Tensile fracture behavior of notched fiber reinforced titanium metal matrix composite

The static fracture behavior of a titanium based metal matrix composite (MMC) with a central hole or a straight notch was investigated. The MMC used was SCS-6/Ti-β21-S with a quasi-isotropic lay-up. Different sizes of hole or notch were used which provided cut-out size to specimen width ratios from 0·1 to 0·4. Two test temperatures were used: ambient and 650°C. At both temperatures, the tested MMC showed a mild hole size effect or notch sensitivity. The failure mechanisms involved the debonding of fibers followed by failure of fibers, and then by failure of the matrix.     

Recrystallized grain size prediction in a particulate reinforced metal matrix composite

The recrystallized grain size following cold rolling and annealing of an Al alloy (AA2014) and a particulate reinforced AA2014 composite was investigated. The composite contained 20 vol% alumina particulates of average diameter 15 m. The recrystallized grain size in the composite was finer than in the alloy, for a given set of conditions; this was most notable for material strained less than 50% cold-work. This behaviour was attributable to a higher nucleation efficiency in the matrix adjacent to coarse alumina particles in the composite. A model was presented for the composite to predict the recrystallized grain size as a function of strain, with respect to the size distribution and number density of alumina particles. This model predicted the strain dependence of the recrystallized grain size and, in particular, the grain size insensitivity to strain at moderate-to-high levels of cold-work.     

界面对颗粒增强金属基复合材料强化性能的影响

为提高颗粒增强金属基复合材料的力学性能,采用基于微观组织的胞元模型建模方法,并利用有限元软件ABAQUS着重分析了界面层厚度以及界面层强度对复合材料性能的影响,通过对复合材料中各组成部分的应力、应变云图的获取,形象地说明了各部分的变形规律.研究结果表明,在弱界面层下,随着界面层厚度的增加,复合材料的强化效果并不显著,而在强界面层下,随着界面层厚度的增加,强化效果非常明显;就界面层强度来说,界面越强,所表现出的强化效果就越明显,但当界面层强度比基体大得多时,随着界面层强度的增加,虽然复合材料的强化呈递增趋势,但是递增的幅度已逐渐降低.     

曲率参数对纤维增强树脂基复合材料构件固化压实的影响

根据有效应力准则和达西定律,结合曲线坐标系,构建了曲面复合材料构件固化过程中的树脂流动和纤维压实控制方程;建立了基于AS4/3501-6纤维树脂体系的层合板仿真模型,并将分析结果与实验数据对比,验证了模型的有效性;研究了曲率参数对复合材料构件非等温固化压实的影响规律,比较和分析了曲率参数与厚度和压力参数耦合作用下对树脂流动行为的影响机制。结果表明:构件曲率参数会对树脂分布产生一定影响,曲率越大,树脂分布的非均匀性越大;曲率参数的作用表达受到厚度与压力参数的影响,当厚度与压力较小时,对曲率的影响不明显。      

A new aluminum-based metal matrix composite reinforced with cobalt ferrite magnetic nanoparticle

A new composite with cobalt ferrite magnetic nanoparticle dispersed in an aluminum matrix has been prepared using the ball-milling technique followed by compaction and sintering. Our efforts were largely focused on investigating the contribution of cobalt ferrite to the enhancement of structural, mechanical and magnetic properties of aluminum. Incorporation of 1–10 weight (wt)% of nanosized cobalt ferrite into the aluminum matrix could affect remarkable change in mechanical properties. Enhancement of hardness value, elastic modulus, and compressive strength was observed in the case of cobalt ferrite-incorporated aluminum matrix as compared to the pure aluminum sample. Incorporation of cobalt ferrite could impart considerable improvement of magnetization value of the aluminum matrix with a saturation magnetization of 17.07 emu/g for the aluminum sample reinforced with 10 wt% of cobalt ferrite. A decrease in coercive force in the sample arising from the increase in surface effects and inter-particle interaction between the ferromagnetic cobalt ferrite and soft phases in the matrix was also observed.     

