Influence of fibre interconnections on the thermomechanical behaviour of metal matrix composites consisting of a Zn–Al alloy reinforced with steel fibres

Interconnected fibre networks presenting transverse isotropic symmetry with variable fibre interconnectivity were prepared by sintering assemblies of low carbon steel fibres. The strength and stiffness of these fibre preforms was found to increase very much when increasing sintering temperature or sintering time. Squeeze cast composites were prepared by infiltrating these preforms with alloy ZA8. Creep tests and tensile tests were carried out at 150°C. Both the creep strength and the back-flow strains at unloading drastically increase with increasing preform sintering temperature or time. Also thermal expansion is much affected by fibre interconnectivity. Especially, during cooling, the matrix dilatation strains brought about by thermal mismatches increase with increasing fibre interconnectivity. These results demonstrate that plastic and viscoplastic behaviours of network reinforced composites depend on the mechanical properties of the network as a whole.     

Influence of cutting conditions on machinability aspects of PEEK,PEEK CF 30 and PEEK GF 30 composites using PCD tools

Polyetheretherketone (PEEK) composite belongs to a group of high-performance thermoplastic polymers, which has high specific properties as compared to conventional metallic materials. Due to its own properties and potential applications in various fields of structural components, it is necessary to investigate the machining of PEEK composites. The present study establishes the relationships between the cutting conditions (cutting speed and feed rate) on two aspects of machinability, namely, power and specific cutting pressure by developing second order mathematical models based on response surface methodology (RSM). The study also focuses on interaction effects between the controllable factors and responses during machining of unreinforced and reinforced PEEK composites using polycrystalline diamond (PCD) tools. The experiments have been planned as per full factorial design (FFD) of experiments. Three types of PEEK composites such as unreinforced polyetheretherketone, reinforced polyetheretherketone with 30% of carbon fibres (PEEK CF 30) and 30% of glass fibres (PEEK GF 30) were used for the machining tests. The analysis of variance (ANOVA) was performed to check the adequacy of the mathematical models. The parametric analysis reveals that, power increases with increase in feed rate while the specific cutting pressure decreases for all the materials tested. The analysis also shows the dependency of both power and specific cutting pressure on cutting conditions. The investigation illustrates that the addition of reinforcements to PEEK in order to improve the material properties affects the machinability.     

金属基复合材料的低压制造

本文提出一种制造含有各种增强材料的金属基复合材料的方法.该技术简单、易行,不需要惰性气体或真空保护,只要适当地控制制造过程,就能制备含有较高体积分数增强材料的金属基复合材料.我们使用该技术成功地制备出碳纤维,石墨和SiC颗粒增强铝基复合材料.     

Matrix flow and densification during the consolidation of matrix coated fibres

The consolidation of titanium alloy metal matrix composites from matrix coated fibres has been modelled using a continuum finite element approach. Predictions of time to achieve full density are in good agreement with experimental data. The predicted matrix flow has been compared with metallographic sections from samples containing novel yttria marker layers, to allow measurements of actual flow during densification. These results are also in good agreement with the predictions of the model. Densification is shown to be strongly influenced by temperature and pressure consistent with the matrix constitutive law used. However, densification is almost independent of fibre volume fraction in the range 10–50% by volume. Densification is most rapid when a uniform densifying pressure is applied, any increase in deviatoric component for the same mean pressure leads to a decrease in densification rate.     

液态挤压制备Al_2O_(3f)/LY12复合材料浸渗过程的数值模拟

液态挤压复合材料浸渗过程是影响基体金属凝固及纤维均匀分布的重要因素。从实际工艺的需要出发 ,建立了液态挤压成形复合材料浸渗过程的数学模型 ,并用相似性解法对其温度场进行了数值模拟 ,得到了浸渗过程温度变化规律以及浸渗压力和纤维体积分数对温度场影响的曲线。     

Fracture and mechanical properties of steel fibre reinforced Zn–5Al (Zamak 5) alloy

Abstract

Steel fibre reinforced Zn–5Al alloy (Zamak 5) metal matrix composite beams with different volume fractions of steel fibres were produced with varying notch to depth ratios. The fracture and mechanical properties of the specimens were investigated for their mode I fracture behaviour using three point bending tests under static loading at room temperature. Steel fibres with contents of 1, 2 and 3% of the total volume of Zn–5Al alloy were used as matrix materials. The critical stress intensity factor was determined using the initial notch depth method.     

