Department of Mechanical Engineering

The present work aims to study the influence of hot deformation on microstructural development and flow behavior in the Al-4.8Mg-0.3Sc alloy produced by the laser powder bed fusion (LPBF) technique. Uniaxial compression tests have been conducted within a temperature regime of 200–350 ºC at a 0.01–1 s?1 strain rate using a Gleeble-3800™ thermomechanical simulator. The major results show that the flow behavior is governed mainly by strain hardening at 1 s?1 strain rate and dynamic recrystallization (DRX) at 0.1 s?1 within 250–350 ºC. The constitutive equations have been developed by employing activation energy (Q) and other material constants to forecast the influence of deformation temperature and strain rates on flow stress. Compared to other Al alloys (114–227 kJ/mol), the mean Q for hot deformation is found to be significantly higher (?340 kJ/mol at a 0.69 true strain), indicating more stress requirement for deformation, also confirmed by the flow curves. Moreover, the processing map developed with MDMM+Poletti instability criteria is found to be appropriate compared to DMM and MDMM models. The safe workable zone is obtained in the range of 250–350 ºC/0.01–1 s?1 with a maximum power dissipation efficiency of 45.8 %. Microstructural analysis shows that recrystallization starts primarily at melt pool boundaries which formed during the LPBF process. The highest recrystallization fraction is observed for the specimen deformed at 350 ºC/0.01 s?1 (59.3 %). SEM analysis of the samples deformed at 200 ºC/0.01–1 s?1 and 250 ºC/1 s?1 depict the formation of various defects, such as voids and micro-cracks, mainly governed by the non-uniform deformation at the particle/matrix interface and due to the presence of voids/pores. A detailed investigation of Q, stress exponent (n), flow stress behavior, and constitutive equations suggests that the hot deformation is mainly governed by both dislocation climb and cross-slip mechanisms.

This study investigates the impact of printing orientation on the mechanical properties and surface characteristics of parts produced using VeroWhitePlus RGD835 polymer material in a layer-based Polymer Jetting Technology process. Tensile, hardness, and surface roughness tests were conducted to evaluate the influence of different printing orientations on the properties of the printed samples. The results show that printing orientation significantly affects both the mechanical strength and surface roughness of the parts. Specifically, samples printed in the XZ, YZ, and vertical orientations exhibited 20–30% higher tensile strength and 15–25% greater hardness compared to those printed in XY and other orientations. Surface roughness values varied by up to 10 µm across orientations but did not directly correlate with tensile strength and hardness, suggesting a complex interaction between orientation, layer bonding, and material properties. This anisotropic behavior is attributed to the non-uniform absorption of light energy during the jetting process, which causes varying layer bonding and material density across different regions of the printed parts. Additionally, areas with higher energy absorption, such as the edges of layers, exhibited smoother surfaces and enhanced mechanical properties, while regions with lower energy absorption showed rougher surfaces and reduced strength. Fracture surface analysis revealed brittle fracture characteristics with localized pressures and voids between layers, weakening the material’s ability to withstand deformation. These findings provide valuable insights into the optimization of Polymer Jetting Technology processes, particularly in selecting printing orientations and adjusting process parameters such as light exposure intensity, to improve mechanical performance and surface quality.

This study explores the fabrication of bone scaffolds using a composite ink of poly-?-caprolactone (PCL), polyhydroxybutyrate (PHB) and synthesized fluorapatite (FHAp) via response surface methodology optimization to achieve optimal Vickers hardness number (VHN). Characterization with X-ray diffraction confirms FHAp presence and increased crystallinity post-sintering, while Fourier-transform infrared spectroscopy reveals fundamental material interactions. Results show PCL’s softening effect at higher concentrations, PHB’s contribution to decreasing hardness and FHAp’s significant role in reinforcing the composite. Contour plots demonstrate peak hardness at lower PCL and PHB concentrations (<11% wt/v) with 18% wt/v FHAp. The optimum hardness values were found at PCL, PHB and FHAp of 9.754% wt/v, 9.473% wt/v and 24.608% wt/v, respectively, yielding 185.34 VHN. These findings offer insights into optimizing composite concentrations for tailored mechanical properties crucial in bone scaffold design, advancing regenerative medicine and tissue engineering

