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Abstract We are entering an era of re-electrification, seeking high-power density electrical machines with minimal resource use. Significant performance gains in electrical machines have been achieved through precise manufacturing processes, including the shaping/cutting of soft magnetic materials. However, most studies have evaluated magnetic performance at a macro level, focusing on components, while the fundamental mechanisms, e.g., how the micromagnetic behaviour is affected by mechanical interference, remain unclear. In this study, we examine the impact of sub-micron deformations at opposing strain rates (10−2 to 101 s−1) on the micromagnetic behaviour of soft magnetic non-oriented electrical steel. Using a diamond probe to indent within a single grain of polycrystalline material at different velocities, we induce quasi-static and dynamic mechanical loading. Our analysis, employing magnetic force microscopy, transmission Kikuchi diffraction, and scanning transmission electron microscopy with a pixelated detector, reveals that magnetic texture disturbances rely on the time-dependent dislocation dynamics of the Fe-BCC material. Additionally, we compress micro-pillars to further investigate these effects under bulk-isolated deformation. These findings highlight the importance of considering even ultra-small loads, such as nano-indentations and micro-pillar compressions, in the manufacturing of next-generation electric machines, as they can affect magnetic texture and performance.

Metal matrix composites (MMCs) offer unique advantageous mechanical properties by strengthening a ductile metal matrix with a ceramic reinforcement (e.g., Ti6Al-4 V/SiCf). However, their heterogeneous composition poses machining challenges including fibre pullout, matrix cracking, and increased tool wear. Whilst pre-heating via laser-assisted machining (LAM) shows promise for improving machinability, traditional LAM implementations with a fixed laser spot size and straight laser path prevent uniform heating. By introducing spatially and temporally controlled LAM that generates homogeneous heating by varying the laser scanning velocity, a technique called fully inverse LAM can be applied for MMCs. This involves calculating separate temperature fields for the matrix and reinforcement to minimise thermal mismatch stresses. The fully inverse LAM decreases subsurface cracks and delamination resulting from conventional milling, whilst localised matrix softening reduces cutting forces by over 62 %. Flank tool wear is also diminished, increasing tool life by 120 %. Material analysis reveals reduced machined surface damage, lower surface roughness, and less formation of intermetallic compounds (Ti2C) compared to traditional LAM.

Yttria stabilized zirconia (6-8YSZ) is widely used as a top coat in Thermal Barrier Coatings (TBCs) to protect metallic substrates. These coatings are exposed to severe high strain rate fields along their life, for example during the impact of debris happening in service or during coating removal in repair processes. In this work a water jet and a high strain rate nanoindenter are used to understand the effect of the strain rate (from 10-3 to 108 s−1) on the behaviour of 8YSZ at a small scale. It is observed how, at extremely high strain rates (106–108 s−1), the material suffers from a brittle-dominated failure which induces localized phase transformation. At lower strain rates (10-3−1 s−1), plasticity dominates, and phase transformation is not observed.

Abstract Biological soft tissues manipulation, including conventional (mechanical) and nonconventional (laser, waterjet and ultrasonic) processes, is critically required in most surgical innervations. However, the soft tissues, with their nature of anisotropic and viscoelastic mechanical properties, and high biological and heat sensitivities, are difficult to manipulated. Moreover, the mechanical and thermal induced damage on the surface and surrounding tissue during the surgery can impair the proliferative phase of healing. Thus, understanding the manipulation mechanism and the resulted surface damage is of importance to the community. In recent years, more and more scholars carried out researches on soft biological tissue cutting in order to improve the cutting performance of surgical instruments and reduce the surgery induced tissue damage. However, there is a lack of compressive review that focused on the recent advances in soft biological tissue manipulating technologies. Hence, this review paper attempts to provide an informative literature survey of the state-of-the-art of soft tissue manipulation processes in surgery. This is achieved by exploring and recollecting the different soft tissue manipulation techniques currently used, including mechanical, laser, waterjet and ultrasonic cutting and advanced anastomosis and reconstruction processes, with highlighting their governing removal mechanisms as well as the surface and subsurface damages.