Degradation of basalt fibre and glass fibre/epoxy resin composites in seawater

Epoxy resins reinforced, respectively, by basalt fibres and glass fibres were treated with a seawater solution for different periods of time. Both the mass gain ratio and the strength maintenance ratio of the composites were examined after the treatment. The fracture surfaces were characterized using scanning electron microscopy. The tensile and bending strengths of the seawater treated samples showed a decreasing trend with treating time. In general, the anti-seawater corrosion property of the basalt fibre reinforced composites was almost the same as that of the glass fibre reinforced ones. Based on the experimental results, possible corrosion mechanisms were explored, indicating that an effective lowering of the Fe²⁺ content in the basalt fibre could lead to a higher stability for the basalt fibre reinforced composites in a seawater environment.     

Processing and properties of copper-coated carbon fibre reinforced aluminium alloy composites

Aluminium alloy matrix composites with carbon fibre reinforcement were prepared by stir casting method. In order to avoid any interfacial reactions in the carbon fibre reinforced composites, the carbon fibres were coated with copper. The fibres were coated by electroless coating method and then characterized. Composites containing different amounts of carbon fibres were prepared by stir casting and then subjected to age-hardening treatment. Fibre distribution was fairly uniform in the composites containing up to 4 wt% carbon fibres. Tensile strength of the composites was found to be increasing up to 4 wt% carbon fibre.     

Progress in Metal Matrix Composites

Abstract

Metal matrix composites are produced by several contrasting manufacturing techniques and in many different shapes and forms. Solid state processing routes are generally favoured for putative aerospace applications, whereas liquid metal routes appear more promising for automobile applications. Both groups of production routes can accommodate reinforcements of continuous fibre, short fibre, particulate and hybrid fibre-particulate types and the reinforcement phase can be distributed uniformly throughout the composite structure or, using preform technology, in selected regions of the casting.

The greatest problem arising during manufacture and during post-production thermal processing of MMCs is that of chemical instability of the constituent phases. Thermodynamic incompatibilities restrict the use of certain manufacturing routes for specific composite couples and limit the working environment of others. Commercial aspects of MMC production, either directly to near net shape or by subsequent machining, indicate high cost penalties for specific limited gains.

The mechanical properties of MMCs are inevitably a compromise between the properties of the matrix and reinforcement phases. In particular, ductility and toughness are frequently sacrificed for higher modulus. Measures to improve toughness whilst maintaining stiffness are being explored. Wear properties of MMCs are extremely good; machinability, on the other hand, can be poor.     

Evaluation of drilling characteristics of high volume fraction fibre glass reinforced polymeric composite

This paper aims to understand the dynamics of drilling of high volume fraction glass fibre reinforced composite. This type of composite is currently used in ballistic applications. At high fibre volume, fibres do not show much relaxation and normal hole shrinkage associated with polymeric composites is not observed during drilling. Peak drilling thrust, dimension of holes drilled and vibration induced during drilling are observed to correlate with each other. Vibrations study has been attempted through wavelet packet transform and the results demonstrated its capability in signal characterisation.     

纤维增强热塑性树脂基复合材料与金属激光连接研究进展

纤维增强热塑性树脂基复合材料与金属的异质构件在轻量化现代装备中的应用日趋广泛,实现异质构件优质、高效、可靠的连接具有重要的学术意义和工程应用价值. 详细综述了异质接头激光连接原理和界面结合机制,以及连接界面结合强度增强方法和激光连接工艺对连接接头抗剪强度的影响. 通过增强机械结合和化学键结合,同时采用控制激光热输入、施加压力、填充树脂材料等措施抑制缺陷的产生,接头抗剪强度已可以满足工业应用对静载强度的要求. 同时展望了纤维增强热塑性树脂基复合材料与金属激光连接技术的发展趋势.     

