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This paper describes an approach for robust design of a mechanical joining process, semi-tubular self-piercing riveting, in real time. Using joining process simulations as a basis, a metamodel is constructed for this purpose, which is subsequently used to optimize the robustness. In this way, joining points can be designed so that there are no impermissible effects on the result quantities in terms of specified scatter input variables.

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.

Self-piercing riveting (SPR) is a cold mechanical joining process used to join two or more sheets of materials by driving a rivet piercing through the top sheet or the top and middle sheets and subsequently lock into the bottom sheet under the guidance of a suitable die. SPR is currently the main joining method for aluminium and mixed-material lightweight automotive structures. SPR was originated half century ago, but it only had significant progress in the last 25 years due to the requirement of joining lightweight materials, such as aluminium alloy structures, aluminium-steel structures and other mixed-material structures, from the automotive industry. Compared with other conventional joining methods, SPR has many advantages including no pre-drilled holes required, no fume, no spark and low noise, no surface treatment required, ability to join multi-layer materials and mixed materials and ability to produce joints with high static and fatigue strengths. In this paper, research investigations that have been conducted on self-piercing riveting will be extensively reviewed. The current state and development of SPR process is reviewed and the influence of the key process parameters on joint quality is discussed. The mechanical properties of SPR joints, the corrosion behaviour of SPR joints, the distortion of SPR joints and the simulation of SPR process and joint performance are reviewed. Developing reliable simulation methods for SPR process and joint performance to reduce the need of physical testing has been identified as one of the main challenges.

Riveting process is widely used to join sheets by using rivets. It can be used in many fields due to its simple process, easy disassembly, and high reliability. In addition, it has incomparable advantage in the joining of light alloy, composite, and dissimilar materials. Conventional riveting belongs to mechanical joining. However, with the advancing of technology, it has been modified and combined to other joining techniques so as to improve mechanical properties of joint. The state-of-art riveting technologies in recent years are reviewed. Modified methods which originate from existing riveting techniques, such as reshaped riveting, restored riveting, self-piercing riveting, clinch riveting, electromagnetic riveting, flow drill screwing, and rivtac, are introduced. Many types of welding have been combined to riveting. Hybrid methods such as laser-arc welding assisted riveting, resistance rivet welding, friction riveting, friction stir blind riveting, friction self-piercing riveting, and friction element welding are also introduced. Latest researches on different riveting techniques have been listed. Forming mechanism of each riveting technique has been discussed. Process parameters that affect mechanical properties of joint have been analyzed. Merits and demerits of each technique have been introduced. Each craft has its own features and can be applied in certain circumstances. Some suggestions on future orientation of riveting are given in text to assist further investigation.

As the fibre reinforced plastic composites gain larger and larger share in industry, the problem of joining them with metal elements becomes significant. The current paper is the first part of the literature review, which gathers and evaluates knowledge about methods suitable for mechanical joining of composite and metal elements. This paper concerns bolted joining, because this method of mechanical joining is widely used for joining composite materials. The paper describes failure modes of bolted joints in composite materials, the influence of the bolt clamping torque, the clearance between the bolt and the hole and aging on the performance of the joint, drilling techniques used in composite materials in order to minimize damages, different fastener types, inspection techniques, and finally, the techniques that have been developed in order to improve the strength of the bolted joints in composites. Since the hole drilled in a composite material in order to perform bolted joining is a weak point of the structure, those techniques: bonded inserts, titanium foil internal inserts, fibre steering, additional reinforcement, and moulded holes, mainly aim to improve the strength of the hole in the composite. The techniques have been discussed in details and compared with each other in the summary section.

As fiber reinforced plastic composites gain an increasingly larger share in aerospace structures, the problem of joining them with metal elements becomes significant. The current paper is the second part of the literature review, which gathers and evaluates knowledge about methods suitable for the mechanical joining of composite and metal elements. This paper reviews the joining methods other than bolted joining, which are discussed in the first part of the review, namely self-piercing riveting, friction riveting, clinching, non-adhesive form-locked joints, pin joints, and loop joints. Some of those methods are full-fledged and employed in commercial applications, whereas others are merely ideas tested at the level of specimens. The current review describes the ideas and the qualities of the joining methods as well as the experimental work carried out so far. The summary section of this paper contains a comparison of those methods with the reference to their qualities, which is important from the point of view of a composite structure designer: possibility of the joint disassembly, damages induced in composite, complication level, weight penalty, range of possible materials to be joined, and the joint strength.

