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•Natural fiber composite products need a fast joining method i.e. ultrasonic welding.•Different energy directors shape (triangular, semicircular and cross) were employed.•Heat ...generation mechanism for joining of NFRCs is also explained in details.•Load bearing capacity was analyzed at four different levels of welding parameters.•Cross energy director performed better at optimal level of welding parameters.
Joints are an integral element of any product and a source of failure under different loading environments. The current experimental investigation explores in detail the ultrasonic welding behavior of banana fiber/HDPE composites. The effect of fiber loading, type of energy directors and process parameters has been investigated on the mechanical and thermal behavior of the welded joints. The comparative assessment has been supported by the results of the dynamic mechanical analysis and the thermal conductivity of the fibers and HDPE. The mechanism of heat generation during welding process has been discussed. The TGA, DTG, DSC and FESEM analysis has been performed to substantiate the results. Composite adherends welded at optimum level of welding parameters with cross energy director profile depicted better load bearing characteristics. The short fibers also participated in the diffusion mechanism during welding. TGA and DTG results showed no significant effect on thermal stability of composites post welding.
The microstructure, hardness, lap shear strength and fracture energy of AA2139–TiAl6V4 spot joints produced by ultrasonic welding were investigated and related to the weld thermal cycle. No obvious ...intermetallic reaction layer was observed in the AA2139–TiAl6V4 welds, even using transmission electron microscopy. The hardness profile of AA2139 side after welding was studied, demonstrating that the heat introduced by the welding process leads to some softening with partial hardness recovery after natural aging. The effects of welding time on peak load and fracture energy were investigated. The peak load and fracture energy of welds increased with an increase in welding time and then reached a plateau, i.e., maximum peak load 5.3kN and maximum fracture energy 3.7kNmm. In all cases, failure occurred by fracture at the weld interface.
Ultrasonic welding additive manufacturing (UWAM) enables the production of metallic components by forming metallurgical bonds between superimposed thin foils using continuous ultrasonic welding. The ...aluminum alloys that were considered in this study were AA5005 (0.8%-wt. Mg), AA5052 (2.4%-wt. Mg), and AA5056 (4.9%-wt. Mg). The influence of Mg content on UAM was investigated with respect to the following criteria: microstructural changes in welded foils, ultrasonic welding energy, geometry of the joints, and tensile properties along different building directions. Joint resistance was found to be correlated to the ultrasonic welding energy input, where the dominant parameters are temperature, welding speed, and the amplitude of vibration. Energy can be raised by decreasing the welding speed or by increasing the amplitude of vibration leading to better joint properties but reducing tensile properties in the two other orthotropic directions of the build. The aluminum components built by AM were characterized with having anisotropic tensile properties due to the process itself and the strain hardening of the foils during fabrication. When comparing tensile results with those of the base material, optimum tensile properties in the longitudinal direction (X) are 5% higher, identical in the transverse direction (Y), and 55% lower for specimens sampled along the direction of deposition (Z). Depending on the orientation of the tensile specimens with regard to the deposition direction (Z), strain at rupture was 25% in the X-direction and 7% along the Y-direction. No specimens could be adequately built using AA5056-H38 foils. Characterization of the few joints that could be produced showed that this behavior was due to the presence of a significant amount of Mg oxide at the interface of neighboring foils paired with a drastic increase of hardness compared to what was measured for the other alloys.