Tensile flow properties of Al-based matrix composites reinforced with a random planar network of continuous metallic fibres

Squeeze casting was used for processing two new types of composites: pure Al matrix composites reinforced with fibres of Inconel 601, and AS13 (Al–12% Si) matrix composites reinforced with fibres of Inconel 601 or stainless steel 316L. The fibres are continuous with a diameter of 12 μm and their volume fraction in the composites varied from 20 to 80%. The processing conditions were such that no trace of interfacial reaction compound or of matrix precipitate resulting from the dissolution of elements of the fibres could be detected. The quality of the process was attested by Young's modulus and electrical conductivity measurements. Tensile tests were carried out from room temperature up to 300°C. The composites with the pure Al matrix present a remarkable tensile ductility. They thus constitute convenient materials for assessing continuum plasticity models for composites. Properties of composites with the AS13 matrix are much affected by interface adhesion strength.     

残余孔洞对莫来石短纤维／ZL109复合材料强度的影响

运用挤压铸造工艺中不同的保压压强：６ ＭＰａ,３０ ＭＰａ ,６０ ＭＰａ ,１１０ ＭＰａ 和１５６ ＭＰａ 制备３种相同纤维体积分数的莫来石短纤维增强铝基复合材料, 并测定其拉伸强度。不同基体的复合材料拉伸强度均随保压压强增高而提高。讨论了莫来石短纤维／ＺＬ１０９ 复合材料残余空洞尺寸与保压压强的关系和残余空洞在Ｔ６ 处理过程中的长大现象及原因。结果表明, 气孔类残余孔洞初始尺寸和最终尺寸与保压压强有关, 并显著影响莫来石短纤维增强铝基复合材料的拉伸强度。     

原位合成TiC和TiB增强钛基复合材料的微观结构与力学性能

利用钛与Ｂ４Ｃ之间的自蔓延高温合成反应经普通的熔钐工艺原位合成制备了ＴｉＣ、ＴｉＢ增强的钛基复合材料。光学金相、ＥＰＭＡ、ＴＥＭ和Ｘ射线衍射的研究结果表明：存在匠两种不同形状的增强体,即短纤维状ＴｉＢ晶须和等轴、近似等轴状ＴｉＣ粒子。ＴｉＢ、Ｔｉ基体界面洁净,没有明显的界面反应,而ＴｉＣ、Ｔｉ基体界面有非化学配比的ＴｉＣ过度层存在。由于增强体承受载荷,基体合金晶粒细化以及高密度位错的存在,制备钛基     

Al2O3短纤维/SiC颗粒混杂增强铝合金复合材料

研究了Ａｌ２Ｏ３ 短纤维和ＳｉＣ 颗粒混杂增强铝合金复合材料在制动过程中的摩擦磨损性能。结果表明复合材料在制动过程中的摩擦系数较稳定, 磨损量较小, 与传统的制动材料铸铁相比, 复合材料的表面温升较低, 铸铁由于表面温升较高而产生了大量的裂纹。复合材料由于增强体的存在, 制动过程中表面易形成致密连续的转移膜, 该转移膜的出现保证了复合材料在制动过程中摩擦系数的稳定, 降低了复合材料的磨损量。与铸铁相比, 复合材料的密度较低, 更适用于作制动材料     

Effects of microwave assisted heating of carbon nanofiber reinforced high density polyethylene

Carbon nanofiber and carbon nanotube reinforced polymer composites have shown promise due to their enhanced mechanical, electrical, thermal, and dielectric properties. In this study, vapor grown carbon nanofiber reinforced polyethylene composites were exposed to microwave radiation in a conventional resonance cavity microwave oven to explore the possibility of using microwave energy to assist the processing of carbon nanofiber reinforced thermoplastic composites and determine the effect of microwave radiation exposure on material properties. Average temperatures of up to 40 °C above ambient were measured after 5 min of microwave exposure. The effect of high power microwave radiation on the physical integrity of the composites via dynamic mechanical analysis, tensile tests, and dielectric analysis is presented. A drop of 50% in failure strain has been observed for composites with 15 and 20 wt% nanofiber concentrations after exposure to microwave radiation.     

