Advanced Materials Research Vols. 44-46

Abstract: Fuel cell bus with hydrogen tanks on its roof is different from traditional one. Its mass is greater than traditional one and its centre of gravity is higher, which makes its rollover more easy and dangerous. During the rollover, the great deformation of the body structure will menace the occupants’ safety, and in addition, the hydrogen leaking will threaten the lives of the occupants. So measures should be taken to ensure the deformation of body structure would not hurt the occupants, and the hydrogen pipelines would not have gas leakage. In the light of this objective, the finite element models of fuel cell bus, survive region and anti-intruding region are established, and the simulation of the bus rollover is carried out according to ECER66. The rollover results indicate that the bus is good at resisting the deformation of the rollover, and at the same time it provides data reference for improving the design of fuel cell bus. Furthermore, the pillar intruding coefficient and the clearance between anti-intruding region and tank cover are introduced in the paper to measure the safety abundance ratio of the survival region and the hydrogen pipeline of the fuel cell bus. According to these data, the description of safety of fuel cell bus can be quantified.

Abstract: The reliability of ship defensive structure subjected to underwater contact explosions is important both in theory and engineering. Because of the complex response of structure under explosions in which the fluid-structure-interaction should be considered, the problem under discussion could not be solved by analytical method. The Monte Carlo combined with FEM method is used to solve this problem in this paper. The samples of basic random variables that are dynamite density, the elastic modulus and ultimate strength of plate material are generated by the random number generate program. Then, with these samples, the simulations of multilayer plate-shell structure subjected to underwater contact explosions are done by LS-DYNA, and the maximum stress of each plate is obtained, which should be validated to obey the normal distribution. Based on the intensity rule, the destroy index is introduced in this paper, then the destroy probability of each plate and system are calculated using the basic theory of reliability.

Abstract: In the engineering structures, the design parameters may be uncertain because of the manufacture errors and inaccuracy in measurement, etc. The uncertainties of structural parameters may lead to large and unexpected excursion of responses that may lead to drastic reduction in accuracy and precision of the operations. Uncertainties in the design parameters are often considered to ensure that the structure is robust with respect to response errors. The paper discusses the robustness of responses of structures with uncertainties, which are described with three models, the random, convex, and interval models. The three corresponding methods for estimating the upper and lower bounds of responses are given, and the upper bounds of responses are used to estimate the robustness of responses of the structure with uncertain parameters. The comparison of the three methods for robustness analysis is given and some important conclusions are drawn.

Abstract: Two kinds of beam specimens made of composite laminated panel were designed and used to do vibration fatigue test for ε-N curves. the shapes of various simulated joint configurations for the specimens were adopted in order to get the accurate results. They were two kinds of double-cantilever beams supplied by T-mode stiffener and L-mode stiffener. All beam specimens were tested under the same shape of narrowband spectrum and the several loadings of random vibration by shaker excitation. The bandwidth of the narrowband random spectrum was 1/3 octave bandwidth whose centre frequency was the first resonance frequency of the cantilever beam, so that it reduced influences of the difference of specimens resonance frequency. Fitting vibration fatigue test results, the ε-N curves would be obtained then. The vibration test shows that this method of getting ε-N vibration curve is feasible. It can be used in practice.

Abstract: In order to evaluate fatigue reliability of single structure under random load, based on rainflow counting range of stress-time history, fatigue strength reliability of structure is obtained by means of stress-strength interference theory and Dirlik’s probability density function of rainflow counting range, as well as by assuming that fatigue limit accords with normal distribution. Also by using Miner’s damage cumulative theory, assuming that fatigue life accords with lognormal distribution, and taking into account dispersion of damage cumulative criterion value, given finite life reliability of structure is obtained by means of Monte-Carlo simulation method. The results show that although maximum range in stress-time history is greater than fatigue limit, when a majority of cycle range in stress-time history is less than fatigue limit, structure has high reliability of fatigue strength. The results of given finite life reliability indicate that although structure has high reliability fatigue strength under single stress-time history, fatigue reliability of structure experiencing many cycles will gradually decrease.

