Welding Of Composites Research Articles

Resistance Welding of Thermoplastic Composites, Including Welding to Thermosets and Metals: A Review.

This review paper presents the current progress in the development of resistance welding techniques for thermoplastic composites, with a particular emphasis on their application in hybrid joints, such as those involving thermosetting composites and metals. Resistance welding, a fusion bonding method, offers significant advantages over adhesive bonding and mechanical joining by eliminating the need for additional adhesive materials and enabling integration into automated manufacturing processes. The study highlights the unique benefits of resistance welding, including lower energy consumption compared to other methods and its compatibility with automated manufacturing, which can reduce production costs by up to 40%. Key findings from the literature indicate that resistance welding is particularly effective in achieving strong, durable joints for complex and large structures, such as those used in the aerospace industry. The review also identifies the main challenges associated with resistance welding, including temperature control, current leakage in carbon-fiber-reinforced polymers, and potential corrosion when using metal meshes. To address these challenges, various strategies are discussed, including surface treatments, the use of nanocomposites, and the integration of carbon nanotubes. The review concludes by emphasizing the need for further research to optimize welding parameters and to develop non-destructive testing methods for industrial applications, ensuring the reliability and long-term performance of welded joints.

Multiphysics computational modelling and experimental analysis of friction stir welding of aluminium alloy metal matrix composites (AAMMCs)

Friction stir welding is a modern method for fabricating aluminium alloy metal matrix composites (AAMMCs) that significantly enhance the properties of the parent materials. In this study, Al2O3 particles were incorporated into a 6061-T6 aluminium matrix. Experimental and numerical modeling provided in-situ observations of particle-aluminium matrix mixing in the weld stir zone (SZ). Two different pin profiles, threaded and square, were used to fabricate the AAMMC joints. The threaded pin profile resulted in uniform dispersion and a homogeneous distribution of Al2O3 particles within the aluminium matrix. In contrast, the square pin profile led to defects in the SZ and a non-homogeneous particle distribution. The volume fraction mixing of the AA6061-T6 matrix and Al2O3 at the workpiece/tool interface from top to bottom was analyzed using a level set technique. Experimental results showed effective mixing of Al2O3 particles in the AA6061-T6 matrix with the threaded pin profile, resulting in a defect-free joint, uniform particle distribution, and ultra-fine grain refinement, with grain sizes reduced to 4.19 µm. The main shear texture components observed in the threaded pin joints included B/B̅ and C, along with deformed and recrystallized texture components such as Copper {112} 〈111〉, Brass {110} 〈112〉, Goss {011} 〈100〉, Cube {001} 〈101〉, and P {011} 〈112〉 . Additionally, joints fabricated using threaded pin profiles exhibited significantly higher tensile strength (up to 270 MPa) and microhardness (average of 120 HV0.2) compared to those with square-shaped pin profiles, which showed lower values of 240 MPa and 105 HV0.2, respectively. Thus, AAMMC joints made with threaded pins demonstrate ultra-fine grain refinement, increased high-angle grain boundaries, enhanced recrystallized texture components, and improved mechanical properties, resulting in superior overall joint performance.

Modeling variability of the electrical conductivity tensor for the induction welding of composites

Modeling variability of the electrical conductivity tensor for the induction welding of composites

Characterization and analysis of conduction welded thermoplastic composite joints considering the influence of manufacturing

Thermoplastic composite welding is a key technology that can help to make the aviation industry more sustainable, while at the same time enable high-volume production and cost-efficient manufacturing. In this work, characterization, testing and analysis of thermoplastic composite conduction welded joints is performed while accounting for the influence of the manufacturing process. Test specimens are designed from welds of a half a meter long welding tool that is developed to weld the stiffened structures of the next-generation thermoplastic composite fuselage. In the design, special attention is paid to the weldability of the laminates, while ensuring fracture occurs only at the welded interface. Two specimen configurations are evaluated for the Double Cantilever Beam and End-Notched Flexure characterization tests. Moreover, Single Lap-Shear specimens are tested in tension and in three-point-bending. Finally, the characterized material properties are introduced in finite element analyses to demonstrate that the cohesive zone modeling approach can be used to conservatively predict the strength of these welded joints. New insights are obtained in the relation between the manufacturing process, the quality of the weld and the mechanical properties of the joints, which are significantly different compared to autoclave consolidated composites.

