Joining Process Research Articles

Effect of Layers on Delamination and Tensile Strength of Woven Fiber Composites with Polyester Matrix

A composite is a combination of 2 or more different materials. The composite joining process can use adhesives or mechanically by making holes. During the process of making holes in the composite, it can cause delamination in the composite. Delamination and layer thickness greatly influence the strength of hollow composite joints. This research aims to determine the effect of delamination factors and the number of layers on the tensile strength value of the composite. The materials used in this research are polyester resin and woven glass fiber. The method used is vacuum bagging with variations in the number of layers, namely 3 layers, 4 layers, 5 layers, and 6 layers. Tensile testing refers to ASTM D638 standards. Specimens that have been cut according to standards will then be perforated in the center with a hole diameter of 4 mm using a milling machine. The highest tensile strength value was obtained in the 6-layer variation of 237.448 MPa and the lowest value was obtained in the 3-layer variation of 186.221 MPa. The delamination value greatly influences the tensile strength of the composite, where the more layers, the delamination value will decrease and increase the tensile strength of the composite.

Extraction, modeling and impact analysis of porosity defects formed in the CFRTP/Al6061 laser direct joining process

AbstractThis study focuses on the influence laws of porosity defects on the performance of the joint formed in the CFRTP/Al6061 laser direct joining process. Image extraction and finite‐element modeling methods are introduced to investigate the porosity defects, so that the model of joint with porosity defects of real characteristics is established. With the model, the failure process of the joints formed under different laser direct joining processes are analyzed, and the change law of the maximum failure displacement and the maximum failure load of the joints are revealed. The maximum error is within 17%. Results suggest that if and only if the porosity defects are distributed in the zone of the joint with the biggest stress under load, the defects will significantly decrease the maximum failure load of the joint; otherwise, the porosity defects will facilitate the cracking propagation process after the joint failure, thereby decreasing the maximum failure displacement.Highlights Porosity defects are identified from CFRTP background by image extraction. Local porosity is defined to illustrate the real distribution of defects. Joints with defects distributed by real characteristics are modeled. Max failure load hinges on relative position of defects and max stress zone. Porosity defect quantity influences cracking propagation rate after failure.

Investigation on the joining process and strength of laser circle welding between Al5052 and CFRP dissimilar materials

Laser welding is an effective approach to joining metal and composite. In the present research, laser circle welding was proposed to join the Al5052 sheet and PA6-CFRP as the first try. A process window was suggested according to the welding results and joint appearance. Single lap shear test was employed to evaluate the mechanical performance of welded joints under different welding conditions. The cross-section and fracture surface were subjected to multi-scale characterizations to subdivide the joining zone and understand the joining process. The result showed that 10 sets in 18 groups of welding parameters can achieve successful bonding. The welding results can be classified into four categories: non-connected, aging-failing, effective-joining and burn-through. The joining zone of laser circle welding was divided into three subregions. The adhesive zone (AZ) presented an interfacial fracture while the local failing passed through plastics basement in cohesive (CZ). The overheating of CFRP generated decomposed zone (DZ). The signal peak of O-C=O bond disappeared in the entire joining zone on CFRP sheet and the intensity of carbide was significant in DZ. The laser circle welded joint presented brittle and ductile fracture modes, which were related to the joining zone component. The joining strength can reach about 656 ± 22 N, 2135 ± 331 N and 3223 ± 257 N under one-circle, double-circle and three-circle scanning, respectively. Increased scanning numbers can decrease the required laser power and improve joining strength by extending heating time, while it also increased the risk of burn-through.

