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Laser ablation is currently used as an effective alternative to mechanical or chemical surface pre-treatments for adhesive-bonded joints due to benefits in terms of adherend surface morphology and surface free energy. Several works have seen production of micro-scale textures on both metallic and polymeric substrates via 3D printing, while others have sought to modify the macroscopic topography by generating serrated profiles on adherends prior to joint assembly. In this work, laser ablation has been used to create micro-scale tooth-like interlocking features forming structured patterns with complementary profiles on aluminium adherends of single lap joints. In a first set of experiments, laser processing parameters were varied while an optical profiler was used to quantify the geometry of induced ablation craters and lines while assessing the distribution of re-melt in and around the exposed region. Subsequently, an ablation strategy was developed to achieve specific interlocking features. Finally, different symmetrical and asymmetrical patterns were generated for each pair of coupled adherends while differentiating the orientation of features with respect to the load direction. The results confirm the critical role that laser ablation plays in strengthening adhesive bonded-joints, with interlocking features providing additional benefits depending on the structure type and load direction. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is a promising technology for fabricating complex components with W/Cu dual metal. To enhance the interfacial bonding of W/Cu dual metal, we propose a novel approach using laser texturing to fabricate micro/nanostructures on the W surface. The micro/nanostructures promoted the spreading of Cu in the liquid, inhibited defects, and considerably increased the contact area between W and Cu by mechanical interlocking. To the best of our knowledge, a W/Cu dual metal was successfully prepared by SLM without a transition layer the first time. The bonding strength of the two materials reached 123 MPa, close to that of a W/Cu dual metal joint prepared by diffusion bonding.

A reliable strategy to enhance the bonding ability in carbon reinforced aluminum laminates (CARALL) is proposed, which is based on the mechanical interlocking effect generated by the surface slot structure of aluminum alloy enhances the structural interface between fibers/resins and aluminum alloy. The characteristic of slot structure is determined, and the strengthening mechanism of bonding interfaces is revealed. The CARALL samples with slot structure are fabricated via an hot pressing process. The micro texture morphologies, mechanical, interlayer bonding properties under different conditions are studied. The results indicate that forming a slot structure on the aluminum surface is beneficial for improving the interfacial bonding performance. Compared with the non‐slotted structure, the interlayer type II fracture toughness of the slotted structure is increased by 112.99%. The slotted structure can reduce the defects at the interface between the layers and improve the interface bonding force. In this work, the interlaminar shear strength (ILSS) of the slotted structure sample was 27.08% higher than that of the non‐slotted structure sample. Highlights: A slotted structure was proposed to solve the problem of insufficient bonding strength.A slotted structure consistent with the direction of adjacent fibers is designed.The interlayer type II fracture toughness of the slotted structure is increased by 112.99%.The final crack propagation of the slotted structure sample is reduced by 40%.The final failure area of the slotted structure sample is reduced by 53.85%. [ABSTRACT FROM AUTHOR]

Hybrid lap joints of polypropylene (PP) and aluminum alloy AA5052 were fabricated using friction stir lap welding under different conditions of tool rotation speed, traverse speed and tilt angle, while placing PP on top. A full factorial design of experiments with three levels of each process parameter was performed, and the lap shear strength was evaluated for each run. The temperature at the interface between PP and AA5052 was measured by thermocouples, and an inverse heat conduction technique was utilized to estimate the approximate temperature distribution in PP. Cross sections of the joint were also examined using optical and scanning electron microscopy. It was found that decreasing the traverse speed, increasing the rotational speed and increasing the tilt angle resulted in an increase in the joint strength. These conditions also resulted in higher process temperatures, which lead to a more uniform weld nugget with less voids, due to the enhanced material flow. Moreover, morphology analysis revealed that mechanical interlocking caused by the anchoring of metal hooks in PP mainly contributed to the strength and performance of the joint. A direct relationship was found between the hook length on the advancing side and the lap shear strength. [ABSTRACT FROM AUTHOR]

Although hydrofluoric acid (HF) surface treatment is known to enhance the joining of metals with polymers, there is limited information on its effect on the joining of AZ31 alloy and carbon-fiber-reinforced plastics (CFRPs) through laser-assisted metal and plastic direct joining (LAMP). This study uses the LAMP technique to produce AZ31-CFRP joints. The joining process involves as-received AZ31, HF-pretreated AZ31, and thermally oxidized HF-pretreated AZ31 alloy sheets. Furthermore, the bonding strength of joints prepared with thermally oxidized AZ31 alloy sheets is examined to ascertain the combined effect of HF treatment and thermal oxidation on bonding strength. The microstructures, surface chemical interactions, and mechanical performances of joints are investigated under tensile shear loading. Various factors, such as bubble formation, CFRP resin decomposition, and mechanical interlocking considerably affect joint strength. Additionally, surface chemical interactions between the active species on metal parts and the polar amide along with carbonyl groups of polymer play a significant role in improving joint strength. Joints prepared with surface-pretreated AZ31 alloy sheets show significant improvements in bonding strength.

