碳纤维/聚苯硫醚热塑性复合材料电阻焊接工艺

本文针对航空器结构用碳纤维/聚苯硫醚(CF/PPS)复合材料为研究对象，开展电阻焊接工艺研究；利用CF/PPS复合材料混编织物作为电阻元件，成功制备了CF/PPS复合材料层板电阻焊接接头；重点利用Taguchi方法和方差分析获取CF/PPS复合材料层板电阻焊接最佳工艺参数(电流为12 A，压力为1.5 MPa，时间为30 min)及各参数对焊接接头剪切强度的贡献(电流为83.37%，压力为9.55%，时间为6.02%)。最佳焊接工艺参数焊接的接头单搭接剪切强度约为17.88 MPa；同时，对最佳参数焊接试样(H-LSS)和较低剪切强度试样(L-LSS)的焊接接头截面和剪切失效断口形貌进行了观察和分析。结果表明:H-LSS试样的焊缝区域树脂填充和浸润良好，且主要剪切失效形式为层间剪切失效，即为纤维与树脂基体脱黏及CF/PPS织物复合材料断裂混合失效；L-LSS试样的焊缝区域树脂填充和浸润较差，存在较多空隙，且剪切失效形式为焊缝界面脱黏失效。      

Moisture effects and acoustic emission characterization on lap shear strength in ultrasonic welded carbon/nylon composites

Carbon/nylon composites were ultrasonically welded under controlled welding pressure and time. The optimized pressure and time for the highest joining strength are found by conducting the lap shear test. The acoustic emission (AE) technique used during the test is able to detect the first-damage load (FDL) and identify the damage mechanisms. Fiber breakage contributes to higher lap shear strength of the specimen, while debonding and pull-out lead to lower strength. Furthermore, the configurations of the AE curves provide the judgment of the magnitude of lap shear strengths of composites. The moisture absorption in welded composites follows Fick's law of diffusion; and lap shear strength of the composite decreases with increasing moisture content, the correlation of which follows an exponential decay function. The reduction of the strength is due to weaker hydrogen bond in the matrix connected between water and amide groups, and damage caused by the swelling of the matrix.     

Investigation of prepreg bonded composite single lap joint

Adhesive bonded single lap joint has been used extensively in laminated composite structures. Using neat resin adhesives, however, the joint strength is comparatively low and the fabrication time is long. In order to increase the joint strength and reduce the fabrication time, two types of fiber pre-impregnated (prepreg) composites were used to bond composite single lap joints. Test specimens were prepared per ASTM D 3165-95 standard. Ninety days of accelerated conditioning using seawater and ultraviolet radiation were conducted to investigate the long-term performance of prepreg bonded single-lap joint in an offshore environment. The shear strength of various specimens was obtained using tension tests. Two types of neat resin bonded specimens were also used for comparisons. Finite element analysis was implemented to justify test results. Parameters affecting the load carrying capacity of prepreg bonded composite single lap joints were investigated based on finite element analysis results.     

An Experimental Study of Resistance Welding of Carbon Fibre Fabric Reinforced Polyetherimide (CF Fabric/PEI) Composite Material

This paper presents an experimental investigation of resistance welding of carbon fibre fabric reinforced polyetherimide composites (CF fabric/PEI). The heating elements were made from a single CF fabric/PEI prepreg sheet with neat PEI films co-moulded to both surfaces. Welding was conducted on a welding area of 25 mm × 12 mm. The quality of the welded specimens was studied using a non-destructive evaluation technique (C-scan) as well as a mechanical test (lap shear strength). The relationships between input power, input energy, welding time and consolidation pressure were studied. Experimental results indicated that sufficient joining was obtained at a power level from 80 to 160 kW/m2, under an initial welding pressure of 0.15 to 0.40 MPa. The maximum lap shear strength achieved through resistance welding was equivalent to that of the compression moulded benchmark. The fracture surfaces of welded specimens showed mostly cohesive-failure or intralaminar failure. An optimum processing window is proposed for the resistance welding of CF fabric/PEI composite system.     

Effect of tool rotational speed and probe length on lap joint quality of a friction stir welded magnesium alloy

The effects of tool rotational speed and probe length on lap joint quality of friction stir welded 2-mm AZ31B-H24 magnesium alloy were investigated in terms of welding defects, microstructure and mechanical properties. Tensile shear load initially increases with increasing tool rotational speed but decreases with further increase. However, the tensile shear load always increases with increasing probe length. The highest shear strength is obtained using a set of welding parameters resulting in a downward hooking defect at the maximum stress location of the top sheet. Sound lap joints with low distortion, lack of cavity, minor kissing bond and preferable hooking defects, and high tensile shear strength were successfully obtained, indicating the great potential of friction stir welding technique for magnesium alloys.     