Microstructural evolution and corrosion responses of friction stir welded SUS301L stainless steel

As a typical manifestation of elemental segregation of stainless steel, chromium depletion was often brought about by welding, leading to undesirable corrosion resistance. In light of this, we employed friction stir welding through WC-W composite welding tools to achieve sound joints of SUS301L stainless steel, with corrosion resistance exceeding that of the base material (BM). A higher austenite fraction of 20.8% enhanced corrosion resistance since the corrosion potential of austenite is nobler than that of martensite. Austenite was not decomposed into harmful σ-phases due to the shorter holding time at the elevated temperature, thus enhancing the homogeneity of the microstructure. The ultimate tensile strength of the welded joints reached 820 MPa, which was equal to 98.9% of BM. The pitting potential of the joint was increased by 0.078 V, indicating that the stability of the passive films was improved, and the ability to resist the corrosive medium was strengthened. Chromium depletion was eliminated, resulting in no sensitivity to intergranular corrosion.

Inline Monitoring of continous Ultrasonic Welding Processes of Thermoplastic Composites via a custom polyCMUT based Ultrasound Array

Ultrasonic welding (UW) of thermoplastic composites (TCs) is an emerging technology in the field of composite joining techniques in the aerospace sector. Through a mechanical oscillator, ultrasound at a frequency of 20kHz is induced into the material via a welding horn, where microscopic friction and damping effects melt the thermoplastic. Under further pressure the weld area cools down, permanently joining both parts together. Like all joining processes in the aerospace industry the resulting joints need to be tested for their quality and structural integrity. The traditional testing method using water-coupled ultrasound includes extra steps. This process could be considerably improved by assessing the quality of the weld directly after or even during the welding process, allowing for immediate rework or discard of the parts in question. Ultrasound is still the best solution for this quality assessment, being inexpensive, well understood, and able to create B-Mode images, allowing a look into the cross-section of the weld. However, there are several major problems: To increase the system complexity as little as possible it is necessary to attach the ultrasound unit next to the welding equipment, and as close to the welding horn and compactor as possible to save space and keep the end- effector manoeuvrable. This brings problems for classic piezoelectric ultrasonic arrays: The low welding frequency and its resonance modes reach into the lower resonance modes of the piezoelectric sensors leading to immense noise, hiding any potential echo from the welding zone. Classic piezoelectric crystals are also very brittle and can suffer damage from sustained exposure to this violent environment. The authors present a novel solution: a custom-made polymer-based capacitive micromachined ultrasonic transducer array (polyCMUT). polyCMUTs are tiny drums with two electrodes. One on the bottom and the other suspended over a cavity sandwiched between two layers of polymers. By applying a DC-bias an electrical field is created and the membrane is set under tension. If then an AC voltage is applied, the strength of the electric field decreases, allowing the membrane to snap back into its original position. If done at the resonance frequency of the membrane, a strong ultrasonic signal is created. To receive this signal the polyCMUT is charged with a DC-bias, allowing it to receive the echo of the transmitted signal by measuring the changing capacitance. Not only is the polymer robust and inexpensive to fabricate, the general architecture of CMUTs also allows a design where the first mode of resonance is the actual mode the CMUT is operating in. By designing for a resonance frequency over 5 MHz all noise from the initial welding process is ignored, leading to a working pulse echo imaging system. The array is then mounted onto a PEEK block attached to the compactor unit of the welding end-effector. This publication is intended to present initial results, the design process of the custom array and the tests leading there.

Resistance Welding of CF/PEI Composites by a Novel Implant of Flame-grown Carbon Nanotubes Grafted Carbon Fibers

