Search Results (32)

Implantable cardiac devices are critical in improving patients’ quality of life through precise and continuous interaction between the device and pathological cardiac tissue. Due to the inherently rigid nature of conventional devices, several complications arise when interacting with soft cardiac tissue, caused by a mechanical mismatch between the device and myocardium. This leads to the excessive formation of fibrous tissue around the implanted device, ultimately compromising both device functionality and tissue health. To address these challenges, flexible electronics based on polymers and elastomers significantly softer than conventional rigid metals and silicon have been explored. The epicardial approach enables the device to conform to the curved myocardial surface and deform synchronously with cardiac motion, thereby improving mechanical compatibility. However, modulus mismatches between soft polymers and cardiac tissue can still lead to mechanical instability and non-uniform adhesion, potentially affecting long-term performance. This review comprehensively summarizes recent research advancements in epicardial patch electronics based on bioadhesive and conductive hydrogels. We emphasize current research directions, highlighting the potential of hydrogels in epicardial electronics applications. Critical discussion includes recent trends, ongoing challenges, and emerging strategies aimed at improving the properties of hydrogel-based epicardial patches. Future research directions to facilitate clinical translation are also outlined. Full article

Traditional narrow gap welding of thick titanium alloy plates easily produces dynamic molten pool flow instability, poor sidewall fusion, and excessive residual stress after welding, which leads to defects such as pores, cracks, and large welding deformations. In view of the above problems, this study takes 16-mm-thick TC4 titanium alloy as the research object, uses low-power pulsed laser-GTA flexible heat source welding technology, and uses the flexible regulation of space between the laser, arc, and wire to promote good fusion of the molten pool and side wall metal. By implementing instant ultrasonic impact treatment on the weld surface, the residual stress of the welded specimen is controlled within a certain range to reduce deformation after welding. The results show that the new welding process makes the joint stable, the side wall is well fused, and there are no defects such as pores and cracks. The weld zone is composed of a large number of α′ martensites interlaced with each other to form a basketweave structure. The tensile fracture of the joint occurs at the base metal. The joint tensile strength is 870 MPa, and the elongation after fracture can reach 17.1%, which is 92.4% of that of the base metal. The impact toughness at the weld is 35 J/cm², reaching 81.8% of that of the base metal. After applying ultrasound, the average residual stress decreased by 96% and the peak residual stress decreased by 94.8% within 10 mm from the weld toe. The average residual stress decreased by 95% and the peak residual stress decreased by 95.5% within 10 mm from the weld root. The residual stress on the surface of the whole welded test plate could be controlled within 200 MPa. Finally, a high-performance thick Ti-alloy plate welded joint with good forming and low residual stress was obtained. Full article

An absolutely conflicting value for the incorporation of the Lode parameter into a fracture criterion was reported in the literature when predicting the ballistic resistance of metallic plates failing through shear plugging. In this study, a combined experimental–numerical investigation was conducted to understand the dynamic shear fracture behavior under compression–shear stress states. Flat-hat-shaped specimens of 30CrMnSiNi2A high-strength steel were loaded using a Split Hopkinson Pressure Bar apparatus, combining the ultra-high-speed photography technique, digital image correlation method, and microstructure observation. Parallel finite element simulations were performed using both a modified Johnson–Cook (MJC) fracture criterion or an extended Xue–Wierzbicki (EXW) fracture criterion with Lode dependence to reveal the value of the Lode parameter incorporation. It was found that deformed shear bands with a width of approximately 0.14 mm form at a critical impact velocity. The EXW criterion correctly predicts the critical fracture velocity and estimates the fracture initiation instants within an error of 5.3%, whereas the MJC fracture criterion overestimates the velocity by 14.3%. Detailed analysis shows that the EXW criterion predicts a combined failure mechanism involving ductile fracture and material instability, while the MJC fracture criterion attributes the failure exclusively to material instability. The improved accuracy achieved by employing the Lode-dependent EXW fracture criterion may be attributed to the compression–shear stress state and the accurate prediction of the failure mechanism of the dynamic shear fracture. Full article