Hot Working behaviour of AI-AI2O3 particulate reinforced metal matrix composite

Abstract

The hot deformation behaviour of a particulate reinforced metal matrix composite, manufactured via a casting route and consisting of a 2000 series matrix reinforced with 20 vol.-%Al₂O₃ particles, was investigated over a range of temperatures and strain rates. The behaviour was compared with the unreinforced alloy deformed under the same conditions. Both materials exhibited similar hot working behaviour. However, under all deformation conditions the composite exhibited flow stresses higher than that of the alloy, but as the deformation temperature increased and the strain rate decreased, this difference became negligible. The activation energy for deformation was determined using constitutive equations. The value determined for the composite was slightly higher than that for the alloy. This suggested that the ceramic particles in the composite force the matrix to undergo additional strain hardening during deformation. Dynamic recovery was the sole restoration process in both materials. No evidence of dynamic recrystallisation was found.     

Laser beam processing of a SiC particulate reinforced 6061 aluminium metal matrix composite

SiC particulate reinforced 6061 Al metal matrix composites were laser beam cut using a 3kW continuous wave CO2 laser. The influence of laser processing parameters such as cutting speed, laser power, and shielding gas on the quality of the cuts were investigated. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to analyse the laser treated zone. Experimental results show that 6061 Al metal matrix composites can cut be successfully using laser. A number of Al4C3/Al4SiC4 plates were formed in the heat affected zones due to a chemical reaction between Si and Al that occurred during the laser processing. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructural characterization of a silicon carbide whisker reinforced 2124 aluminium metal matrix composite

The microstructure of a silicon carbide whisker (SiC_w) reinforced 2124 aluminium metal matrix composite was characterized using scanning transmission electron microscopy (STEM). The SiC whiskers ranged in length from approximately 2 to 10 µm, and demonstrated good bonding to the aluminium matrix. In a few cases, the interface between SiC whiskers and the aluminium matrix exhibited wavy characteristics. The size of subgrains in the aluminium matrix was found to be dependent upon that of SiC whiskers. In addition, two types of intermetallic compounds were observed in the composite.     

Influence of autofrettage on fracture toughness

A specimen, called the ring specimen, was developed to determine the fracture toughnessK _tc, under conditions of autofrettage. Tests were carried out on standard arc shaped specimens and ring specimens without autofrettage to obtainK _tc values of a gun barrel steel chosen for study and seen to yield similar results. Tests were also performed on autofrettaged (100 percent overstrain) ring specimens at various crack lengths producing results with a dramatic decrease inK _tc of 60 per cent. From this, it may be inferred that the critical length of a crack in an autofrettaged gun barrel made of this material will be less than anticipated. Although cold work or autofrettage enhances fatigue life by decreasing crack propagation rate, it is seen to decreaseK _tc creating, from this point of view, more dangerous conditions. For a design which must guarantee long life, the accompanying decrease in critical crack size may indeed prove a liability. Of course, this is a result for one particular material with a specific heat treatment and therefore not general; other materials must be tested, as well.

---

Résumé On a étudié une éprouvette, dénommée éprouvette en anneau, en vue de déterminer la ténacité à la ruptureK _tc sous des conditions d'auto-frettage. Des essais ont été effectués sur des éprouvettes standards en forme d'arc et sur des éprouvettes en anneau sans auto-frettage en vue d'obtenir les valeurs deK _tc dans le cas d'un acier pour âme de canon choisi pour l'étude. Ces essais ont conduit à des résultats similaires. Des essais ont également été effectués sur des échantillons en anneau auto-frettés à 100% de sur-dilatation correspondant à diverses longueurs de fissure. Les résultats ont montré une diminution deK _tc de l'ordre de 60%. On peut déduire de cette observation que la longueur critique relative à une fissure dans une âme d'un canon auto-fretté réalisé dans ce matériau sera plus faible que prévu. Bien que l'écrouissage où l'auto-frettage améliore l'endurance en fatigue par des croissances de la vitesse de propagation d'une fissure, on constate qu'elle diminue leK _tc, occasionnant de ce point de vue des conditions plus dangereuses. Dans le cas d'une construction qui doit garantir un service de longue durée, la décroissance de la dimension critique d'une fissure peut être pénalisante. Bien entendu, ceci n'est qu'un résultat pour un matériau particulier avec un traitement thermique spécifique, qui dès lors ne peut être généralisé. D'autres matériaux doivent être également testés.

