基于爆破试验的CFRP固体火箭发动机壳体的可靠性设计

根据GJB 1878-94制备了8个碳纤维缠绕复合材料压力容器，通过试验获得壳体的纤维强度、缠绕角、几何尺寸、爆破压强等随机变量特征值，利用这些实验数据对固体火箭发动机壳体进行可靠性设计，并与传统的安全系数法设计进行比较。结果表明，使用可靠性安全系数法设计可以实现安全性和经济性的统一。分析了材料的力学性能参数及壳体的几何参数等随机变量的变异系数对CFRP固体火箭发动机壳体爆破压强分散程度的影响。纤维应力、壳体纤维层厚度和壳体半径的变异系数的大小直接影响了爆破压强的分散程度；而纤维缠绕角除其变异系数的大小直接影响爆破压强的分散程度外，其参数均值也对爆破压强的分散程度有影响。     

A practical approach for predicting fatigue reliability under random cyclic loading

The purpose of this paper is to provide a simple approach for reliability analysis based on fatigue or overstress failure modes of mechanical components, and explain how this integrated method carries out spectral fatigue damage and failure reliability analysis. In exploring the ability to predict spectral fatigue life and assess the reliability under a specified dynamics environment, a methodology for reliability assessment and its corresponding fatigue life prediction of mechanical components using a supply-demand interference approach is developed in this paper. Since the methodology couples dynamics analysis and stochastic analysis for fatigue damage and reliability prediction, the conversion of the duty cycle history for the reliability study of an individual component is also presented. Using the proposed methodology, mechanical component reliability can be predicted according to different mission requirements. For an explanation of this methodology, a probabilistic method of deciding the relationship between the allowable stress or fatigue endurance limit and reliability is also presented.     

基于概率断裂力学的老龄钢桥使用安全评估

我国交通线上存在大量老龄钢桥,这些老龄钢桥承受着日益繁重的交通荷载,其疲劳剩余寿命已受到桥梁管理部门的高度重视。为确保老龄钢桥的使用安全,避免不必要的维护与更换,建立老龄钢桥疲劳剩余寿命与使用安全评估方法十分必要。建立了反映老龄铆接钢桥疲劳破坏机理的脆断和韧断概率失效模型,给出了用于疲劳可靠性分析的极限状态方程,合理确定了随机变量的参数取值。建立了铆接钢桥构件单角钢概率疲劳破坏模型,基于MonteCarlo算法实现了铆接钢桥构件单角钢疲劳断裂失效概率的计算,编制了相应的概率断裂分析程序SAPFF。进而将铆接构件概率断裂模型应用于上海市浙江路桥的时变疲劳可靠度分析,并给出了浙江路桥概率疲劳剩余寿命评估结果与维护对策。     

Fatigue reliability evaluation using probability density evolution method

Probability density evolution method is extended to analysis of fatigue reliability. The joint probability density evolution equation of random parameters and fatigue damage is derived based on the principle of preservation of probability, and a finite difference algorithm in terms of TVD theory is presented. For a given damage threshold, cycle-dependent fatigue reliability can be calculated by the proposed method without assuming the probabilistic distribution of fatigue damage in advance. Two validation examples indicate that the proposed method is able to give reasonable results for constant-amplitude loading and variable-amplitude loading. The predicted fatigue reliability under constant-amplitude loading shows a considerable accuracy. In addition, reliability isolines of fatigue damage can be used to predict the fatigue life with a specified failure probability.     

岸桥起重机随机风振疲劳可靠性分析

基于时域方法研究岸桥起重机的风振疲劳可靠性问题。采用谐波叠加法给出了符合Davenport风速谱的多维脉动风速时间历程,基于Bernoulli方程得到相应的风压时间历程,并将相应的风压荷载作用于有限元模型,采用雨流计数法处理结构关键点的应力响应。基于疲劳失效的Basquin方程、Miner线性累积损伤准则和Goodman平均应力修正方程导出疲劳累积损伤的概率模型。考虑平均风速的概率分布,提出了基于概率累积损伤机制的风振疲劳可靠度和可靠性寿命计算方法,为岸桥起重机的风振疲劳可靠性分析作了一些有益的探索和研究。     

