Search Results (212)

Metallic nanofoams with amorphous structures demonstrate exceptional properties and significant potential for diverse applications. However, their mechanical properties at different temperatures are still unclear. By using molecular dynamics simulation, this study investigates the mechanical responses of representative CuZr amorphous metallic nanofoam (AMNF) under uniaxial tension and compression at various temperatures. Our results reveal that the mechanical properties, such as Young’s modulus, yield stress, and maximum stress, exhibit notable temperature sensitivity and tension–compression asymmetry. Under tensile loading, the Young’s modulus, yield strength, and peak stress exhibit significant reductions of approximately 30.5%, 33.3%, and 32.9%, respectively, as the temperature increases from 100 K to 600 K. Similarly, under compressive loading, these mechanical properties experience even greater declines, with the Young’s modulus, yield strength, and peak stress decreasing by about 34.5%, 38.0%, and 41.7% over the same temperature range. The tension–compression asymmetry in yield strength is temperature independent. Interestingly, the tension–compression asymmetry in elastic modulus becomes more pronounced at elevated temperatures, which is attributed to the influence of surface energy effects. This phenomenon is further amplified by the increased disparity in surface-area-to-volume ratio variations between tensile and compressive loading at higher temperatures. Additionally, as the temperature rises, despite material softening, the structural resistance under large tensile strains improves due to delayed ligament degradation and more uniform deformation distribution, delaying global failure. Full article

Body-centered cubic (BCC) metals, extensively utilized in low-alloy high-strength steels and heat-resistant alloys, exhibit a pronounced ductile–brittle transition (DBT) at cryogenic temperatures, marked by a well-defined yet narrow ductile–brittle transition temperature (DBTT) window. This paper overviews the research progress regarding the DBT mechanism of BCC metals. This mechanism was recently found to be related to the mobility of screw dislocation relative to edge dislocation, a decrease in which can induce a critical drop in the proliferation efficiency of dislocation sources. Furthermore, this paper summarizes the current research on the dilute solution softening effect of BCC metals, which has been frequently observed and studied in refractory alloys. The mechanism of this effect involves the low-temperature mobility of screw dislocations that could be promoted by specific solute atoms through kink pair nucleation. This offers a potential strategy for reducing the DBTT of low-alloy steels using a dilute solution, namely microalloying in metallurgy. However, the current understanding of the relationship between the macroscopic ductility of BCC alloys and the dilute solution softening effect is limited. This review aimed to draw attention to this relationship and strengthen related research. Full article

We studied the influence of annealing on the magnetic properties and microstructure of ultrathin (metallic nucleus diameter ≈ 5 μm, total diameter ≈ 19 μm) Heusler-type NiMnGa glass-coated microwires prepared using the Taylor–Ulitovsky method. The as-prepared NiMnGa microwires exhibit unexpectedly strong magnetic anisotropy, characterized by a coercivity exceeding 3 kOe at room temperature. Furthermore, their Curie temperature (T_c) lies above room temperature. Additionally, a spontaneous exchange bias of approximately 120 Oe is observed in the as-prepared sample at 100 K. Annealing the microwires leads to a decrease in coercivity, spontaneous exchange bias, and T_c values. Notably, the annealing process shifts the T_c of the samples closer to room temperature, making them more suitable for magnetic solid-state refrigeration applications. Moreover, the hysteresis observed in the temperature dependence of magnetization for the samples annealed for 1 h and 2 h, along with the magnetic softening observed at around 260 K, is attributed to a first-order phase transformation. The observed changes are discussed in the context of internal stress relaxation after annealing, the nanocrystalline structure of both the as-prepared and annealed samples, the recrystallization process, and the magnetic ordering of phases identified in the as-prepared sample and those appearing during recrystallization. The glass coating on microwires offers benefits like better flexibility and resistance to damage and corrosion. However, it is important to recognize that this coating can substantially alter the microwires’ magnetic characteristics. Consequently, precise control over the annealing process is vital to obtain the specific martensitic transformation needed. Full article