During the last decades, environmental concerns and limited resources have set focus of research on lightweight, mechanically high-performing structures for the transportation industry, in order to reduce fuel consumptions and CO2 emissions. Friction Stir Joining (FSJ), as a variant of the Friction Stir Welding (FSW), is an innovative friction-based joining technique for metal-composite hybrid structures. Joining in the plasticized state below the melting temperature of the metal leads to a comparatively small heat-affected zone, so that only minor metallurgical changes occur. Additionally, only a short processing time and no additional weight in form of fasteners is needed. The main objective of this study is to evaluate the feasibility of metal-composite structures via FSJ, intending to enable a macro-mechanical interlocking bonding mechanism. Main focus was given to the integration of an aluminium nub inserted in a carbon fiber-reinforced polyphenylene sulfide (CF-PPS) sheet, to ensure sufficient plasticization of the aluminium part and no degradation in the polymer part. Residual stress arising from the friction stir joining process was also characterised using the Contour method. In this study, aluminium alloy 6082-T6 and CF-PPS composite sheets were used to produce long lap joints. Results have shown that the joints were created at almost constant peak temperature slightly above the melting temperature of the PPS but no physical-chemical changes were detected in the PPS. In addition, the influence of a PPS film as interlayer between the sheets was investigated in order to explore a method for preventing galvanic corrosion. Preliminary results indicate that it is not possible to integrate a metal nub to the CF-PPS without interrupting the PPS film. However, it is possible to create a nub within the PPS film. [ABSTRACT FROM AUTHOR]

Aqueous soluble and stable Cu(I) molecular catalysts featuring a catenane ligand composed of two dicationic, mutually repelling but mechanically interlocked macrocycles are reported. The ligand interlocking not only fine‐tunes the coordination sphere and kinetically stabilizes the Cu(I) against air oxidation and disproportionation, but also buries the hydrophobic portions of the ligands and prevents their dissociation which are necessary for their good water solubility and a sustained activity. These catenane Cu(I) complexes can catalyze the oxidative C−C coupling of indoles and tetrahydroisoquinolines in water, using H2O2 as a green oxidant with a good substrate scope. The successful use of catenane ligands in exploiting aqueous Cu(I) catalysis thus highlights the many unexplored potential of mechanical bond as a design element for exploring transition metal catalysis under challenging conditions. [ABSTRACT FROM AUTHOR]

The cold spray (CS) process is an advanced material deposition method that has emerged as a versatile method to create high-performance coatings and functional components. This process offers unique advantages in achieving exceptional material adhesion and properties without needing high-temperature melting or heating. The CS process enables the deposition of cermets, allowing it to combine the favorable properties of their constituent phases. This review article explores the bonding mechanism specific to the CS deposition of cermets, highlighting its contrast with that of pure metals. It subsequently investigates the pivotal role played by ceramic particles in the overall efficiency of the CS deposition process, emphasizing the need for a comprehensive understanding of particle properties to achieve quality coatings for specific applications. The paper explores the challenges and limitations imposed by the CS process of cermets in optimizing the crucial parameters. It dissects the influence of interfacial bond strength and porosities on the tribological and corrosion properties of CS-deposited coatings. The discussion extends to the significant role played by substrate in shaping the coating's characteristics. The potential for enhancing coating properties through post-processing treatments is also thoroughly examined. The review article also discusses current advancements in the field and contemplates potential future directions, offering a comprehensive exploration of CS deposition of cermets and its multifaceted considerations. [ABSTRACT FROM AUTHOR]

• AZ31 alloy/CFRP joints were produced by laser joining with/without HF treatment. • NEXAFS technique demonstrated that HF treatment imparted reactive sites on the alloy surface for chemical bonding. • H-F bond through the interaction of MgF 2 and polar amide group of polymer resulted in high adhesion strength. Although hydrofluoric acid (HF) surface treatment is known to enhance the joining of metals with polymers, there is limited information on its effect on the joining of AZ31 alloy and carbon-fiber-reinforced plastics (CFRPs) through laser-assisted metal and plastic direct joining (LAMP). This study uses the LAMP technique to produce AZ31-CFRP joints. The joining process involves as-received AZ31, HF-pretreated AZ31, and thermally oxidized HF-pretreated AZ31 alloy sheets. Furthermore, the bonding strength of joints prepared with thermally oxidized AZ31 alloy sheets is examined to ascertain the combined effect of HF treatment and thermal oxidation on bonding strength. The microstructures, surface chemical interactions, and mechanical performances of joints are investigated under tensile shear loading. Various factors, such as bubble formation, CFRP resin decomposition, and mechanical interlocking considerably affect joint strength. Additionally, surface chemical interactions between the active species on metal parts and the polar amide along with carbonyl groups of polymer play a significant role in improving joint strength. Joints prepared with surface-pretreated AZ31 alloy sheets show significant improvements in bonding strength. [Display omitted] [ABSTRACT FROM AUTHOR]