Abstract Bone cutting is of importance in orthopaedic surgery but is also challenging due to its nature of brittleness—where severe mechanical and thermal damages can be introduced easily in conventional machining. Laser machining is a new technology that can allow for complex cut geometries whilst minimising surface defects i.e., smearing, which occur in mechanical methods. However, comparative studies on the influence of lasers with different pulse characteristics on necrotic damage and surface integrity have not been reported yet. This paper for the first time investigates the effects of laser type on the necrotic damage and surface integrity in fresh bovine cortical bone after ex-situ laser machining. Three lasers of different pulse widths, i.e., picosecond, nanosecond and continuous wave lasers have been investigated with different feed speeds tested to study the machining efficiency. The cutting temperature, and geometrical outputs have been measured to investigate the thermal influence on the cooling behaviour of the bone samples while high-speed imaging was used to compare the material removal mechanisms between a pulsed and continuous wave laser. Furthermore, an in-depth histological analysis of the subsurface has revealed that the nanosecond laser caused the largest necrotic depth, owing to the high pulse frequency limiting the dissipation of heat. It has also been observed that surface cracks positioned perpendicular to the trench direction were produced after machining by the picosecond laser, indicative of the photomechanical effect induced by plasma explosions. Therefore, the choice of laser type (i.e., in terms of its pulse width and frequency) needs to be critically considered for appropriate application during laser osteotomy with minimum damage and improved healing.

Deep-eutectic fluids (DEFs) are a novel class of materials that, to date, have been generally used in a single-phase (liquid) for a growing number of applications (e.g., extraction, catalysis, synthesis, etc). In contrast, we present a novel approach to utilise the advantages associated with dual-phase control of DEFs. In this study, we exploit the compositional tunability of DEFs to adapt their functional response. Specifically, we demonstrate the synthesis and application of a crystalline DEF (SolBar) that melts in a controlled manner and under desired conditions. We show how the concept of dual-phase control of a DEF can reduce thermo-mechanical loads developed during shear-based machining operations and offer a substitute for conventional cooling/lubrication means. To this end, we formulated the chemistry of SolBar (a citric acid and choline chloride DEF) so that, as it transforms into liquid, it directly affects lubrication and cooling at the tool-workpiece interface. This was demonstrated by temperature and force measurements. The generation of a tribo-active layer was evidenced through X-ray photoelectron spectroscopy. This layer enhances the lubrication capabilities of the DEF. The concept is not limited to machining, which serves to demonstrate a useful application in this study but can be extended to multiple fields where surfaces are in contact and control of the physico-chemical response of the system is required. Here, we pave the way to new, environmentally friendly, and cost-effective alternatives to conventional tribological media.

The escalating demand for heating and the widespread use of CO2-emitting fossil fuels during cold seasons have imposed significant pressure on our natural resources. As a promising alternative to coal-fired boilers, electrical thermal storage devices (ETSDs) for space heating are gaining popularity. However, designing ETSDs for space heating involves significant challenges, which involve their storage rate and operational stability. In contrast to the research of directly developing mid-temperature ETSDs to manage heat release during long heating hours, this study proposed a new ETSD that uses K2CO3–Na2CO3 for high-temperature storage to match the off-peak hours and thereby gain potential economic benefits. This study used experimental and simulation methods to investigate the ETSD’s temperature distribution. An operational strategy was also proposed to achieve more efficient temperature distribution and higher economic benefits. The ETSD with two steel plates and two insulation layers with a power rating of 1.6 kW was found to be the optimum structure, due to its improved heat storage rate (2.1 °C/min), uniform temperature, and material heat resistance (

Understanding the microstructural evolution mechanisms in machining of advanced materials is essential to achieve excellent surface integrity levels within the manufacture of safety–critical components. However, as thermal and mechanical effects are coupled in conventional cutting operations, it is difficult to attribute their individual role on microstructural evolution and integrity. To investigate the temperature-dependency of microstructural evolution in cutting, a new experimental set-up has been developed to perform machining experiments under controlled temperatures. Results show that an onset in chip shear localisation with nanocrystalline grain refinement can be induced uniquely by an increase in cutting temperature under fixed cutting parameters, which microstructurally controls the transition from continuous to serrated chip formation. Increase in mechanical effects at HT leads to the formation of a continuous chip grain refinement layer, associated to a change in energy partition at the tool-workpiece interface. These small-scale behaviours are found to control the reduction in cutting forces and energy at higher temperatures, with a decrease of ∼ 25–30%. Nevertheless, despite the lower deformation energy, HT cutting induced larger amounts of microstructural deformation because of thermal softening effects, further disclosing the role of thermal effects on the interplay between shear localisation, microstructural evolution and surface integrity.