Objective: Interface enhancement between resin and fiber has been a longstanding goal for manufacturing composite material. Using carbon nanomaterials in combination with macro-materials for composite materials is an important application of advanced manufacturing technology. Methods: This study examined the use of carbon nanotubes (CNTs) wrapped carbon fibers (CFs) (CFs@CNT), a cross-scale composite component incorporating CNTs and CFs, as an implant for resistance welding of composites containing carbon-fiber-reinforced polyetherimide (CF/PEI). Results: The correlation of growth time (tg) on growth morphology of CNTs on implant and strengths of joints were studied. The surface of CF was gradually covered by CNTs and finally completely wrapped, and CNTs appeared as multi-walled CNTs. The interface structure of resistance welded joints and their mechanical properties were evaluated. The PEI resin was sufficiently melted and obtained a perfect bonding joint with stronger mechanical properties when tg was 2min and 3min. The cracks were found at the edge of the bonding interface and a collapse first appeared in joint when tg was 4min and 5min, respectively. The defects were caused by the accumulation of amorphous carbon at the top of the CNTs. The strength of joint welded by CFs@CNT implant increased to 37.8MPa compared with the joint obtained by pure CFs implant alone only 24.2MPa when tg was 3min. Conclusion: The purpose of strengthening the joint was achieved by improving the wettability of PEI resin on CFs@CNT lead to the CFs was fully wrapped by molten resin during welding process.

Study on the Effect of Preheating Temperature on Residual Stress in Laser Arc Composite Welding of Dissimilar Aluminum Alloys

Study on the Effect of Preheating Temperature on Residual Stress in Laser Arc Composite Welding of Dissimilar Aluminum Alloys

A review on recent developments in ultrasonic welding of polymers and polymeric composites

A review on recent developments in ultrasonic welding of polymers and polymeric composites

Experimental characterisation and statistical modelling of woven carbon fibre weld conductors for electrical resistance welding of thermoplastic composites

Resistance welding of high-performance thermoplastic composites is a promising joining technique for the structural assembly of aerospace components. Knowledge of the weld conductor resistance as a function of its dimensions, as well as external boundary conditions such as contact preparation and pressure, can be used to scale welding parameters. This paper presents a comprehensive review on the weld conductor contact preparation, length, width and contact pressure dependent resistance with respect to the Toray 5HS T300JB carbon woven prepreg 281 gsm fibre architecture. The study is based on a 4-wire resistance measurement of the carbon fibre fabric weld conductors and was conducted to provide a solid basis for defining the weld conductor’s resistance, considering the dependence on length, width and contact pressure. The experimentally determined resistance values were approximated using linear and non-linear regression functions and combined into a general formulation with respect to the investigated carbon fibre fabric architecture. The least squares fit of experimental versus model data confirmed a very high model confidence. Thus, the model allows a simplified transfer of electrical properties for process pre-design and scaling considering weld conductors with the same fibre architecture.

Rotating gliding arc plasma: Innovative treatment for adhesion improvement between stainless steel heating elements and thermoplastics in resistance welding of composites

Rotating gliding arc plasma treatment was conducted on a stainless-steel heating element (HE) for the resistance welding of carbon fiber/polyetheretherketone (CF/PEEK) thermoplastic composites. The lap shear strength of 51.7 MPa, corresponding to an improvement of 14.63 % compared to that of joints welded using untreated HE, was successfully achieved after the plasma treatment. The results of the surface characterization tests revealed that owing to the cleaning and oxidation effects, the wettability as well as the surface bonding of the HEs were remarkably improved after plasma treatment. Moreover, the reduction of void defects within the welded joints was disclosed via nondestructive inspection of cross-sections, indicating that the enhancement of HE wettability resulted in the improved resin impregnation and void elimination. Besides, according to the fractographic analysis, the main failure mode changed from the HE/PEEK interfacial damage to a CF/matrix interfacial failure, indicating that the HE/matrix interfacial adhesion was highly strengthened after plasma treatment.

Dispersion of reinforcing micro-particles in the laser welding of metal matrix composites: High-fidelity modeling with experimental characterization

Understanding the interaction mechanism between keyhole, solid phase (ceramic particles), and liquid phase (metal matrix) will offer key insights into laser welding/additive preparation of high-performance metal matrix composites. The laminar SiC particle–reinforced Al matrix composite, which is extensively used in aviation structural parts, is utilized as the experimental model. The effect of the keyhole mode on the migration behavior of SiC particles in the weld pool was revealed by simulating the multiphysical thermal fluid flow during the laser-welding process. The simulation results revealed that the flow of the molten pool and the keyhole mode have significant effects on the migration behavior of particles. The variation of keyhole mode leads to considerable changes in molten pool dynamics and corresponding SiC particle distributions in the molten pool. The observed selective distribution of SiC particles is due to the flow characteristics of the molten pool. In addition, results showed that the keyhole mode can maximize the uniform distribution of SiC particles in the melt pool, thereby addressing the nonuniformity problem of SiC particles. This work is a fundamental advancement in the modeling of laser-welded SiC particle–reinforced Al matrix composites and provides unprecedented details on the effects of keyhole patterns on weld pool dynamics. This work can further offer practical guidance for “temperature field–regulating reaction behavior” and “velocity field–regulating distribution behavior.”