Under the carbon peaking and carbon neutrality strategy, biomass has attracted much attention due to its characteristics of regeneration, low pollution and zero carbon emissions. The imperfects of biomass, such as the loose structure and low energy density, can be effectively solved by briquetting, and the resulted fuel pellets can be used as a substitute for fossil fuels, which is of great significance for the construction of new energy system. In the paper, the influencing factors of the hot briquetting process of biomass were summarized, and the evolution behavior and binding mechanism of biomass particles during the hot briquetting process were analyzed and discussed. Biomass briquetting process mainly includes cold briquetting and hot briquetting. Compared with cold briquetting process of biomass, hot briquetting with lower energy consumption can produce the biomass fuel pellets with higher quality. The moisture content (4%−15%) of the raw biomass has greater influence, the briquetting temperature (70−150 ℃) has relatively smaller effect on the density of the fuel pellets, and the briquetting pressure (60−130 MPa) and the particle size ( < 2.5 mm) of the raw material show the different impact on the density of the fuel pellets from different biomass. During the hot process, cellulose mainly plays the role of supporting skeleton, hemicellulose and lignin play the role of binder. In the microcosmic process of hot briquetting process, the inertia movement and subsequent viscoelastic-plastic deformation of the biomass particles occur and the mechanical interlock is formed between the particles. The brittle particles are broken and the natural viscous components are released, and thus, the bridge linkage between the particles is formed under the integrated effects of moisture, temperature and pressure. Mechanical interlocking and bridging reduce the distance between biomass molecules and promote the generation of intermolecular forces. Based on the above-mentioned mechanism of the hot briquetting of biomass, the quality of the resulted fuel pellets can be improved by biomass component adjustment, biomass blending or hydrothermal pretreatment. In the future, the molecular dynamics simulation method will be used to investigate the biomass briquetting process to obtain the molecular bonding mechanism of biomass components, which is conducive to further exploring the hot briquetting mechanism of biomass, and provide important guiding significance for the preparation of fuel pellets and molding materials from biomass.

Achieving high-strength welding joint of aluminum to steel is a highly pressing and challenging task in the manufacturing industries, and friction stir lap welding (FSLW) has advantages for joining these two metals. To further heighten the strength of dissimilar aluminum and steel metals (Al/steel) FSLW joint, the ultrasonic-assisted FSLW (UAFSLW) process was used, and the upper 2024-T4 aluminum alloy and the lower 304 stainless steel were chosen as research object. The results show that the addition of ultrasound eliminates the micro pores, changes the aluminum-rich intermetallic compounds (IMCs) into the iron-rich IMCs and enhances the micro and macro mechanical interlocking structures along the Al/steel lap interface. Under the rational IMCs layer thickness lower than 1.5 μm, the UAFSLW joint has the failure load higher than the traditional FSLW joint. The maximum failure load of UAFSLW joint reaches 7.06 kN, and the loading capacity of this joint is higher than that of reported Al/steel traditional FSLW joint. The UAFSLW process is an effective way to fabricate the high-strength Al/steel lap joint. [ABSTRACT FROM AUTHOR]

The growing demand for lightweight materials in the automotive and aerospace industries has driven research on joining dissimilar lightweight alloys, particularly Al and Mg alloys (Al/Mg). Friction stir welding (FSW) is a promising technique for joining Al/Mg alloys, as it works below the base metal's melting temperature, leading to refined microstructures, reduced porosity, and enhanced productivity. The strength of Al/Mg friction stir weldment depends on the evolved interface, which is primarily characterized by micromechanical interlocks, type, and intermetallic compounds (IMCs) distribution. Different interfaces for butt joints have been discussed in the literature. However, the mechanism of interfacial interaction together with the ways to enhance the interface have not been reviewed yet. This review article fills the gap by analyzing the retrospective data for process parameters and mechanical properties. Joining mechanisms and the evolution of different interfaces at the microstructural level have been discussed. Lastly, ways to enhance the interface for improved mechanical properties are explained. By offering essential insights into FSW techniques and Al/Mg weld interfaces, this review article paves the way for developing FSW procedures for Al/Mg butt welds aiming for enhanced strength and performance. This review article is expected to be of interest to researchers and engineers working in the field of FSW, particularly for Al/Mg lightweight applications. It provides an overview of the current state of knowledge and identifies key areas for future research.

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Surface preparation before adhesive bonding is crucial to improve the resistance and durability of the joint by altering the surface properties of the adherend. The purpose of surface treatment is to clean the surface from contaminants, activate the adherend surface and create an optimal surface structure to promote adhesion mechanisms. In that context, this work aims to investigate the influence of substrate surface texturing on the resistance of adhesive joints. Two bio-inspired surface textures were investigated, Fish scale (FS) and Tree frog (TF). Polycarbonate (PC) specimens with different surface patterns were manufactured using the fused deposition modelling process. Surface morphology, such as pattern dimension (shape and depth), surface roughness (Ra), and wettability, were used to characterise the substrates. The influence of these texture patterns on the shear strength of adhesively bonded joints was evaluated through the standardised block shear test method ASTM D4501-01. Moreover, the shear strength of the structured joints was compared to the results from bonding with polished surfaces (surfaces abraded with 80, 600 and 1000 grit paper), and with as-printed surfaces. The results revealed that the FS and TF surface textures enhanced the shear strength by 242% and 283% compared to the adhesive joints with polished surfaces. It was also shown that the variation in depth of the bio-inspired surface texture has no significant impact on the joint strength. Failure analysis demonstrated that the fracture mode of bonded joints with polished surfaces was the adhesive failure while mixed failure (cohesive and adhesive) characterises the as-printed, TF and FS surfaces. Worthy results are obtained rising the effectiveness of surface texture for the PC's bonded joints. Graphical Abstract This is a graphical representation of the abstract. [ABSTRACT FROM AUTHOR]