Laser-processing technologies are often applied to enhance the properties of ceramics, such as laser glazing of Yttria Stabilised Zirconia (YSZ). However, very limited attention was paid to the solidification phenomena and mechanisms of YSZ. In this paper, two coexisting solidification behaviours of laser-melted YSZ have been identified, namely grain bending (crystals with curved grain boundary geometry under the surface) and grain surface sealing (in-plane surficial crystals cover vertical columnar grains). Although these phenomena have been reported, this is the first time the two phenomena coexist in the same material. A new cellular automata (CA) approach has been proposed to explain the formation mechanisms of these two phenomena. This new CA method consists of the separation of growth modes into dendritic and planar growth, whose critical transition value is calculated based on the supercooling theory. Besides, the proposed model for planar growth is far less computationally expensive than the widely used decentred octahedron algorithm. A good agreement with the EBSD data of longitudinal cross-sections and the top surface has been observed which proves that the proposed method can become a more realistic and efficient way to predict the grain microstructure in laser processing, allowing to capture dendritic and planar growth simultaneously.

The micro-defects on KH2PO4 (KDP) optic surfaces are mainly repaired by the micro-milling technique, while it is very easy to introduce brittle cracks on repaired surfaces, as KDP is soft and brittle. To estimate machined surface morphologies, the conventional method is surface roughness, but it fails to distinguish ductile-regime machining from brittle-regime machining directly. To achieve this objective, it is of great significance to explore new evaluation methods to further characterize machined surface morphologies. In this study, the fractal dimension (FD) was introduced to characterize the surface morphologies of soft-brittle KDP crystals machined by micro bell-end milling. The 3D and 2D fractal dimensions of the machined surfaces and their typical cross-sectional contours have been calculated, respectively, based on Box-counting methods, and were further discussed comprehensively by combining the analysis of surface quality and textures. The 3D FD is identified to have a negative correlation with surface roughness (Sa and Sq), meaning the worse the surface quality the smaller the FD. The circumferential 2D FD could quantitively characterize the anisotropy of micro-milled surfaces, which could not be analyzed by surface roughness. Normally, there is obvious symmetry of 2D FD and anisotropy on the micro ball-end milled surfaces generated by ductile-regime machining. However, once the 2D FD is distributed asymmetrically and the anisotropy becomes weaker, the assessed surface contours would be occupied by brittle cracks and fractures, and corresponding machining processes will be in a brittle regime. This fractal analysis would facilitate the accurate and efficient evaluation of the repaired KDP optics by micro-milling.

Abrasive waterjet peening (AWJP) is a promising method of surface treatment for modifying mechanical properties of components by introducing compressive residual stress (CRS) to a workpiece surface. Many efforts have been paid so far to modelling and optimisation of the AWJP process, however, most of these studies focus on the forward problems, i.e. estimating the CRS of workpiece surface according to processing parameters. There are still significant challenges in implanting different CRS at target areas in workpiece surface, which is the foundation of implanting uniform distribution of CRS on free-form surface or workpiece with uneven initial stress state. In this paper, a novel temporally and spatially controlled method for AWJP has been proposed, where the distribution of CRS can be adjusted by the optimisation of the abrasive waterjet parameters. That is, to achieve the AWJP system configuration for specific CRS on a target area, an inverse problem of CRS distribution has been modelled and solved, where the pump pressure, traverse speed and centre distance were optimised together to reach a prescribed CRS distribution. The proposed method was validated through experiments of implanting uniform distribution and non-uniform distribution of CRS at target areas. The results revealed that the maximum error between target and experimental CRS was only 14.25% in 18 sets of experiments. In addition, microstructure analysis of the AWJP surface suggested that a relatively low pump pressure and traverse speed can be selected to induce grain refinement and strain hardening layer on the workpiece surface without cracks and heavy surface topography fluctuations.