Large-area joining of CF/Epoxy skin and Al alloy web by an advanced continuous resistance spot welding technology to manufacturing wind turbine blade

The large-area resistance welding of resin matrix composites and metal has always been a pursuit for manufacturing of hybrid structure. Herein, an advanced continuous resistance spot welding technology of CF/Epoxy composite and Al alloy based on multipoint sequential welding was developed, which was performed by a stainless-steel mesh implant at 0.4 MPa. A CF/Epoxy-Al alloy joint bonded was composed mainly by implant/resin and Al alloy/resin interfaces, shown a shear strength with about 17.9 MPa. Both types interfaces were analyzed and display similar results: C–O–metal bond formation at the interface is key reaction mechanism.

Laser welding of ZrO2 ceramics and 304 stainless steel with Cu/AgCuTi composite welding

In this paper, Cu/AgCuTi composite material was used as an interlayer to join 304 stainless steel with ZrO2 ceramic by + 2 mm laser offsetting and laser power of 384 W. By retaining the unmelted Cu interlayer as the diffusion barrier, the stress of the joint interface is reduced and there was no obvious crack in the whole joint. Only on the ceramic side, due to the temperature gradient, a small amount of small cold cracks were generated in the area with a thickness of 30 μm. The unmelted Cu interlayer can absorb the welding stress at the interface through plastic deformation and creep. The fracture position of the joint started from the AgCuTi-ZrO2 ceramic bond interface and extended to the ZrO2 ceramic surface with a maximum tensile strength of 83 MPa.

Numerical simulation and experimental study of residual stress in dissimilar aluminum alloy laser composite welding

The study combined experimental and numerical simulation methods to investigate the distribution of residual stress in laser composite welding of dissimilar aluminum alloys 6063 and 5083. Using the Simufact Welding simulation software and a combined volume heat source, the distribution patterns of transverse and longitudinal residual stress fields at different welding speeds were analyzed. The blind hole method was used to test the residual stress after welding. The results showed that the use of a combined volume heat source model for heat source calibration yielded ideal results, and the thermal cycle curve was basically consistent with the simulation and experimental results of residual stress. As the welding speed decreased, the longitudinal residual stress of the parent material on both sides significantly decreased, while the transverse residual stress increased. The majority of tensile and compressive stresses on both sides of the 5083 and 6063 aluminum alloys decreased with a decrease in welding speed. The Von Mises equivalent stress indicated that the cooling process is the main stage for residual stress generation. When the welding speed decreased, the peak value of longitudinal residual stress on the 6063 aluminum alloy side decreased from 230 to 90 MPa, while that on the 5083 aluminum alloy side decreased from 304 to 150 MPa. These findings provide an important basis for controlling and reducing the residual stress and deformation of dissimilar aluminum alloy laser arc composite welded components.

Composite welds reinforced in volume with lanthanides

Under the conditions of dynamic impact of high‑speed clusters of powdered micro‑particles on the volume zone of welding between 110G13 and St.10 steel plates, longitudinal strengthening channel elements are formed, and rare earth elements such as lanthanum and cerium are also synthesized.

Investigating the Effect of Interface Temperature on Molecular Interdiffusion during Laser Transmission Welding of 3D-Printed Composite Parts.

The present study investigated the influence of temperature on molecular interdiffusion at the interface during the laser transmission welding of 3D-printed continuous carbon-fiber-reinforced thermoplastic composites. In order to accurately measure the temperature at the weld interface, a series of thermocouples were embedded in the laser-absorbent composite part. Two different molecular interdiffusion models were implemented to calculate the degree of healing and to predict the effects of temperature on the welding process. The degree of healing and the weld line width were computed and compared with microscopy observations. The discrepancy between the two proposed numerical models was less than 6%. Both models showed good agreement with the experimental data, with an average error of 13.28% and 7.26%, respectively. The results revealed a significant correlation between the thermal history and molecular interdiffusion at the interface. Furthermore, the relationship between the welding parameters (laser beam scanning speed) and weld line width was established. The findings of this study provide a comprehensive understanding of the underlying mechanisms involved in the laser welding of 3D-printed composites and offer insights to optimize the welding process for enhanced weld quality and superior mechanical properties in the final product.