Abstract: In order to understand the influence of Heat-Affected Zone (HAZ) on fatigue properties of 16Mn steel, a series of cyclic torsional tests were conducted on 16Mn weld metal, the base metal, and the HAZ metal. The specimens of 2mm diameter were uniformly-spaced taken from a bulk 16Mn plate, which included a V-style welded joint in the center, and the space for each specimen was 4mm. From cyclic fatigue tests performed on specimens at different positions, one can observe that the fatigue damage evolution in the HAZ is faster than those in the weld and the base metal, i.e., HAZ has a significant effect on fatigue life of 16Mn. In addition, the peak stress decline curves of HAZ specimens in different rows are considerably diversified, but the damage evolution and fatigue properties of HAZ metal are similar in spite of their locations.

Abstract: Generally, a safe margin equation is established by critical load coefficient and external load coefficient of the system in structural integrity stable reliability analysis, and then the reliability index of structural integrity stability is educed. Critical load coefficient is always obtained on condition that structure is acted on by one load. Actually, besides one load acting on the structure, their distribution is not always the same. In addition, because of the stochastic characteristic of structure system itself (e.g., cross-section of element, length, modulus of elasticity etc. are random variables), it is difficult for structural integrity stable reliability analysis. According to the theory of structure system stability and basal concept of reliability, the safe margins of structure system under different distribution loads are presented in this paper. The expression of safe margin sensitivity is given by stochastic finite element method because the safe margin is the expression of implicit function. Furthermore, the reliability indexes of the safe margin under different condition are educed by the advanced first order second moment method (AFOSM). By comparison and analysis, the structural integrity stable reliability index is ultimately obtained.

Abstract: The rubbing phenomenon occurs when a rotating element eventually hits a stationary part of the rotating machinery. Increasing the rotor speed and decreasing the radial clearance between the rotating and the non-rotating parts can enhance the performance of the rotating machinery. This leads to an increased risk of rubbing contact. Rotor rubbing is the source of numerous different phenomena, for example sub- and super-harmonic vibrations, amplitude jumps and rotor instability. So the reliability analysis and sensitivity analysis of rotor system with rubbing is important for design purposes. Reliability analysis can help the designer to establish acceptable tolerance on rotor system. Sensitivity analysis can help the designer to know which problem in rotor system with rubbing is being solved and how the solution may affect the design of rotor system for system correction and reanalysis. On the basis of the dynamic equations of the cracked rotor system model and with consideration of the random parameters including shaft stiffness and damping, disk damping, radial clearance and stator radial stiffness, the random responses of cracked rotor system are researched. The reliability and sensitivity analysis of the cracked rotor system with rubbing are studied. According to the discretization of random process and stress-strength interference theory, the transient reliability model of cracked rotor system with rubbing is proposed. The reliability for rubbing in cracked rotor system is obtained by way of statistical fourth moment method, Edgeworth series technique and first passage theory. Numerical results are also presented and discussed.

Abstract: The initial investigations are presented into three equipment design and manufacture companies, and their issues relating to information loss and inaccuracies, and present the employment of an extended product model framework to assist the engineers in overcoming the issues identified. Three key scientific issues in this field are addressed. They are the customer driven goals and practices, design change capture and product models, and the methodology employed to answer the problem stated. The information generated during the service engineer’s visit and the redesign process is encapsulated within a new ExProMod, so that it could potentially be revisited and retrieved throughout the whole product life. A case study has shown that the proposed ExProMod is able to record the information generated in a constraint-based design/redesign so that it has the capability to assist the designers to assimilate and digest constraint-based design, assist the designers to assimilate and digest constraint-based design, offer information management benefits for the machine redesign in the industry, and Presents a tool to capture redesign changes and their respective rationale. In addition, the directions for future research are also prospected.

Abstract: In this publication a problem of production order planning is considered. The concept of a critical resource and a critical process, a constraint-based approach has been proposed. The question considered regards of an admissible production flow organization-guaranteeing completion of the production order under assumed limits, while taking into account the logistics constraints imposed. In that context the approach proposed can be seen as one following the Goldratt’s Theory of Constraints (TOC).