Welding of maraging steels leads to a microstructural gradient from base material (BM) to weld metal (WM). During post-weld heat treatment (PWHT) the precipitation and reverted austenite (γ_r) reactions will occur defining the mechanical properties. These reactions are affected by the microstructure and local chemical composition of each zone in the “as welded” (AW) condition. This effect has not been clearly described yet nor the evolution of the microstructure. The objective of this work was to analyse the phase transformations at the different zones of the welded joint during the PWHT to explain the microstructure obtained at each zone. Samples of C250 maraging steel were butt-welded by GTAW-P (Gas Tungsten Arc Welding—Pulsed) process without filler material. The AW condition showed an inhomogeneous microhardness profile, associated with a partial precipitation hardening in the subcritical heat affected zone (SC-HAZ) followed by a softening in the intercritical (IC-HAZ) and recrystallized heat affected zone (R-HAZ). A loop-shaped phase was observed between low temperature IC-HAZ and SC-HAZ, associated with γ_r, as well as microsegregation at the weld metal (WM). The microstructural evolution during PWHT (480 °C) was evaluated on samples treated to different times (1–360 min). Microhardness profile along the welded joint was mostly homogeneous after 5 min of PWHT due to precipitation reaction. The microhardness in the WM was lower than in the rest of the joint due to the depletion of Ni, Ti and Mo in the martensite matrix related with the γ_r formation. The isothermal kinetics of precipitation reaction at 480 °C was studied using Differential Scanning Calorimetry (DSC), obtaining a JMAK expression. The average microhardness for each weld zone was proposed for monitoring the precipitation during PWHT, showing a different behaviour for the WM. γ_r in the WM was also quantified and modelled, while in the IC-HAZ tends to increase with PWHT time, affecting the microhardness. Full article

The mechanical performance of poly(methyl methacrylate) (PMMA) is highly sensitive to moisture absorption, which induces plasticization and softening. In this study, we investigated the ductilization mechanism of PMMA by incorporating various metal salts with different cations (Li⁺ and Mg²⁺) and controlling water absorption through hygroscopic interactions. A nonequilibrium constitutive model is introduced, in which localized water domains around salt-rich regions gradually diffuse into the PMMA matrix during tensile deformation. The stress–strain behavior is described by combining rigid (dry) and soft (hydrated) matrix components, connected through an internal kinetic variable governed by the strain-dependent diffusion rate. The model successfully reproduces experimental tensile data and captures the transition from brittle to ductile behavior as a function of the moisture content. Notably, Mg salts exhibit stronger water binding and slower moisture redistribution than Li salts, resulting in distinct mechanical responses. These findings provide a mechanistic framework for tailoring the ductility of hygroscopic polymer systems via ion–water–polymer interactions. Full article

The metallic shaped charge liner (SCL) is widely utilized in the defense industry, oil perforation, cutting, and other industrial fields due to the powerful penetration performance. However, quantitative law and underlying mechanisms of material properties affecting SCL penetration performance are unclear. Based on the real and virtual material properties, by combining numerical simulation with machine learning, the influence of material properties on SCL penetration performance was systematically studied. The findings in the present work provided new insights into the penetration mechanism and corresponding influencing factors of the metal jet. It indicated that penetration depth was dominated by the melting point, specific heat, and density of the SCL materials rather than the conventionally perceived plasticity and sound velocity. Average perforation diameter was dominated by the density and plasticity of the SCL materials. Particularly, the temperature rise and thermal softening effect of the SCL controlled by the melting point and specific heat have a significant effect on the “self-consumption” of the metal jet and further on the penetration ability. Additionally, the density of the SCL influences the penetration depth deeply via dynamic pressure of the jet, but the influence of density on penetration depth decreases with the increase in density. The correlation between the key properties and penetration performance was obtained according to a quadratic polynomial regression algorithm, by which the penetration potential of SCL materials can be quantitatively evaluated. Overall, the present study provides a new SCL material evaluation and design method, which can help to expand the traditional penetration regime of the SCL in terms of the penetration depth and perforation and is expected to be used for overcoming the pierced and lateral enhancement trade-off. Full article

Springback represents the deflection of a workpiece after releasing the forming tools or dies, which influences the quality and precision of the final products. It is basically governed by the elastic strain recovery of the material after unloading. Most approaches only implement reverse bending to determine the final shape of the formed product. However, stretch plays significant role whe the blank is held by a blank holder. In this paper, an algorithm is presented to calculate the contributions of both stretch loads and bending moments to elastic deformation during springback for each element, and to combine them mathematically and geometrically to achieve the final shape of the product. Comparing the results of this algorithm for different sheet metal forming processes with experimental measurements demonstrates that this technique successfully predicts a wide range of springback with reasonable accuracy. The advantage of this approach is its accuracy, which is not sensitive to hardening and softening mechanisms, the magnitude of plastic deformation during the forming process, or the size of the object. The application of the proposed formulation is limited to long profiles (plane-strain cases). However, it can be extended to more general applications by adding the effect of torsion and developing equations in 3D space. Due to the explicit nature of the calculations, data-processing time would be reduced significantly compared to the sophisticated algorithms used in commercial software. Full article