Here, a planar design of a filtering antenna is presented. The design mainly comprises a semi-circular substrate integrated waveguide (SIW) cavity as a driven element and a rectangular parasitic patch with loaded metallic vias. The coax feed is used to excite the SIW cavity and the cavity excites the rectangular patch by a coupling mechanism. The loaded four metallic vias help realize the gain characteristic’s sharp selectivity with radiation null at both edges of the operating band. The simulated investigation shows that broadband response is achieved by using such a topology. The measured results show a broad band response of 7.90% impedance bandwidth with a flat realized gain performance of 7.34 dBi in the entire operating band. The proposed design offers attractive features such as small foot prints, high gain, small cross polarization, high selectivity, and a high front-to-back ratio

This study examines the impact of sinusoidal time-dependent injection velocities on miscible thermo-viscous fingering instabilities observed in enhanced oil recovery. Linear stability analysis (LSA) and nonlinear simulations (NLS) are used to investigate fingering dynamics, considering parameters such as thermal mobility ratio (R?), solutal mobility ratio (Rc), Lewis number (Le), and thermal-lag coefficient (?). The LSA employs a quasi-steady state approximation in a transformed self-similar coordinate system, while NLS uses a finite element solver. Two injection scenarios are explored: injection-extraction (?=2) and extraction-injection (?=?2), with fixed periodicity (T=100). Results show that for unstable solutal and thermal fronts (Rc&gt;0,R?&gt;0), increasing Le with fixed ??1 leads to more prominent mixing and interfacial length for ?=2 compared to constant injection and ?=?2. While for unstable solutal fronts (Rc&gt;0) and stable thermal fronts (R?&lt;0), increasing Le results in more prominent mixing and interfacial length for ?=?2, except during early diffusion. Thus, when porous media are swept using cold fluid, increasing the Lewis number intensifies the level of flow instability for ?=?2; whereas when hot fluid is used, the instability enhances for ?=2. Furthermore, it is observed that the high thermal diffusion (Le?1) and enhanced thermal redistribution between solid and fluid phases (??1) effectively mitigate destabilizing effects associated with positive R?, reducing overall instability. Overall, in extraction-injection scenarios, the phenomenon of tip-splitting and coalescence is attenuated, and the channeling regime is observed

In aerospace applications, engine parts, especially those around the rotor blade tips, are coated with an abradable seal, a specific material layer. Its design produces a tighter seal without harming the blades by allowing it to wear down or “abrade” somewhat when the blade tips come into contact. In turbines and compressors, this reduces gas leakage between high- and low-pressure zones, increasing engine efficiency. Abradable seals are crucial to contemporary jet engines because they enhance performance and lower fuel consumption. The materials selected for these seals are designed to balance durability and abrasion resistance under high temperatures and speeds. Metal matrix, oxide particles, and porosity are the three most prevalent phases. An ideal mix of characteristics, such as hardness and erosion resistance, determines how effective a seal is, and this is accomplished by keeping the right proportions of elements in place throughout production. The primary objective of this research is to optimize abradability by utilizing various FEM tools to simulate the rub rig test and modify testing parameters, including Young’s modulus, yield stress, and tangent modulus, to analyze their impact on the wear behavior of the abradable seal and blade. Two microstructure models (CoNiCrAlY–BN–polyester coating) were found to perform optimally at porosity levels of 56% and 46%, corresponding to hardness values of 48 HR15Y and 71 HR15Y, respectively. Changing factors like yield stress and tangent modulus makes the seal more abrasive while keeping its hardness, porosity, and Young’s modulus the same. Furthermore, altering the Young’s modulus of the shroud material achieves optimal abradability when tangent modulus and yield stress remain constant. These findings provide valuable insights for improving material performance in engineering applications. To improve abradability and forecast characteristics, this procedure entails evaluating the effects of every single parameter setting, culminating in the creation of the best abradable materials. This modeling technique seems to provide reliable findings, providing a solid basis for coating design in the future

