复合材料机械连接强度影响因素的研究进展

简要介绍了复合材料机械连接强度的影响因素，主要有几何参数、板厚、铺层顺序、扭紧力矩、装配间隙等，并分别讨论了其对连接强度的影响规律，最后提出提高复合材料机械连接强度的方法。     

Investigation into the microstructure and mechanical properties of diffusion bonded TiAl alloys

TiAl alloys are potential candidates for replacing conventional Ti-alloys in gas turbine applications in the relatively lower temperature sections, owing to their low density and excellent high temperature properties. However, their intolerable ambient temperature brittleness hinders their use in such applications. Recently, TiAl alloys with some room temperature ductility were developed through alloy development programmes using special production routes such as powder metallurgy. However, the room temperature brittleness of these alloys could not be overcome. Sound joining of these alloys is a fundamental prerequisite for their successful integration into high temperature aerospace applications. It has been well demonstrated that diffusion bonding, a commonly used joining technology in conventional Ti-alloys, can successfully be used in joining of TiAl alloys both in as-cast or special-rolled conditions. In this study, diffusion bondability of a recently developed C containing TiAl alloy with a duplex microstructure using bonding parameters in the range of commercially available equipments was studied. Microstructural investigations in the joint area of the bonds were conducted to observe the presence of any weld defect. Additionally, the mechanical behaviour of the bonds was determined by shear testing to find out the optimum bonding parameters. Furthermore, the effect of post-bond heat treatment on the mechanical properties was investigated.     

金属与复合材料搅拌摩擦搭接焊的研究现状

金属与复合材料连接研究目前处于初级阶段。在焊接方面,搅拌摩擦焊作为一种固相连接技术,可以在较低温度下实现物理化学性能差异较大的金属与复合材料的连接。综述了国内外金属与复合材料搅拌摩擦搭接焊的研究现状,在接头形式、焊具设计、焊接参数优化以及连接机制等方面做了详细介绍。结果表明,静止轴肩可有效提高接头表面成形质量及抗拉强度;接头内的锚结构能够有效增加接头的机械互锁能力;通过优化焊具形貌及工艺参数可以增加锚结构尺寸。金属与复合材料的连接机制主要为机械互锁、化学键合以及较弱的范德华力。此外,对金属与复合材料搅拌摩擦焊的发展提出了相关建议。     

T型接头搅拌摩擦焊接的研究进展

T型接头是满足轻量化需求的关键结构之一,但传统熔化焊在T型构件焊接方面并无优势。作为一种固相焊接技术,搅拌摩擦焊采用特殊的焊接夹具,对中、薄板T型构件实行单面焊三面成型技术,显著降低焊接热输入、减少焊接变形,因此T型接头搅拌摩擦焊可能是一种极具发展前景的工艺方法。从搅拌摩擦焊接T型接头(FSW-T)的焊接工艺、焊接缺陷、显微硬度、力学性能与数值模拟方面概述了国内外研究现状,揭示了FSW-T焊接领域尚需解决的关键科学问题,对该领域未来的研究方向提出了展望。     

The effect of weld parameters on friction stir welding of brass plates

More successful results have been obtained in butt‐ and overlap‐joining of Al‐alloy plates by a recently developed solid state joining technique, namely friction stir welding (FSW), than in more conventional fusion welding processes. In this joining technique, no fusion takes place in the joint area of the plates welded. This novel joining method also offers the potential to weld some other materials rather than Al‐alloys, such as Mg‐alloys, brasses and low strength steels. In this study, the applicability of friction stir welding to brasses, namely 90 %Cu‐10 %Zn and 70 %Cu‐30 %Zn alloys, has been investigated. The joint performance was determined by conducting optical microscopy, microhardness mesurements and mechanical testing (e.g. tensile and bend tests). The effect of welding speed on the joint quality at a given rotational speed of the stirring pin (i.e. 1600 rpm) was also determined for both alloys. The highest joint performances were obtained at a welding speed of 210 mm/min for both alloys.     

