Homogenization of metallic fiber-reinforced composites under stochastic ageing

The main aim of this paper is to present an application of the generalized stochastic perturbation technique to model stochastic ageing processes of the metallic fibre-reinforced periodic composite materials in terms of their effective properties. Those ageing processes are modelled here as two-parametric time series having Gaussian random initial values and time rate, both defined uniquely by their expectations and standard deviations. Computational homogenization procedure is discrete and based on the Finite Element Method program MCCEFF as well as the computer algebra system MAPLE, where the Response Function Method and the stochastic analysis are entirely implemented. This numerical strategy is used to analyze probabilistic moments of the effective elastic tensor of the few metal matrix composites as well as to simulate stochastic ageing of two representative composites - MoSio₂-SiC and Ti-SiC. The approach proposed and results of computations may be further applied in the reliability analysis of metallic or the other composites.     

Modeling rolling contact fatigue lives of composite materials based on the dual beam FIB/SEM technique

Rolling contact experiments of (TiB + TiC)/Ti–6Al–4V composites reveal that inhomogeneous reinforcements reduce the materials’ rolling-contact fatigue (RCF) lives. The composite microstructures are examined and reconstructed based on the dual-beam focus ion beam scanning electron microscopy (FIB/SEM) technique. Integration of the microstructure-based stress analysis approach and Zaretsky’s RCF life prediction methodology leads to a new numerical RCF life modeling method. The newly developed mesh differential refinement scheme, together with the fast Fourier Transform techniques, is utilized to improve the efficiency and versatility of the proposed method. The RCF lives of the composites predicted by the new model are then compared with the experimental data, illustrating the effectiveness of the proposed method.     

On the application of the stochastic approach in predicting fatigue reliability using Miner's damage rule

The present paper investigates the application of the stochastic approach when the commonly adopted Miner's linear damage rule is implemented, both in its traditional and modified forms to include the presence of a random stress threshold (random fatigue limit), below which the rate of damage accumulation is reduced. Main steps are provided to obtain the simulated distribution of the accumulated damage under variable amplitude loading. When the stochastic approach is applied in the presence of a random fatigue limit, an additional correlation structure, which takes into account the fatigue limit value, must be introduced in the analysis. If the number of cycles to failure under constant amplitude loading is Weibull (Log‐Normal) distributed, then the corresponding accumulated damage is Fréchet (Log‐Normal) distributed. The effects of the correlation structure on reliability prediction under variable amplitude loading are also investigated. To this aim, several experimental datasets are taken from the literature, covering various metallic materials and variable amplitude block sequences. The results show that the choice of the damage accumulation model is a key factor to value the improvement in the accuracy of reliability predictions introduced by the stochastic approach. Comparison of the predicted number of cycles to failure with experimental data shows that larger errors are non‐conservative, regardless of the adopted correlation structure. When the analysis is limited to reliability levels above 80%, for these large non‐conservative errors, it is the quantile approach to be closer to actual experimental data, thus limiting the overestimation of component's life. For the experimental datasets considered in the paper, adoption of a stochastic approach would improve the accuracy of Miner's predictions in 10% of cases.     

Composite materials for wind energy applications: micromechanical modeling and future directions

The strength and reliability of wind turbine blades depend on the properties, mechanical behavior and strengths of the material components (glass or carbon fibers and polymer matrix), and the interaction between them under loading. In this paper, ideas, methods and concepts of micromechanical modelling of materials for wind turbine blades are briefly reviewed. Using the variety of the modeling methods reviewed here, one can predict the strength, stiffness and lifetime of the materials, optimize their microstructures with view on the better usability for wind turbines, or compare the applicability of different groups of the materials to the application in wind turbine blades. Some examples of the analysis of the microstructural effects on the strength and fatigue life of composites are shown.     

橡胶复合材料断裂力学疲劳研究进展

综述了断裂力学方法在橡胶复合材料中的应用现状,着重介绍了撕裂能理论在预测疲劳裂纹增长速率以及预报疲劳寿命方面的应用。     

铜基石墨复合材料的研究进展

铜基石墨复合材料是一种广泛应用于摩擦材料和电接触材料等领域的金属基复合材料.综述了铜基石墨复合材料在改善铜基体与石墨增强体结合方面的研究进展,主要包括基体合金化、石墨的表面处理、添加粘结剂等,重点介绍了铜基石墨复合材料的制备工艺方法,并概述了其导电导热性能、摩擦磨损性能、工艺性能及应用,最后展望了铜基石墨复合材料的研究重点和发展方向,认为取代现有的易切削铅黄铜合金将成为铜基石墨复合材料今后研究和应用的一个亮点.     