This study examines the microstructural, mechanical, and fractographic characteristics of friction-welded (FW) joints between SA 213 T12 and SA 213 F12 low alloy steels at rotational speeds of 55, 60, and 65 rps. Microstructural analysis using optical and SEM imaging revealed distinct weld zones, including the interface (IF), partially deformed zone (PDZ), and heat-affected zone (HAZ). The IF exhibited refined bainite and acicular ferrite, with increased dynamic recrystallization at 60 rps, leading to enhanced mechanical properties. Elemental mapping through EDS confirmed uniform chromium and molybdenum diffusion across the IF, with greater mechanical mixing at higher speeds. Microhardness profiling showed peak values at the IF, particularly on the SA 213 F12 side, decreasing towards SA 213 T12. The hardness distribution narrowed at higher speeds due to increased flash generation. Tensile testing revealed that all joints exceeded the base metals in ultimate tensile strength (UTS), with the highest UTS at 60 rps. Fractographic analysis confirmed a predominantly ductile failure, with finer dimples at 60 rps, correlating with improved elongation and strength. These findings demonstrate that an optimal rotational speed of 60 rps yields superior mechanical performance and microstructural refinement, providing valuable insights for optimizing FW parameters in high-performance applications.Cette étude examine les caractéristiques microstructurales, mécaniques et fractographiques de joints soudés par friction (FW) en aciers faiblement alliés (LAS) SA 213 T12 et SA 213 F12 à des vitesses de rotation variées (55, 60 et 65 tour/s). L’analyse de la microstructure à l’aide de micrographies optiques et MEB a révélé des zones distinctes à travers la soudure, incluant l’interface (IF), une zone partiellement déformée (PDZ) et une zone thermiquement affectée (HAZ). L’IF présentait des microstructures raffinées dominées par la bainite et la ferrite aciculaire, avec une recristallisation dynamique accrue à 60 tour/s, ayant pour résultats des propriétés mécaniques supérieures. La cartographie élémentaire au moyen de balayages de lignes d’EDS a confirmé une diffusion uniforme du chrome et du molybdène à travers l’IF, avec un mélange mécanique amélioré, observé à des vitesses de rotation plus élevées. Le profil de la microdureté a montré que l’IF présentait systématiquement une dureté plus élevée que les PDZ, HAZ et métaux de base environnants, attribuée à l’écrouissage et au raffinement de la microstructure. On a observé les valeurs de pointe de dureté du côté du SA 213 F12, avec une diminution progressive vers le côté du SA 213 T12. La répartition de la dureté était fortement influencée par la vitesse de rotation, les zones aux duretés les plus élevées se rétrécissant aux vitesses plus élevées en raison de la génération accrue de bavures et de l’extrusion du matériau. Les essais de traction ont indiqué que tous les joints surpassaient les métaux de base en termes de résistance ultime à la traction (UTS), la valeur d’UTS la plus élevée atteinte à 60 tour/s. La rupture s’est produite systématiquement dans le métal de base, mettant en évidence la résistance supérieure des joints soudés. L’analyse fractographique a confirmé un mode de rupture principalement ductile, avec une morphologie plus fine à alvéoles à 60 tour/s en corrélation avec un allongement et une résistance améliorés. L’étude démontre qu’une vitesse de rotation optimale de 60 tour/s produit des joints présentant des propriétés mécaniques et des caractéristiques de microstructure supérieures en raison des effets thermiques et mécaniques équilibrés. Ces résultats offrent un aperçu valable sur l’optimisation des paramètres de la FW pour l’assemblage fiable des aciers faiblement alliés dans les applications à hautes performances