Aluminum and steel are widely used in automotive and aerospace industries. As a new type of solid-phase welding, ultrasonic spot welding is an effective way to achieve joints of high strength. In ...this paper, ultrasonic welding was carried out on aluminum-steel dissimilar alloys to investigate the influences of welding parameters on joint strength. Designed and conducted a 3-factor, 3-level comprehensive test. The analyses of test results show that there are 3 kinds of fractures on the welding joint with different welding parameters. The highest strength can reach 3910N. Clamping force and vibration amplitude not significantly impact the tensile strength. Vibration time significantly impact the tensile strength although its significance level is close to the threshold. The interaction between welding parameters all can significantly impact the tensile strength. The artificial neural network optimized by Genetic Algorithm was used to establish an analytical model. The supplemental experiment and residual analysis were conducted to verify the accuracy of the analytical model. The analytical model show that with the increase of clamping force, the changes of optimal and minimum strength are limited, but the range of welding parameters to obtain a higher strength change significantly; the optimal welding parameters from lower vibration amplitude and higher vibration time shifts towards to higher vibration amplitude and shorter vibration time gradually; for 0.3Mpa clamping force, the influences of vibration amplitude and vibration time on tensile strength are not significant.
The processes of ultrasonic spot welding and ultrasonic additive manufacturing are modelled by approximating the weld interface as rough metallic surfaces in sliding contact. It is assumed that ...bonding is due to athermal plastic deformation of surface asperities and the associated growth of metallic junctions along the weld interface. To link the process variables and the extent of junction growth, an expression for the real contact area at the weld interface is combined with process-specific frictional heating models developed here. The resulting framework is validated by comparing its predictions of the weld strength with data from the ultrasonic welding literature. The close agreement between the framework's predictions and the experimental data demonstrates that the surface asperities soften due to frictional heating, while acoustic softening effects are insignificant. The junction growth model is used to identify parameter sets for ultrasonic spot welding and ultrasonic additive manufacturing that maximize the weld strength while simultaneously minimizing the thermal excursion at the weld interface. It is found that in ultrasonic spot welding, certain processing conditions can cause interfacial melting, although melting is not required to form strong bonds. It is also shown that in ultrasonic additive manufacturing, the deposition rate is highest when the positions of the peak temperature and complete interfacial bonding coincide underneath the sonotrode. If the position of complete interfacial bonding leads the position of the peak temperature, there is excessive heating of the build, and the sonotrode velocity can be increased without degrading bond quality.
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This paper presents an approach to evaluate the local distribution of lap shear strength in the joining zone of ultrasonically welded single lap joints of aluminum and fiber-reinforced ...thermoplastics, which also show a sufficient resistance against ageing or galvanic corrosion. Both the characteristics of the process and the microscopic evaluation of the fracture surfaces suggest that the strength is distributed inhomogeneously over the joining area and is composed of adhesive and cohesive fractions. For this evaluation, two procedures were developed to subdivide the joining zone into sections and to investigate them separately. Subsequently, a local strength distribution in the joining area can be determined using mathematical operations. With the help of this interpretation, different bonding mechanisms can be identified and assigned. Additionally to mechanical investigation, Finite Element simulations were used to calculate the stress distribution of the joints depending on the carrying cross section to validate the experimental data. Despite the change of the geometry e.g. due to drilling, the calculated stress distribution pattern did not change.
The welded joints of copper (Cu) to aluminum (Al) were increasingly being used for electric vehicle battery applications. To better understanding the interface connection mechanism of the Cu/Al ...joints produced by high power ultrasonic welding (HUSW), the texture and intermetallic compounds of Cu/Al HUSW joints were systematically investigated. The grain morphology and size of pure copper along welding interface had little change with the increasing welding time, whereas the microstructure of aluminum alloy changed from elongated grains to equiaxed grains and the grain size increased rapidly at the welding time from 0.3 s to 0.5 s. The texture intensity of both copper and aluminum alloy decreased at first owing to ultrasonic softening and then increased due to the shear work hardening. The texture type of the copper had little change, whereas the gaussian texture {110}〈110〉 and the cubic rotation texture{001}〈110〉 were formed in aluminum alloy owing to the occurrence of recrystallization driven by the severe shear deformation. The formation mechanism and accelerated growth behavior of intermetallic compounds at the welding interface during HUSW were discussed based on the atom rapid diffusion and the effective thermal formation model.