Influence of the process time on a self-piercing riveting process with tumbling kinematic

The increasing significance of ecological responsibility, stricter political regulations and economic objectives are driving innovation in research fields such as lightweight construction. One of the most important popular methods is the use of multi-material systems. Due to the different geometric and mechanical properties of the various materials used, resource efficient applications and utilizations are possible. Great challenges arise for the joining processes to realize these multi-material systems, since conventional joining processes reach their limits. In the field of mechanical joining processes, there are continuously new approaches, such as superimposing the punch in a self-piercing riveting process with a tumbling kinematic, to increase the number of adaptable process parameters and enhance the process control. Through various preliminary tests, a good understanding of the process has been developed, which allows to directly control the geometric joint parameters by configuring the tumbling strategy. A major challenge, particularly with regard to future industrial applications, is the process time, which is comparatively high due to the tumbling kinematics. In the investigations, a reduction of approximately 90% of the process time is targeted by adapting the joining and tumbling strategy. Therefore, the correlation of the traverse velocity and the tumbling velocity are examined in a gradual series of experiments. To represent realistic applications, the experiments are carried out with a dual-phase steel and a precipitation-hardening aluminum alloy. For identifying the influence of the process parameters on the joining process, a constant rivet–die combination is applied. Further, the examination of force–displacement curves is conducted. Moreover, the determination of geometric joint parameters is reliant upon macrographs to assess the influence of the joining time on the geometric joint formation. The test results show that a significant increase in joining speed with a resulting reduction in process time is feasible. Although the joining properties are affected, reliable joining is possible. In particular, the shaft thickness of the rivet is influenced by the varying proportion of the tumbling process in the joining operation and increases with higher joining speeds.

Influence of interfacial micro-textures on CFRTP-TC4 hybrid joint formation with laser assistant joining technique

To investigate the influence of interfacial micro-textures on the carbon fiber reinforced thermoplastic composites (CFRTP)-TC4 alloy hybrid joint formation process, a finite element model with micro-textures was established. The joint formation mechanism and the impact of joining parameters on heat input were analyzed. The results show that the existence of interfacial micro-textures will lead to an uneven distribution of the temperature field on the surface of polyamide and reduce the heat transferred to the surface of CFRTP. And, mechanical interlocks and new chemical bonds are generated in the joining process because of these micro-textures, which enhances the joining strengthen significantly. The optimized joining parameter window was also obtained and the joining strength was predicted by numerical simulation. With the numerical assistant, the CFRTP-TC4 joint with highest shear strength was obtained as the laser power and the welding speed is 130 W and of 2 mm/s, respectively.

Shear properties and failure mechanisms of adhesive bonded composite joint: Effect of glass particle reinforcement

AbstractHigh‐performance composite structures and effective joining processes are important for shipbuilding, and aerospace sectors to perform better in challenging situations. The importance of this study is to analyze the effect of glass powder‐modified adhesive and joining techniques such as co‐curing (CC), co‐bonding (CB), and secondary bonding (SB) on flexural, shear, and free vibrational characteristics such as natural frequency and damping factor for glass fiber‐reinforced polymer (GFRP) composites. Results revealed that, compared to SB and CB composite joints, 1 wt.% glass powder‐modified CC composite single lap joints (SLJ) enhanced the shear properties by 103.04% and 111.74%, respectively, due to rougher surface formation in the adhesive layer. As a result, it enhanced the fiber's adhesion to the matrix. On the other hand, CC bonded joints with 1 wt.% of glass powder exhibited the highest flexural strength (85.99 Mpa). The experimental free vibrational analysis showed that 1 wt.% glass powder CC composite had a high natural frequency, whereas higher wt.% glass powder increased the damping properties due to the matrix and fiber interaction. The current research reveals that CC technique with 1 wt.% of glass powder provided a significant improvement to the adhesively bonded composite's mechanical and free vibrational characteristics.Highlights Four distinct wt.% of glass powder were used to prepare the glass powder‐modified adhesive by sonication. SLJ glass fiber‐reinforced polymer composite joints were fabricated through CC, CB, and SB techniques Maximum shear and flexural strength were found at CC SLJ 1 wt.% glass powder. CC SLJ 1 wt.% glass powder enhanced better vibrational behavior. Failure surface analysis was conducted using FE‐SEM images.