Sheet metal forming is one of the key processes in the manufacturing of parts for several industries, such as automotive, aerospace and packaging. However, it is often constrained by the onset of plastic instability, which limits uniform deformation. To address this challenge, considerable attention has been given to methods that enhance strength, formability, and energy absorption during forming processes. One such method is the continuous-bending-under-tension (CBT) deformation mechanism, which has shown potential in mitigating localized instability during plastic deformation. This study presents a numerical investigation of the CBT process using Abaqus 2017 to evaluate the forces generated in both the CBT equipment and material when processing high-strength materials. The reference material used is the USS CR980XG3™ AHSS, a third-generation, high-strength, high-elongation steel grade with retained austenite (980T/600Y). The study systematically analyzes the effects of key parameters, such as roll diameter, distance between rolls, depth setting, specimen thickness, and the number of deformation cycles, on the evolution of forces during the CBT process. The results demonstrate that both the forces applied by the rolls and those experienced by the specimen are significantly influenced by the distance between rolls, depth setting, and specimen thickness. In contrast, the roll diameters have minimal influence. These findings contribute to the optimization of the CBT process and provide valuable insights for future studies aimed at enhancing the performance and formability of various materials. Full article

Acoustic emission (AE) is a powerful tool for investigating the intermittency of plastic flow by capturing elastic waves generated by dislocation rearrangements under load. This study explores the correlation between AE and plastic instabilities, such as Lüders bands, the Portevin–Le Chatelier (PLC) effect, and necking, each showing distinct AE signatures. Lüders and PLC bands generate significant AE during discontinuous yielding, with a sharp rise in AE levels and a shift in the spectrum to lower frequencies—characteristic of localized deformation. In contrast, necking exhibits limited AE activity, due to reduced strain hardening and dislocation mobility during late-stage deformation. A phenomenological model, based on dislocation dynamics and initially devised for uniform deformation, is discussed to explain the observed AE spectral features during localized plastic flow. This study underscores AE’s potential for non-destructive evaluation and failure prediction in structural metals, emphasizing its sensitivity to microstructural changes and instabilities. Understanding AE behavior across deformation stages offers valuable insights into improving material reliability and predicting failure. Full article

Nanostructuring burnishing is an effective and mature process for enhancing the surface properties of metallic workpieces. Through severe mechanical deformation, nanostructuring burnishing forms a very hard and smooth surface layer that improves the wear resistance and other properties of the workpiece. This surface treatment requires careful control of process conditions, as the application of large forces and sliding velocities can easily damage the workpiece either through overheating or self-excited oscillation, resulting in an uneven surface. In this paper, we investigate one possible source of such instabilities, namely, unstable stick–slip motion in the sliding direction. When combined with the coupling of normal and tangential stresses through the von Mises yield criterion, the resulting fluctuations of the coefficient of friction can temporarily decrease the effective indentation hardness in the normal direction and thereby produce an uneven indentation track. A dynamical model based on this mechanism is investigated numerically, and the results are found to be in qualitative agreement with experimentally observed surface irregularities encountered in the burnishing of a long drive shaft. The influence of the local bending stiffness at various points along the shaft is also taken into account. Full article

To achieve the rapid heat dissipation of components in the industrial field, the heat dissipation coating is prepared on the surface, which is conducive to improving the service life of the parts and greatly reducing the industrial costs. In this paper, metallized diamond/Cu composite coatings were fabricated on 1060Al substrate by supersonic laser deposition. The composite coatings were prepared at a nitrogen pressure of 3.0 MPa, a scanning speed of 10 mm/s, and a 1060 nm semiconductor coupled fiber laser with different laser power. The research results show that the laser power affects the interface bonding by affecting the temperature of adiabatic shear instability during particle impact. The metallized diamond forms a good bonding at the interface through the plastic deformation of the Cu matrix. Appropriate parameters ensure that the jet does not affect the subsequent particle deposition and build a good heat transfer bridge to elevate the heat transfer efficiency. The coating prepared at a laser power of 1000 W has the highest thermal diffusion coefficient of 89.3 mm²/s and thermal conductivity of 313.72 W/(m·K), which is 8.92% higher compared to the coating prepared without laser. Experiments with thermal imaging have also demonstrated that the coating at optimal parameter transferred heat faster. Our research provides a technical guidance for rapid preparation of high-quality heat dissipation coatings in industry. Full article