Although high-power ultrasonic welding (HPUSW) can provide better welding results about highly conductive materials, the welding mechanism is not well understood. In this study, the effects of ...welding pressure on dynamic process and joint characteristics (strength and fracture) of HPUSW were investigated. High pressure produces lower vibration amplitude of the upper and bottom specimens. Under excessive pressure, the vibration amplitude of sonotrode is significantly reduced, as compared to that under lower pressure during the initial welding period. The distribution of plastic strain follows the principle of crack growth and expansion. Excessive pressure results in the extrusion of trace elements from base material to the interface, which affects the process of interfacial diffusion. The maximum welding strength is obtained as the depth of penetration of sonotrode reaches its maximum value without the production of cracks. The results obtained in this work provide guidelines for optimizing the ultrasonic welding parameters.
Electrochemical devices such as batteries, fuel cells, and capacitors employing a carbon nanotube (CNT) electrode can be improved by lowering the contact resistance between CNTs and metallic ...contacts. The current work investigates two simultaneous strategies to enhance the contact by using chemical doping of CNTs with potassium tetrabromoaurate (KAuBr4) and ultrasonic welding to a metal foil. The specific contact resistivity was measured using the transfer length method (TLM) to evaluate CNT test structures having ultrasonically welded Cu contacts with and without KAuBr4 doping. Purified CNT-Cu samples had a specific contact resistivity of 5.4 mΩ cm2, whereas the KAuBr4 doped CNT-Cu samples were 2.2 mΩ cm2. Confirmation of selective doping to the weld region was made using measured differences in the emissivity of purified and KAuBr4 doped CNTs, which were 0.84 and 0.56, respectively. The lower contact resistance from KAuBr4 doped CNT-Cu ultrasonic welds also reduced the extent of Joule heating beyond the contact region when applying increasing current to failure in a 2-terminal test structure. The benefit of selectively doped CNT-Cu welds was demonstrated across rectangular ribbon and electrode form factors up to an area of 6 cm × 8 cm (typical of electrochemical pouch-cell current collectors). Each form factor showed a 1.5× reduction in peak temperature when selective doping of the CNTs was performed prior to ultrasonic welding of the Cu contact. Thus, the combination of selective doping and ultrasonic welding demonstrates a viable method to fabricate low electrical resistance between CNT electrodes and metallic contacts for electrochemical devices.
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•Novel ribbons with geometrically spaced tabs (RGT) yield comparable specific contact resistivity to standard TLM geometry.•RGT TLM structures enable assessment of selective CNT doping and Cu welding on specific contact resistivity.•Spatially identify dopant location using thermal imaging based on emissivity differences of purified and KAuBr4 doped CNTs.•Selective CNT doping and Cu welding reduces Joule heating beyond the contact region and is scalable in large area designs.
A glass fiber/polypropylene semi-impregnated lamina was added to an epoxy laminate, prior to the resin infusion, to overcome its limited weldability. Ultrasonic welding of the hybrid composite was ...conducted by varying welding pressure, time, and vibration amplitude, and using the thermoplastic layer as adjoining surface. Welded joints were analyzed by visual inspection, X-ray tomography, and lap shear testing. Welding time significantly influenced the lap-shear strength, the weld interface quality, and the process stability, promoting the proper intermixing of the thermoplastic layer and the formation of a weld area with strong adhesion. Amplitude and pressure, on the other hand, mostly affected the power absorption. Lower pressure, intermediate amplitude, and longer duration led to an improvement in the lap-shear strength (approximately 5 MPa in the best case). High strength was linked to high exposed-fiber surface area in the fracture surface, while its reduction was attributed to the presence of unwelded areas within the polypropylene interface. X-ray tomography highlighted the correlation between the occurrence of defects in the weld interface and the power profiles, where multiple peaks indicated the material friction and a progressive intermixing of the polymeric interlayer, while flattened profiles and lower peaks are associated to discontinuous and poorly adherent interfaces.
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