A Study of Polyimide in Transmission Laser Micro-Joining of Polyimide to Titanium-Coated Glass

The use of a laser beam in high precision joining of two dissimilar materials has become a very valuable technique. It has potential application in biomedical implants and their encapsulation process. Laser beam offers a unique combination of high speed, precision and low heat distortion. In this research, an analytical method is developed to determine the optimum condition of joining two dissimilar materials namely titanium and polyimide. The accuracy of the current analytical model was verified by comparing sample results with experimental data. Also, these results were compared with the results of finite element method (FEM) by using ANSYS software. The results are very close to each other. This gave us confidence that the current method could be used for other combinations of materials. We observed that for a specific value of laser power, good bonding between dissimilar materials is a function of laser scanning speed. A scanning speed that is too high will not produce any significant increase in temperature at the bimaterial interface. An increase in temperature is necessary to achieve a good chemical bond. On the other hand, if the scanning speed is too slow an excessive increase in temperature will occur resulting in burnout condition for polyimide. For the range of parameters investigated in the current study, we observed that for a laser heat flux of 4.0 W, good quality bonding occurs for a laser scanning speed between 10 and 30 mm/S. We also observed that increased scanning speed causes the temperature contour to stretch in the horizontal direction.     

玻璃与金属连接方法的研究进展

玻璃与金属的异种材料连接技术已广泛应用于精密制造、电子封装、通信遥感和航空航天等领域,进行有关玻璃与金属的连接技术研究具有重要的学术价值和潜在的工程应用价值.简要讲述了玻璃与金属连接时的有关基础问题:界面润湿、界面反应和接头应力.较为全面地介绍了目前研究较多的玻璃与金属之间的连接技术:钎焊、激光焊接、匹配封接、阳极键合和胶接等,并提出未来在大气条件和较低连接温度下实现玻璃与金属连接的可能性.     

Experimental study of initial strengths and hygrothermal degradation of adhesive joints between thin aluminum and steel substrates

Growing usage of lightweight materials such as Al and Mg alloys and composites in automotive body manufacturing has come to a point that bonding of dissimilar materials is a realistic problem to address. A significant issue related to the bonding of dissimilar materials is that the differences in substrate surface conditions, substrate chemical and physical properties often lead to bond failure at strength levels far less than the bond strength established by the adhesive manufacturer for a balanced joint. This research experimentally studied several important factors influencing initial shear strengths and hygrothermal degradation of adhesively-bonded single lap shear (SLS) joints. The effects of surface treatments such as lubrication and zinc coating on the substrates were first investigated. It was observed that even a very small change in the amount of lubricant applied to an aluminum alloy affected the initial shear strength. On the other hand, varying the amount of mill oil on a galvanized steel surface had little effect. Next, the comparative study of the initial joint strength between electro-galvanized (EG) steels and hot dipped galvanized (HDG) steels revealed that the two coatings exhibited no difference in terms of the initial strength. Also, various combinations of aluminum alloys and steel substrates were studied to observe the effect of substrate materials. It revealed that the strength of a dissimilar joint constructed of a strong substrate and relatively weak substrate fell below the strength of the like-material joint made of the relatively strong substrate, and was closer to the strength of the like-material joint composed of the relatively weak substrate. Ageing tests were performed on SLS joints at various temperatures with and without humidity. The shear strength barely changed after 60-days of exposure at various temperatures with room humidity, but degraded significantly at high temperature with high humidity.     

Investigate the influence of bonding temperature in transient liquid phase bonding of SiC and copper

Joining of ceramics to metals provide timeless challenges in nuclear engineering industries. There is a pressing need for developing a suitable technique for joining silicon carbide (absorber) to copper radio frequency structures in Compact Linear Collider. Transient liquid phase bonding is a promising candidate that could be employed for joining of dissimilar materials with high re-melt temperature. In the present work, experiments were carried out on Transient Liquid phase bonding of silicon carbide and copper using metal interlayer. Lead, which has high wettability, is selected as an interlayer in the Transient Liquid Phase (TLP) bonding process. Experimental results of mechanical testing reveal the strength of the SiC/Cu joints and its integrity. Since, the bonding temperature is the most important parameter to achieve sound joint with good mechanical properties, its influence is studied through experimental trials. From the experimental studies, it is found that the bonding temperature should be 230 °C to obtain the good quality SiC/Copper joints.Favorable temperature distribution is achieved at this bonding temperature and consequently, the joining efficiency of SiC/Copper joints is increased..     