This study investigates the joining of metal to polymer by material extrusion additive manufacturing. Direct joining by layered extrusion was used to fabricate hybrid single lap joints of acrylonitrile butadiene styrene (ABS) and aluminum alloy 5052. The influence of the printing speed, bed temperature, and nozzle Z-offset on the lap shear strength was studied experimentally. The interface between the two materials was also observed under scanning electron microscope, and the chemical state of the polymer after printing was analyzed using differential scanning calorimetry (DSC), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results revealed that elevated bed temperature and pressure application through lowering the Z-offset promoted better polymer filling of the metal surface structure and improved the joint strength by mechanical interlocking. Also, long exposure time to the heated build plate corresponding to low printing speeds lowered the mechanical performance of the polymer bulk due to thermal degradation. Mechanical interlocking was the main joining mechanism, but under high bed temperatures where the carbonyl group had formed due to degradation, a (C-O-Al) chemical bond was detected. [ABSTRACT FROM AUTHOR]

Intestinal retentive devices have applications ranging from sustained oral drug delivery systems to indwelling ingestible medical devices. Current strategies to retain devices in the small intestine primarily focus on chemical anchoring using mucoadhesives or mechanical coupling using expandable devices or structures that pierce the intestinal epithelium. Here, the feasibility of intestinal retention using devices containing villi‐inspired structures that mechanically interlock with natural villi of the small intestine is evaluated. First the viability of mechanical interlocking as an intestinal retention strategy is estimated by estimating the resistance to peristaltic shear between simulated natural villi and devices with various micropost geometries and parameters. Simulations are validated in vitro by fabricating micropost array patches via multistep replica molding and performing lap‐shear tests to evaluate the interlocking performance of the fabricated microposts with artificial villi. Finally, the optimal material and design parameters of the patches that can successfully achieve retention in vivo are predicted. This study represents a proof‐of‐concept for the viability of micropost‐villi mechanical interlocking strategy to develop nonpenetrative multifunctional intestinal retentive devices for the future. [ABSTRACT FROM AUTHOR]

Highlights Spray‐dried cellulose nanocrystal (SDCNC) particles have attracted intense interest as reinforcements in polymer composites because of their unique physical and mechanical properties. This work aims to develop homopolymer polypropylene (HPP) composites with different loading levels of SDCNC particles (5, 10, 15, and 30 wt%) to understand their impact on composite mechanical, morphological, and thermal properties. The SDCNC‐reinforced HPP composites were manufactured using a C.W. Brabender bowl internal mixer with a masterbatch concept and an injection molding process. The mechanical, morphological, and thermal properties of the composites were investigated. Compared to pure HPP, the tensile, and flexural modulus of elasticity (MOE) of composites with 30 wt% SDCNC significantly increased by up to 67% and 49%. The impact strength of the composites with the absence of a compatibilizer significantly increased by up to 19%, which was attributed to the mechanical interlocking network established between SDCNC particles and HPP. Additionally, increasing SDCNC loading in the composites led to higher crystallization peak temperatures and increased the degree of crystallinity (especially at 30 wt% SDCNC content), indicating that the SDCNC particles can act as heterogeneous nucleating agents during the crystallization process. The thermal stability of the composite was slightly improved upon SDCNC introduction. With the incorporation of spray‐dried cellulose nanocrystal (SDCNC), the tensile modulus of elasticity (MOE), flexural MOE, and impact strength of filled homopolymer polypropylene (HPP) composites were significantly improved by up to 67%, 49%, and 19%, respectively. Mechanical interlocking network established between SDCNC and HPP contributed to the enhanced the impact strength. SDCNC particles can act as heterogeneous nucleating agents to promote the crystallization process of HPP. SDCNC particles slightly enhanced the thermal stability of HPP composite. [ABSTRACT FROM AUTHOR]

Two large groups of materials, namely metals and ceramics, are used in mass quantities in today's industry because of their outstanding properties. To achieve higher product performance dissimilar materials need to be combined in assemblies, but their joining is challenging. Using friction surfacing technology Al 2 O 3 ceramic substrates were coated with an aluminium alloy (AlMg4.5Mn0.7). Earlier research by the authors suggested that two major bonding mechanisms, namely mechanical interlocking and van der Waals forces, are responsible for the bonding strengths achieved between the coating and the substrate. Further scanning electron microscopy, scanning transmission electron microscopy, high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy analysis at a sub nanometre resolution were conducted and are presented in this article. These analytical methods revealed that the aluminium coating and the Al 2 O 3 grains form a sharp boundary without evidence of either a chemical reaction or diffusion at the interface and suggest that the main bonding mechanisms for the Al/Al 2 O 3 system are van der Waals forces. In addition, mechanical interlocking may serve to hold in position the interface surfaces, to preserve their close proximity, allowing the van der Waals forces to persist. [ABSTRACT FROM AUTHOR]

The chemistry of mechanically interlocked molecules (MIMs) such as catenane and rotaxane is full of new opportunities for the presence of a mechanical bond, and the efficient synthesis of these molecules is therefore of fundamental importance in realizing their unique properties and functions. While many different types of preorganizing interactions and covalent bond formation strategies have been exploited in MIMs synthesis, the use of cucurbit[6]uril (CB[6]) in simultaneously templating macrocycle interlocking and catalyzing the covalent formation of the interlocked components is particularly advantageous in accessing high‐order catenanes and rotaxanes. In this review, catenane and rotaxane obtained from CB[6]‐catalyzed azide‐alkyne cycloaddition will be discussed, with special emphasis on the synthetic strategies employed for obtaining complex [n]rotaxanes and [n]catenanes, as well as their properties and functions. [ABSTRACT FROM AUTHOR]