纤维缠绕聚合物基复合材料压力容器的可靠性设计

为对纤维缠绕聚合物基复合材料( FWRP) 压力容器进行可靠性设计和安全测评, 引入可靠性理论; 应用统计学原理, 以同一失效概率为标准进行FWRP 压力容器结构设计, 以取代目前应用的传统安全系数法设计。根据国家标准制备8 个玻璃纤维缠绕复合材料( GFWRP) 压力容器, 通过实验获得纤维强度、缠绕角、几何尺寸、爆破压力等随机变量特征值。GFWRP 压力容器结构可靠性设计值(纤维缠绕壁厚) 与实验结果基本吻合, 并明显小于传统安全系数法设计值。通过对不同纤维强度随机分布可靠性设计理论计算结果的比较, 确知纤维强度的离散程度是FWRP 压力容器可靠性设计的重要影响因素。传统安全系数设计法只考虑纤维强度(均值) 大小, 而无视纤维强度随机分布特征值对FWRP 压力容器结构抗力的影响, 显然是不合理的。可靠性设计实现了安全性与经济性的有效统一。      

Setting reliability requirements based on minimum failure‐free operating periods

A new reliability methodology and tools have been created for setting reliability requirements. At the heart of the new methodology are reliability requirements based on specified minimum failure‐free operating (MFFOP) intervals and a maximum acceptable level of the probability of premature failure. These types of requirements are suitable to industries where the consequences of failure and the cost of intervention for maintenance are very high (e.g. deepwater offshore oil and gas industries). The methodology proposed includes models and tools for: (i) setting reliability requirements to limit the risk of premature failure below an acceptable level; (ii) setting reliability requirements to minimize the total losses; and (iii) setting reliability requirements to guarantee a set of MFFOP intervals. An advantage of the MFFOP approach is that it directly links the reliability requirements with health, safety, environmental and business risks. Another advantage is that the MFFOP requirements are suitable for non‐constant hazard rates where the mean time to failure (MTTF) reliability measure is often misleading. A solution to the important problem of determining the maximum hazard rate that guarantees with a required probability the existence of a specified set of MFFOP intervals has also been found. The reliability tools proposed also permit the extraction of useful information from data sets containing a given number of random failures, in cases where the failure times are unknown. Copyright © 2003 John Wiley & Sons, Ltd.     

短纤维增强三元乙丙薄膜拉伸破坏率相关Tsai-Hill强度准则

短纤维增强三元乙丙（EPDM）薄膜材料是一种应用于固体火箭发动机装药的新型绝热结构材料,其密度小、耐烧蚀且力学性能良好。基于正交各向异性单向板的Tsai-Hill强度准则,引入率相关函数法和率强度因子法改进,预测材料在不同偏轴方向下的抗拉强度,从而建立一种适用于准静态条件下的率相关各向异性通用准则。研究表明：轴向强度和抗剪强度随应变率的增加而增加;相比于率强度因子法,基于率相关函数法的Tsai-Hill强度准则对材料抗拉强度的预测精度较高;率强度因子法预测抗拉强度的误差与参考速率的选取和率强度因子的函数表达式有关。     

Reliability analysis of a buried concrete target under missile impact

This paper presents the methodology for reliability analysis of a buried concrete target against normal missile impact. The expressions for the depths of penetration in buried target have been derived using the methodology proposed in the literature. These equations have then been employed for reliability estimation. Design points, important for the probabilistic design, have been located on the failure surface. Sensitivity analysis has been carried out to study the influence of various random variables on target safety. Some parametric studies have also been included to obtain the results of field interest.     

Probabilistic analysis of a pull-out test

This paper presents a sensitivity analysis of the pull-out strength of reinforcement embedded in concrete. Considering both European and French design codes, this failure strength depends on the variability of uncertain parameters such as Young’s modulus of concrete and yield stresses of materials (concrete and steel); moreover, two failure modes can be observed in the studied experimental test. A methodology allowing the characterization of the sensitivity of the pull-out strength to these uncertain parameters is derived. These parameters are modeled by Lognormal random variables. Results show the evolution of the pull-out strength for different anchorage lengths. Probability density functions of the random variable modeling the failure strength are computed using probabilistic methods. A finite element model is also built to quantify uncertainties concerning failure modes, computing 95% confidence intervals.     