Fatigue and failure behaviour of friction welded steel joints under normal and shear stresses

Rotary friction welding is a fast and efficient joining process with the possibility to join materials that are not weldable by conventional GMAW-processes. If done properly, the welds have a static and fatigue strength higher than the base material. However, in literature, there exists only sparse information on the design and assessment of these joints in terms of fatigue. The fatigue strength of two material combinations, S355-S355 and S355-1.4301, is investigated based on two specimen conditions, (1) with flash and (2) with flash mechanically removed. In the majority of tests, failure occurred outside the weld zone, in the base material. The derived endurable nominal stresses are compared to the design S-N curve of conventionally welded specimens and show a more than 50% higher fatigue strength.

Effect of Short-Fiber Orientation on the Tensile Strength of Epoxy Adhesives

Short-glass-fiber-reinforced adhesives are state-of-the-art materials used in the bond lines of wind turbine blades. Various alignments of the short fibers are emerging, which depend on the adhesive flow during the application and joining processes. This induces a spectrum of direction-dependent mechanical properties. The tensile strength, for instance, can vary by about 20% depending on the load direction. Therefore, the adhesive performance, which is normally determined under controlled laboratory conditions and implemented in bond line design routines, can deviate from the in situ application. This work investigates the effect of the short-fiber alignment on the tensile strength distribution of an industry-standard adhesive used in wind turbine rotor blades. The smeared short-fiber orientation of the tensile specimens tested is estimated locally near the damaged surface using a material model that is fed with thermomechanical measurements and calibrated via micro-computed-tomography analysis. A linear correlation between tensile strength and short-fiber alignment has been identified. This augments the identification of the material’s upper and lower strength limits for bond line design purposes.

Influence of workpiece geometry and natural frequencies on ultrasonic metal welding

Ultrasonic metal welding is a well-established solid state joining process for electrical applications. The process relies on the friction between workpieces and welding tools for joint formation. This friction is generated by the process force and the ultrasonic oscillation of the welding tools imposed on the workpieces. At such high frequencies, the occurrence of resonances in actual workpiece geometries is not surprising. It is known that critical dimensions in length and width lead to nearly no bond, depending on the welding frequency and the mechanical properties of the material. In real applications, this limits the possible designs of terminals and leads to extensive testing of clamping devices. It is also known that machine learning (ML) models for quality prediction based on power signals or tool oscillation can account for changes in welding position. In this study, we investigated the impact of part resonance and antiresonance on horn and anvil oscillation, power consumption and bond strength to identify typical behaviors induced by the workpieces. The influence of material thickness and roughness was considered, and numerical analysis of the natural frequencies of the workpieces was conducted. It can be shown that the results allow a distinction between the welding positions and workpiece geometries without directly measuring the oscillation patterns of the workpieces, allowing a simple validation of geometry weldability and clamping device in applications. Furthermore, the investigation allows the knowledge based specific deduction of signal parameters for future ML models, allowing a consideration of welding position and workpieces geometry with reduced test data.

Metallurgical characteristics of aluminum-steel joints manufactured by rotary friction welding: A review and statistical analysis

Rotary friction welding (RFW) is a solid-state joining process that can be used to join different alloy systems such as aluminum-steel alloys. Rotary friction welding has become increasingly appealing for various industries due to the sustainable advantages that it offers, including overall cost reduction, weight minimization, and unique properties. However, the formation of brittle intermetallic compounds (IMCs) at the interface can be a challenge in the welding process of aluminum-steel alloys. This paper reviews the metallurgical characteristics of aluminum-steel alloy joints manufactured by rotary friction welding. The different types of intermetallic compounds that can form at the interface, as well as the factors that affect their formation, are discussed. The effects of rotary friction welding parameters on the microstructure and mechanical properties of the joints are also presented. Specifically, minimizing interfacial reaction layers via post-weld heat treatment and controlling the heat input during the process is crucial to suppressing the formation of intermetallic compounds. This study employed artificial intelligence modeling, specifically the artificial neural network - multilayer perceptron, to investigate the effect of various parameters on the ultimate properties of the parts welded together. Overall, this paper provides an excellent resource for industries looking to embrace rotary friction welding to tackle the challenge of dissimilar Al-steel joining.