Ceramic matrix composites (CMCs) are composite materials made by using structural ceramics as matrix and reinforcing components such as high-strength fibers, whiskers, or particles. These materials are combined in a specific way to achieve a composite structure. With their excellent properties, including high specific strength, high specific stiffness, good thermal stability, oxidation resistance, and corrosion resistance, CMCs are widely used in the aerospace, automotive, energy, defense, and bio-medical fields. However, large and complex-shaped ceramic matrix composite parts are greatly influenced by factors such as the molding process, preparation costs, and consistency of quality, which makes the joining technology for CMCs increasingly important and a key trend for future development. However, due to the anisotropic nature of CMCs, the design of structural components varies, with different properties in different directions. Additionally, the chemical compatibility and physical matching between dissimilar materials in the joining process lead to much more complex joint design and strength analysis compared to traditional materials. This paper categorizes the joining technologies for CMCs into mechanical joining, bonding, soldering joining, and hybrid joining. Based on different joining techniques, the latest research progress on the joining of CMCs with themselves or with metals is reviewed. The advantages and disadvantages of each joining technology are summarized, and the future development trends of these joining technologies are analyzed. Predicting the performance of joining structures is currently a hot topic and challenge in research. Therefore, the study systematically reviews research combining failure mechanisms of ceramic matrix composite joining structures with finite element simulation techniques. Finally, the paper highlights the breakthroughs achieved in current research, as well as existing challenges, and outlines future research and application directions for ceramic matrix composite joining.

In recent years, with the development of materials science, the joining technology is also constantly upgraded, ultrasonic testing technology can more accurately detect the defects or failures of new materials in the new joining process, which has extensive applications in the field of engineering joining, such as welding, mechanical joining, and adhesive bonding. This paper introduces the common non-destructive testing techniques, including magnetic particle testing, eddy current testing, penetration testing, radiographic testing, and ultrasonic testing. The main principles and devices of ultrasonic testing are introduced, including air-coupled ultrasonic testing, electromagnetic ultrasonic testing, laser ultrasonic testing, and so on. The current status of the application of ultrasonic testing in welded joints, riveted joints, bonded joints, and bolted joints is summarized and reviewed. Finally, the drawbacks of ultrasonic testing in this field are discussed, as well as prospective research directions.

In industries such as aerospace, defense, and automotive, mechanical joining methods are widely adopted. However, the stress concentration effects have diminished the fatigue performance of these connections. Interference fit has emerged as a method proven to effectively enhance the fatigue resistance of such joints, yet traditional theoretical frameworks have not fully elucidated the mechanisms behind its fatigue strengthening, hindering the advancement and application of this technology. This article meticulously assesses and synthesizes key research findings and applications of interference fit from the past 15 years, delving into its classifications, installation processes, and their impacts on the mechanical performance of joints, followed by an in-depth analysis of its fatigue strengthening mechanisms and the limitations of current theories. Furthermore, the article explores hybrid reinforcement techniques that combine interference fit with other methods, offering an advanced strategy for joint reinforcement. Finally, several key challenges are identified for further exploration. The aim of this review is to lay the groundwork for future research, deepen the understanding of interference-fit technology, and promote the design of more robust and reliable mechanical joints.

Adhesive bonding is widely seen as the most optimal method for joining composite materials, bringing significant benefits over mechanical joining, such as lower weight and reduced stress concentrations. Adhesively bonded composite joints find extensive applications where cyclic fatigue loading takes place, but this might ultimately lead to crack damage and safety issues. Consequently, it has become essential to study how these structures behave under fatigue loads and identify the remaining gaps in knowledge to give insights into new possibilities. The fatigue life of adhesively bonded composite joints is influenced by various parameters, including joint configuration and material properties of adherends and adhesive. Numerous studies with varying outcomes have been documented in the literature. However, due to the multitude of influential factors, deriving conclusive insights from these studies for practical design purposes has proven to be challenging. Hence, this review aims to address this challenge by discussing different methods to enhance the fatigue performance of adhesively bonded composite joints. Additionally, it provides a comprehensive overview of the existing literature on adhesively bonded composite joints under cyclic fatigue loading, focusing on three main aspects: Adherends modification, adhesive modification, and joint configurations. Since the effect of modifying the adhesive, adherends, and joint configurations on fatigue performance has not been comprehensively studied in the literature, this review aims to fill this gap by compiling and comparing the relevant experimental data. Furthermore, this review discusses the challenges and limitations associated with the methods that can be used to monitor the initiation and propagation of fatigue cracks.