To address the challenges of heat input in wire arc additive manufacturing (WAAM), this study employed the pulsed cold metal transfer (PCMT) technique to fabricate Incoloy 825 (IN825) components. PCMT, characterized by controlled droplet transfer and reduced heat input, enhanced mechanical performance and microstructural quality. Comprehensive analyses, including microstructural examination, X-ray diffraction, energy-dispersive X-ray spectroscopy (EDS), and element mapping, were performed. Titanium and molybdenum-rich secondary particles were identified through EDS. The mechanical properties of PCMT-fabricated components were compared with both wrought IN825 and those produced by gas metal arc additive manufacturing (GMAAM). Results demonstrated that PCMT components, particularly those fabricated at a 45° orientation, achieved approximately 113% of the ultimate tensile strength (UTS) and 131% of the elongation compared to wrought IN825. This marked a significant improvement over GMAAM-fabricated components. The reduced heat input and enhanced cooling rates in the PCMT process contributed to finer microstructures and superior mechanical properties. Fractography studies revealed that PCMT components exhibited ductile fractures with significant plastic deformation and some brittle regions. These findings underscored the advantages of PCMT in producing high-performance IN825 components compared to traditional GMAAM.

This study shows the free vibration response of functionally graded metal-ceramic sandwich plates for the validation of the frequency parameter according to classical plate theory (CPT) using ANSYS software by considering the finite element solution approach. The faces of the functionally graded sandwich plate have layers, which are considered to be isotropic. Volume fraction, modulus of elasticity, density, and Poisson’s ratio of the different faces of the functionally graded material (FGM) plate are presumed to differ with power law distribution. For this study, the Functionally graded plate is symmetric from the middle plane. The core layer or the middle layer is ceramic and has an isotropic and homogenous nature. The model chosen for the analysis is 1:1:1 having same thickness ratio for top, core, and bottom, and frequency variation with different volume index is obtained for the clamped boundary condition considering classical plate theory. Impacts of change in aspect ratio, volume fraction index over frequency have been studied. Variation of frequency for different mode shapes is studied. Also, the impact of nodes and elements on frequency is investigated.

This study explores the joining of AA6061-T6 aluminium alloy and AZ31B magnesium alloy using the Cold Metal Transfer (CMT) process with ER4043 aluminium filler wire. The influence of wire feed speed (WFS), welding speed (WS), and arc length correction (ALC) on weld bead geometry, microstructure, and mechanical properties of Al/Mg joints was investigated. The results indicate that WFS, WS, and ALC significantly affect weld characteristics. Increasing WFS leads to higher heat input, improving reinforcement height, penetration, and bead width. At 4700 mm/min WFS, optimal reinforcement height was achieved, while 5000 mm/min further enhanced penetration and bead width. Higher WS reduced heat input, resulting in narrower bead width, shallower penetration, and lower reinforcement height. ALC influenced arc behaviour, with 10% ALC minimising the weld metal area and 15% significantly increasing it. Microstructural analysis identified MgO, Mg solid solution, Mg2Al3, and Mg17Al12 at different joint regions. The optimized parameters (4700 mm/min WFS, 280 mm/min WS, 10% ALC) yielded the highest tensile strength of 34 MPa and hardness of 120 HV. Fracture occurred mainly at the Mg/weld interface and near the fusion line. This study underscores the importance of welding parameters in enhancing the mechanical properties of Al/Mg joints and provides insights for optimising aluminium-magnesium welding.Cette étude explore l'assemblage de l'alliage d'aluminium (Al) AA6061-T6 et de l'alliage de magnésium (Mg) AZ31B à l'aide du procédé de transfert de métal à froid (CMT) avec un fil d'apport en aluminium ER4043. La recherche examine l'influence des paramètres clés du procédé – vitesse d'alimentation du fil (WFS), vitesse de soudage (WS) et correction de la longueur de l'arc (ALC) – sur la géométrie du cordon de soudure, la microstructure et les propriétés mécaniques des joints Al/Mg dissemblables. Les résultats indiquent que l'interaction de WFS, WS et ALC influence significativement les caractéristiques de la soudure. Une augmentation de WFS conduit à un apport de chaleur plus élevé, résultant en une plus grande hauteur de renforcement, une profondeur de pénétration améliorée et un cordon plus large. À une WFS de 4700mm/min, on a observé une hauteur du renforcement optimale, avec de nouvelles augmentations de WFS de 5000mm/min améliorant la pénétration et la largeur du cordon. Inversement, une WS plus élevée réduit l'apport de chaleur, conduisant à un cordon plus étroit, une pénétration moins profonde et une hauteur de renforcement plus faible. Le paramètre ALC influence davantage le comportement de l'arc, avec un ALC de 10% minimisant la zone de métal fondu (WM) et un ALC plus élevé (par exemple, 15%) l'augmente significativement. L'analyse microstructurale a révélé la présence de différentes phases à des positions variées dans le joint. Au niveau du substrat de Mg, on a observé du MgO et une solution solide de Mg. Près de l'interface du métal fondu, on a également trouvé du MgO et une solution solide de Mg. L'interface a montré la formation de phases de Mg2Al3 et de Mg17Al12, tandis que près de l'interface du métal fondu, on a détecté du Mg2Si, du MgO et une solution solide d'Al. Dans le métal fondu, les phases prédominantes consistaient de Mg2Al3 et de solution solide d'Al. Les joints fabriqués a l'aide des paramètres optimisés – 4700mm/min WFS, 280mm/min WS et 10% ALC – exhibaient la résistance à la traction de 34MPa et la dureté de 120 HV les plus élevées. L'analyse des fractures a montré que la rupture se produisait principalement à l'interface Mg/soudure et près de la ligne de fusion du côté du Mg. Cette étude souligne le rôle critique des paramètres de soudage dans l'amélioration des propriétés mécaniques des joints dissemblables d'Al/Mg et offre un aperçu des développements futurs du soudage des alliages aluminium-magnésium.

