Polymer-metal Hybrid Structures Research Articles

An efficient/accurate multi-scale fatigue prediction method for Metal-Polymer hybrid (MPH) interface

Metal-polymer hybrid (MPH) structures, featuring a micro-structure interlocking design, combine the high strength of metal with the exceptional formability of polymer-based composites and have gained significant attention in automotive load-bearing components. Challenges persist in accurately predicting MPH structure fatigue life using small samples with diverse interlock parameters and swiftly generating static strength and fatigue life response surfaces for automated optimization. We introduce a simplified model for predicting fatigue at the interfaces of MPH structures. Our multi-fidelity prediction method integrates this model with limited high-fidelity data samples to assess both the static strength and fatigue life effectively. This method predicts the deviation with less than 3% error compared to FSR-FEM, achieving a reduction in prediction time of over 60%. Additionally, we elucidate the non-synergistic mechanisms of key interfacial locking parameters between static strength and fatigue life at the micro-scale. Finally, we propose and apply a multi-objective synergistic optimization strategy to the MPH thrust rods in vehicles. By utilizing our optimization method, we achieve a 27.9% weight reduction compared to steel counterparts, while enhancing overall tensile strength by 11.8% and significantly improving fatigue life by 46.7% compared to MPH torque rods lacking an interlock interface.

Effect of Process Parameters on Joint Performance in Hot Pressure Welding of 6061 Aluminum Alloy to CF/PA66.

Polymer-metal hybrid structures combine the merits of polymer and metal materials, making them widely applicable in fields such as aerospace and automotive industries. However, the main challenge lies in achieving efficient and strong connections between the metal and polymer components. This paper uses the jet electrochemical machining (Jet-ECM) method to customize the surface morphologies on 6061 aluminum alloy (AA6061) sheets. The connection between AA6061 and carbon fiber-reinforced PA66 (CF/PA66) is then achieved through hot pressure welding (HPW). The effects of aluminum alloy surface morphology, welding force, and welding time on the mechanical properties and microstructure of the joint are investigated. The optimal process parameters are determined by the design of the experiment. The results show that the aluminum alloy surface morphology has the greatest impact on the mechanical property of the welded joint. The optimal process parameters are surface morphology with wider, shallower, and sparsely distributed grooves on the aluminum alloy surface, the welding force is 720 N, the welding time is 12 s, the welding temperature is 360 °C, the cooling time is 16 s, and the optimal peak load of the joint is 6690 N. Under the optimal parameters, the fracture morphology in the AA6061 side is almost entirely covered with CF/PA66. The joint experiences cohesive failure in most areas and fiber-matrix debonding in a small area.

Experimental evaluation of T-peel strength on functionally graded Al5083 and HDPE tri-laminated composites fabricated by colding-assisted friction stir additive manufacturing

Functionally graded composites offer impressive promise in overcoming the inherent weaknesses of Metal-polymer hybrid structures. In this study, functionally graded 5083 aluminum (Al5083) and high-density polyethylene (HDPE) tri-laminated composites were fabricated by colding-assisted friction stir additive manufacturing (CA-FSAM) and friction stir additive manufacturing (FSAM). Functionally graded laminate composites have been used to overcome these drawbacks by varying the thickness of the raw laminate. The thickness changes in the user sheets were functionally 0.75 mm compared to the previous laminate. Finally, the initial sheets were transformed to three thicknesses: 3, 2.25, and 1.5 mm. The bond strength between the sheets was measured using the T-peel test. In the T-peel test, the initial crack length was 25 mm and the length of the weld zone was 111 mm. The results showed that the bond strength between the laminates improved with cooling after the CA-FSAM process. The bond strength is essentially determined by the amount of covalent bonding, which, in turn, is a function of the density on the treated surface. Dislocation forest at the surface of the tri-laminate composite can be considered a consequence of T-peel test. The joining mechanism could be ascribed to mechanical interlocking, adhesion bonding at the interface of the Al5083 alloy and HDPE polymer, and metal-chip reinforcement in HDPE of the stir zone. The maximum force (Fmax) obtained in the FSAM and CA-FSAM specimens were 1057.58 and 1254.20 N, respectively. Average force of T-peel test (Favg peel) obtained in the FSAM and CA-FSAM specimens was 984.36 and 1024.32 N, respectively.

