Advanced Materials Research Vols. 118-120

Abstract: An energy-based fracture mode has been derived for the mode I crack kinking and branching. The classic -integral has been further explored by a new partial integral path and the analytical solution of the energy release rate for crack kinking and branching from a mode-I crack tip has been established. The crack kinking/branching angle has also been analytically derived. It shows that the Griffith’s theorem and conservation law can be applied to both model I crack extension and model I crack kinking and branching. The branching mechanism for quasi-static mode-I crack has been theoretically investigated. The branching toughness and the K-based criterion for crack branching have been defined. The crack branching phenomena predicted by the present model are in well agreement with the experimental observations reported in the literatures.

Abstract: As a new tool of statistical analysis, Copula is introduced to build reliability model for structural system consisting of identical components, by which the complex feature of failure dependence can be depicted. Aiming at symmetric structure systems, typical failure-dependence mechanism of components is discussed firstly. Considering the failure-dependence mechanism, modeling steps based on Gauss Copula and Archimedean Copulas are put forward, in which the twin stress, components strength are chosen as the basic variables and the safety margins are chosen as the analytic variables. Compared with Gauss Copula, Archimedean Copulas have powerful capability of describing the failure-dependence mechanism owing to the adjustable parameters can be determined according to the rank correlation coefficient and the information about the critical failure point. Archimedean Copula-based reliability models are applicable to non-normal situations. A numerical example is given to show that the new method is reasonable and feasible. Copula-based reliability models can give a new path for reliability analysis of complex systems with failure-dependence.

Abstract: For high-speed railway carbody structure durability analysis problems in China, one integrated method based on MBS (multibody simulation) is proposed here. Firstly, one EMU (Electricity Multiple Unit) full vehicle was performed to dynamic modeling and simulation. The numerical simulation results were applied to illustrate the vehicle dynamic characteristics. And the relationships between structural strength, stiffness, and frequency characteristics were also studied. Secondly, the multidisciplinary design technique was used to solve multi-mode coupled vibration of carbody structure on the cumulative effects of local vibration and damage effects, as well as structure light-weighting and other parallel optimization problems. Finally, the effective measures were proposed to control carbody structure’s physical failure.

Abstract: The prediction of the hardenability of gear steel has been carried using stepwise polynomial regression and artificial neural networks (ANN). The software was programmed to quantitatively predict the hardenability of gear steel by its chemical composition using two calculating models respectively. The prediction results using artificial neural networks have more precise than the stepwise polynomial regression model. The predicted values of the ANN coincide well with the actual data. So an important foundation has been laid for prediction and controlling the production of gear steel.

Abstract: This research makes comparisons of empirical fatigue-lives between AC8A Al alloy and the metal matrix composites (Al/Al2O3, Al/Al2O3/Al2O3p), and also includes comparisons of fatigue-lives between empirical fatigue-lives and estimated fatigue-lives from regular-periodic load testing, acoustic emission (AE) method to predict fatigue-crack initiation before visible in sight and SEM (Scanning Electron Microscope) photographs of each material. According to the test results of the notched specimen, the fatigue life of the hybrid metal matrix composites and the metal matrix composites, which are more brittle than the base matrix was shorter than that of the base matrix under both types of loads. In addition, the fatigue-life estimated from the damage summation method and that from experiments at random loads were fairly identical.

Abstract: Based on some practical problems in maintenance, a new model for K-out-of-N Markov repairable systems is introduced in this paper. The model focuses on that repair times that are sufficiently short (less than some threshold value) do not affect the system operation. We can say that such a repair time is omitted from the downtime record, and the system can be considered as being operating during this repair time. A model is built in which the threshold value is regarded as a constant at first. And then the model is generalized to allow the threshold value to be a non-negative random variable. Both instantaneous availability and steady-state availability are calculated for these new models as reliability indices. Some numerical examples are presented to verify the validity of these models.

Abstract: Most current common cause failure models are static models in which failure rate is assumed constant. The assumption is unrealistic in numerous situations, especially for mechanical systems. Based on the idea of shock models, this paper modifies unreasonable assumptions in conventional models and describes common cause failure process with non-homogeneous Poisson process, power-exponential process. A dynamic model is obtained. The parameters are estimated with neural network. The model presented in this paper, which is based on time-related power-exponential failure rate like bathtub curve, has more advantages and wider application than the model based on constant failure rate. Examples are given to illustrate its feasibility and precision of computation.

Abstract: A reliability analysis method for the shiplift gear according to the system-level load-strength interference model is presented. The gear is regarded as a series system with dependent failure and multiple failure models. Its reliability is obtained by calculating the probability that the minimum order statistic of the strengths exceeds the maximum order statistic of repeated random loads. The load probability distribution of gear is then obtained using Monte Carlo on the basis of load information. The contact strength and bending strength are calculated. On the basis of system-level load-strength interference analysis, system reliability of a gear is straightforward built up. Finally, system reliability of a gear is worked out, which shows a high reliability.

Abstract: In this research, the turning parameters of steel are optimized via multi-objective genetic algorithm and multi-objective harmony research algorithm. These two algorithms are known as strong and powerful tools in optimization of engineering problems. The stock removal rate and surface roughness, as two main of output parameters are the target function and have been considered to be optimized. Since, there are two functions here; we can not use the ordinary optimization method with single-objective algorithm. In steel machining, the stock removal rate usually decreases with the surface finishing and visa versa. Therefore, it is necessary to define the weight of these parameters. In this paper the importance of each of these parameters are determined with weight sum method. In this research, the optimization methods to solve the problems via these two algorithms are discussed first. Then, the steel samples are machined and the output data are analyzed and optimized.

Abstract: The objective of the study is to discuss the instability of the center subspace of a nonlinear rotor system with gyroscopic, inertial and potential forces, and nonlinear forces of the shaft, whose linear approximation has a m-multiple non-semi-simple zero eigenvalues. That is to discuss how the parameter changes affect the variations of non-semi-simple zero eigenvalues of the center subspace. The Puiseux expansion is used to develop the expressions of variations of non-semi-simple eigenvalues. The method for computing the generalized modes of the center subspace are given, and expression of variations of 2-multiple non-semi-simple zero eigenvalues is transformed into a more convenient form.