Joining of aluminium foams with fasteners and adhesives

This paper describes methods of joining aluminium foams with mechanical fasteners and with adhesives, and characterises the mechanical properties of the resulting joints. Different techniques of joining were investigated under monotonic and cyclic pull-out and bearing loads. The effects of fastener geometry on pull-out and bearing-load failure are modelled. Cyclic loading reduces the maximum load a fastener can carry without failure to 0.35 of the static failure load. Epoxy adhesive joints are stronger than the foam itself in all modes of loading: failure always occurs remote from the joint.     

Fundamental mechanisms and their interactions in shear‐clinching technology and investigation of the process robustness

The compliance with increasingly stricter emission standards is a challenge for the automotive industry, which requires the utilization of lightweight materials e. g. aluminium and high‐strength steels. Hereby, the load‐optimized design of body parts and the reduction of wall thicknesses are enabled. But, due to the use of dissimilar materials, common joining technologies are reaching their limits. On the one hand, joining by welding is often not possible because of different melting temperatures. On the other hand, joining by forming with additional fasteners increases the cycle time and the costs. However, joining by forming without fasteners is often limited by the mechanical properties of the joining partners. The innovative shear‐clinching technology combines shear‐cutting and clinching in a single stage process and thereby enables joining by forming of materials with high differences regarding their mechanical properties. However, by the combination of the sub‐processes cutting and joining, the complexity of the technology is increased. Thus, within the scope of this work, the fundamental mechanisms in shear‐clinching and their interactions as well as the robustness of the process are analysed, in order to promote the applicability of the technology.     

A review on ultrasonic spot welding of copper alloys

As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided.     

Microstructure and mechanical properties of friction stir welded joints made from ultrafine grained aluminium 1050

In order to obtain ultrafine grained structure, commercially pure aluminium (Al 1050) plates were subjected up to 8 passes of Incremental Equal Channel Angular Pressing (IECAP) following route C. Plates in different stages of IECAP were joined using Friction Stir Welding (FSW). All welded samples were investigated to determine their mechanical properties and structure evolution in the joint zone. The joining process reduced mechanical strength of material in the nugget zone, which was explained by the grain growth resulting from temperature rise during FSW. Nevertheless, the obtained results are promising in comparison to other methods of joining aluminium.     

OPTIMUM JOINING CONDITIONS IN A MECHANICAL PRESS JOINT

Mechanical press joining has been used in sheet metal work because it is a simple process and offers the possibility of joining dissimilar sheet metals, such as steel and aluminum alloy sheets. The mechanical press joint strength was found to vary with joining conditions, such as sheet thickness and punch diameter. The optimum joining conditions of the mechanical press joint under complex loading can be determined by correlating strength ratio with diameter ratio and sheet thickness ratio. The failure mode was considered during estimation of the joining strength. Under this experimental condition, the optimum strength ratio was acquired at a sheet thickness ratio of 1.0 and a diameter ratio of 1.683.     

Butt-welding technology for double walled Polyethylene pipe

In this study, mechanical analyses of a butt welding technology for joining Polyethylene pipe are presented. The pipe had unique structure with double wall, and its section topology was not flat. For an effective repair of leakage and replacements of the pipe, the butt welding technology was developed and tested. For the material characterizations, thermodynamic analyses such as thermal gravimetric analysis and differential scanning calorimetry were performed. Based on the test results, the process temperature and time were determined to ensure safe joining of the pipes using a hot plate apparatus. The welding process was carefully monitored by measuring the temperature. Then, the joined pipes were tested by various methods to evaluate the quality. The analyses results showed the detail process mechanism during the joining process, and the test results demonstrated the successful application of the technology to the sewage pipe repairs.     