Evaluation of wear test on functionally graded metal-polymer tri-laminate composite interfaces of cooling-assisted friction stir additive manufacturing

In this study, a new friction stir welding (FSW) based additive manufacturing (AM) process called "cooling-assisted friction stir additive manufacturing (CA-FSAM)" was introduced to join sheets of metal-polymer hybrid structures (MPHS). Dry ice was introduced as the coolant. Thickness variations of the raw high-density polyethylene (HDPE) and 5083 aluminum alloy (Al5083) sheets were functionally graded at a rate of 0.75 mm from the former layer. The arrangement of layers in terms of thickness was arranged in the order of 3, 2.25, and 1.5 mm. Functionally graded metal-polymer tri-laminate composite fabricated with CA-FSAM technology was investigated using the pin-on-disk wear test. The results showed that mechanical locking between the layers affected the bond strength. Cross-sectional morphology examination revealed defect-free, strong joints. X-ray diffraction (XRD) results confirmed the formation of Mg2Si; however, the XRD peak was low, indicating a slight effect on the interface properties. Thermal gravimetric analysis (TGA)-Fourier transform infrared spectroscopy (FT-IR) characterization highlighted that the main evolved products during tri-laminate composite joining were CO, CC, CH3, CH2, and CH2. Oxidation occurred in the FTIR peak in the absorption band (1029.92 cm−1 to 1370.63 cm−1). Disk loading resulted in the buildup of an internal drag force that caused the dislocation/rupture of the CC or CH bonds. Defects, such as deep grooves, pits, and delamination at the interface, were observed in the composite specimen. The wear path was not visible in the worn composite material. The wear rate at 4 kg load on Al5083, HDPE, and metal-polymer tri-laminate composite specimens was 3.15 ± 0.22, 4.72 ± 0.36, and 3.42 ± 0.18 × 10−6 mm3/N. m, respectively.

Self-Pierce Riveting: Development and Assessment for Joining Polymer-Metal Hybrid Structures in Lightweight Automotive Applications.

In recent years, the transportation industry has faced the challenge of cutting costs, meeting increasingly stringent environmental regulations, and significantly increasing transportation volumes. One approach to meeting these challenges is to develop new, improved transportation vehicles using new materials and innovative joining techniques. Multi-material structures are becoming an alternative to body parts. Self-pierce riveting technology plays a crucial role in this process, and hybrid structures depend exclusively on it. In this article, recent advances in self-pierce riveting technology are analyzed to meet today's challenges and future multi-material applications.

Direct joining of PP-Al5052 hybrid with high bonding strength by two-step anodization treatment and polymer modification

Polymer-metal hybrid (PMH) structures with excellent physical and chemical properties are widely required in aerospace, electrical, automotive and many other fields. It is one of the key challenges for the joining operation between the metal and polymer at the interface. In this study, pretreatment on aluminum alloy (Al5052) sheet by two-step anodization and maleic anhydride-grafted polypropylene (PP-g-MAH) were applied to enhance the bonding performance of PMH structures via injection-molded direct joining process. The effects of anodization treatments on the interfacial wettability, surface morphology and tensile strength were investigated. Besides, the bonding mechanism was further analyzed by molecular dynamics (MD) simulation method. Experimental results showed that the hierarchical nanopores and branched structures were formed after the two-step anodization process, which greatly improved the surface wettability. Using oxalic acid solution as the electrolyte in the second anodization, the bonding strength of PP-Al5052 sheet was greatly improved. With PP-g-MAH resin, the bonding strength reached a maximum of 17.54 MPa, resulting in a tensile failure at the PP-g-MAH part itself. MD simulations revealed that the MAH groups contributed to enhancing the interfacial interactions, while the existence of phosphate ions decreased the chemical interactions at the interface.