基于导热板的碳纤维增强聚醚醚酮复合材料感应焊接温度调控

研究了碳纤维增强聚醚醚酮(CF/PEEK)复合材料感应焊接中厚度方向及焊接面内的温度分布及调控。基于对温度分布结果的分析,使用导热板结合真空袋压的方式对CF/PEEK进行感应焊接,结合使用合适的功率及加热时间,测试了焊接件的单搭接强度,观测分析了焊接件的断裂形貌。结果表明,导热板对层合板表层和边缘均有良好的散热效果;焊接功率越低,焊接面的加热均匀性增加,但是会延长加热时间。在真空袋中对层合板上表面和两侧添加导热板,在输出功率示数为600时感应焊接300 s,焊接件的单搭接剪切强度达到41.57 MPa。      

Mechanical and microstructural investigation of friction spot welded AA6181-T4 aluminium alloy

Friction spot welding (FSpW) is a solid state welding process suitable for spot joining lightweight low melting point materials like aluminium and magnesium alloys. The process is performed by plunging a rotating three-piece tool (clamping ring, sleeve and pin) that creates a connection between sheets in overlap configuration by means of frictional heat and mechanical work. The result is a spot welded lap connection with minimal material loss and a flat surface with no keyhole. FSpW has been performed in a 1.7 mm-thick AA6181-T4 aluminium alloy using different welding parameters (rotation speed and joining time) aiming to produce high quality connections in terms of microstructure and mechanical performance. Microstructural features of the FSpW connections were analysed by optical microscopy; while mechanical performance was investigated in terms of hardness and tensile testing. Connections with shear strength close to 7 kN were obtained with high reproducibility. The results also showed that geometric features of the connection play an important role on the fracture mechanism and hence on the mechanical performance of the connections.     

The optimization of friction spot welding process parameters in AA6181-T4 and Ti6Al4V dissimilar joints

Friction spot welding is a relatively new solid-state joining process able to produce overlap joints between similar and dissimilar materials. In this study, the effect of the process parameters on the lap shear strength of AA6181-T4/Ti6Al4V single joints was investigated using full-factorial design of experiment and analyses of variance. Sound joints with lap shear strength from 4769 N to 6449 N were achieved and the influence of the main process parameters on joint performance was evaluated. Tool rotational speed was the parameter with the largest influence on the joint shear resistance, followed by its interaction with dwell time. Based on the experimental results following response surface methodology, a mathematical model to predict lap shear strength was developed using a second order polynomial function. The initial prediction results indicated that the established model could adequately estimate joint strength within the range of welding parameters being used. The model was then used to optimize welding parameters in order satisfy engineering demands.     

Modeling and prediction of weld shear strength in friction stir spot welding using design of experiments and neural network

Friction Stir Spot Welding (FSSW) is a kind of the friction stir welding (FSW) process, creates a spot, lap‐weld without bulk melting work materials. The tensile shear strength of the FSSW welded joints mainly depends on the pin height, tool rotation and welding time. In the present study, two of the techniques, namely factorial design and neural network (NN) were used for modeling and predicting the tensile shear strength of EN AW 5005 aluminum alloy. Tensile shear strength was taken as a response variable measured after welding pin height, tool rotation and welding speed were taken as input parameters. Relationships between tensile shear strength and welding parameters have been investigated. The level of importance of the FSSW parameters on the tensile shear strength was determined by using the analysis of variance method (ANOVA). The mathematical relation between the tensile shear strength and FSSW welding parameters were established by regression analysis method. This mathematical model may be used in estimating the tensile shear strength of FSSW joints without performing any experiments. Finally, predicted values of tensile shear strength by techniques, NN and regression analysis, were compared with the experimental results and their nearness with the experimental values assessed. Results show that, NN is a good alternative to empirical modeling based on full factorial design.     

Influence of the properties of externally bonded CFRP on the shear behavior of concrete/composite adhesive joints

This paper concerns the strengthening of concrete structures with externally bonded composite reinforcement, and focuses mainly on the influence of the FRP characteristics on the mechanical behavior of the composite to concrete interface. An experimental investigation was conducted, based on the characterization of such bonded assemblies and using a double lap joint shear test. Twelve different series of specimens were studied in order to evaluate the influence of various parameters related to the FRP material (i.e. the use of carbon or aramid and of fiber reinforced systems, the type of manufacturing process, the values of the Young modulus, the thickness of the FRP and the bonded length) as well as several parameters related to the adhesive joint (i.e. the lap joint thickness, the curing conditions and the elastic modulus of the epoxy adhesive). Analyses of the strain and shear stress distributions along the lap joints emphasized significant effects of the FRP properties and epoxy curing conditions on the interfacial strength. In addition, a bond strength model is proposed in the last part of the study.     