Cu matrix composites, because of their high mechanical strength, are often used as conductors in high-performance electrical applications. These composites are manufactured through thermomechanical processing, which introduces a high density of particles that act as obstacles to dislocation motion. Increasing the density of these particles enhances the mechanical strength of the conductors, which we tested under static loading. Under cyclic loading, especially pulsed electrical mechanical loading, conductors may soften, harden, or even fail. Failure is likely to occur whenever the applied stress exceeds the flow stress of the conductors. Understanding and predicting the performance of conductors under cyclic loading can help researchers estimate the lifespan of any apparatus made from these conductors. The performance of conductors depends on whether the strengthening particles are characterized by ionic interatomic bonding or metallic bonding. During fabrication, we observed both the accumulation of dislocations and the dissolution of particles (which added more solute atoms to the matrix). Because both dislocations and solute atoms tend to migrate at room temperature or higher, the complexity of microstructure changes increases in composites under cyclic loading. To minimize such complexity, we designed our test to determine fatigue properties at 77 K. We subjected the conductors to cyclic fatigue tests using a load-controlled mode (the mode most commonly used in applications). This work sheds light on the correlation between tensile properties and fatigue properties in our composite conductors. We found that the correlation varied, depending on whether the conductors had been strengthened by ionic bond or metallic bond particles. Full article

This study aims to improve firestop application standards by experimentally analyzing changes in fire-resistance performance due to variations in opening size, penetrant diameter, and firestop material volume. Fire-resistance tests were conducted for 120 min in accordance with KS F ISO 10295-1, using eight specimens with systematically varied cross-sectional areas of openings and penetrants. For nonmetallic pipes, which soften or melt at elevated temperatures, the results show that the completeness of the opening seal and the amount of firestop material are the primary factors governing fire resistance. When the firestop-to-opening area ratio decreased from 95–91%, the maximum temperature on the unexposed surface was, on average, 15–30 °C lower, confirming that modest reductions in firestop material volume for small openings do not compromise performance. In contrast, metallic pipes retained structural integrity and acted as direct heat-transfer paths; fire-resistance performance was more strongly influenced by penetrant diameter and cross-sectional area than by opening size. These findings provide quantitative evidence to support flexible design criteria for firestop systems and offer a practical basis for transitioning toward performance-based approval standards. Full article

Correlations have been found for the base value of hardness (as the ratio between the heat of fusion and molar volume) and the softening temperature (as the ratio of heat of fusion and specific heat capacity). The relative change of bulk hardness as a function of temperature, H(T), is studied by three new parametric formulas beside the well-known exponential decay and Arrhenius-type expressions. Mathematically, two formulas can be considered as deriving from the exponential decay; the third one is a new rational fraction expression based on the power of normalized temperature. The normalizing temperature is taken as the softening temperature. In the Arrhenius expression, a temperature-dependent activation energy is introduced, which increases steadily with heating but never surpasses the value of self-diffusion. This rational fracture expression has been shown to be applicable to both pure metals and alloys with arbitrary H(T) curve shapes, from convex (pure metals) to concave (alloys). A detailed description of the fitting of these parametric formulas is given, applying the H(T) data from the literature and from our own measurements. Measuring our refractory high entropy alloy (RHEA) samples, an early softening temperature, smaller than the expected half of the melting point (Ts < Tm/2) was detected, signaling a phase instability in the case of Ti-, Zr- and Hf-containing alloys. Full article

Over the last two decades, the use of photovoltaic panels for the production of electricity has increased significantly, which leads to the need to solve the problems concerning the decommissioning and disposal of the panels and the development of appropriate technologies for their recycling. One of the key steps in this process is the separation of the tempered glass layer. Various technologies and devices are known for separating the glass of the solar panel by cutting it with a knife, as well as other instruments, with the different methods being based on mechanical, chemical, and thermal processes and accordingly having their own advantages and disadvantages. This article proposes an innovative approach for the mechanical delamination of solar panels using a metal wire heated by Joule heating, with the potential to become an energy-efficient, economical, and environmentally friendly method. This publication presents results from experiments using this type of tool to separate the layers of solar panels. Photos from a thermal camera are presented, showing the heat distribution in the panel and the reached operating temperature of the heated metal wire, necessary to soften the EVA bonding layer. Full article