Interface constitutive modeling and failure propagation mechanisms of integrated polymer-metal hybrid (PMH) structures

Interface constitutive modeling and failure propagation mechanisms of integrated polymer-metal hybrid (PMH) structures

A Comprehensive Technical Review of the Friction Stir Welding of Metal-to-Polymer Hybrid Structures

Metal-polymer hybrid structures are becoming desirable due to their wide range of applications in the automotive, aerospace, biomedical and construction industries. Properties such as a light weight, high specific strength, and design flexibility along with the low manufacturing costs of metal-polymer hybrid structures make them widely attractive in several applications. One of the main challenges that hinders the widespread utilization of metal-polymer hybrid structures is the challenging dissimilar joining of metals to polymers. Friction stir welding (FSW) shows a promising potential in overcoming most of the issues and limitations faced in the conventional joining methods of such structures. Several works in the literature have explored the FSW of different metal-to-polymer combinations. In some of the works, the joints are examined based on processing parameter optimization, microstructural characteristics, and mechanical performances. It is, therefore, important to summarize the findings of these works as a means of providing a reference to researchers to facilitate further research on the utilization of FSW in joining metals to polymers. Thus, this work aims to present a comprehensive technical review on the FSW technique for joining metals to polymers by reviewing the reported literature findings on the impact of materials, tools, process parameters, and defects on the strength and microstructure of the produced joints. In addition, this work reviews and presents the latest practices aiming to enhance the metal-polymer joint quality that have been reported in the literature.

Laser surface treatment to enhance the adhesive bonding between steel and CFRP: Effect of laser spot overlapping and pulse fluence

Adhesive bonding is widely applied in joining between steel and carbon fiber reinforced plastics (CFRP), while the surface characteristics of steel have a significant effect on the joint strength. To improve the adhesive bonding between DP590 steel and CFRP, surface modifications of steel by laser surface treatment with different overlap rate of laser spot and pulse fluence were applied and investigated. The evolution of surface morphology, contact angle, surface energy, and surface chemical composition of DP590 steel after laser treatment with different parameters were also studied. The results showed that surface roughness, surface energy and polar component of surface energy after treatments were closely related to the interfacial bonding strength between steel and adhesives. Specifically, higher pulse fluence can increase the surface roughness of the steel, which reduced the contact angle and improve the surface energy, thus not only leading to a better mechanical interlocking effect, but also improving the surface wettability of the adhesive to the steel surface. When there was 50 % overlapping of the laser spots, the surface wettability was further improved. In addition, the strengths of steel-CFRP joints obtained with both epoxy adhesive E-120HP and polyurethane adhesive PU6700 were significantly enhanced by laser surface treatment. Especially for the joints bonded with E-120HP, which is a high-strength and poor-toughness adhesive, the shear strength can be increased by 299 %, from 4.10 ± 0.17 MPa to 16.35 ± 0.89 MPa after laser treatment. More importantly, the adhesive failure along steel-adhesive interface was entirely avoided. This study provides both technical and theoretical guidance of laser surface treatment for fabricating high-performance metal-polymer hybrid structures by adhesive bonding.

Research Progress on Characterization and Regulation of Forming Quality in Laser Joining of Metal and Polymer, and Development Trends of Lightweight Automotive Applications

Metal–polymer hybrid structures have been widely used in research into their lightweight automotive applications, because of their excellent comprehensive properties. As an efficient technology for automatic connection of dissimilar materials, laser joining has great application potential and development value in the field of lightweight automotive design. However, due to the physical and chemical differences between metals and polymers, the formation quality of the hybrid joint is seriously affected by defects, low bonding strength, and poor morphology. Meanwhile, it is difficult to meet the demands for lightweight automobiles by considering only bonding strength as the target for forming quality. Therefore, the technological characteristics of metal–polymer hybrid structures for use in lightweight automotive applications are analyzed, the advantages and problems of laser-joining technology are discussed, and the characterization indexes and regulation measures of forming quality in laser joining are summarized. This paper which provides reference and guidance for reliable forming, intelligent development, and lightweight application of laser joining for polymer–metal hybrid structures.