[Display omitted] Characterizing the microstructure of an ice/surface interface and its effect on the icephobic behavior of surfaces remains a significant challenge. Introducing X-ray Computed Tomography (XCT) can provide unprecedented insights into the internal (porosity) and interfacial structures, i.e. wetting regime, between (super)hydrophobic surfaces and ice by visualizing these optically inaccessible regions. Frozen droplets with controlled volume were deposited on top of metallic and polymeric substrates with different levels of wettability. Different modes of XCT (3D and 4D) were utilized to obtain information on the internal and interfacial structure of the ice/surface system. The results were supplemented by conventional surface analysis techniques, including optical profilometry and contact angle measurements. Using XCT on ice/surface systems, the 3D and 4D (imaging with temporal resolution) structural information can be visualized. From these datasets, qualitative and quantitative results were obtained, not only for characterizing the interface but also for analyzing the entire droplet/surface system, e.g., measurement of porosity size, shape, and location. These results highlight the potential of XCT in the characterization of both droplets and substrates and proves that the technique can aid to develop hydrophobic surfaces for use as icephobic materials. [ABSTRACT FROM AUTHOR]

The study presents a bibliometric analysis of studies conducted on multi-materials printing of electronic components via additive manufacturing technologies. Using the R package and the associated biblioshiny, the study analyzed publications from Web of Science and Scopus. The study analyzed 405 research articles after removing 104 duplicates. The study applied performance analysis, keyword analysis, and network analysis. The performance analysis showed that the publications on multi-materials additive manufacturing are multi-disciplinary. Whilst the publications span almost three decades, most contributions started after 2015. The United States of America is the country with the highest production. The keyword analysis showed a changed focus before and after 2015. The trending topics show that the most recent trend is in the ‘aerospace industry’. Finally, the thematic analysis shows that the emerging themes in the area are interfaces, moisture, diffusion, microstructure, mechanical properties, and powder metallurgy. These emerging themes are discussed as they are conceived as the future directions of multi-materials printing of electronic components and devices. The current trend of research focuses on understanding and improving the interfacial bonding between the various multi-material interfaces. Overcoming the weak interfacial bonding issues would improve the mechanical properties of multi-materials electronic components.

Achieving high-strength welding joint of aluminum to steel is a highly pressing and challenging task in the manufacturing industries, and friction stir lap welding (FSLW) has advantages for joining these two metals. To further heighten the strength of dissimilar aluminum and steel metals (Al/steel) FSLW joint, the ultrasonic-assisted FSLW (UAFSLW) process was used, and the upper 2024-T4 aluminum alloy and the lower 304 stainless steel were chosen as research object. The results show that the addition of ultrasound eliminates the micro pores, changes the aluminum-rich intermetallic compounds (IMCs) into the iron-rich IMCs and enhances the micro and macro mechanical interlocking structures along the Al/steel lap interface. Under the rational IMCs layer thickness lower than 1.5 μm, the UAFSLW joint has the failure load higher than the traditional FSLW joint. The maximum failure load of UAFSLW joint reaches 7.06 kN, and the loading capacity of this joint is higher than that of reported Al/steel traditional FSLW joint. The UAFSLW process is an effective way to fabricate the high-strength Al/steel lap joint.

The natural fibre containing cellulose as its main component that can be used as an alternative material to improve the strength of polymer composites. Paper focused on the determination of the best volume fraction of sugarcane fibre-reinforced polymer composites. Three variants of alkalization time were carried out. The highest average value of the tensile test results was obtained at an alkalization time of 1.5 h with a tensile strength of 41 N mm−2 and elongation correspond to 11.806% where the highest bending test results were obtained at an alkalizing time of 0.5 h with a bending strength of 24.89 N mm−2. The results of mechanical interlocking have been observed on macrostructure photo and at 1.5 h of alkalization are better than 0.5 h and 1 h of alkalizing time. [ABSTRACT FROM AUTHOR]

Complex concentrated alloys (CCAs) are structural and functional materials of the future with excellent mechanical, physical, and chemical properties. Due to the equiatomic compositions of these alloys, cost can hinder scalability. Thus, the development of CCA-based coatings is critical for low-cost applications. The application of cold spray technology to CCAs is in its infancy with emphasis on transition elements of the periodic table. Current CCA-based cold spray coating systems showed better adhesion, cohesion, and mechanical properties than conventional one-principal element-based alloys. Comprehensive mechanical behavior, microstructural evolution, deformation, and cracking of cold spray CC-based coatings on the same and different substrates are reviewed. Techniques such as analytical models, finite element analysis, and molecular dynamic simulations are reviewed. The implications of the core effects (high configurational entropy and enthalpy of mixing, sluggish diffusion, severe lattice distortion, and cocktail behavior) and interfacial nanoscale oxides on the structural integrity of cold spray CCA-based coatings are discussed. The mechanisms of adiabatic heating, jetting, and mechanical interlocking, characteristics of cold spray, and areas for future research are highlighted. [ABSTRACT FROM AUTHOR]