Evaluation and optimization of textile ultrasonic welds for textile temperature control elements using transient thermal numerical analysis

Ultrasonic welding is an efficient method of joining thermoplastic fabrics or other textile semi-finished products in a watertight manner. It is applied in the making of functional clothing, such as chemical protective clothing, sportswear or smart clothing, or other technical products. Another special field of application developed at the Chair of Development and Assembly of Textile Products is the use of coated textiles as temperature control elements. For this type of product, it is necessary to design the ultrasonic welds in such a way that the media-tight coating is not damaged and the joint is continuous. This paper presents the option of evaluating and optimizing the ultrasonic welding process for the production of the textile tempering systems using transient thermal analysis in order to improve the overall quality of the seam and ensure media tightness along the seam.
 In the following article, the status of the welding process, in particular the ultrasonic process, the textile materials, the heating of the textile and the joining process of welding is presented. In addition, the transient heat flow through the textile is investigated with the aid of FEM methods; taking into account, various seam structures.

In-situ observation of molten brazing filler metal permeating gap

Generally, brazing is completed when the brazing filler metal permeates the gap by uniform wetting. It is believed that the joining process is completed with the formation of joint defects ‘voids’ in the process of uniform wetting. However, previous studies have shown that what occurs when brazing is performed is non-uniform wetting. It is suggested that this non-uniform wetting is the cause of void generation. Wetting and spreading of brazing filler metal is tested on a metal plate, as described in JIS Z 3191. This is used to investigate the wetting of the brazing filler metal. However, this method does not cover the wetting of the molten brazing filler metal as it moves into the gap. Therefore, it is suggested that the JIS Z 3191 experiment is insufficient to evaluate the wetting of the molten brazing filler metal that penetrates into the gap. In this experiment, we created new specimen. It is called us ‘V-groove specimen’. Specimens were created with two base metals. They are pure copper and lead-free brass in which bismuth was used as an alternative element. In order to do in situ experiments, it was not possible to observe the inside of a conventional electric furnace. Therefore, we produced a furnace with a window for in-situ observation and experimented with it. As a result of experiments with V-groove specimens, it was found that there are two types of wetting of brazing filler metal. They are called ‘primary wetting’ and ‘secondary wetting’. The shape of the specimen was measured and evaluated for two types of wetting. The results showed that the primary wetting was measurable in shape and spread evenly. However, the shape of the secondary wetting could not be measured, and it was found to be non-uniformly spread.

Controlling the weld penetration depth of laser beam micro welding by using an iterative learning approach

AbstractIn order to meet the increasing demand for high‐speed joining processes, laser beam micro welding is used to reproducibly weld metallic joining partners such as steel. Long weld seams or high cycle speeds, however, remain a challenge to achieve a constant welding depth throughout the entire welding process without major fluctuations. This paper shows the development and evaluation of a weld penetration depth control system based on interferometric measurement of the depth of the vapor capillary. High path speeds and small weld depths are challenging for real‐time depth control. Therefore, the offline data of the interferometric measurements are used to implement an iterative learning control of the weld penetration depth. The quality of the control is verified by welding with and without spatial power modulation on 1.4301 steel while following a linear and sinusoidal trajectory.