Chemical Reaction and Bonding Mechanism at the Polymer-Metal Interface.

Polymer-metal hybrid structures have attracted significant attention recently due to their advantage of great weight reduction and excellent integrated physical/chemical properties. However, due to great physicochemical differences between polymers and metals, obtaining an interface with high bonding strength is a challenge, which makes it critically important to clarify the underlying bonding mechanisms. In the present research, we focused on revealing the underlying bonding mechanisms of a laminated Cr-coated steel-ethylene acrylic acid (EAA) strip prepared by hot roll bonding from the microscale to the molecular scale with experimental evidence. The microscale mechanical interlocking was analyzed and proven by scanning white light interferometry and scanning electron microscopy (SEM) by means of observing the surface and cross-sectional morphologies. Additionally, interfacial phases and chemical compositions were analyzed by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). More directly and effectively, the interface was successfully exposed for X-ray photoelectron spectroscopy (XPS) analysis. Combined with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and depth profiling analysis, the formation of -(O═)C-O-Cr and -C-(O-Cr)2 covalent bonds through chemical reactions at the interface between -COOH and Cr2O3 was verified. Based on these characterization results, interfacial bonding mechanisms for the laminated Cr-coated steel-EAA strip were clearly identified to be chemical bonding and micromechanical interlocking, along with hydrogen bonding, which were all demonstrated with solid experimental evidence. In addition, 3D-render view and cross-section images of typical ion fragments at the interface were used to reveal the interfacial structure more comprehensively. The contributions of hydrogen bonds and covalent bonds to the interface were evaluated and compared for the first time. This study provides both methodological and theoretical guidance for investigating and understanding interfacial bonding formation in polymer-metal hybrid structures.

Evaluation of nanocomposite structure printed by solid-state additive manufacturing

Properties of polymer-metal hybrid structure printed by fed friction stir additive manufacturing (FFSAM) were evaluated. FFSAM is advanced solid-state additive manufacturing for the printing of macro-scale components for large stress-bearing situations. With the FFSAM, layer by layer printing of polymer and metal sheets convert to paste phase and join together as a uniform structure. With this process, during printing of hybrid structure, nanocomposite polymer is injected at the interface of base materials to fill voids and recover properties of the polymer matrix: polypropylene (PP) and stainless steel (SS) fabric selected as raw materials. During the printing process, Fe2O3 nanoparticles fed into the interface of PP and steel sheets. The mechanical and metallurgical characterization of printed [email protected]@Fe2O3 nanocomposite structure is evaluated. Macrostructure, tensile strength, hardness, and thermo-chemical properties of the printed structure were assessed and discussed. The result indicated that the In-situ feeding mechanism improves the physical and chemical properties of the printed structure. Reasonable properties achieved due to minimizing shrinkage gap in polymer side and improving sealing adhesion at interfaces of printed materials.

Influence of temporal pulse-shaping on laser surface texturing of metals using fast modulated cw-fiber laser radiation

Remote ablation cutting with continuous wave laser radiation is a process commonly used for the surface pretreatment of large area metallic parts before joining of metal-polymer hybrid structures, due to their cost-effectiveness and high average powers when compared to short-pulsed lasers. The process requires high power-densities and multiple irradiations at high scanning speeds to achieve the desired kerf depth. In this work a fast modulated cw fiber laser is used to investigate the possibilities of increasing the material removal rate by periodically dropping the laser power and therefore modifying the recoil pressure at the vapor-liquid interface in the interaction zone to assist in melt expulsion. It was found that power modulation with frequencies in excess of 10 kHz can lead to an increased material removal rate when compared to continuous wave processing at comparable average and peak power levels, enabling higher kerf aspect ratios in a single irradiation.