Optimization of weld bonding process parameters of austenitic stainless steel 304L and low carbon steel sheet dissimilar joints

Weld bonding is a hybrid joining process used to produce weld joints between similar or dissimilar metallic materials. In this work, a systematic study has been undertaken to investigate the effect of the input process parameters on the weld joint quality of dissimilar materials i.e. austenitic stainless steel 304L and low carbon steel sheet, in terms of joint strength. Experiments were planned on the basis of response surface methodology technique with three control factor and their three levels of process parameters. Experimental results were used to develop a mathematical model to predict the tensile shear strength and peel strength of the weld joint. A mathematical model, correlating the process parameters and their interaction on responses, was also established. The developed model was validated with the confirmation test case experiment, and it has been observed that the developed model is capable to evaluate weld joint strength within the range of process parameters being used. Numerical optimization technique was applied to find out the optimal set of input parameters.     

激光处理对CFRP与铝胶接性能的研究

碳纤维增强复合材料(CFRP)具有轻质高强的特点,被广泛应用于汽车、航空航天、建筑等领域。但CFRP表面惰性高,使得CFRP与其他异质材料复合时的胶接强度低,不能满足使用。采用激光(光纤激光器)对CFRP进行表面处理后,再与铝进行胶接测试。利用SEM、接触角测试和光学轮廓仪测试对不同脉宽的激光处理后的CFRP表面形貌、表面能、表面粗糙度进行研究。结果表明,随脉宽增加,处理后的CFRP表面树脂残留量减少,表面粗糙度增加,表面自由能也相应增加。对比激光处理与机械打磨两种方式与铝的胶接性能发现,激光处理的CFRP与铝的胶接强度比未处理提高了1.95倍,比打磨处理提高了1.02倍。对其胶接断面进行分析可知,激光处理试样的断裂模式主要为纤维撕裂破坏。     

Influence of Laser Surface Modification on Bonding Strength of Al/Mg Adhesive Joints

Key properties of magnesium alloys, such as the high strength-to-density ratio, are driving the production of lightweight structural components in the automotive and aeronautical industries. Many efforts have been carried out on various aspects of processing and fabrication, but the joining of Mg alloys to dissimilar materials is a subject which attracted much research interest in the last decades. In the present work a preliminary investigation on the strength of Al/Mg (AA6082/AZ31B) single-lap epoxy bonded joints was carried out. To this aim, Mg and Al substrates were laser irradiated using a pulsed ytterbium fiber laser. For comparison, and in order to estimate the beneficial action of the laser surface treatment, single lap joints with grit-blasted substrates were prepared and tested. The interaction between laser treated surfaces and two different epoxy adhesives was also analyzed. Finally, the results and discussion were supported by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) executed on treated and post-failure sample surfaces.     

Mechanical fastening of polymer composites

In structures composed of polymer materials and polymer matrix composite materials, components must be joined such that the overall structure retains its structural integrity while it is performing its intended function which can include both mechanical loads (static and dynamic) and environmental loads (temperature and humidity). The use of composite materials in complex structures almost always reduces the number of components in the structures compared to the use of metallic alloys for the same structure. Thus, using composite materials not only results in great savings in weight, but also through a reduced number of joining operations, results in significant savings In assembly, inspection, parts storage, and movement, resulting in increased reliability and lower cost. Yet joining is still required. Joining metallic structures is a mature technology involving riveting, bolting, welding, glueing, brazing, soldering, and other methods. However, for most polymer matrix composites only adhesive bonding and mechanical fastening can be utilized. Attention has been given recently, however, to localized welding of thermoplastic polymer matrix composites. Inherently, adhesive bonding is preferable to mechanical fastening because of the continuous connection, whereas in drilling holes for bolts or rivets, fiber or other reinforcements are cut, and large stress concentrations occur at each discrete fastener hole. However, in many structures, it is necessary to employ mechanical fasteners in order to remove components or to have access to the interior of the structure. Hence, both adhesive bonding and mechanical fastening are important in joining structural components of polymer or polymer matrix materials. The following is a review of much of the literature dealing with mechanical fastening of polymer matrix composite structures. Hopefully, it provides an overall introduction for detailed study of the referenced documents as well as others, and a catalyst for further research.     