Digital Photoelasticity: Principles, Practice and Potential

The enormously enhanced power of photoelasticity resulting from adoption of digital technologies is highlighted and discussed. An overview of the principal techniques of digital fringe processing is provided within a single theoretical framework. The practical application of the new technologies using both conventional instruments and novel optical devices is discussed. Experiments involving more 1 × 10⁶ quantitative fringe order measurements are possible and practical on a routine basis using the current technology. Products based on this research are beginning to appear on the market so that many new application areas are opening up for photoelasticity, such as dynamic events, real‐time fatigue crack analysis, monitoring polarisation changes at a microscopic level in materials; detailed validation of numerical simulations, particularly of complex geometry and loading; and in‐service monitoring using reflection photoelasticity of damage in both homogeneous and heterogeneous materials, such as composites.     

加载循环数对2D针刺C/SiC复合材料疲劳剩余强度的影响

为研究陶瓷基复合材料的低周疲劳失效机理,通过试验和细观分析对其疲劳特性进行了探讨。研究了室温下加载循环数对2D针刺C/SiC复合材料拉-拉疲劳剩余强度的影响,并采用光学显微镜和扫描电子显微镜对该材料的断口形貌和微观结构进行了观察。结果表明:2D针刺C/SiC复合材料具有较好的抗疲劳特性,在85%极限拉伸强度(UTS)载荷下的循环数超过106;随着加载循环数的增加,剩余强度先增大然后下降。断口分析表明:纤维拔出长度随着加载循环数的增加而增加,说明在疲劳加载过程中,纤维/基体的界面结合强度降低,减缓了材料内部受力的不均匀性,提高了材料的承载能力,使2D针刺C/SiC复合材料出现了疲劳强化现象。      

航空发动机用树脂基复合材料应用进展与发展趋势EI北大核心CSCD

树脂基复合材料具有比强度和比模量高、疲劳性能和耐腐蚀性能好等优点,已经成为航空发动机冷端部件的应用和发展趋势。国外航空发动机用树脂基复合材料研究起步较早,已经在多型发动机的风扇叶片、风扇机匣、外涵机匣、短舱等部件得到成熟应用,并朝着结构形式更优、材料性能更好、制造成本更低、自动化程度更高的方向发展。国内树脂基复合材料发展基础良好,但与国外相比在发动机上应用比例不高,需要进一步提升设计、材料、制造、实验技术水平及工程化能力。本文重点论述国外航空发动机复合材料构件的结构、材料和工艺发展现状,分析发展趋势,从建立航空发动机用复合材料体系、加强应用研究和设计牵引、推进预研成果转化和自动化技术应用等方面提出相关建议。     

基于健康监测系统的大跨多荷载桥梁的 疲劳可靠度评估

考虑到火车、汽车与风荷载的长期作用以及多荷载的随机性,评估大跨多荷载桥梁的疲劳可靠度是一项富有挑战的任务。该研究基于健康监测系统提出了大跨多荷载悬索桥的疲劳可靠度分析框架,并应用到香港青马大桥。首先,定义了疲劳可靠度的极限状态函数,基于监测数据建立火车、汽车与风荷载的概率模型。基于概率模型和蒙特卡洛模拟方法,利用疲劳关键位置上多荷载的每日随机应力响应,估计每日应力幅m次方之和的概率分布。假设交通保持不变,可确定在给定时段内应力幅m次方之和的概率分布。最终得到桥梁不同疲劳关键位置不同时间点的疲劳失效概率。结果表明,在目前的交通状态下,青马大桥的疲劳健康状况可保持良好。     

Load spectrum modification effects on fatigue of impact-damaged carbon fibre composite coupons

The sensitivity of carbon fibre composite aircraft materials to low-level impact damage leads to some concern about possible long-term degradation of these materials by fatigue, particularly under compression-dominated loading. The testing of carbon fibre composites under realistic flight-by-flight loading is complicated by the fact that composites display good fatigue properties combined with a higher level of scatter than is the case for metals; the duration of fatigue tests can therefore be considerable. This paper investigates the effects of using a modified loading spectrum for accelerated fatigue testing, and examines the growth rates of realistic impact damage in tests which represent flight-by-flight loading of an aircraft wing.     