Oxide dispersion in high-entropy alloy (HEA) improves mechanical properties, corrosion resistance, and high-temperature oxidation. Several studies have been reported on oxide-dispersed high-entropy alloys prepared by Spark plasma sintering and hot pressing, but only a few on coating. This study aims to investigate a novel Fe-free Co1.7 Cr0.4Ni2.5Al2.4 Nb0.23 HEA dispersed with oxide (1wt % Y2O3) for bond coat application in the thermal barrier coatings (TBC) System. The elemental powders in desired stoichiometry along with yttria were milled for 5h in a planetary ball mill with a ball-to-powder ratio of 10:1 at a speed of 300rpm followed by heat treatment at 1050°C for 1h in argon. ODHEA bond coat and yttria-stabilized zirconia (YSZ) topcoat was coated by high-velocity oxygen fuel (HVOF) and air plasma spray on a nickel superalloy substrate, respectively. The coating shows the formation of FCC, BCC and Laves phase. The hardness and Young’s modulus for the coating were approximately 610 HV and 172GPa. Good oxidation resistance with an average TGO layer thickness of less than 7µm was observed after 100h of isothermal oxidation.

Enhancing the productivity and quality of the Submerged Arc Welding (SAW) process is crucial for the welding industry, given its extensive use in critical and heavy-duty applications. While traditional single-wire direct current electrode positive (DCEP) SAW is widely used, optimizing this process can yield significant benefits, particularly when improvements can be integrated into existing systems. Productivity in SAW primarily depends on the filler wire melting rate, whereas weld quality is influenced by multiple factors, including visual inspection, macroscopy, weld chemistry, hardness, and microstructural analysis of the weld and heat-affected zone (HAZ). This study investigates the effects of welding current, filler wire form, and wire size on both productivity and quality. Metal Cored Tubular Wire (MCTW) was evaluated for its potential to enhance performance compared to conventional solid wire. Bead-on-plate (BoP) trials were conducted using two commonly used wire sizes for both solid and MCTW across a broad current range. The deposited weld metal was analysed using comprehensive testing methods, and the optimal combination of welding current, wire form, and size was identified. These findings provide practical recommendations for reducing welding time and costs while achieving superior weld quality