Evaluation of the CFRP grafting and its influence on the laser joining CFRP to aluminum alloy

In the case of laser direct joining carbon fiber reinforced plastic (CFRP) to A6061 aluminum alloy, the strength of the dissimilar joint is low. The UV grafting of acrylic acid was proposed to modify the CFRP surface before the laser joining process. The result showed that the shear strength of the joint could be enhanced from 5.3 to 30.1 MPa when optimized parameters (irradiation distance: 10 mm; irradiation time: 30 s) of UV grafting were applied. X-ray photoelectron spectroscopy and scanning electron microscope were applied to study the surface characteristic of grafted CFRP and the strengthening mechanism of the grafting modification. The C=O bond and O–C=O bond on the CFRP increased after the modification with UV grafting. It could be figured out that new chemical bonds, including Al–C and Al–O–C, were produced between Al and the matrix resin of the CFRP and it played a key role in improving the strength of grafted CFRP/A6061 dissimilar joint. Thus, as a high-efficient and effective technique, UV grafting is a promising method to improve the laser joining CFRP to aluminum.     

Adhesive bonding of polymer composites

In structures composed of polymer matrix composite materials, components must be joined such that the overall structure retains its structural integrity while it is performing its, intended function which can include both mechanical loads (static and dynamic) and environmental loads (temperature and humidity). The use of composite materials in complex structures almost always reduces the number of components in the structures compared to the use of metallic alloys for the same structure. Thus, using composite materials not only results in great savings in weight, but also through a reduced number of joining operations, results in significant savings in assembly, inspection, parts storage, and movement, resulting in increased reliability and lower cost. Yet joining is still required. Joining metallic structures is a mature technology involving riveting, bolting, welding, glueing, brazing, soldering, and other methods. However, for most polymer matrix composites only adhesive bonding and mechanical fastening can be utilized. Attention has been given recently, however, to localized welding of thermoplastic polymer matrix composites, and this will be discussed briefly later. Inherently, adhesive bonding is preferable to mechanical fastening because of the continuous connection, whereas in drilling holes for bolts or rivets, fibers or other reinforcements are cut, and large stress concentrations occar at each discrete fastener hole. The following is a review of much of the literature dealing with adhesive bonding of polymer matrix composite structures. It is Intended not only to be a review, but also a background for detailed study of the referenced and other documents, and a catalyst for future research.     

Joining of polymers and polymer–metal hybrid structures: Recent developments and trends

The development of new materials and fabrication techniques has become a matter of success for industrial sectors such as transportation. Polymers, polymeric composites, and polymer–metal structures are being increasingly employed in several products mainly due to the associated weight savings. The main joining methods for polymer and polymeric composites are mechanical fastening, adhesive bonding, and welding. On the other hand, polymer–metal structures are more difficult to join by traditional joining methods, mostly due to their strong dissimilar physical–chemical features. Constant efforts on developing improved alternative joining techniques for these hybrid structures, such as the FricRiveting and injection over molding, have contributed to the dissemination of such structures in industrial applications. This work shows that the field of joining of polymers, polymeric composites, and polymer–metal hybrid structures for industrial applications is still a growing research and development area. This is due to the increasing aspirations for more environmental‐friendly technologies and lightweight materials. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Prospects and limitations of eddy current shearography for non-destructive testing of adhesively bonded structural joints

ABSTRACT

Structural adhesive bonding has become increasingly important for the joining of dissimilar materials as well as for the reduction of weight of joined structures. To ensure the quality of these bonds, non-destructive testing (NDT) such as ultrasonic testing (UT) or radiographic testing (RT) is used. However, both testing methods have the disadvantage that the measurement takes too long to be used for mass productions.

Shearography is an optical method with suitable capability for automated NDT of adhesively bonded joints. It is a contact-free method with an extensive measuring field. For the measurement, an object is illuminated with coherent light. The reflection on the surface causes a speckle pattern on a detector. During the measurement, the object is stressed with the help of thermal or mechanical excitation (e.g. flashlight, underpressure). Changes in deformation of the object’s surface can be calculated by recording two stress scenarios. Flaws in the bonding area cause a local change of deformation and can be detected with shearography.