Prediction of peak temperature value in friction lap welding of aluminium alloy 7475 and PPS polymer hybrid joint using machine learning approaches

In the automotive and aerospace sectors, vehicle weight has been a major concern for the past decades. Incorporating metal-polymer hybrid structures reduces weight without compromising structural performance. In this work, Friction Lap Welding (FLW) technique was used to join aluminium alloy 7475 with PPS polymer. To conduct the FLW experiments, a design matrix was developed with the help of Response surface methodology. For each experimental run, the peak temperature value was recorded. The possibility of machine learning algorithms for predicting peak temperature during joining has been assessed. The maximum correlation coefficient (i.e., 0.999) and minimum root mean square error (i.e., 0.068) were observed for the support vector machining (SVM) model with the PUK kernel. So, SVM-PUK approach was determined to be the most efficient.

A State-of-the-Art Review on Advanced Joining Processes for Metal-Composite and Metal-Polymer Hybrid Structures.

Multi-materials of metal-polymer and metal-composite hybrid structures (MMHSs) are highly demanded in several fields including land, air and sea transportation, infrastructure construction, and healthcare. The adoption of MMHSs in transportation industries represents a pivotal opportunity to reduce the product’s weight without compromising structural performance. This enables a dramatic reduction in fuel consumption for vehicles driven by internal combustion engines as well as an increase in fuel efficiency for electric vehicles. The main challenge for manufacturing MMHSs lies in the lack of robust joining solutions. Conventional joining processes, e.g., mechanical fastening and adhesive bonding involve several issues. Several emerging technologies have been developed for MMHSs’ manufacturing. Different from recently published review articles where the focus is only on specific categories of joining processes, this review is aimed at providing a broader and systematic view of the emerging opportunities for hybrid thin-walled structure manufacturing. The present review paper discusses the main limitations of conventional joining processes and describes the joining mechanisms, the main differences, advantages, and limitations of new joining processes. Three reference clusters were identified: fast mechanical joining processes, thermomechanical interlocking processes, and thermomechanical joining processes. This new classification is aimed at providing a compass to better orient within the broad horizon of new joining processes for MMHSs with an outlook for future trends.

Atomistic Investigation on the Wetting Behavior and Interfacial Joining of Polymer-Metal Interface.

Polymer-metal hybrid structures can reduce the weight of components while ensuring the structural strength, which in turn save cost and subsequently fuel consumption. The interface strength of polymer-metal hybrid structure is mainly determined by the synergistic effects of interfacial interaction and mechanical interlocking. In this study, the wetting behavior of polypropylene (PP) melt on metal surface was studied by molecular dynamics simulation. Atomistic models with smooth surface and nano-column arrays on Al substrate were constructed. Influences of melt temperature, surface roughness and metal material on the wetting behavior and interfacial joining were analyzed. Afterwards the separation process of injection-molded PP-metal hybrid structure was simulated to analyze joining strength. Results show that the initially sphere-like PP model gradually collapses in the wetting simulation. With a higher temperature, it is easier for molecule chains to spread along the surface. For substrate with rough surface, high density is observed at the bottom or on the upper surface of the column. The contact state is transitioning from Wenzel state to Cassie–Baxter state with the decrease of void fraction. The inner force of injection-molded PP-Fe hybrid structure during the separation process is obviously higher, demonstrating a greater joining strength.

Refill Friction Stir Spot Welding of Dissimilar AA6014 Al Alloy and Carbon-Fiber-Reinforced Polymer Composite

Both Al and carbon-fiber-reinforced polymer (CFRP) are being investigated as lightweight materials for automobile applications. To form effective hybrid materials from Al and CFRP, strong bonding between these two dissimilar materials is critical. Here, we analyzed the microstructure and tensile shear strength of joints between an Al alloy (AA 6014) and CFRP fabricated using refill friction stir spot welding (RFSSW). A maximum tensile shear load of 1.6 kN was measured for untreated AA 6014/CFRP specimens. Microscopy images of the Al–CFRP joints exhibited tight bonding along the joint interface without any noticeable defects. Moreover, Al–O–C, C–C, and C=O chemical bonds were detected on the tensile–shear fracture surfaces of both the Al alloy and CFRP sheets using X-ray photoelectron spectroscopy. Micro-mechanical interlocking and chemical bond formation were the key factors contributing to the tensile shear strength of the RFSSW joint. This study demonstrated that the RFSSW technique is a suitable bonding method for manufacturing metal–polymer hybrid structures.

