of the proposed technique.

Abstract: Based on BAYES data processing theory, a new method of fuzzy probability is proposed for the parameter reliability of small sample. Prior distribution of fuzzy parameter is obtained by stochastic weighted method, then posterior distribution of fuzzy parameter is got by the method of conjugate distribution. In the end, the formula of fuzzy membership function is constructed, and probability of fuzzy events is solved.The study of this paper aims at the membership function which is deduced in the condition that mean is known and deviation is unknown in normal population distribution. At the same time using information of small sample of actual experiment, the study fully utilizes prior information, so, it is convincing to evaluate reliability of fuzzy parameter. It is obviously economical.

Abstract: In the reliability-based analysis of mechanical joints, as each factor has different effect on the failure of mechanical joints, the effects of design parameters on reliability of the mechanical joints are determined with the reliability-based sensitivity analysis method. Furthermore, the reliability of mechanical joints can be effectively designed. As a matter of fact, if a change of a certain random parameter has great effect on the reliability of mechanical joints, the parameter must be strictly controlled in the course of design and manufacture to ensure reliability. Whereas if a change of a certain random parameter has unobvious effect on the reliability of mechanical joints, it can be treated as a deterministic value to reduce the complexity of the analysis. In this paper, based on the reliability design theory, the sensitivity analysis method and the fourth moment technique, the reliability sensitivity of the mechanical joints with arbitrary distribution parameters is extensively discussed and a numerical method for reliability sensitivity design is presented. The variation regularities of reliability sensitivity are obtained and the effects of design parameters on reliability of the mechanical joints are studied. The method presented in this paper provides reasonable and necessary reliability basis for the design, manufacture, use and evaluation of the mechanical joints.

Abstract: With the application of explicit dynamics and probability finite element method, reliability virtual experiment of deep groove ball bearing is carried out. Based on self –adaptive mesh module of the ANSYS/LS-DYNA, true numerical simulation of the working process is presented after the three-dimensional finite element bearing model is built. Then, the contact stress and strain among balls, retainer and inner (outer) race and also the pressure law during the contact process are obtained. As the randomness of manufacture and assemblage tolerance is inevitable, Monte Carlo method is adopted when samples the bearing system. From the random sampling, a large sample data of the maximum contact stress is got and the reliability coefficient is calculated; and the contribution of each original manufacture error to the reliability sensitivity of the bearing is analyzed. Reliability virtual experiment offers a theoretical reference to fatigue strength calculation and dynamic optimum design of the bearing system, and the analysis process is easy to be program controlled.

Abstract: Friction brake is still an absolutely necessary way of brake in high speed vehicle today. Complex nonlinear vibration phenomena appear in friction brake system because of dry friction between friction pairs. The resulted brake squeal and brake chatter may cause strength failure and fatigue damage of the disk brake element. Therefore, it is necessary to consider chatter in strength calculation and structure life prediction of disk brake element. In this paper, the finite element model of disk brake element is built. Vibration displacements and dynamic stresses are calculated for chatter character analysis and strength evaluation.

Abstract: In advanced electronic products, electromigration-induced failure is one of the most serious problems in fine pitch flip chip solder joints because the design rule in devices requires high current density through small solder joints for high performance and miniaturization. The failure mode induced by electromigration in the flip chip solder joint is unique, owing to the loss of under bump metallurgy (UBM) and the interfacial void formation at the cathode contact interface. In this study, Electromigration of flip chip solder joints has been investigated under a constant density of 2.45×104 A/cm2 at 120 °C. The in-situ marker displacements during the electromigration test was measured and found to show a rough linear change as a function of time. Scanning electron microscopic images of the cross section of samples showed the existence of voids at the interface between Al interconnection and under bump metallurgy. The void movement was matched with the marker displacements during the electromigration test, and voids moved to the cathode interface between Al interconnection and under bump metallurgy in the downward electron flow (from chip to substrate) joint. The mechanism of electromigration-induced void migration and failure in the flip chip are discussed. During electromigration, a flux of atoms is driven from the cathode to the anode or a flux of vacancies in the opposite direction. It can lead to two possible mechanisms of void migration. First, if we regard the void as a rigid marker of diffusion, it will be displaced towards the cathode by the atomic flux in the electromigration, Second, if we consider surface diffusion on the void surface, electromigration will drive atoms on the top surface of the void to the bottom surface of the void, and consequently the void will move towards the cathode.

Abstract: Partial slip rolling contact was analyzed in this paper by the finite element method with the application of a robust cyclic plasticity model. The repeated rolling contact process was carried out by translating the normal pressure and the tangential traction across the contact surface step by step. The normal pressure and the tangential traction were applied to the nodes through the time-dependant amplitude functions as the concentrated nodal forces. With the detailed stress-strain responses output from the FE analysis, a general multiaxial fatigue criterion was used to predict fatigue initiation life and initiation position. The influences of partial slip conditions on the residual stresses, residual shear strain and the initiation lives are obtained.

Abstract: In this investigation two fatigue crack growth models based on the different physical assumptions were systematically analyzed. One model makes use of the size of the stable damage distribution zone near crack as the major contributor to the fatigue crack growth. This model is based on the concept that a material point failures and a new crack will form when the fatigue damage value of the material point reach the critical damage. The other model supposes that fatigue growth can be described as a process with sequentially breaking small volume elements behind the crack tip. The fatigue crack growth can be regarded as successive crack re-initiation over a critical distance. The fatigue crack growth rate can be determined as the ratio of the critical distance to the average life within critical distance. Both models use macro parameter to describe the microscopic mechanism. An elastic-plastic finite element analysis (FEA) was used to obtain the detailed stress-strain history of the notched component with a detailed consideration of the cyclic plasticity of the material using a robust cyclic plasticity model. The fatigue damage distribution and the average damage within the critical distance near the crack tip can be obtained by combining the fatigue damage parameter with the stress strain distribution from the finite element analysis. These two models were evaluated using the experimental results obtained from the crack grow experiments on compact specimens made from 16MnR. The predicting results using these two models correlate well with the experimental data. The results show that two models can well describe the notch effect on the fatigue crack growth.