Cocoa is a major commodity in the global food industry. Heavy metal contamination, particularly cadmium (Cd), raises significant concerns. This work demonstrates the use of laser-induced breakdown spectroscopy (LIBS) for fast Cd quantification in commercial cocoa powder across a wide range of concentrations (70–5000 ppm). Cocoa powder presents unique challenges due to its physical properties, such as the tendency to soften and liquefy at elevated temperatures, which complicates sample preparation. To address these issues, a mechanical mixing and pelletization protocol was implemented to ensure uniformity. Pellets were doped with known cadmium concentrations for calibration. Cadmium atomic lines at 340.36 and 361.05 nm were used to construct quantification curves. A special algorithm for background subtraction was implemented, and the LIBS plasma was characterized to ensure local thermodynamic equilibrium conditions. Out of eighteen samples, five double-blinded unknowns were evaluated. The concentrations agreed well within normalized standard deviations of 9.73% and 5.88% for the two cadmium lines. The limits of detection for the lines were 0.4 and 0.08 μg/g, respectively. LIBS is confirmed as a rapid and versatile analytical tool for Cd detection and quantification in complex food matrices, with potential applications in field-based and industrial monitoring systems. Full article

Traditional Beidou Navigation Satellite System anti-jamming array antennas mostly use PCB plates, but in extreme vibration environments, their rigidity may cause the antenna structure to be more susceptible to damage. Especially in an extremely high-temperature environment, it may cause thermal expansion, softening, and even melting of metal materials, which will affect the structure and performance of the antenna; In this paper, a Beidou array antenna integrating high seismic resistance, high-temperature stability, and anti-interference ability is designed and studied. The structural parts of the antenna are composed of 7075 aluminum alloy and high-temperature ceramic material technology, which has a compact structure and strong corrosion resistance, which is especially suitable for aviation and marine environments. The antenna works stably at 400 °C and has excellent heat resistance. Built-in shock-absorbing elements or shock-absorbing materials are used to effectively absorb and disperse vibration energy and reduce the direct impact on the internal components of the antenna. Considering the anti-interference performance caused by the size of the array spacing and the mutual coupling between the array elements, the array spacing is designed to be between λ/4 and λ/2. In simulations and experiments, the designed antenna array shows good performance and proves its applicability for high-temperature applications. The antenna frequency includes the B3 band (1250.618~1286.423 MHz) and B1 band (1559.052~1591.788 MHz) of the Beidou Navigation Satellite System. The following article includes the introduction, proposed array antenna structure and dimension, antenna simulation results, antenna protype and environment test, conclusions and future work. Full article

Ultrasonic vibration (UV) has been employed in various plastic forming processes due to its special effect known as acoustoplasticity. Mostly, UV is applied along the longitudinal direction in experimental investigations. However, very few studies have focused on normal UV-assisted uniaxial tension, which is more similar to the loading state of sheet metal in actual forming processes. Herein, normal UV-assisted tension tests on a TA1 thin sheet are performed to study its mechanical properties and microstructure evolution. The macro-mechanical behavior is demonstrated by stress–strain curves under different ultrasonic amplitudes and strain rates. Fracture morphology and microstructure evolution are characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to reveal the UV softening mechanism at the micro level. The results show that the stress reduction induced by UV reaches 20% when the ultrasonic amplitude is 13.9 μm. Fracture mode changes from ductile fracture to brittle fracture with increasing amplitude. Microstructure examinations show that low-angle grain boundary (LAGB) fraction, kernel average misorientation (KAM), and geometrically necessary dislocation (GND) density in the samples experiencing normal UV-assisted tension are all decreased, leading to a reduction in deformation resistance. The inverse pole figures (IPFs) further reveal that the plastic deformation mechanism of the TA1 thin sheet is diversified with the superposition of normal UV. Full article

Ultrasonic vibration (UV)-assisted forming technology has emerged as a significant advancement in the field of bulk micro-forming. This study presents a comprehensive experimental investigation into the micro-scale deformation behavior of metallic materials and its influence on size effects under UV, with a specific focus on the UV-assisted T-shaped micro-upsetting of T2 copper. Utilizing a custom-designed UV-assisted micro-upsetting apparatus, the flow stress, filling height, and microstructural evolution of T2 copper are systematically examined, considering various grain sizes, die opening angles, and ultrasonic amplitudes. The findings demonstrate that UV significantly mitigates the influence of grain size effects. Notably, the softening effect induced by UV becomes more pronounced with decreasing grain size, concomitantly leading to increased filling height. As the die opening angle expands, the required forming load increases. The enhancement of ultrasonic amplitude not only increases the V-groove filling height but also improves the surface quality. The optimal V-groove filling performance is achieved at an ultrasonic amplitude of 8.01 μm. It is crucial to note that increased ultrasonic amplitude generally improves forming performance, while excessive ultrasonic amplitude may lead to micro-crack formation within the material, thereby decreasing the formability of T2 copper. These results provide valuable insights into the complex interplay between ultrasonic parameters and material response in micro-forming processes, offering significant implications for the optimization of UV-assisted forming technologies in precision manufacturing applications. Full article