Joining of metal to plastic using friction lap welding

Friction lap welding (FLW) is a new conception of joining method developed in Joining and Welding Research Institute (JWRI). The efficiency of joining metal and plastic using FLW was demonstrated through a case study on aluminium alloy AA6061 and MC Nylon-6. The lap joints with high shear strength were obtained over a wide range of welding parameters. A linear relationship was observed between FLW parameters (R/ν)^0.5 and the thickness of melted nylon (H). The influences of FLW parameters on bubbles and shear strength were investigated. The morphologies of the fractured surfaces of AA6061 alloy fell into seven types based on the scanning electron microscopy examination. Statistical analysis showed that the contribution to shear strength of these regions followed such an order: region II > region V > region VI > region VII > region IV > region I or III.     

Co-cured in-line joints for natural fibre composites

Little attention has been paid to joining unidirectionally-reinforced high strength natural fibre composites in the manufacture of engineered structures. Therefore the main objective of the paper is to investigate the effect of joint geometry on the strength of natural fibre composite joints. Epoxy-bonded single lap shear joints (SLJs) between henequen and sisal fibre composite elements were manufactured and tested in tension to assess the shear strength of the structural bonds. The performance of co-cured joints, termed “intermingled fibre joints” (IFJs) and “laminated fibre joints” (LFJs) was also evaluated. These IFJ and LFJ configurations possess much higher lap shear strengths than the single lap shear joints and the failure modes of the three joint configurations are compared. SLJ and LFJ joints have been modelled using finite element analysis, allowing interpretation of the experimental observations.     

SiCp/Al复合材料电阻点焊剪切断口形貌

为了优化SiC p/Al复合材料电阻点焊工艺参数,采用不同焊接电流和焊接时间对SiCp/Al复合材料进行了电阻点焊连接,对接头进行了剪切强度试验,用扫描电镜对不同的点焊剪切断口进行微观形貌分析.结果表明:最优的焊接电流和时间匹配值为焊接电流I=14.6 kA,焊接时间t=0.2 s,配合电极压力F=2 500 N点焊,熔核直径适中,接头拉剪力可达1 693 N;撕开后的焊点断口两侧分别呈规则的圆凸台和圆孔状,呈纽扣型断裂,接头成型良好.当焊接电流和时间的匹配值小于最优参数时,点焊接头只有少量的点形成冶金结合,呈结合面断裂,焊接强度较低;当焊接电流和时间的匹配值大于最优参数时,点焊接头易过热,断口上出现气孔、裂纹、电极粘附烧蚀缺陷,接头强度降低.     

Experimental investigations on the polypropylene behavior during ultrasonic welding

The polypropylene material meets the needs and requirements in automotive industry due to its features such as wide range of physical properties, ease of processing, and low cost. This research has focused on the investigation of the behavior of polypropylene during ultrasonic welding process. The lap welded samples were examined by modern methods such as Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR). Also, the morphology of the non-welded and welded regions of the polypropylene samples was analyzed by Scanning Electronic Microscopy (SEM) method. TGA and DSC results showed a negligible difference between the mass loss of the molded and the welded propylene materials. Furthermore, the SEM images revealed the formation of voids in close correlation with vibration amplitude. The weld strength and bond integrity appears to be higher for higher vibrations, emphasizing that the lap joint interface strength is higher when the tendency of voids formation is decreasing. The stress-strain curve of the material, plotted for three ultrasonic welding variants, illustrated that increasing the main process parameters (pressure, time, and vibration amplitude) makes the weld strength higher, but a decrease in plasticity was noticed in the welded polypropylene samples.     

Optimization of process parameters of friction stir spot welding of polycarbonate sheets and morphological analysis

Friction stir spot welding has a great impact on the joining process of thermoplastics. In this work, effects of varying rotational speed, plunge depth, and dwell time were investigated on polycarbonate sheets and a filler sheet was utilized to reduce the keyhole size of friction stir spot welded joints. The welding parameters were arranged according to Taguchi L₉ orthogonal design of experiments to determine the optimum levels of process parameters. Lap shear tests were performed to examine the mechanical properties. Using analysis of variance and signal to noise ratio, influences of each welding parameter on the lap joint shear load were evaluated. According to achieved results, tool rotational speed has the highest effect while plunge depth has minimum effect on the mechanical behavior of friction stir spot welded joints. Optimum process parameters were attained as 1000 min⁻¹ for rotational speed, 10.5 mm of plunge depth, and 40 s of dwell time. Optimized process parameters showed 15 % improvement compared to the initial welding parameters. Cross-sectional appearances of welded samples which play an important role in determining lap joint shear load were analyzed by morphological and visual comparisons. Failure modes of the fractured samples for lowest, moderate and highest lap joint shear loads were also observed.     