This paper presents the prospects and limitations of shearo-graphy for adhesively bonded structural joints. The stress in the specimen was achieved by thermal expansion caused by eddy currents. The evaluation included similar and dissimilar structural bonds of metal (e.g. deep drawing steel, aluminum) and CFRP substrates. The target of the examination is the characterization of the detectability of different bonding flaws such as missing adhesive, voids within the adhesive and kissing bonds.     

Adhesively bonded composite tubular joints: Review

The aim of this review article is to examine solutions and challenges associated with adhesively bonded fibre reinforced polymer (FRP) pipe sections. FRP materials have been used in piping systems for more than 40 years. Higher specific mechanical properties and corrosion resistance of FRP makes it a potential candidate for replacing metallic piping structures. Another advantage of FRP structures is the large number of design variables available. Despite the advantages associated with FRP structures, their application is still limited, partly due to unsatisfactory methods for joining composite subcomponents and inadequate knowledge of failure mechanisms under different loading conditions. Adhesively bonded joints are attractive for many applications, since they offer integrated sealing and minimal part count and do not require pipe extremities with complex geometries such as threads or bell and spigot configurations. Normally, an adhesive joint results in more uniform stress distribution, undamaged fibre architecture, and smooth surface contours. In the present article, a comprehensive review of various joining techniques for FRP piping through adhesive bonding is presented and damage mechanisms for different loading conditions are examined.     

Static mechanics analyses of different laser weld bonding structures in joining AZ61 Mg alloy

This paper presents the results of recent investigations on laser seam weld bonding (LWB) of magnesium alloy AZ61 sheets. There are two types of LWB structures: perpendicular weld seam (LWB-PE) and parallel weld seam (LWB-PA). In this paper the differences between the two structures are compared and discussed. In tensile shear tests, both LWB-PE and LWB-PA joints can offer higher failure force than that of laser welding or adhesive bonding alone, and LWB-PA joint offers better performance than LWB-PE joint. This is because the weld seam can increase the peel resistance at the free end of the adhesive bonded part, where a stress concentration exists. Maximum T-Peel strengths of LWB joints depend on the laser seam weld. The LWB-PA joint has both the advantages of maximum failure force caused by laser weld and the peel displacement caused by adhesive, so a synergistic effect is obtained in energy absorption.     

Adhesive bonding of CFRP: a comparison of different surface pre-treatment strategies and their effect on the bonding shear strength

A promising joining technology for thermoset CFRP is adhesive bonding. However, the mechanical performance is influenced negatively by contaminants, like release agents, as well as an excess of matrix in the top layer. In order to generate most suitable surface qualities prior to the bonding process, carbon fibre reinforced plastics are treated with different – UV (355 nm) and IR (1064 nm) – lasers. The results are compared to commonly applied grinding surface preparation. The preliminary results on surface properties, e.g. energy and topography point towards high levels of free surface energy, as well as new originated surface structures. After the bonding process mechanical tests are subsequently carried out in Mode II, to characterize the final joint by its tensile shear strength. Finally, the individual fracture behaviour is examined in post mortem analysis. The results indicate that it is possible to increase the tensile shear strength of the joints to a maximum, which equals the interlaminar shear strength of the CFRP-laminate. Therefore, ultrashort pulsed IR-laser techniques show the best reproducibility and the highest tensile shear strength. In addition, IR-laser treatment is expected to have the highest potential for later applications.     

High temperature rapid reactive joining of dissimilar materials: Silicon carbide to an aluminum alloy

An effective method for bonding of silicon carbide (SiC) ceramic to 5083 Aluminum metal-alloys was developed. This method employed the concept of high-temperature rapid heterogeneous combustion reaction to joint dissimilar materials. Scaled-up welding apparatus, which can accommodate specimens of up to 5″ in diameter and 6″ in height and allow a rapid (～10 ms) load application (up to 1000 MPa) on the joining stack during reaction, was designed and built. An exothermic mixture of titanium and carbon powders (molar ratio 1:0.4) was utilized as a joining reactive layer. Uniform crack-free bonding of SiC to 5083 Al-alloy was accomplished both without and with application of loads. SEM and focused ion beam (FIB) images revealed that ～10 μm (without load) and ～500 nm (with load) transitional joining layers along the interfaces were observed, respectively. Compositional and mechanical properties of joined samples were also characterized by EDS analysis and Vickers microhardness investigations.     