Abrasive waterjet peening (AWJP) is a new mechanical surface treatment where particles are delivered by a waterjet to induce plastic deformation and achieve surface strengthening effects on a workpiece. Although fatigue strength can be improved by inducing compressive residual stress, the prediction of residual stress distribution remains challenging because particle–workpiece interaction occurs with randomicity, superposition, and overlapping. In this paper, a theoretical model is proposed for predicting workpiece plastic deformation and compressive residual stress by analysing i) the non-uniform energy distribution of the AWJP beam caused by the non-uniformity of the abrasive size, spatial distribution, and impact velocity; ii) material hardening among multiple impacts by abrasive particles; and iii) overlapping traces induced by the changing position of the AWJP beam. The AWJP experiments were conducted in single-pass/multiple-pass/multiple-overlapping footprints with different pump pressures, traverse speeds, and jet centre distances of the adjacent traces to validate the model. The results showed good agreement with the predicted surface roughness and compressive residual stress. Compressive residual stress increased with the pump pressure, whereas the effect of pump pressure change rate decreased when the pump pressure was increased; further, residual stress is nearly constant with the variation in traverse speed and jet centre distance of the adjacent traces when it decreases to a certain value. These results can act as references for the control of residual stress and the prediction model can aid industrial manufacturing in AWJP parameter optimisation (e.g. pump pressure, traverse speed, surface roughness, compressive residual stress, and centre distance between two adjacent traces).

Non-oriented electrical steel (NOES) laminations are commonly used to manufacture the rotor and stator core of electric machines. To achieve high machine efficiencies, it is desirable for these NOES laminations to be able to achieve a high saturation magnetisation whilst incurring minimal core losses. It is known that inappropriate machining of these laminations could cause significant deterioration in their magnetic properties. However, the mechanisms by which machining influences this deterioration are less understood. This study investigates the magnetic deterioration after four nonconventional machining methods: Abrasive Waterjet, Wire Electric Discharge Machining, Pulsed Laser, and Continuous Wave Laser. An in-depth investigation of surface integrity through a range of methods, i.e., surface topography, scanning electron microscopy (SEM), nanoindentation, electron backscatter diffraction (EBSD), and magnetic domain imaging, were conducted to study the mechanisms causing magnetic deterioration. The surface integrity after machining using conventional methods (e.g., microstructure and texture), was found to not be of high relevance unless this is combined with analysis on how machining affects the micro-magnetic domain structure. This paper, for the first time, highlights this aspect and attempts to make initial quantitative evaluations on how the magnetic domains are affected in the superficial layer that is the result of non-conventional machining.

Integrating the exergy and economic analyses of water electrolyzers is the pivotal way to comprehend the interplay of system costs and improve system performance. For this, a 3D numerical model based on COMSOL Multiphysics Software (version 5.6, COMSOL, Stockholm, Sweden) is integrated with the exergy and exergoeconomic analysis to evaluate the exergoeconomic performance of the proton exchange membrane water electrolysis (PEMWE) under different operating conditions (operating temperature, cathode pressure, current density) and design parameter (membrane thickness). Further, the gas crossover phenomenon is investigated to estimate the impact of gas leakage on analysis reliability under various conditions and criteria. The results reveal that increasing the operating temperature or decreasing the membrane thickness improves both the efficiency and cost of hydrogen exergy while increasing the gas leakage through the membrane. Likewise, raising the current density and the cathode pressure lowers the hydrogen exergy cost and improves the economic performance. The increase in exergy destroyed and hydrogen exergy cost, as well as the decline in second law efficiency due to the gas crossover, are more noticeable at higher pressures. As the cathode pressure rises from 1 to 30 bar at a current density of 10,000 A/m2, the increase in exergy destroyed and hydrogen exergy cost, as well as the decline in second law efficiency, are increased by 37.6 kJ/mol, 4.49 USD/GJ, and 7.1%, respectively. The cheapest green electricity source, which is achieved using onshore wind energy and hydropower, reduces hydrogen production costs and enhances economic efficiency. The growth in the hydrogen exergy cost is by about 4.23 USD/GJ for a 0.01 USD/kWh increase in electricity price at the current density of 20,000 A/m2. All findings would be expected to be quite useful for researchers engaged in the design, development, and optimization of PEMWE.