     

纤维增强树脂基复合材料防弹性能影响因素及破坏机制

以超高分子量聚乙烯(Ultra High Molecular Weight Polyethylene,UHMWPE)纤维、S-玻璃纤维、芳纶1414纤维和杂环芳纶纤维增强聚烯烃(Polyolefin,PO)和水性聚氨酯(Waterborne Polyurethane,WPU)树脂,采用热压工艺制备正交单向无纬(UD)结构复合材料装甲板;通过装甲板弹道极限速度测试,研究了纤维增强树脂基复合材料装甲板防弹性能的影响因素;通过体视显微镜观察装甲板侵彻破坏形貌,分析了纤维增强树脂基复合材料的破坏机制。结果表明:UHMWPE纤维增强PO树脂基复合材料的防弹性能与UHMWPE纤维的强度和模量呈正相关,但纤维模量对复合材料防弹性能的影响随着纤维模量的增大而逐渐变弱;在WPU树脂体系下,四种纤维的防弹性能由高到低依次是UHMWPE纤维、杂环芳纶纤维、芳纶1414纤维、S-玻璃纤维;纤维增强树脂基复合材料装甲板中纤维破坏方式有迎弹面纤维被剪切冲塞、中部被纤维拉伸变形后剪切、背弹面纤维被拉伸断裂,中部纤维拉伸变形是消耗子弹动能的主要方式。     

Development of novel specimens for mechanical testing of fibre reinforced titanium metal matrix composite

Abstract

Specimens used to date for testing titanium metal matrix composites (Ti MMCs) have severe limitations in the data obtained. In the present work, novel specimens have been developed to ensure that data obtained are indicative of the material as it appears in engineering components. For the longitudinal orientation, a modified dogbone with large shoulder radii is successful in improving the integrity of data. In the transverse orientation, selective reinforcement of monolithic Ti with MMC has allowed the production of a cruciform specimen in which the‘uprights’ are made of monolithic Ti and are gripped in the testing machine and the ‘cross’ is made of MMC and acts as a gauge length. The cruciform geometry ensures that surface defects, which blight conventional specimens, do not have such a deleterious effect. A unique specimen has been developed to enable the MMCs to be loaded in the through thickness direction, thus allowing a comparison of mechanical properties for the three geometric axes.     

Influence of SiC reinforcement on precipitation and hardening of a metal matrix composite

The influence of fibre reinforcement (10 vol % SiC fibres) on the precipitation and hardening behaviour of a metal matrix composite was studied using microhardness tests and transmission electron microscopy observations. It was shown that the hardening kinetics is enhanced by the SiC reinforcement due to the fact that precipitation preferentially develops on dislocation lines. Moreover, the high-temperature deformation strongly increases the precipitation rate as the material is reinforced.     

Hot isostatic pressing of metal reinforced metal matrix composites

Metal reinforced Metal Matrix Composites (MMMCs) made by combining an aluminium alloy matrix with stainless steel reinforcing wires are potentially cheaper and tougher than continuous fibre ceramic reinforced Metal Matrix Composites (MMCs). Although they do not give as great enhancements in stiffness and strength, worthwhile gains are achieved. Such MMMCs can be produced by Hot Isostatic Pressing (HIPping), which reduces interfacial reactions in comparison with liquid metal routes. Here, stainless steel (316L) and commercial purity aluminium wires were used to make bundles which were inserted into mild steel cans for HIPping at 525 °C/120 min/100 MPa. Some stainless steel wires were pre-coated with A17Si, to examine the effect of coatings on mechanical properties. Specimens were evaluated in terms of their tensile and fatigue properties. During HIPping, cans collapsed anisotropically to give different cross-section shapes, and for larger diameter cans, there was also some longitudinal twisting. Wires tended to be better aligned after HIPping in the smaller diameter cans, which produced material having higher modulus and UTS. Higher volume fractions of reinforcement tend to give better fatigue properties. Composites with coated stainless steel wires gave higher composite elongation to failure than uncoated wires. Both uncoated and coated wires failed by fatigue during fatigue testing of the composite. This contrasts with ceramic reinforced MMCs where the fibres fracture at weak points and then pull out of the matrix.     