Plasma-sprayed coatings as adherend surface pretreatments

As part of the National Center for Manufacturing Sciences contract on adhesive bonding of dissimilar materials, UTRC, as a sub-contractor, is evaluating environmentally acceptable surface preparation techniques for selected metals and composites. The selected processes are automatable and capable of being transferred into the manufacturing arena. One aspect of the programme is the evaluation of plasma-sprayed, microporous, thin coatings as surface pretreatments for both resin-based composites and metals. Mechanical test results are presented which demonstrate the viability of this approach to achieve acceptable joint strengths with steel, titanium and aluminium bonded to several types of resin-matrix composite. The environmental impact, by elimination of organic primer systems and strong acid etching and anodizing solutions, will be discussed.     

Influence of the mechanical behaviour of different adhesives on an interference-fit cylindrical joint

Hybrid adhesive joining techniques are often used in many industrial sectors to design lightweight structures. A hybrid adhesive joint results from the combination of adhesive bonding with other traditional joining methods such as welding and mechanical fastening, with the aim of combining the advantages of the different techniques and overcoming their drawbacks.This study focuses on the interference fitted/adhesive bonded joining technique. In this application, two cylindrical components are coupled together by inserting one into the other, after having placed an adhesive between them. Generally anaerobic acrylic adhesives, also known as “retaining compound” are used for this application. However the effect of the adhesive nature and of its mechanical and adhesive responses on the performance of the hybrid joint is still unclear. The aim of the present research is to improve the understanding of the behaviour of different adhesives, including rigid epoxies and flexible polyurethanes, in the presence of an interference-fit. Static strength of bonded and unbonded interference fit joints have been compared in order to investigate the role of the different adhesives.     

Joining of Cf/SiC composites and Si3N4 ceramic with Y2O3–Al2O3–SiO2 glass filler for high-temperature applications

C_f/SiC composites and Si₃N₄ ceramics are candidate materials for applications in thermal protection system. This paper investigated the joining of C_f/SiC and Si₃N₄ using Y₂O₃–Al₂O₃–SiO₂ glass. The reliability of joints was evaluated by thermal shock tests. In this present work, the typical joint structure was C_f/SiC-glass-Si₃N₄. The results demonstrate that Direct bonding has been identified as the interfacial bonding mechanism at the SiC/glass and glass/Si₃N₄ interfaces. The maximum shear strength of the C_f/SiC–Si₃N₄ joint was ~34 MPa, which delivered an effective method to achieve strong, reliable bonding between the dissimilar materials. In addition, after thermal shock for 10 cycles, the residual strength remained ~13 MPa. Bubbles instead of microcracks formed in the glass filler, which was the main factor causing the degradation of the joint performance. It is suggested that improving the high temperature resistance of joining materials is the key to realize the application of this joint structure.     

Laser surface texturing of ceramics and ceramic composite materials – A review

The surface texturing of ceramics is generally performed through acid-based etching and machining; however, laser texturing may be considered as a more precise, reproducible and eco-friendly process. Furthermore, laser ablation may be used to produce complex patterns on ceramic surfaces, thus offering new surface engineering opportunities. The studies so far conducted on this topic have mainly been application-driven, and since a wide variety of lasers have been used for surface texturing, it is difficult to have a comprehensive understanding of this technique applied to ceramics and ceramic composite materials. Laser texturing requires a great deal of knowledge of the material and the laser source parameters to optimise the process in order to obtain the expected results. It is therefore important to expand the research on the laser texturing of ceramics and CMCs in order to build a relevant amount of literature that can be used to identify the most appropriate parameters for each application. This review provides an overview of most of the technological aspects considered relevant for the laser surface texturing of ceramics and CMCs, and includes the fundamentals of laser-material interactions and a summary of the used equipment and parameters. Furthermore, most of the techniques related to the modifications of surface material induced by a laser are critically reviewed, and the new horizons that are opening up, in the context of the modification of surfaces to improve the performances of materials for several applications, are discussed.