Bayesian methodology for reliability model acceptance

This paper develops a methodology to assess the reliability computation model validity using the concept of Bayesian hypothesis testing, by comparing the model prediction and experimental observation, when there is only one computational model available to evaluate system behavior. Time-independent and time-dependent problems are investigated, with consideration of both cases: with and without statistical uncertainty in the model. The case of time-independent failure probability prediction with no statistical uncertainty is a straightforward application of Bayesian hypothesis testing. However, for the life prediction (time-dependent reliability) problem, a new methodology is developed in this paper to make the same Bayesian hypothesis testing concept applicable. With the existence of statistical uncertainty in the model, in addition to the application of a predictor estimator of the Bayes factor, the uncertainty in the Bayes factor is explicitly quantified through treating it as a random variable and calculating the probability that it exceeds a specified value. The developed method provides a rational criterion to decision-makers for the acceptance or rejection of the computational model.     

A micromechanics-based strength prediction methodology for notched metal-matrix composites

An analytical micromechanics-based strength prediction methodology was developed to predict failure of notched metal-matrix composites. The stress/strain behaviour and notched strength of two metal-matrix composites, boron/aluminium (B/Al) and silicon carbide/titanium (SCS-6/Ti-15-3), were predicted. The prediction methodology combines analytical techniques ranging from a three-dimensional finite element analysis of a notched specimen to a micromechanical model of a single fibre. In the B/Al laminates, a fibre failure criterion based on the axial and shear stress in the fibre accurately predicted laminate failure for a variety of lay-ups and notch-length-to-specimen-width ratios with both circular holes and sharp notches when matrix plasticity was included in the analysis. For the SCS-6/Ti-15-3 laminates, a fibre failure criterion based on the axial stress in the fibre correlated well with experimental results for static and post-fatigue residual strengths when fibre/matrix debonding and matrix cracking were included in the analysis. The micromechanics-based strength prediction methodology presented here offers a direct approach to strength prediction by modelling behaviour and damage on a constituent level, thus explicitly including matrix non-linearity, fibre/matrix interface debonding and matrix cracking.     

基于Ansys的重型包装钢架箱工程轻量化设计

目的以某重型装备的运输用框架结构为研究对象,提出工程轻量化的设计准则及设计方案,以解决重型装备过度包装的问题。方法利用Ansys软件对运输用钢架包装箱的起吊工况和堆码工况进行数值仿真分析,并基于分析结果对经验设计方案进行改进。结果优化后的钢架箱质量减少了942kg,质量减少比例达到了43%,起吊工况静强度安全系数为2.14,堆码工况静强度安全系数为1.94,稳定性安全系数有4.96倍。结论工程轻量化设计后的钢架箱满足屈服强度失效准则和稳定性失效准则规定的安全性能,提高了材料的使用效率,包装成本显著减少。     

在役腐蚀管道动态非概率可靠性分析简

 腐蚀失效是压力管道失效的主要形式之一,研究腐蚀管道的可靠性具有重要理论意义和应用价值.在对腐蚀管道可靠性分析时,概率可靠性模型和模糊可靠性模型对于数据信息的要求较高.而在掌握不确定性信息很少情况下,为了充分利用管道的不确定性信息弥补原始数据的不足,可将腐蚀管道可靠性分析中的材料屈服强度、管道直径、缺陷深度和操作压力等不确定参数视为区间变量,基于区间模型建立一种在役腐蚀管道动态非概率可靠性模型,给出了腐蚀管道剩余寿命预测的简便方法.结合工程实例计算与分析,表明了文中所提出方法的可行性和合理性,并在此基础上,分析了管道的壁厚、缺陷深度、实际压力和腐蚀速率这些区间变量的不同变异系数对非概率可靠性指标的影响,分析结果表明非概率可靠性指标对管道壁厚的变异系数最为敏感.     