Einfluss der Schweißparameter auf das Ermüdungsverhalten hochfester Baustähle

High strength low alloy steels are used in many different engineering areas. A commonly used joining technique for those steels is fusion welding. Generally, these components have to withstand fatigue due to dynamic loading. Using thermal joining techniques affect the mechanical properties of the steel. This study focuses on the influence of the heat input on the microstructure of high strength low alloy steels (S690). Furthermore, the fatigue behaviour with special regard to crack initiation and crack propagation is characterized.     

碳纤维增强树脂基复合材料与铝/镁合金连接研究进展EI北大核心CSCD

运载工具的轻量化是解决当前能源危机和环境问题的重要手段之一,得到国内外学者的高度重视。碳纤维增强树脂基(carbon fiber-reinforced polymer,CFRP)复合材料和以铝镁为代表的轻合金具有一系列优异的力学性能与加工特性,是极具应用前景的轻量化材料,实现这两种材料之间的有效连接,成为当下研究的热点。然而由于异种材料之间理化性能差异较大,在生产过程中混合应用多种轻量化材料仍面临巨大挑战。本文通过对胶接、机械紧固、搅拌摩擦及其变种工艺连接技术的研究进展、优缺点、发展趋势进行汇总分析,考察不同连接方式下获得接头的微观形貌,总结了CFRP与铝镁轻合金搅拌摩擦连接的三种机理包括宏观锚定、微观机械嵌合与化学键连接。最后,基于以上三种连接机理,指出进一步提升混合接头性能的关键在于增大金属母材表面粗糙度,增加熔融高分子面积和采用混合连接工艺。     

MIG Brazing of Galvanized Thin Sheet Joints for Automotive Industry

MIG welding of zinc-coated thin plates in the automotive industry leads to major issues, mainly zinc evaporation followed by a decrease of corrosion resistance, as well as residual strains and stresses difficult to minimize. The use of a lower heat input technique for joining galvanized steels would bring significant benefit, if the final overall mechanical properties of the joints are adequate for the application. The use of MIG brazing (MIGB) with the recently commercialized alloyed copper-based filler metal is an alternative worth considering. The present paper addresses the MIGB processes, describing the influence of the different shielding gases and the process parameters on the mechanical, corrosion, and metallurgical properties of the joint, when lower heat input procedures are targeted. The paper describes the influence of the gases on the mechanical properties of the brazed joint, both in normal conditions after joining and after corrosion in a salt water environment. Microstructural features of the different zones are discussed. Results of corrosion and tensile tests are presented and interpreted.     

Functional characterisation of mechanical joints to facilitate its selection during the design of open architecture products

New trends in product design require the use of modularity as key feature aimed to improve functional performance and the generation of open architecture products. For mechanical systems, one of the challenges during early design stages of these products involves the proper selection of joining methods among their constructive components. A robust joint selection process must consider product requirements, life cycle analysis and eventual procedures for assembly and disassembly. However, the general approach towards a Design-for-Assembly (DFA)/Design-for-Disassembly (DFD) only considers design, manufacturing and in some cases final disposal stage. Additionally, most of the works found in the literature are merely focused on assembly operations, disregarding economic and environmental benefits from optimising disassembly complexity. Herein, a functional characterisation of mechanical joint methods for the assembly and disassembly activities that take place throughout the product life cycle is proposed, focusing on open architecture products. Additionally, a classification of joining methods, a joint complexity metric valuation and a selection process are proposed for the conceptual design stage. The approach integrates both DFA and DFD principles in a formal methodology. The proposed selection roadmap can be implemented to increase product sustainability positively regarding resources optimisation, operational time and costs in reuse, remanufacturing and recycling tasks.     