The current review work studies the adiabatic shear banding (ASB) mechanism in metals and alloys, focusing on its microstructural characteristics, dominant evolution mechanisms and final fracture. An ASB reflects a thermomechanical deformation instability developed under high strain and strain rates, finally leading to dynamic fracture. An ASB initially occurs under severe shear localization, followed by a significant rise in temperature due to high strain rate adiabatic conditions. That temperature increase activates thermal softening and mechanical degradation mechanisms, reacting to strain instability and facilitating micro-voiding, which, through its coalescence, results in cracking failure. This work aims to summarize and review the critical characteristics of an ASB’s microstructure and morphology, evolution mechanisms, the propensity of materials against an ASB and fracture mechanisms in order to highlight their stage-by-stage evolution and attribute them a more consecutive behavior rather than an uncontrollable one. In that way, this study focuses on underlining some ASB aspects that remain fuzzy, allowing for further research, such as research on the interaction between thermal and damage softening regarding their contribution to ASB evolution, the conversion of strain energy to internal heat, which proved to be material-dependent instead of constant, and the strain rate sensitivity effect, which also concerns whether the temperature rise reflects a precursor or a result of ASB. Except for conventional metals and alloys like steels (low carbon, stainless, maraging, armox, ultra-high-strength steels, etc.), titanium alloys, aluminum alloys, magnesium alloys, nickel superalloys, uranium alloys, zirconium alloys and pure copper, the ASB propensity of nanocrystalline and ultrafine-grained materials, metallic-laminated composites, bulk metallic glasses and high-entropy alloys is also evaluated. Finally, the need to develop a micro-/macroscopic coupling during the thermomechanical approach to the ASB phenomenon is pointed out, highlighting the interaction between microstructural softening mechanisms and macroscopic mechanical behavior during ASB evolution and fracture. Full article

High-efficiency maintenance and control of the deep coal roadway surrounding rock stability is a reliable guarantee for the sustainable development of a coal mine. However, it is difficult to control the stability of a roadway in soft and thick coal beds. To maintain the roadway with soft and thick coal beds under strong mining effect, the novel technology of “anchor bolt (cable) support-presplitting-grouting” is proposed. In this technique, the surface of the surrounding rock was supported by high-strength anchor bolts (cables) and metal mesh to prevent the rocks from falling off; pre-splitting roof cutting was adopted to improve the stress state of deep-part surrounding rocks, and the grouting reinforcement technology was used to reduce fractures and improve lithology. To investigate the deformation characteristics of surrounding rocks under this special condition, the equivalent load calculation model of stress distribution in roadway surrounding rocks was established, and the key area of roadway deformation and instability was defined. According to the theoretical model, the UDEC 7.0 software was employed to analyze the impacts of roof cutting depth, angle, and distance of presplitting kerf on the surrounding rock deformation. Based on the data analysis for simulation results with the Response Surface Method (RSM), the influences of single factors and multi-factor horizontal interactions on the stability of surrounding rocks and the internal causes were analyzed, and the optimal cutting parameters were ultimately defined. The in situ application of this technology shows that the fractures on the coal pillar side and the shear failure of surrounding rocks in the bed were effectively controlled, which provides a reference for roadway control under similar conditions. Full article

During aircraft landing on water, the intense impact load may lead to significant local deformation of the fuselage skin. Ensuring the aircraft’s integrity and reliability is of paramount importance. This paper investigates the fuselage skin’s dynamic response during water entry. In the simulation of complex water entry problems, the smoothed particle hydrodynamics (SPH) method can fully leverage the advantages of the particle method. However, the traditional SPH method still suffers from the drawbacks of tensile instability, significantly affecting the computational accuracy. Therefore, this paper first introduces the improved SPH model addressing fluid and solid tensile instability issues. Furthermore, the Riemann-based contact algorithm at the fluid–solid interface is also demonstrated. Based on the above improved SPH model, the simulation of water entry of the elastic cylinder is performed to validate the efficacy of the improved SPH model. Then, the dynamic response characteristics of elastic fuselage skin and the skin–stringer–floor–column structure when it enters the water are analyzed, including the deformation features and slamming force. Lastly, based on the presented damage model, a study is conducted on the water entry of the metallic elastic–plastic skin–stringer–floor–column structure, analyzing the locations of failure and providing guidance for the structural safety design of engineering. Full article

The welding and construction processes for H-type thick-plate bridge steel involve complex multi-pass welding processes, which make it difficult to ensure its welding performance. Accordingly, it is crucial to explore the inherent correlations between the welding process parameters and welding quality, and apply them to welding robots, eliminating the instability in manual welding. In order to improve welding quality, the GMAW (gas metal arc welding) welding process parameters are simulated, using the Q345qD bridge steel flat joint model. Four welds with X-shaped grooves are designed to optimize the parameters of the welding current, welding voltage, and welding speed. The optimal welding process parameters are investigated through thermal–elastic–plastic simulation analysis and experimental verification. The results indicate that, when the welding current is set to 230 A, the welding voltage to 32 V, and the welding speed to 0.003 m/s, the maximum deformation of the welded plate is 0.52 mm, with a maximum welding residual stress of 345 MPa. Both the simulation results of multi-pass welding, and the experimental tests meet the welding requirements, as they show no excessive stress or strain. These parameters can be applied to building large steel-frame bridges using welding robots, improving the quality of welded joints. Full article