L12-(Al,Si)3Ti + TiC hybrids reinforced laser welded SiCp/2A14Al joint with extraordinary strength

The interfacial reaction 3SiC + 4Al → Al4C3 + 3Si has bottlenecked the fusion welding of aluminum matrix composites for decades, hindering further improvement of the mechanical properties of high-strength lightweight SiCp/Al joints. Using unweldable SiCp/2xxxAl as an experimental model, we designed a targeted reinforcing phase that can be alloyed in situ with Si and C elements. L12–(Al,Si)3Ti and TiC were generated in situ from Si and C precipitated from SiC particles. In addition, the in situ-formed Al3Ti adhered to the surface of the SiC particles, enhancing the load transfer of the alloy film during the tensile process. The mechanism of titanium on the joint grain nucleation and refinement and the contribution of each strengthening mechanism to mechanical properties were discussed in detail. Quantitative calculations showed that the combined effects of the nanoscale TiC phase (Orowan strengthening) and high density of the geometrically necessary dislocations (dislocation strengthening) increase the yield strength of the joints. The ultimate tensile strength of the joint was 393 MPa (with a strength coefficient of 83%), which was highly comparable to that of SiCp/Al joints prepared by friction stir welding. This work provides fundamental guidance for the welding of high-strength SiCp/2xxxAl alloy.

Effect of process parameters on surface quality and bonding quality of brass cladding copper stranded wire prepared by continuous pouring process for clad

Brass cladding copper stranded wire with an outer diameter of 10 mm and core material of d2.12mm × 7 strand was prepared by solid-liquid composite method with continuous pouring process for clad. Compared with the cladding welding method which requires multiple drawings to make the composite welding wire achieve metallurgical bonding, it saves a lot of manpower and material resources and shortens the production cycle. The bonding mechanism of brass and copper was analyzed by experiments, meanwhile, the effects of brass melt temperature and casting speed on the surface quality and interface bonding quality of the composite wire were investigated. The results show that, on the one hand, increasing the melt temperature of brass and reducing the casting speed can inhibit the surface defects of the composite. On the other hand, reducing the temperature of the brass melt and increasing the casting speed can inhibit the excessive element diffusion at the bonding interface, thereby reducing the degree of surface erosion of the copper strand. The final reasonable process parameters are as follows: the brass melt temperature is 970 °C–990 °C, the traction speed is 40 mm/min∼80 mm/min, and the cooling water volume of the crystallizer is 450L/h. The prepared brass cladding copper stranded wire has good quality, Vickers hardness is between 80 - 85HV, and tensile strength is between 265 - 297 MPa. Elongation after fracture is 40.3%∼43.9%, conductivity is 53.8–62.1% IACS.

Microstructure evolution, interface and mechanical properties of SiCp/2A14 joint during laser keyhole welding

Welding problems have restricted the applications of lightweight SiCp/Al composites in aerospace. In this work, the controllability of the keyhole mode, nucleation mechanism, and mechanical properties of the laser-welding process are studied in detail. The extrusion effect formed by the open keyhole pushes SiC particles to the bottom of the molten pool. To observe the nucleation and growth mechanism of the Al4C3 of keyhole laser-welded SiC/2A14Al composites, the dissolution–precipitation behavior of the SiC particles and growth behavior of the Al4C3 tip were observed. Owing to its high chemical properties, Al4C3 mainly begins nucleating from the open edges of the SiC particles and its formation is mainly distributed along the direction of Al grains. Al4C3 was the main crack source and propagation path while the small-sized SiC particles hindered the crack propagation. This work innovatively regulates the keyhole mode to achieve ‘small damage breakdown’ laser welding, greatly reducing the volume fraction of Al4C3. It also provides new insight into fusion welding of SiC particle-reinforced Al matrix composites.