In bone cutting, the tissue is exposed to necrosis due to temperature elevation, which can significantly influence postoperative results in orthopaedic surgeries. This damage is usually revealed through histological analysis to show the necrotic extent; however, this technique does not capture mechanical damage, which is essential for a full material integrity assessment. Here, with micro-mechanics, it is demonstrated that machining-induced damage in bone extends beyond the necrotic region. Drilling with different conditions was performed on ex-vivo bovine cortical bone, inducing different damage degrees. Micro-pillar compression tests were performed in the machined sub-surface to identify changes in properties and failure modes caused by drilling. It was revealed that at high cutting temperatures, the bone near the machined surface suffers from lower modulus (−42%), strength (−41%) and brittle behaviour, whereas the bulk bone remains undamaged with pristine properties and ductile behaviour. Histology was also performed to evaluate necrosis and, surprisingly, it was found that the brittle and weaker bone layer is more than three times larger when compared to the necrotic layer, clearly showing that the drilling thermo-mechanical effect could affect not only biologically, but also micro-mechanically. Consequently, these results reveal another kind of bone damage that has so far been neglected.

Micromachining repair of surface defects on KH2PO4 (KDP) optics is an emerging technique in the construction of Inertial Confinement Fusion facilities for obtaining clean nuclear fusion energy. However, this method is yet facing considerable challenges owing to the soft-brittle nature of single-crystal KDP, hence it is necessary to understand its ductile-regime cutting mechanism to generate crack-free surfaces. This paper seeks to investigate the evolution of different cutting mechanism with the change of uncut chip thickness (UCT) in KDP orthogonal cutting processes. A transition of cutting modes from plastic cutting to shear-crack cutting and then fracture cutting with the rise of UCT has been revealed. To explain these cutting phenomena, a novel theoretical model was proposed by calculating the specific energy dissipation for crack/fracture propagations during cutting processes based on fracture mechanics. This analytical model was well validated by the analysis of cutting forces and machined surface quality. Nevertheless, three kinds of surface defects have been observed, i.e. micro pits, micro craters and edge chipping. These surface defects were caused by tearing and spalling of materials with elastic recovery, crack propagation along cleavage planes with ploughing effect, and the peeling away of large-size fracture, respectively. The presented results of great significance for promoting the application of micromachining processes in future engineering repair of KDP optics.

While laser-assisted machining can significantly improve the machinability of nickel-based superalloy, the mechanism of surface integrity evolution and its influence on the material functional performance is still not clear. The present study gives a comprehensive investigation on the surface integrity of laser-assisted milling (LAMill) process with an in-depth study of the mechanism of chip formation, microstructural and mechanical alternations, supported by key outcomes from the two constitutive processes, conventional milling (CMill) and single laser scanning (LS). Although the high thermal affected layer in LAMill process has been removed through the cutting chips, a significant bending effect has been found in both the LAMill and LS workpiece. More interestingly, a combined impact of the residual stress from LS and CMill has been found on LAMill workpiece while a lattice evolution has been revealed regarding both the thermal and mechanical influence. Specifically, inadequate fatigue performance on LAMill and LS workpiece has been found due to the high thermal effect in the superficial layer regarding the residual tensile stress distribution and microstructure variation. While LAMill is generally considered as a promising machining method with improved machinability of difficult-to-cut materials, this research shows a poor workpiece functional performance (fatigue) and justifies its application prospect.