含金属内衬的复合材料缠绕薄壁容器自紧设计的工程方法

基于薄壁容器理论及卸载后容器内衬残余应变为零的假设, 提出了一种含金属内衬的复合材料缠绕薄壁容器自紧设计的工程方法, 在自紧压力预测中可分别考虑金属内衬的双线性随动和等向强化特征。通过与有限元分析结果比较, 证明了本文中提出的自紧设计方法的简便性和有效性。以一典型容器为例, 研究了在自紧工艺后内衬的残余应变场和工作压力时应力场分布, 证明了采用本文中提出的自紧设计可明显提高容器的承载能力。      

Torsional and compressive behaviours of a hybrid material: Spiral fibre reinforced metal matrix composite

Armouring metals with strong wires or fibres is a common way of providing them with extra mechanical strength. A metal–metal composite armoured with twisted (spiral-shaped) wires is a particularly attractive option. We propose such a design that can be realised by twisting of a pre-assembled metallic matrix with embedded reinforcing fibres. An analytical model was developed to predict the torsional behaviour and the torque–twist requirements in the twisting stage to fabricate such a metal–metal hybrid material. Also, a semi-analytical multi-shell model was developed based on the upper bound theorem to estimate the plastic deformation behaviour of the hybrid material under axial compression. Samples of commercially pure Cu as the metallic matrix and stainless steel fibres as the reinforcing components were fabricated. A fair agreement of the experimental torque vs. twist data for torsional deformation and compressive load vs. stroke data of the compression test with the model predictions was found. The structural performance of the metal–metal hybrid showed an improvement of properties compared to the solid part without the fibres.     

A low cycle fatigue model of a short-fibre reinforced 6061 aluminium alloy metal matrix composite

A low cycle fatigue model has been developed to predict the fatigue life of both the unreinforced aluminium alloy and the short-fibre reinforced aluminium alloy metal-matrix composites based solely on crack propagation from microstructural features. In this approach a crack is assumed to initiate and grow from a microstructural feature on the first cycle. The model assumes that there is a fatigue-damaged zone ahead of the crack tip within which the actual degradation of the material takes place. The low-cycle fatigue crack growth and the condition for failure are controlled by the amount of cyclic plasticity generated within the fatigue-damaged zone ahead of the crack tip and by the ability of the short fibres to constrain this cyclic plasticity. The fatigue crack growth rate is directly correlated to the range of crack-tip opening displacement. The empirical Coffin–Manson and Basquin laws have been derived theoretically and applied to compare with total-strain controlled low-cycle fatigue life data obtained on the unreinforced 6061 aluminium alloy at 25 °C and on the aluminium alloy AA6061 matrix reinforced with Al₂O₃ Saffil short-fibres of a volume fraction of 20 vol.% and test temperatures from −100 to 150 °C. The proposed model can give predicted fatigue lives in good agreement with the experimental total-strain controlled fatigue data at both high strain low-cycle fatigue and low strain high-cycle fatigue regime. It is remarkable that the addition of high-strength Al₂O₃ fibres in the 6061 aluminium alloy matrix will not only strengthen the microstructure of the 6061 aluminium alloy, but also channel deformation at the tip of a crack into the matrix regions between the fibres and therefore constrain the plastic deformation in the matrix. The overall expected effect is therefore the reduction of the fatigue ductility.     

Reliability analysis of hybrid ceramic/steel gun barrels

ABSTRACT Failure of the ceramic gun‐barrel lining during single‐shot and burst firing events has been studied by combining a finite‐element method based thermo‐mechanical analysis with a structural reliability analysis. An initial distribution of residual stresses in the lined barrel, as introduced during shrink‐fitting of the steel jacket over the ceramic lining, is taken into account. Forced‐convection boundary conditions at the inner surface of the barrel are determined by carrying out an internal‐ballistic analysis, followed by compressible boundary‐layer modeling of the heat transfer coefficient. The results obtained reveal that due to thermal expansion of the steel jacket during single‐shot and burst ballistic events, tensile axial stresses develop in the ceramic lining near the barrel ends. These stresses are sufficiently high, particularly in the case of burst firing, that they can induce formation of circumferential cracks and, in turn, failure of the lining. Using the Weibull structural reliability analysis, the failure probability for the lining has been computed as 0.0025 and 0.0121 for the single‐round and the 10‐round firing modes, respectively. Optimization of the main design, materials and processing parameters in order to minimize the failure probability for the lining is also discussed.     

碳纤维增强树脂基复合材料的应用研究进展

简述了碳纤维增强树脂基复合材料的性能特点及各种成型工艺,结合该复合材料的优异性能,介绍其在航空航天、交通运输、风电、医疗等领域的应用进展.最后对碳纤维增强树脂基复合材料的发展前景及可回收利用前景进行了展望.