Conformal contact with skin is a critical requirement for wearable electronics in medical healthcare, artificial electronics, and human–computer interfaces. Tattoo‐like electronics exploiting water‐dissolvable polymers have been introduced to directly transfer electronics to the skin increasing conformality and adhesion. However, water‐dissolvable polymers cannot be anchored on the skin while maintaining electrical properties because water‐based sweat can destroy the polymer substrate. In this study, we present a transparent and skin‐attachable electrode (TSE) composed of highly conductive silver nanowires and biocompatible polyurethane composite using surface redissolution by ethanol. The TSE can be fabricated into various patterns by a simple fabrication method and firmly mounted on the skin. There was no reddishness or residue on the attached spot after detachment. Additionally, the TSE showed low mechanical modulus of 225 kPa and an optical transmittance of ≈70% at 550 nm. Stable and conformal contact with the skin leads to effective body motion sensing and sensitive electrophysiological signal acquisition due to the low electrical interfacial impedance. [ABSTRACT FROM AUTHOR]

Combining dissimilar parts has become imperative for developing the structures based on lightweight materials, such as metal alloys, polymers or polymer matrix composites, and this has become one of the solutions to reverse the current trend of CO2 emissions in the transport sector. However, given the usual property disparities, joining dissimilar materials in multi-material and multi-purpose structures raises new engineering challenges. Advanced joining processes, such as friction stir welding (FSW), have emerged and have been applied across several sectors as a promising alternative to conventional joining processes, such as mechanical fastening or adhesive bonding. In the present work, and in order to avoid the development of intermetallic compounds (IMCs), a different approach from the conventional technique of friction stir welding was applied to the production of dissimilar overlapping joints. These dissimilar joints were fabricated using a high strength aluminum alloy (AA7075-T651) and a titanium alloy (Ti-6Al-4V), both materials widely used in automotive, aeronautics and space industries. To perform a systematic investigation, the Taguchi method was used to determine the process parameter combinations to enable the fabrication of this type of dissimilar joints. The joints were subjected to quasi-static tensile shear tests to assess their mechanical performance and were compared to conventionally riveted joints in different configurations, namely, single and double connection points. The joints produced by the FSW based method showed higher mechanical performance. To assess the local properties, some of the fractured regions of the joints were subjected to hardness assessments, revealing no significant change in the hardness in the tested areas. Finally, a statistical study was performed to analyze the main effects and interactions of the process parameters, to identify their influences on the mechanical performance of the joints. [ABSTRACT FROM AUTHOR]

The tribological properties of neat polyimide (PI) are incompatible with service conditions, necessitating the urgent modification of its tribological properties. Carbon fibers (CFs) were surface modified with in-situ grown metal-organic frameworks (MOFs) incorporated into PI coating towards the goal of improving its mechanical and tribological properties in combination with graphite (Gr). It is successfully demonstrated that the enhanced interfacial adhesion between the CFs and PI, due to the mechanical interlocking effect of the MOFs, improved the load-carrying capacity and anti-wear properties of the coatings. Additionally, the friction-reduction effect of Gr further contributed to the improvement of tribological properties of MCFs/5Gr/PI coating. Overall, findings of the present study promote the development of engineering plastics with enhanced tribological properties. [ABSTRACT FROM AUTHOR]

The friction stir butt joint process experiment of 6061 aluminum alloy/AZ31B magnesium alloy plate with thickness of 4 mm was carried out. The material flow in transverse cross-section and horizontal-section, the thickness of the intermetallic compound layers, the mechanical interlocking, and the tensile properties of conventional friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW) were compared and analyzed. The action mechanism of ultrasonic vibration was explored. The results show that ultrasonic vibration can promote material flow and heat transfer in different parts of the joint, thereby reduce or even eliminate weld defects. When ultrasonic vibration is applied, the intermetallic compound layer at the aluminum/magnesium interface is thinned, and the mechanical interlocking on the interface is enhanced, so the tensile strength of the UVeFSW joints is improved compared to the FSW joint under the same process parameters. The maximum tensile strength of the UVeFSW joints reaches 174.20 MPa.

Friction surfacing (FS) is a solid-state cladding method that produces a coating with minimum dilution and good metallurgical bonding. Deposition of aluminium over mild steel with using fusion based joining process is not feasible sue to the formation of iron aluminide and Fe and Al are metallurgically immiscible to each other. Hence, deposition of aluminium on steel with solid-state condition is feasible and most viable option. During the process, a rotating consumable rod is rubbed against the substrate plate under an applied axial load. The friction between rod and substrate generates a visco-plastic layer at the end of rod tip. The high temperature and pressure at interfaces aids in the cladding of the rod material on the substrate. Aluminium alloy 6351 T6 rod of 22 mm diameter was used as consumable material for surfacing on a 6mm thick SA516 Gr70 steel substrate plate. Optimized process parameters were used for the final experimental trials. Multilayer samples generated at constant Friction Surfacing variables were subjected to Pin-on-disc wear test at 40N load. Mechanical interlocking was also observed at the interface of the layers. The process was also observed to produce extremely fine grain microstructures of the deposited material due to the hot forging action involved resulting in superior wear properties.