DEVELOPMENT OF FRICTION STIR WELDING TOOL FOR HIGH-DENSITY POLY-ETHYLENE (HDPE)–CASE STUDY: FIBERGLASS COMPOSITE MATERIAL

This study aims to develop an effective Friction Stir Welding (FSW) method for composite material of High-Density Poly-Ethylene (HDPE) Pipes. The development of welding tool, there was the addition of an external heating source on the shoulder and probe/pin to overcome the problem of lack of heat resulting from friction between the tool and the material to be welded. The case study was conducted to join the short fiberglass-HDPE composite with a type of ratio of 30% by weight of short fibre and 70% by weight of HDPE, which optimizing parameters such as rotating speed, welding speed, and preheating temperature. The FSW joining process for short fiberglass-HDPE composite sheets was carried out using a Fanuc Series 21i-M CNC milling machine as the driving tool with rotational speed (ω) varied in 3 conditions, namely 600 rpm, 800 rpm and 1000 rpm, and welding speed (v) or feeding at 5 mm/minutes and 10 mm/minutes. The temperature was controlled according to the liquid point of High-Density Poly-Ethylene, which was 130oC, and raised to 150oC and 170oC. The 12 pieces of thermocouple were used along the track on the material and jig plates at the top, middle and bottom. Then, the results of joining the sheets were made in the form of specimens with sizes according to ASTM 3039. The tensile tests of the specimens were carried out at a rate of 0.01 mm/s. The results showed the highest tensile strength was an average value of 24.52 MPa at a rotational speed of 800 rpm, the feeding of 5 mm/min and the temperature of 130oC. The lowest tensile strength was an average value of 17.54 MPa at a temperature of 170°C with a speed of 600 rpm.

Towards Practical Oblivious Join Processing

Towards Practical Oblivious Join Processing

Abnormal rapidly homogenized joining of aluminum alloys through a cross-scale diffusion

Rapidly homogenized joining has been a longstanding pursuit in the forming manufacturing of lightweight alloys structures. In this study, ultrasound energy was introduced into the joining process to accelerate cross-scale diffusion (direct grain migration rather than atomic-scale diffusion), and a homogeneous 6063Al joint was fabricated using a Zn-40Sn alloy at 360 °C in air. The network architecture joint composed entirely of α-Al grains was formed with a sandwich structure consisting of Sn@Al2O3/MgO as the grain boundary. The tensile strength of the joints was higher than that of the base metal in only a very short diffusion time (180 s). Physical effects of ultrasound in the Sn-Zn molten metal induced violent intergranular penetration, resulting in the decohesion and migration of the α-Al grains from the base metals and realizing a rapidly homogenized joining. This provides a foundation for full-strength joining of high-strength aluminum alloys with low thermal damage.

Simulating chemical mixing and molten pool shape in dissimilar welds using thermal fluid dynamics

Estimating the properties of dissimilar metal welded joints made using modern high-energy beam techniques presents significant challenges due to the complex nature of the process. These complexities arise from the different thermal and mechanical properties of the materials involved. The properties of a welded joint are primarily determined by the element mixing and final chemical composition when two dissimilar metals are fused together, or when a dissimilar filler material is used. Hence, a representative model capable of tracking elemental distribution and temperature is essential for accurately estimating the micro-scale and macro-scale mechanical properties of the joint, thus optimising the joining process. In this work, a high-fidelity thermal fluid flow model in the multiComponentlaserbeamFoam computational fluid dynamics (CFD) solver is used to simulate the process of laser beam welding. For this purpose, the joining process of AISI 304 stainless steel with a low alloy steel filler material (G3Si1) is simulated. This framework is rigorously validated with experimental results showing the capabilities of such modelling approach. Different strategies to model the filler and material properties are explored: a stationary filler model, applied through the parent material's thickness, was found to accurately mirror experimental results. This model is then used to study the flow properties, thermocapillary effect, and diffusion on the intermixing of composition, aspects that have not been previously examined in depth. The thermocapillary forces were concluded to be the most significant, dictating the peak composition value, the shape and topology of the molten pool. Diffusion fluxes were found to be negligible and not responsible for the majority of the mixing.