The present study focuses on the thermo-mechanical bending investigation of functionally graded material (FGM) sandwich plates with temperature-dependent material properties. For engineering applications, FGMs are typically made of metal and ceramic, where metal provides high rigidity and ceramic delivers high thermal resistivity. Material properties of FGM sandwich plate are considered temperature dependent and assumed to be continuously graded in thickness direction. Sigmoid and power law distributions are adopted to obtain the smooth and continuous variation of mechanical and thermal properties of FGM plate. To carry out thermo-mechanical bending, one dimensional heat conduction equation is utilized to obtain temperature variation in thickness direction. Sinusoidal shear deformation theory (SSDT) is a type of non-polynomial shear deformation theory which accounts for sinusoidal distribution of transverse shear stress and satisfies the traction free boundary condition. The governing equations for thermo-mechanical bending analysis for FGM sandwich plates are derived using Hamilton’s variational principle following SSDT and Navier’s solution. Closed form solutions are obtained to predict centre deflection, and normal and shear stresses of simply supported FGM sandwich plates. The effect of temperature-dependent material properties, power and sigmoid law, gradation index, temperature difference, side to thickness ratio, and aspect ratio over central deflection, normal stress, and shear stress are carried out and analysed. It may be concluded from the analysis that temperature-dependent material properties and gradation index for power and sigmoid law considerably influence the central deflection, normal stress, and shear stress. A good agreement amongst the obtained and available results of existing shear deformation theory is found to validate the accuracy of the SSDT

Property mapping, an indentation technique, was employed to investigate the nano-mechanical behaviour of austenite, ferrite, and interphase regions in duplex stainless steel (DSS). The influence of furnace cooling and water quenching heat treatment processes on the deformation behaviour of individual phase regions was quantitatively assessed in both the transverse and longitudinal sections of DSS samples. Property evaluation across these regions was conducted through load-displacement curves and associated material parameters such as empirical property ratios, elastic-plastic indentation work values, and other mechanical properties. This study reveals the heterogeneous and anisotropic nature of the mechanical behaviour of DSS phase regions across the sections, which can assist in improving structural design(s).

Wire arc additive manufacturing (WAAM) using the cold metal transfer (CMT) process has emerged as a transformative method for producing near-net-shape metal components with tailored microstructures and enhanced mechanical performance. This study investigates the wear characteristics of components fabricated using CMT-based WAAM with ER70S-6 low-carbon steel (LCS) and 316LSi stainless steel (SS), focusing on their potential for abrasive and erosive wear applications. Microstructural analysis, including phase transformations and grain morphology, was performed in both the deposition (X) and building (Y) directions. Wear testing was conducted on a pin-on-disc machine under varying loads (1.5–3.5 kg) and sliding speeds (150–450 rpm) to evaluate wear rates, coefficients of friction (COF), and wear track morphology. The microstructure of the WAAMed LCS component is characterized by lamellar structures of ferrite and pearlite, with variations observed along the X- and Y-directions. The X-direction shows ferrite structures including polygonal ferrite and Widmanstätten ferrite (?WD), while the Y-direction exhibits acicular ferrite (?ac) and bainite (B) phases. The WAAMed 316LSi SS shows austenitic structures with residual ferrite, exhibiting lathy ferrite morphology in the X-direction and vermicular ferrite in the Y-direction. At the highest load and speed, the wear rate of 316LSi SS was reduced by 83.51% compared to LCS, with wear rates ranging from 0.74×103 to 1.98×103 g/m for 316LSi SS, and from 1.64×104 to 2.65×104 g/m for LCS. The COF for 316LSi SS remained within 0.34–0.45, significantly lower than the 0.53–0.57 observed for LCS. SEM analysis of worn surfaces identified abrasive, adhesive, and delamination wear as predominant mechanisms for LCS, whereas 316LSi SS showed minimal material loss due to its higher hardness (193–227 HV0.5 vs. 160–187 HV0.5 for LCS) and stable microstructure. These results establish WAAM-fabricated 316LSi SS as a promising material for wear-critical applications, providing a foundation for optimizing processing parameters and material properties.