A probabilistic fracture mechanics model including 3D ductile tearing of bi-axially loaded pipes with surface cracks

This paper presents a probabilistic fracture mechanics model established from three-dimensional FEM analyses of surface cracked pipes subjected to tension load in combination with internal pressure. The models are particularly interesting for offshore pipelines under operational conditions or during laying, where inelastic deformations may occur. In the numerical models, the plastic deformations, including ductile tearing effects, are accounted for by use of the Gurson-Tvergaard-Needleman model. This model is calibrated to represent a typical X65 pipeline steel behaviour under ductile crack growth and collapse. Several parameters are taken into account, such as crack depth, crack length and material hardening. Another important topic is the examination of the influence of bi-axial loading due to internal pressure on capacity. From the results of the deterministic analyses a probabilistic fracture mechanics model is established using the response surface methodology. Two failure criteria are examined to represent the structural capacity. Based on the established model, we illustrate the methodology by examples employing the two different failure criteria solved with first and second order reliability methods.     

Probabilistic risk analysis of corrosion associated failures in cast iron water mains

This paper proposes a method using probabilistic risk analysis for application to corrosion associated failures in grey cast iron water mains. External corrosion reduces the capacity of the pipeline to resist stresses. When external stresses exceed the residual ultimate strength, pipe breakage becomes imminent, and the overall reliability of a water distribution network is reduced. Modelling stresses and external corrosion acting on a pipe involves uncertainties inherent in the mechanistic/statistical models and their input parameters. Monte Carlo (MC) simulations were used to perform the probabilistic analysis. The reduction in the factor of safety (FOS) of water mains over time was computed, with a failure defined as a situation in which FOS becomes smaller than 1. The MC simulations yielded an empirical probability density function of time to failure, to which a lognormal distribution was fitted leading to the derivation of a failure hazard function. A sensitivity analysis revealed that the contribution of corrosion parameters to the variability of time to failure was more significant than the combined contributions of all other parameters. Areas where more research is needed are identified.     

New probabilistic approach to estimate vehicle failure trajectories in curve driving

The vehicle trajectories analysis on dangerous bends is an important task to improve road safety. This paper proposes a new methodology to predict failure trajectories of light vehicles in curve driving. It consists to use a stochastic modelling and reliability analysis in order to estimate the failure probability of vehicle trajectories.Firstly, we build probabilistic models able to describe real trajectories in a given bend. The models are transforms of scalar normalized second order stochastic processes which are stationary, ergodic and non-Gaussian. The process is characterized by its probability density function and its power spectral density estimated starting from the experimental trajectories. The probability density is approximated by using a development on the basis of Hermite polynomials.The second part is devoted to apply a reliability strategy intended to associate a risk level to each class of trajectories. Based on the joint use of probabilistic methods for modelling uncertainties, reliability analysis for assessing risk levels and statistics for classifying the trajectories, this approach provides a realistic answer to the tackled problem. Experiments show the relevance and effectiveness of this method.     

NOTCHED FATIGUE BEHAVIOUR OF TWO COLD ROLLED STEELS

Abstract— A SAE1010 plain carbon steel and a SAE945X HSLA steel were cold rolled to various thickness reductions. Centre notched specimens were tested under stress control at a stress ratio of—1. The effect of loading direction on the fatigue strength was examined. The notched specimen fatigue strength was only slightly increased by cold rolling, since two opposing factors: the smooth specimen fatigue strength and the notch sensitivity, were increased by cold rolling. The notched specimen fatigue strength in the transverse direction was approximately the same as that in the longitudinal direction. An empirical equation and equations derived from fracture mechanics and Neuber's rule were applied to predict the fatigue notch factor for the sharp and blunt notch geometries examined. A reasonable agreement between the predictions and the experimental results was observed for the sharp notches. For the blunt notches, the predicted fatigue notch factors were conservative.     

Optimum design of helically wound composite pressure vessels

The optimum design of dome shapes in helically wound composite pressure vessels which have been used as rocket motor cases, etc. is discussed, as a first step, based on the membrane stress theory. Some methods for determining the optimum dome shapes are proposed based on the two different kinds of criteria. One is based on the failure criteria of composite materials, and the simple formulae for determining the dome shapes are derived. The other is based on the performance factor for a rocket motor case, and the dome shape is analyzed by using mathematical optimization techniques. The dome shapes obtained are compared with the isotensoid dome shape derived from the netting analysis.