Fuzzy decision-making in laser-assisted joining of polymer-metal hybrid structures

A fuzzy decision-making approach was developed to optimize laser-assisted joining process of polymer-metal hybrid structures. A systematic approach based on Design of Experiment was adopted to identify and explain the effect of each process parameter, i.e. laser energy and laser power, on the response variables, i.e. maximum operating temperature and shear strength. Then, a combined fuzzy-genetic algorithm model was developed to find the best input parameters’ combination capable to satisfy the requirement of the best processing performances, in terms of appropriate range of operating temperature and highest shear strength. The use of genetic algorithms involved the choice of the best nominal regression model and the optimisation of the fuzzy numbers. This enabled to account most of the experimental data in combination with the smallest uncertainty level. Experimental results showed the success of the joining process ensuring sufficient adhesion of the hybrid structure over time, with shear strength of almost 29 MPa by using a laser power of 150 W and energy of 2 kJ. Moreover, the fuzzy process maps enable the selection of the process parameters with the aim of achieving desired process output along with the lowest uncertainty level. In addition, it also provides the amount of uncertainty of the model. The results indicated that a low laser energy level of 2250 J and a laser power in the range 120–140 W would provide the optimal solution in terms of operating temperature (i.e. between 343 and 520 °C), shear strength (i.e. greater than 26 MPa) and uncertainty level (i.e. membership level greater than 0.9).

MECHANICAL AND OPTICAL INVESTIGATION OF LASER WELDED STRUCTURAL STEEL - POLY(METHYL-METHACRYLATE) HYBRID JOINT STRUCTURES

Modern welding processes that can easily be automated (such as friction stir welding, laser welding and ultrasonic welding) are gaining popularity in joining metal-polymer hybrid structures. This field of science is intensively studied around the globe, as a dependable, productive joining method that directly produces structurally sound joints between a metal and a polymer structure could unleash unforeseen possibilities in the vehicle industry. In our experiments, we manufactured hybrid steel-poly(methyl-methacrylate) (PMMA) joints with laser welding, using the 2p design of experiment method. We measured the effect of cellulose reinforcing fibres (in varying weight percentages) on the transparency and weldability of the PMMA material and the effect of welding parameters on the mechanical properties of the joints. We also examined the vicinity of the welded seam with scanning electron microscopy.

Evaluation of Joint Formation and Mechanical Performance of the AA7075-T6/CFRP Spot Joints Produced by Frictional Heat.

The development of lightweight hybrid metal–polymer structures has recently attracted interest from the transportation industry. Nevertheless, the possibility of joining metals and polymers or composites is still a great challenge. Friction Spot Joining (FSpJ) is a prize-winning friction-based joining technique for metal–polymer hybrid structures. The technology is environment-friendly and comprises very short joining cycles (2 to 8 s). In the current work, aluminum alloy 7075-T6 and carbon-fiber-reinforced polyphenylene sulfide (CF-PPS) friction spot joints were produced and evaluated for the first time in the literature. The spot joints were investigated in terms of microstructure, mechanical performance under quasi-static loading and failure mechanisms. Macro- and micro-mechanical interlocking were identified as the main bonding mechanism, along with adhesion forces as a result of the reconsolidated polymer layer. Moreover, the influence of the joining force on the mechanical performance of the joints was addressed. Ultimate lap shear forces up to 4068 ± 184 N were achieved in this study. A mixture of adhesive–cohesive failure mode was identified, while cohesive failure was dominant. Finally, a qualitative comparison with other state-of-the-art joining technologies for hybrid structures demonstrated that the friction spot joints eventually exhibit superior/similar strength than/to concurrent technologies and shorter joining times.