This review explores the use of magnetic bone tissue scaffolds in hyperthermia treatment. It is a therapy that heats cancer cells to damage or destroy them while minimising harm to healthy tissues. Hyperthermia leverages the greater heat sensitivity of cancer cells, potentially enhancing treatment outcomes. Bone scaffolds, typically composed of biocompatible materials like ceramics or polymers, have emerged as promising tools for hyperthermia by incorporating magnetic nanoparticles that generate heat under an alternating magnetic field. This study aims to evaluate the current advancements in magnetic bone scaffolds for hyperthermia therapy, focusing on the materials, fabrication methods, and magnetic properties that influence their performance. The review also addresses key challenges in optimising scaffold design and offers recommendations for future research to improve therapeutic efficacy. Conclusions indicate that magnetic scaffolds have significant potential for targeted cancer treatment and bone regeneration, yet further studies are needed to enhance their clinical application. This review can guide future efforts toward optimising scaffold-based hyperthermia therapies.

This study investigates the effect of forging pressure on the microstructural evolution, mechanical properties, and fracture behaviour of rotary friction welded (RFW) low-alloy steel (LAS) joints. Three forging pressures—0.76, 0.84, and 0.91MPa/s—were applied to evaluate their influence on hardness, tensile strength, and ductility. Microstructural analysis revealed that at 0.84MPa/s, significant grain refinement occurred in the heat-affected zone, promoting superior mechanical properties. The ultimate tensile strength increased from 473MPa at 0.76MPa/s to 488MPa at 0.84MPa/s, before slightly decreasing to 482MPa at 0.91MPa/s due to grain coarsening. A maximum elongation of 40.01% was achieved at 0.84MPa/s, representing a 27.05% improvement compared to 0.76MPa/s. Hardness variations followed a similar trend, with peak values observed at intermediate forging pressure. Fractographic analysis confirmed a ductile fracture mode at 0.84MPa/s, characterised by deep equiaxed dimples, while coarser fracture features were noted at higher pressures. These results demonstrate that an optimal forging pressure enhances strength–ductility synergy by refining the microstructure and preventing excessive grain growth. The findings provide valuable insights into optimising forging conditions for high-performance RFW LAS joints in structural and industrial applications

A critical requirement for rehabilitation robots is achieving high transparency in user interaction to minimize interference when assistance is unnecessary. Cable-driven systems are a compelling alternative to rigid-link robots due to their lighter weight and reduced inertia, enhancing transparency. However, controlling cable tension forces remains a significant challenge, as these forces directly affect the interaction between the user and the robot. Effective strategies must maintain low tension during non-assistive phases while preventing slackness. This paper introduces PACE-R (Passive Active CablE Robot), a novel lightweight actuation system for cable-driven rehabilitation devices. The PACE-R module utilizes remote actuation and an open-loop, discrete state control, where the cable is coupled to the motor only during active intervention. When not assisting, the cable is passively decoupled from the motor, and a low-stiffness spring maintains minimal tension, enabling high transparency. Benchtop tests showed that the module consistently produced force impulses proportional to motor input with delays not exceeding 15 ms. In the treadmill push-off assistance demonstration, PACE-R contributed about 20% to total ankle moment and power. Transparency analysis revealed negligible interference, with only 1% and 0.5% contributions to peak total ankle moment and power, respectively.

The mandates of safety standards in manual material handling tasks have spurred the development and commercialization of many back-assist exoskeletons. These devices prevent back pain injuries by redistributing the applied loads, reducing the effort and fatigue in heavy and repetitive loading tasks. The majority of them employ passive and active actuation paradigms. The passive ones are known for better transparency and energy efficiency, while the active ones provide a higher degree of assistance and quickly adapt to task severities. The present work investigates the feasibility of a hybrid actuation paradigm for load-carriage under symmetric loading conditions. The preliminary results suggest that the proposed modifications to an existing passive exoskeleton effectively economize energy expenditure and improve adaptability.