SiC纤维增强钛基复合材料界面研究及构件研制

首先介绍了作者近年来在SiC纤维增强钛基复合材料界面反应机理、应力分布和界面调控方面的工作进展,然后介绍了作者在磁控溅射法和箔-纤维-箔法复合材料工艺及构件研制方面的研究工作。     

Improving vibration weld joint strength through process and equipment modifications

Abstract

Vibration welding is a process used to join thermoplastic components. Currently, under optimised low pressure welding, the weld strength of butt joints of unreinforced polymer can be equivalent to the strength of unwelded material. However, in short glass fibre reinforced polymer, the optimised weld strength is significantly lower than that of unwelded material and is closer to the strength of the resin matrix. This lower strength is attributable to the unfavourable orientation of the short glass fibres in the weld zone. The fibres tend to align parallel and in the plane of the weld zone and thus provide no reinforcement in the direction perpendicular to the weld zone. In the present work the impact of various modifications to the existing vibration welding technology was examined, with the objective of increasing the current achievable weld strength of glass reinforced nylon. The introduction of a secondary vibratory motion perpendicular to the weld plane during welding resulted in strengths 20% higher than those of samples welded using the standard vibration welding process.     

横向压缩载荷下CF/Al复合材料微观损伤演化与断裂力学行为

针对真空压力浸渗制备的单向碳纤维增强铝基复合材料(CF/Al复合材料),采用细观力学数值模拟和实验相结合的手段研究了其在横向压缩载荷下的损伤演化与断裂力学行为,并分析了界面结合性能和纤维体积分数对复合材料横向压缩力学性能的影响。结果表明:基于纤维对角正方形分布RVE建立的细观力学有限元模型,可以较好地计算预测复合材料横向压缩变形力学行为。压缩变形初期界面首先发生损伤和失效现象,进而诱发界面附近基体合金的局部损伤;随压缩应变增加,界面和基体损伤逐渐发展并导致纤维的失效,复合材料横向压缩断口呈现出界面脱粘和纤维断裂共存的微观形貌。复合材料横向压缩弹性模量和极限强度随着界面强度增大而增大,而受界面刚度的影响较小;在相同界面性能条件下,复合材料横向压缩极限强度和弹性模量均随纤维体积分数的增大而减小。     

Grain refinement and tensile strength of carbon nanotube-reinforced Cu matrix nanocomposites processed by high-pressure torsion

In recent years, the processing of metallic materials via severe plastic deformation has been widely applied to manufacture bulk specimens of ultrafine grained/nanocrystalline structures. In this study, bulk nanocomposites of carbon nanotube-reinforced Cu were manufactured by consolidation of mixtures of coarse grained Cu powders and CNTs of two volume fractions (5 vol% and 10 vol%) using high-pressure torsion, a typical SPD method. The effects of CNT reinforcements on the microstructural evolution of the Cu matrix were investigated using electron backscatter diffraction and scanning/transmission electron microscopy; the results showed that the Cu matrix grain size was reduced to ～114 nm, and the CNTs were well dispersed in the matrix. Due to the effect of the UFG Cu and CNTs, the tensile strength (350 MPa) of the nanocomposite was higher than that (190 MPa) of Cu processed by the powder HPT process without CNTs. However, the Cu-CNT 10 vol% indicated a decreased tensile strength due to an increased interface area between the matrix and CNTs at high volume fractions of CNTs.