Fatigue-life distributions and failure probability for glass-fiber reinforced polymeric composites

There has been an upsurge in the application of composite materials in the last few decades, due to high demands on material performance placed by advanced technologies. Most of these applications include the situations where degradation of strength and life by fatigue process is most likely. In this investigation, rotating bending fatigue tests have been conducted on two types of unidirectional glass-fiber reinforced polymeric composites, having vinylester and Epoxy as matrix materials. It has been observed that the probabilistic distribution of fatigue-life of these glass-fiber reinforced composites, at a particular stress level, can be modeled by two-parameter Weibull distribution, with statistical co-relation coefficient values exceeding 0.90. Various methods have been used to obtain the parameters of Weibull distribution. Kolmogorov–Smirnov goodness-of-fit test has also been used to reinforce the above findings. The two-parameter Weibull distribution has also been employed to incorporate failure probability into S–N relationships.     

纤维桥连疲劳裂纹扩展的首次穿越扩散过程模型

纤维桥连效应对纤维加强基体复合材料疲劳过程中的裂纹增长具有重要影响。由于纤维桥连疲劳裂纹相关的数据呈现出一定的统计特性,因此本文建立了纤维桥连疲劳裂纹扩展的首次穿越扩散过程随机模型。首先基于Paris定律,考虑到材料的非均匀性和外载的随机性,将纤维桥连疲劳裂纹增长过程假定为扩散的Markov过程,且应用随机平均法,建立了转移概率密度满足的FPK方程;其次建立了首次穿越纤维桥连疲劳裂纹扩展时间的条件矩应满足的微分方程,并且解得第k阶条件矩。从数值结果得出,建立的随机模型对于模拟纤维桥连是比较有效的。      

The potential for composites in structural automotive applications

The primary use of fiber-reinforced composites in automobiles, with the exception of a few specialized low volume vehicles, has been in semi-structural or decorative parts. Use of composites in primary structural areas of the vehicle, such as body structures, has been very limited to date. Such applications offer a tremendous opportunity for future expansion of composites in the automotive industry. In addition to materials cost, there are two over-riding criteria for significant application of FRP materials in automotive structures: (1) proof of structural functionality/durability; and (2) development of rapid, reproducible fabrication procedures to optimize manufacturing economics.

From a structural viewpoint, there are two major categories of material response which are critical to the application of composites to automobiles: fatigue (durability) and energy absorption. An abundance of evidence is accumulating relating the functional properties of these materials in simple structures. It is clear that the fundamental requirements of energy absorption and fatigue resistance are satisfied by composites and the main challenge is to translate these capabilities into complex structures with less well-defined load inputs. The less quantifiable, but equally important, functional requirement of ride quality (usually defined in terms of noise, vibration and ride harsness, NVH) also appears to be attainable through the utilization of composites. Even though this factor has been historically related to vehicle stiffness, and composite materials are less stiff than steel, all the indications are that the effective stiffness of composite structures meet NVH requirements—the elimination of joints through part integration plays a critical role in achieving such synergistic effects.

Many of the properties of composite structures depend on the control of fiber location and part integration which in turn are a direct fucntion of the fabrication process. Current high production rate fabrication processes such as compression molding of sheet molding compound (SMC) type materials go only part way to optimizing the properties and economics. Optimum automotive composite structures will probably require a combination of processes, some of which will need significant development, to realize the enormous potential for composites in the automotive industry. Full-scale structures may involve SMC type molding, thermoplastic stamping and the developing preform molding (HSRTM) process which hasm perhaps, the greatest potential of all the processes of revolutionizing the use of composite structures. Technological breakthroughs in fabrication technology do not appear to be necessary, the main requirement is the development of existing assorted techniques combined with a concerted effort by all aspects of the composite and automotive industry.     