Laser structuring is by far the most investigated metal surface-pretreatment method for creating adhesion in polymer–metal hybrids. Especially, cone-like protrusions show excellent wetting behaviour as well as high compound strength. However, the processing time is extremely high. Therefore, this paper assesses a process strategy for creating pin structures with scalable height by single pulse drilling with an Nd/YVO4 nanosecond laser system on EN AW-6082 aluminium alloy. The strength testing is carried out by butt-bonded hollow cylinder torsion. The samples are manufactured by heat-conduction thermal joining with polyamide 6. Ten different surface structures with two different ablation diameters are investigated and compared to cone-like protrusions in terms of processing time, wetting behaviour, shear strength and fracture behaviour. The experimental results show that pulse drilling pins structures with high aspect ratio reach-strength values close to cone-like protrusions but with 31 times higher processing rate. [ABSTRACT FROM AUTHOR]

In this work, a characterization study of the interfacial interaction between different types of graphene nanoplatelets and an epoxy matrix is computationally performed. To quantify the discrete mutual graphene–epoxy "interfacial interaction energy" (IIE) within the nanocomposite, molecular dynamics simulations with a reactive force field are performed on a localized model of the suggested nanocomposite. Pull-out molecular dynamics simulations are also performed to predict the interfacial shear strength between the two constituents. The results indicate a significant increase in interfacial adhesion of functionalized nanoplatelets with the hosting epoxy matrix relative to virgin graphene nanoplatelets. The obtained results also demonstrate a dramatic increase in the interfacial interaction energy (IIE) (up to 570.0%) of the functionalized graphene/epoxy nanocomposites relative to the unmodified graphene/epoxy nanocomposites. In the same context, the surface functionalization of graphene nanoplatelets with the polymer matrix leads to a significant increase in the interfacial shear strength (ISS) (up to 750 times). The reported findings in this paper are essential and critical to producing the next generation of lightweight and ultra-strong polymer-based nanocomposite structural materials. [ABSTRACT FROM AUTHOR]

Stretchable electronics are emerging for personalized and decentralized clinics, wearable devices and human–machine interactions. Nowadays, separated stretchable functional parts have been well developed and are approaching practical usage. However, the production of whole stretchable devices with full functions still faces a huge challenge: the integration of different components, which was hindered by the mechanical mismatch and stress/strain concentration at the connection interfaces. To avoid connection failure in stretchable devices, a new research focus is to improve the interfacial binding strength between different components. In this review, recent developments to enhance interfacial strength in wearable/implantable electronics are introduced and catalogued into three major strategies: (i) covalent bonding between different device parts, (ii) molecular interpenetration or mechanical interlocking at the interfaces and (iii) covalent connection between the human body and devices. Besides reviewing current methods, we also discuss the existing challenges and possible improvements for stretchable devices from the aspect of interfacial connections. [ABSTRACT FROM AUTHOR]

In this study, a new shear bonding system was created that uses a CO2 laser to form a pattern of conical spots on a zirconia prosthesis surface to improve mechanical interlocking. Four types of zirconia substrates were employed, which underwent particle abrasion after being polished, machined, spotted, and spot-particle abraded. The surface roughness of each substrate was measured via scanning electron microscopy and X-ray diffraction (XRD). A shear bond strength test was performed with the zirconia-based material and a composite resin assuming abutment construction. XRD did not indicate that forming spots caused a phase transformation in zirconia with respect to machined zirconia. The shear bond strength was approximately twice that of the machined samples and approximately 2.3 times that of the samples that underwent particle and spot-particle abrasion. Surface modification by spotting improved the mechanical fitting force. However, no significant difference was observed between particle abrasion and spot-particle abrasion. [ABSTRACT FROM AUTHOR]

Accelerated bridge construction has received widespread attention globally owing to its cost-effectiveness. The integrity of the connections between precast bridge piers and other members of the structure is crucial for developing assembly substructures. This issue was examined in the present study. A novel corrugated steel tube socket connection (CSSC) was developed for column–foundation connections. The CSSC method is a rapid bridge construction method in which a prefabricated corrugated steel tubular concrete column and a corrugated steel pipe in the foundation are connected using concrete or ultra-high-performance concrete. A vertical monotonic static load experiment was performed on six CSSC specimens and one cast-in-place (CIP) specimen to investigate the slip performance, failure modes, and load-transfer mechanism. The side shear performances was compared among specimens with different parameters (connection method, embedment depth, presence of studs, and presence of concrete under the columns). The experimental results indicated that the CSSC specimens had better ductility values and higher axial bearing capacities than the CIP specimen. Increasing the embedment depth, adding studs, and adding concrete under the columns increased the ultimate bearing capacity. To accurately estimate the side shear performance of the CSSC, a reliable finite-element model was developed. An additional parametric analysis was performed to investigate the effects of different parameters on the vertical performance. The CSSC is effective connection type in the prefabricated column-foundation connection and is suitable for bridge high-gravity superstructures. Finally, design recommendations regarding the construction details of the CSSC were presented.