It is essential for superalloys (e.g., Inconel 718) to obtain an anticipated surface integrity after machining, especially for safety critical areas (e.g., aerospace). As one of the main characteristics for cutting tools, the rake angle has been recognized as a key factor that can significantly influence the machining process. Although there are large research interests and outcomes in the machining of nickel-based superalloys, most of them focus on the surface integrity and macroscale temperature observation, whereas the temperature distribution in the tool rake face is not clear. Thus, it is necessary to investigate the basic role of rake angles and the tool–workpiece interaction mechanism to determine the machining condition variations and surface integrity. In the present study, both experimental and numerical methods are employed to explore the cutting force, thermal distribution, and shear angles during the process and the metallurgy characteristics of the subsurface after machining, as well as the mechanical properties. The research has emphasized the importance of rake angles on both the cutting process and machined surface integrity, and has revealed the microscale temperature distribution in the tool rake face, which is believed to have a close relationship with the tool crater wear. In addition, it is clearly presented that the surface generated with positive rake angle tools generates the minimum subsurface deformation and less strain hardening on the workpiece.

This paper presents a numerical study that aims at investigating the effects of different parameters on the dynamic performance of single and multi-layer encapsulated phase material (PCM) thermocline tanks. A transient, one-dimensional, two-phase, concentric-dispersion model is formulated to evaluate such performance. Encapsulated paraffin waxes having different melting-points are used as PCMs, with water as heat transfer fluid. Comprehensive comparisons between single-PCM and multiple-PCMs systems are numerically analyzed first. Second, the effects of the PCM volume fraction (VF) and the inverse Stefan number have been discussed. The results show that among the various cases the single-PCM70 system has the highest performance in terms of charging and discharging efficiency, followed by a multiple-PCMs system with average performance. Compared with the PCM40 case, the PCM70 case has a 29% increase in the output energy from the system. The VF of PCMs influences the system output, both in terms of energy storage and release, the heat storage period and the total energy stored increased by 4.5%, when the VF of the PCM70 increases from 33.33% to 50%, respectively. Furthermore, it increases the system’s overall efficiency and total utilization ratio by 13.7% and 25%, respectively, when compared to the arrangement in which the PCM40 occupies 50% of the total bed height. The effect of the inverse Stefan number has a significant impact on the system’s utilization ratio. Compared with all other 3-PCM systems, the scenario with the lowest inverse Stefan number in the middle PCM has the highest charging and discharging efficiencies of 83.9% and 80.8%, respectively. The findings may be beneficial for the design and optimization of packed-bed tanks.

The fabrication of form-stable phase change materials (FS-PCMs) usually involves four manufacturing processes: mixing, immersion, stabilization, and sintering. In each process, the operation parameters could affect the performance of the fabricated PCM composite. To gain an efficient and low-cost method for large-scale production of the molten salts/expanded graphite (EG) composite FS-PCMs, the effects of different operating parameters were investigated, including the stirring speed, evaporation temperature, melt-impregnation, cold-pressing pressure, and sintering temperature on the densification, microstructure, and thermophysical properties of the composite FS-PCMs. It was found that the microstructure, the morphology and durability, and the thermophysical properties such as thermal conductivity and specific heat enthalpy depended highly on the operating parameters. The following optimal operating parameters of the Ca(NO3)2–NaNO3/EG composite FS-PCMs are suggested: the stirring speed of 20 rpm, the evaporation temperature of 98 °C, the melt-impregnation temperature of 280 °C, the cold-pressing pressure of 8 MPa, and the sintering temperature of 300 °C. The results of the present work can provide valuable insights for the large-scale production of the composite FS-PCMs.

An electrical thermal storage (ETS) device for space heating is designed in this study. The proposed device is charged by the off-peak electricity and releases its thermal energy to warm the space all day long. The natural convection occurring in the flow channel drives the flowing of air to be heated up and warm the space. The dynamic process of a fully charging/discharging cycle of the device is tested. Meanwhile, a three-dimensional model is developed to simulate the transient thermal behavior. It is found that the experimental and numerical results agree with each other which indicates the validation of the proposed numerical model. The results show that the temperatures of the bricks and the outlet air can be as high as 1002 K and 835 K, respectively. The natural convection occurring in the flow channel transfers 40.4% of the total electrical heating energy to the space for the charging process and 26.9% for the discharging process. Heat losses to the space through the adiabatic material shares 13.3% of the total heating energy for the charging process and 7.2% for the discharging process. Based on those findings, three methods are recommended to improve the device in the successive research.