FATIGUE PROPERTIES OF C/Al METAL-MATRIX COMPOSITES WITH DIFFERENT INTERFACIAL BONDS

The fatigue properties of four kinds of composite wires with different interface bonds, together with the effects of a notch in the surface of the composite wires, have been studied. Fatigue endurance (S-N) curves of these materials revealed that no definitive fatigue limit was obvious. The C/Al composites with weak interfacial bonds were insensitive to the notch, but the notch was an important source of cracks which propagated rapidly when the interface bonding was strong. Although initial cracks would occur very early in the fatigue life, their propagation were arrested by the internal structure of the composite wires with suitable interface bonds.     

孔隙演化与C/C复合材料的疲劳行为

孔隙是C/C复合材料结构中重要的组成部分,它直接影响着材料的疲劳行为,因此,在研究C/C复合材料的疲劳行为时,考察基体以及界面中孔隙的变化具有重要的意义.综述了C/C复合材料原始孔隙结构的特点,分析了在疲劳加载过程中碳/碳复合材料孔隙结构的演化规律,强调了孔隙结构变化对碳/碳复合材料疲劳强化所作出的积极贡献,进而为其疲劳机理的研究提供依据.     

The needs of understanding stochastic fatigue failure for the automobile crankshaft: A review

This paper reviews the fatigue failure mechanisms for the automobile crankshaft under service loading through the stochastic point of view. Fatigue failure of crankshafts are reviewed in general, as it is a major concern due to the uncertainties that arise i.e. randomness in structural materials, the geometric shape of the component and randomness of service loads. There has been very little research carried out in assessing the fatigue failure using the stochastic process in predicting the fatigue life of crankshafts. This review paper discusses the durability aspects of the component and is followed by a review of the characteristics of loading and the stochastic fatigue failure effect on the components. In addition, the stochastic approach from empirical model aspect using a safe-life approach from the more recent advances in computational methods to assess stochastic fatigue failure was discussed and reviewed in the context of this paper. The integration between the empirical and probabilistic methods can be quantified using statistical models, which evaluate the damage that leads to fatigue and eventually fatigue failure. Hence, this review provides a platform for understanding the stochastic fatigue failure for an accurate predictive prediction on the structural integrity of components, especially in the automobile industry.     

Numerical analysis of wheel cornering fatigue tests

In automotive engineering, the wheels are one of the most critical components and their function is of vital importance n human safety. The cornering fatigue test is one of the traditional durability tests for wheel prototype verification. In this paper, a bi-axial load–notch strain approximation for proportional loading is proposed to estimate the fatigue life of a passenger car wheel during the cornering fatigue test under plane stress conditions. The elasto-plastic strain components are calculated analytically using the total deformation theory of plasticity. The input for the load–notch strain analysis is the measured or calculated plastic strain state at the notch together with the materials stabilised cyclic stress–strain curve evaluated with unnotched tension specimens. The damage accumulation is based on the Palmgren–Miner rule. The methodology is implemented in a program called “Metal Fatigue Prediction and Analysis” (MFPA). The life prediction of a passenger car wheel during the cornering fatigue test is performed. The results of the analysis is compared with two cornering tests on the same design. The result is very encouraging and the application of the developed MFPA program provides time and the cost savings in the analysis of wheel cornering fatigue tests.     

Flexural fatigue damage analyses of recycled rubber‐modified epoxy‐based composites reinforced with alumina fibres

Manufacturers have been working towards finding clean and cost‐efficient solutions by utilizing recycled materials to produce new components. Recycled rubber is one such material widely used in aeronautic and automotive industries. In this study, fresh scrap ethylene‐propylene‐diene‐monomer (EPDM) rubber is mixed with epoxy to manufacture novel composites with the addition of alumina (Al₂O₃) fibres. These composites can potentially be used to manufacture components subjected to cyclic loading, and to ensure reliability of such components, fatigue behaviour of these composites should be evaluated. This article describes the manufacturing of recycled rubber‐modified epoxy‐based ternary composites and their fatigue behaviour as well as toughening mechanisms. Dynamic mechanical analysis (DMA) was performed to determine thermomechanical properties. Three‐point bending and flexural fatigue tests and Shore D hardness measurements were carried out to determine mechanical properties. After static/fatigue fracture, fracture surfaces were observed with scanning electron microscope (SEM) to determine toughening mechanisms in these composites.