Al及其合金作钎料或中间层连接陶瓷—金属

综述了Ａｌ及其一些合金对陶瓷的润湿性,以及用Ａｌ及其合金连接陶瓷－金属的各种影响因素,阐述了用Ａｌ及其合金连接陶瓷－金属要解决的主要问题是预防连接过程中Ａｌ的氧化和如何提高接头的高温性能。     

Mechanical properties of bio compatible functional prototypes for joining applications in clinical dentistry

In the presented research, work investigations have been made for mechanical properties of the functional prototypes prepared from biocompatible filament of fused deposition modelling (FDM), comprising of hydroxyapatite (HAp), polypropylene (PP) and polyvinyl chloride (PVC). The functional prototypes will be used in clinical dentistry (mainly for joining application for job-type production activities). The filament has been prepared in house using twin screw extrusion process. For evaluation purpose, standard tensile specimens as per ASTM D-638 have been prepared on FDM. This study highlights the effect of three parameters of FDM (namely: infill percentage, layer thickness and speed of extrusion head) on the mechanical properties (namely: load at peak and load at break). The results of the study suggest that infill density has majorly contributed, 92% on load at peak and 89% for load at break, and deposition speed has very less contribution i.e., 1% towards the mechanical strength of the specimen. Further, the results are supported with thermal analysis using differential scanning calorimeter (DSC), which ensures that the specimen prepared are thermally stable and can be put in for joining applications for job-type production activities in clinical dentistry.     

Joining Technology in Metal-Ceramic Systems

Metallic alloys and ceramic materials are employed in aggressive and hostile environments, ranging from aerospace to energy production, from offshore to biological applications. Today, production requires materials able to survive for a long time at high temperatures, in highly aggressive atmospheres, both from the chemical and the mechanical points of view. No single material can offer these characteristics, so that “composite” structures (composites, multilayer materials, metal-ceramic joints) are designed and tested under extreme conditions.

In this paper are presented the basic principles underlying joining technologies, a short discussion of the thermodynamic background of wetting processes, recent developments related to non-reactive and reactive wetting, the influence of trace chemical elements (in the solid, liquid and gaseous phases), and some specific aspects of diffusion bonding, brazing and transient liquid phase joining processes.     

Influence of process parameters on mechanical performance and bonding area of AA2024/carbon-fiber-reinforced poly(phenylene sulfide) friction spot single lap joints

The effects of friction spot joining process parameters on the bonding area and mechanical performance of single lap joints were investigated using full-factorial design of experiments and analysis of variance. On one hand, the main process parameters with significant influence on the bonding area were joining pressure, tool rotational speed and joining time. On the other hand, tool rotational speed and joining pressure displayed the highest influence on the lap shear strength of the joints followed by tool plunge depth, whereas the joining time was not statistically significant. The interaction between the rotational speed and joining time was the only interaction with a significant effect on the mechanical performance. Joints with ultimate lap shear forces varying between 1698 ± 92 N and 2310 ± 155 N were obtained. It was observed that generally a larger bonding area as a result of higher heat input leads to an increased mechanical performance of the joints. The generated regression model by the analysis of variance was used to identify an optimized set of parameters for increasing the lap shear strength of the joints to 2280 ± 88 N. Furthermore, the process temperature was monitored, which varied in the range of 370–474 °C.     

The effect of preheat & post weld heat treatment on the laser weldability of AISI 420 martensitic stainless steel

The martensitic stainless steels are widely used in many industries with their excellent mechanical properties and sufficient corrosion resistance. These steels usually are used for a wide range of applications like nuclear power plants, steam generators, mixer blades, pressure vessels, turbine blades, surgical tools, instrument manufacturing and so on. Contrary to good mechanical and corrosion properties of martensitic steels, poor weldability and cold cracking sensitivity are major problems that are faced in joining of these steels. In this study, the weldability of AISI 420 (X30Cr13) martensitic stainless steel by CO₂ laser beam welding method has been investigated. Effects of pre and post weld heat treatments on mechanical properties and microstructure of laser welded AISI 420 martensitic stainless have also been determined. As a conclusion, it was determined that pre and post weld heat treatments sufficiently improved the mechanical properties of the welds.