Substantial waste of wool textiles, along with a lack of effective treatment technology, has resulted in a significant resource and environmental constraints. Integrating wasted wool textiles with polymer is an effective way to prepare lightweight structural materials, but the resulting properties is closely linked to the interfacial interaction. Here, we proposed an interfacial manipulation strategy to direct interfacial diffusion and aggregation of amide-based nucleating agents (WBG) in polypropylene (PP)/wool fiber (WF) composites. Accordingly, the branched WBG fibers were anchored onto the WF surface to construct an interlocking interface between WF and PP so as to strengthen the interfacial interaction. The formation and regulation mechanism of the branched WBG fibers were demonstrated. Benefited from mechanical interlocking and β-nucleating function of the branched WBG fibers, the interfacial interaction between the WF and PP matrix was enhanced while the formation numerous β-PP was cultivated, endowing the composite with excellent strength and ductility. To demonstrate the application potential of this strategy, waste wool textiles were alternately embedded between WBG-containing PP sheets to create an interlocking interfacial laminate with an exceptional combination of strength and toughness, which is important to upcycle waste wool textiles. [Display omitted] [ABSTRACT FROM AUTHOR]

Premise: For vascular epiphytes, secure attachment to their hosts is vital for survival. Yet studies detailing the adhesion mechanism of epiphytes to their substrate are scarce. Examination of the root hair–substrate interface is essential to understand the attachment mechanism of epiphytes to their substrate. This study also investigated how substrate microroughness relates to the root–substrate attachment strength and the underlying mechanism(s). Methods: Seeds of Anthurium obtusum were germinated, and seedlings were transferred onto substrates made of epoxy resin with different defined roughness. After 2 months of growth, roots that adhered to the resin tiles were subjected to anchorage tests, and root hair morphology at different roughness levels was analyzed using light and cryo scanning electron microscopy. Results: The highest maximum peeling force was recorded on the smooth surface (glass replica, 0 µm). Maximum peeling force was significantly higher on fine roughness (0, 0.3, 12 µm) than on coarse (162 µm). Root hair morphology varied according to the roughness of the substrate. On smoother surfaces, root hairs were flattened to achieve large surface contact with the substrate. Attachment was mainly by adhesion with the presence of a glue‐like substance. On coarser surfaces, root hairs were tubular and conformed to spaces between the asperities on the surface. Attachment was mainly via mechanical interlocking of root hairs and substrate. Conclusions: This study demonstrates for the first time that the attachment mechanism of epiphytes varies depending on substrate microtopography, which is important for understanding epiphyte attachment on natural substrates varying in roughness. [ABSTRACT FROM AUTHOR]

The present study is a detailed literal survey on the bond behavior of FRP (Fiber Reinforced Polymer) reinforcing bars embedded in concrete. There is an urgent need for the accurate assessment of the parameters affecting the FRP–concrete bond and quantification of these effects. A significant majority of the previous studies could not derive precise and comprehensive conclusions on the effects of each of these parameters. The present study aimed at listing all of the physical parameters affecting the concrete-FRP bond, presenting the effects of each of these parameters based on the common opinions of the previous researchers and giving reasonable justifications on these effects. The studies on each of the parameters are presented in detailed tables. Among all listed parameters, the surface texture was established to have the most pronounced effect on the FRP–concrete bond strength. The bond strength values of the bars with coarse sand-coating exceeded the respective values of the fine sand-coated ones. However, increasing the concrete strength was found to result in a greater improvement in bond behavior of fine sand-coated bars due to the penetration of concrete particles into the fine sand-coating layer. The effects of fiber type, bar diameter and concrete compressive strength on the bar bond strength was shown to primarily originate from the relative slip of fibers inside the resin of the bar, also known as the shear lag effect. [ABSTRACT FROM AUTHOR]

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The bonding mechanisms of a wide range of metallic materials in cold spraying have been studied, mainly attributed to adiabatic shear instability (ASI) at high strain rates, whereas the impact and deformation behavior of high entropy alloys (HEAs) onto various substrates has not been widely explored. HEAs have been characterized by excellent strain-hardening ability and high resistance to shear localization, which can influence their bonding mechanism during cold spray. In this study, experimental and numerical analyses of single-particle impact behavior during cold spraying of CoCrFeNiMn onto commercially pure aluminum (CP Al), aluminum alloy (Al6082), stainless steel (SS304), and titanium alloy (Ti6Al4V) substrates were carried out. The impact morphology revealed ASI in the HEA particle, and SS304 and Ti6Al4V substrates. The HEA/SS304 pair showed a higher critical velocity compared to HEA/Ti6Al4V due to the lower density and thermal conductivity of Ti6Al4V compared to SS304. Mechanical interlocking was observed on CP Al and Al6082 substrates and was attributed to the localized deformation of the substrates. An empirical equation showed this is influenced by the particle density and substrate hardness. This work critically evaluates and provides a better understanding of HEA particle–substrates deformation behavior, expanding its applicability to a wider range of substrates. [ABSTRACT FROM AUTHOR]

Laser spot welding was used for the dissimilar joining of aluminum alloy to steel in the keyhole mode. The results showed that the defocusing amount and laser power had significant influence on the weld formation. The aluminum alloy was prone to the formation of welding defects, such as porosity and cracks in the fusion zone, which resulted in an extremely instable welding process and poor joint strength. In order to improve the weld quality, a copper heat sink was placed under the aluminum alloy, which effectively absorbed the heat of the aluminum alloy and reduced the previous reported welding defects. The influence of laser power, defocusing amount, welding time, and shielding gas on the joint characteristics was also investigated. The microstructure analysis showed that a conelike fusion zone and sparsely distributed Fe-Al intermetallic compounds were formed. Hence, a combination of metallurgical bonding and mechanical interlocking was achieved in the laser keyhole spot welds, enhancing the joint mechanical properties. The joint strength of the laser keyhole spot welds reached 620 N/mm, which was comparable to that obtained in resistance spot welds. [ABSTRACT FROM AUTHOR]