Understanding the formation mechanism of SiC/Al joints by U-TLP bonding with the inactive Zn interlayer

The ultrasonic-assisted transient liquid phase (U-TLP) bonding process is extremely fast, which is a great challenge to reveal the inherent mechanisms. Understanding the joint formation mechanism of U-TLP is essential for the joining process design. In this study, the SiC ceramics and 6063Al alloys were joined by U-TLP using a Zn interlayer. The process of removing the oxide film on the base metal involved cracking, flaking off, suspending, and fragmenting. The migration of the eutectic liquid phases frontier was very fast (within 1 s). The relationship between the thickness of the liquid layer and the ultrasonic action time was a power function. The typical microstructure of the SiC/6063Al joints was SiC/amorphous Al2O3/Zn-Al eutectic/ Zn-Al eutectoid/6063Al. The shear strength of SiC/6063Al joints increased with the interfacial bonding ratio and reached up to 27 MPa for the ultrasonic action time of 5 s. The metallurgical bonding at the SiC/bond metal interface was formed through the amorphous Al2O3 transition layer. The formation mechanism of the Al2O3 reaction layer was revealed based on the thermodynamics, kinetics, and acoustics cavitation theory. This will provide a guideline for the future U-TLP process design.

The Energy Consumption of the Process of Joining Steel Sheets with the Use of Clinching With and Without an Additional Rivet, and Analysis of Sheet Deformation and Mechanical Strength of Joints

This paper presents the results of research on the impact of the use of different tools and the shape of the additional rivet, on the geometric quality of the joint, the energy consumption of the forming process, the distortion of the steel samples, and the load capacity of the joints. The tests were carried out for DX51D steel sheets with a thickness of 1.5 [mm] joined by using three different sets of tools. A steel rivet with a hardness of 400HV1 and various shapes was used for the tests. In addition to the full rivet, two types of rivet were used, the first with a through hole and the second with a depth of hole of 3 [mm]. The holes in the rivet had different diameters: 1.0, 1.5, 2.0 and 2.5 [mm]. The influence of changing the shape of the rivet (hole and its diameter) on the change in forming force and energy consumption of the joining process was analyzed. The lowest forming force was achieved for a rivet with a through hole and a hole diameter of 2.5 [mm]. The lowest joint forming force was obtained for the die with movable segments. For joints made with three tool arrangements and a series with a modified rivet, the amount of sheet metal deviation was analyzed. Of the three cases of arrangement of tools used to form the joint, the largest deviation of the sheets occurred at the clinch joint formed with a solid round die. In the case of a series of clinch-rivet joints with a modified rivet, the greatest deviation of the sheets occurred for the rivet with a hole of 1.5 [mm]. Changes in the geometric structure of the joint were also studied, and changes in the surface of the sheets in the joint area were observed. The highest value of the interlock in the joint was obtained when a solid rivet was used in the clinch-riveting technology. The strength of the joints was also identified in the lap shear test and the energy consumption at failure was determined. The use of a rivet increased the maximum load capacity to almost twice that of the clinch joint.Graphical abstract

Steel Sheet Deformation in Clinch-Riveting Joining Process

This paper presents the deformation of a joined sheet after the clinch riveting process. The DX51D steel sheet with zinc coating was used. The samples to be joined with clinch riveting technology had a thickness of 1 ± 0.05 mm and 1.5 ± 0.1 mm. The sheet deformation was measured before and after the joining process. The rivet was pressed in the sheets with the same dimension between the rivet axis and three sheet edges: 20, 30, and 40 mm. For fixed segments of the die, from the rivet side close to the rivet, the sheet deformation was greater than that of the area with movable segments. The movement of the die’s sliding element caused more sheet material to flow in the space between the fixed part of the die and movable segments. Hence, the sheet deformation in these places was smaller than for the die’s fixed element—the sheet material was less compressed. For sheet thickness values of 1.5 mm and a width value of 20 mm, the bulk of the sheet was observed. For a sheet width of 20 mm, it was observed that the deformation of the upper and lower sheets in the area of the rivet was greater than for sheet width values of 30 or 40 mm.