Development of response surface model for tensile shear strength of weld-bonds of aluminium alloy 6061 T651

The development of a response surface model to study the influence of process parameters of weld-bonding on tensile shear strength of the weld-bond of 2 mm thick aluminium alloy 6061 T651 sheets has been reported. Significant and controllable process parameters of the weld-bonding (surface roughness, curing time, welding current, welding time and electrode pressure) and their ranges were identified by conducting pilot experiments. Welding current, welding time and welding pressure were identified as significant and controllable parameters. Influence of the significant process parameters and their interaction on the tensile shear strength of the weld-bonds was studied using response surface methodology (RSM). Using model, the optimal combination of weld bonding process parameters for maximum tensile shear strength of the weld bond was obtained. The validity of the model was evaluated on weld bonds developed using different levels of process parameters and testing their tensile shear strength. The model error was found to be in a range of 3–7%.     

Resistance welding of carbon fibre reinforced thermoplastic composite using alternative heating element

The focus of this work is the use of a metal mesh as an alternative heating element for the joining of carbon fibre fabric reinforced polyetherimide composite laminate. A more homogeneous temperature distribution was generated by the metal mesh at the bonding surface. Glass fibre fabric reinforced PEI (GF/PEI) was used as an electrical insulator between the heating element and adherend laminates. Experimental results show that the GF/PEI prepreg could effectively prevent current leakage and enlarge the welding area. Welding parameters, such as input power level, welding time and pressure, were optimized according to the results of mechanical and microstructure characterization. Mechanical performance of composite specimens joined using metal mesh, in terms of lap shear strength and Mode I interlaminar fracture toughness, was equivalent to that of compression moulded benchmarks. Fracture surfaces of welded specimens showed mostly cohesive failure or intralaminar failure, indicating that good bonding between the PEI matrix and metal mesh was achieved.     

Adhesive bonding of carbon fiber reinforced composite using UV-curing epoxy resin

Carbon fiber reinforced materials are widely used in a variety of products due to their stiffness, high strength and light weight. However, the strength of fiber reinforced composites will dramatically decrease when they have suffered damage from impact. Therefore, repair is necessary to maintain integrity. In many cases, speed of this repair is paramount. In this work, UV resins adhered to a damaged panel to form a hard patch are considered for fast repair. The challenge in using UV curing resins on carbon fiber reinforced materials is the non-UV transparency of the composite. In this work, a cationic UV epoxy resin is used due to its characteristic of dark polymerization after UV exposure. ASTM lap shear testing showed the shear stress was above 1000 psi. However, the large scale testing failed due to partial curing of adhesive before repair indicating that control in dosing and resin delivery is critical, yet problematic.     

Ultrasonic Welding of Ni and Cu Sheets

Ultrasonic metal welding is widely used in various fields due to its ability to weld a variety of materials such as new materials and sheet structures. In this study, a special horn with four-point tips was developed for the ultrasonic welding of Ni and Cu sheets used as electrode materials of the secondary cell. The effects of welding parameters (welding time, clamping pressure, and vibrational amplitude) on weldability were investigated using the developed horn. The weldability of Ni/Cu sheet was assessed via the tensile test, scanning electron microscope observation, and EDX-ray analysis of the weld zone. Experimental results showed that the optimal welding parameters were a welding time of 0.25 s, pressure of 0.20 MPa, and vibrational amplitude of 80%, with a welding strength of 87.45 N under these conditions. It was also confirmed that solid-state diffusion by vibrational and frictional heat was clearly generated at the welding interface under good welding conditions.     

Strength calculation of composite single lap joints with Fiber-Tear-Failure

The Fiber-Tear-Failure (FTF) is a common mode of failure in the adhesively bonded single lap joint having continuous fiber reinforced composite. Within single lap joints, presence of material and geometric discontinuities restrict the applicability of strength of material based approach for failure load prediction. Zone based approach appears promising in tackling discontinuity issues provided the right failure criterion and critical zone size are known. In this paper, a right failure prediction criterion is identified that can be used for the Fiber-Tear-Failure load prediction using zone based approach. Using a carbon fiber composite and an epoxy paste adhesive, failure modes were generated experimentally using different dimensions of lap joints. Several stress/strain based failure criteria for composite were tested. Critical zone size was calculated by performing the finite element analysis on a single lap joint with known failure load. For other joints, failure loads were calculated by adjusting the input loads in the analysis such that the failed zone size became the same as the critical zone size. The result reveals that Azzi–Tsai (Norris) criterion is capable of predicting failure loads of single lap joints with FTF.