A novel upsetting method, called Cone End Billet Upsetting (CEBU), is proposed in this paper to control bulging during the upsetting of large height-to-diameter ratio (LHDR) billets. This new upsetting method is mainly characterized by prefabricating a conical shape at the billet end, which aims to reduce the friction effect between the billet end and the anvil. In order to validate CEBU, the metal flow characteristics during upsetting of LHDR billets with traditional upsetting (TU) and CEBU were analyzed and compared by the finite element method. Experiments were also carried out to examine the deformation characteristics and microstructure of pure copper samples. The results show that, compared with TU, CEBU has a great advantage in restraining bulging and enhancing the compaction effect of upsetting. Meanwhile, bulging can be eliminated in CEBU with a 50% reduction ratio. In addition, aided by the cone end, the metal flow is no longer sensitive to the friction effect at the billet end. From the point of view of restraining bulging, a small taper angle is necessary prior to use. Furthermore, to avoid instability deformation, the height-to-diameter ratio of the billet should be below 3.0. CEBU is effective in suppressing the generation of bulging, but it also increases the pre-forming process for the end of the billet. The study on CEBU in this article is under laboratory conditions, and exploring the industrial application of CEBU will be the focus of our future research. Full article

In the case where an interstitial atom is located in a close-packed atomic row of the crystal lattice, it is called a crowdion. Crowdions play an important role in the processes of mass and energy transfer resulting from irradiation, severe plastic deformation, ion implantation, plasma and laser processing, etc. In this work, supersonic N-crowdions ($N=1, 2$) in fcc lattices of lead and nickel are studied by the method of molecular dynamics. Modeling shows that the propagation distance of a supersonic 2-crowdion in lead at a high initial velocity is less than that of a supersonic 1-crowdion. In other fcc metals studied, including nickel, supersonic 2-crowdions have a longer propagation distance than 1-crowdions. The relatively short propagation distance of supersonic 2-crowdions in lead is due to their instability and rapid transformation into supersonic 1-crowdions. This feature of the dynamics of supersonic N-crowdions in lead explains its high radiation-shielding properties. Full article

Wrinkle topographies have been studied as simple, versatile, and in some cases biomimetic surface functionalization strategies. To fabricate surface wrinkles, one material phenomenon employed is the mechanical-instability-driven wrinkling of thin films, which occurs when a deforming substrate produces sufficient compressive strain to buckle a surface thin film. Although thin-film wrinkling has been studied on shape-changing functional materials, including shape-memory polymers (SMPs), work to date has been primarily limited to simple geometries, such as flat, uniaxially-contracting substrates. Thus, there is a need for a strategy that would allow deformation of complex substrates or 3D parts to generate wrinkles on surfaces throughout that complex substrate or part. Here, 4D printing of SMPs is combined with polymeric and metallic thin films to develop and study an approach for fiber-level topographic functionalization suitable for use in printing of arbitrarily complex shape-changing substrates or parts. The effect of nozzle temperature, substrate architecture, and film thickness on wrinkles has been characterized, as well as wrinkle topography on nuclear alignment using scanning electron microscopy, atomic force microscopy, and fluorescent imaging. As nozzle temperature increased, wrinkle wavelength increased while strain trapping and nuclear alignment decreased. Moreover, with increasing film thickness, the wavelength increased as well. Full article

Deformation instability is a macroscopic and microscopic phenomenon of non-uniformity and unstable deformation of materials under stress loading conditions, and it is affected by the intrinsic characteristics of materials, the structural geometry of materials, stress state and environmental conditions. Whether deformation instability is positive and constructive or negative and destructive, it objectively affects daily life at all times and the deformation instability based on metal-bearing analysis in engineering design has always been the focus of attention. Currently, the literature on deformation instability in review papers mainly focuses on the theoretical analysis of deformation instability (instability criteria). However, there are a limited number of papers that comprehensively classify and review the subject from the perspectives of material characteristic response, geometric structure response, analysis method and engineering application. Therefore, this paper aims to provide a comprehensive review of the existing literature on metal deformation instability, covering its fundamental principles, analytical methods, and engineering practices. The phenomenon and definition of deformation instability, the principle and viewpoint of deformation instability, the theoretical analysis, experimental research and simulation calculation of deformation instability, and the engineering application and prospect of deformation instability are described. This will provide a reference for metal bearing analysis and deformation instability design according to material deformation instability, structural deformation instability and localization conditions of deformation instability, etc. From the perspective of practical engineering applications, regarding the key problems in researching deformation instability, using reverse thinking to deduce and analyze the characteristics of deformation instability is the main trend of future research. Full article