Search Results (433)

Enhancing the mechanical performance of aluminium-based materials remains a critical challenge for their application in demanding environments. In this context, aluminium-based hybrid nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs) and nano-sized silicon carbide (nSiC) have been developed to overcome inherent limitations of pure aluminium, such as relatively low hardness, limited compressive strength and poor wear resistance. The composites were fabricated via powder metallurgy by incorporating a fixed 1 wt.% MWCNT content along with varying nSiC additions in the range of 0–4 wt.%, enabling a systematic evaluation of the effect of hybrid reinforcement on the overall material properties. Compared to pure aluminium, the composites exhibited significant improvements in mechanical and tribological properties, with the Al–1 wt.% MWCNT–4 wt.% nSiC composition showing the highest enhancement, achieving increases of ~149% in hardness and ~45% in compressive strength. Microstructural analysis revealed strong matrix–reinforcement bonding, notable grain refinement, and a largely uniform reinforcement distribution, with minor agglomeration at higher nSiC content. The hybrid nanocomposites also demonstrated superior wear resistance, while fractography indicated a transition from ductile fracture in pure aluminium to a mixed intergranular–transgranular mode, promoting effective load transfer and improved performance. Full article

Mechanical components subjected to dynamic loading require materials that combine adequate strength with effective vibration-damping capability. Austempered ductile iron (ADI) is a promising candidate for such applications because of its ausferritic matrix, which provides a useful combination of strength, toughness, wear resistance, and energy dissipation. However, the damping behaviour of manganese-alloyed ADI and its dependence on austempering parameters have not been sufficiently clarified. In this study, ductile iron containing 0.3, 0.6, and 0.9 wt% Mn was austempered at 320, 370, and 420 °C for 1, 1.5, and 2 h using a full-factorial experimental design. The damping response was evaluated through impact hammer-based experimental modal analysis and correlated with hardness, ausferritic morphology, and the volume fraction of carbon-enriched/high-carbon austenite. The results showed that manganese content and austempering temperature significantly influenced the loss factor, whereas austempering time had only a minor effect within the selected range. The highest damping performance was obtained for the alloy containing 0.6 wt% Mn austempered at 370 °C, where a favourable balance was achieved between stabilized high-carbon austenite, refined ausferritic morphology, ferrite/austenite interface density, and controlled matrix hardness. At 320 °C, limited austenite stabilization restricted damping improvement, while at 420 °C, ausferritic coarsening reduced the effective interface-related energy dissipation. ANOVA confirmed manganese content and austempering temperature as the dominant factors, contributing approximately 59% and 39%, respectively, to the variation in loss factor. The regression model showed strong predictive capability within the investigated process window. Overall, the study demonstrates that damping behaviour in manganese-alloyed ADI can be effectively tailored through controlled alloy chemistry and austempering temperature, supporting its potential use in vibration-sensitive engineering components. Full article

This study aimed to assess the risks associated with ultraviolet radiation (UVR) exposure among military outdoor workers at Lohatla Military Base, South Africa, and to inform targeted risk reduction strategies. A quantitative, cross-sectional design was employed, using a questionnaire survey with 161 participants (81% completion rate; 58.39% male; the largest age group was 19–25 years) and five days of objective environmental monitoring. Environmental data confirmed the presence of elevated solar ultraviolet radiation conditions, with peak irradiance levels recorded between 12:00 PM and 1:00 PM, while temperature highs frequently exceeded 35 °C (peaking at 39 °C). Statistical analysis using Spearman’s rank-order correlation revealed strong positive associations among sun protection behaviours, including wearing protective clothing, hat use, sunscreen use, and avoidance of peak sun exposure hours (ρ values up to 0.764, p < 0.001), indicating the clustered and interdependent nature of effective sun safety practices. Furthermore, engagement in protective behaviours was significantly associated with improved health outcomes, including a lower incidence of sunburn (ρ = 0.407, p < 0.001) and reduced hyperpigmentation (ρ = 0.438, p < 0.001). These findings indicate that combined protective strategies are associated with reduced self-reported dermatological outcomes. Despite the benefits of individual behaviours, military personnel remain exposed to high levels of environmental ultraviolet radiation, underscoring the need for institutional, evidence-based policy interventions to mitigate occupational exposure risks. The study concludes that military organisations should implement mandatory administrative controls (e.g., schedule adjustments), standardise high-ultraviolet-protection-factor protective gear, and enhance targeted health literacy training to mitigate long-term UV-related health risks and improve the operational effectiveness of their workers. Full article

Lubricant additive optimisation, such as using an Organic Friction Modifier (OFM), often relies on empirical methods because the role of interfacial energetics in boundary lubrication remains uncertain. This study explores how interfacial energy interactions affect the tribological performance of glycerol monooleate (GMO)–polyalphaolefin-4 (PAO4) blends using ball-on-disk friction and wear tests. The 7 wt% GMO blend showed the best results, with friction reduced by about 4 times and the wear scar diameter by nearly 6 times compared to neat PAO4. Film-thickness estimates indicate that all tests operated within the boundary-to-mixed lubrication regime, suggesting that friction reduction is associated with interfacial interactions rather than hydrodynamic film formation. The Owens–Wendt–Kaelble surface energy analysis reveals that increasing GMO concentration shifts the lubricant’s dispersive–polar balance, with the 7 wt% formulation exhibiting dispersive–polar characteristics closer to those of the steel substrate. Low friction persisted as sliding velocity increased, and rupture-threshold analysis is consistent with improved tribological response under increasing load and sliding conditions. These findings suggest that the favourable tribological response observed for the investigated formulations may be associated with balanced interfacial energetic characteristics, particularly between dispersive and polar interactions. The observed friction and wear behaviour under increasing sliding conditions is interpreted in terms of friction and wear responses under boundary-dominated conditions, rather than through direct structural characterisation of boundary films. These trends are interpreted in relation to changes in dispersive and polar interactions at the interface. The results provide an interpretive framework for designing OFM systems that may be relevant to high-shear environments, including applications such as hydrogen internal combustion engines. Full article

Wire electrical discharge machining (WEDM) is widely used for the precision cutting of difficult-to-machine materials, including nickel-based superalloys. Wire electrode wear, however, remains a practical limitation, because it affects process stability, wire consumption, and machining cost. This work examines the wear behaviour of a gamma-phase Cu₅Zn₈-coated copper-core wire electrode (Elecut X, ø 0.25 mm) during the WEDM of Inconel 718 using direct gravimetric measurement. A 3³ full factorial experiment was carried out with three electrical parameters: pulse-on time (A), pulse-off time (B), and servo reference voltage (Aj). The discharge process was monitored with an oscilloscope so that measurements only started after the programmed pulse-off time had been reached. Electrode wear was evaluated as the mass loss Δm of 4 m wire segments after 5 min cutting intervals on a Charmilles Robofil 310 machine, and factor significance was assessed by analysis of variance (ANOVA). Pulse-on time was the dominant factor, accounting for 88.45% of the total variation in Δm, followed by servo reference voltage and pulse-off time. SEM/EDS examination showed material transfer from the Inconel 718 workpiece to the worn electrode surface, with local nickel content reaching 16.84 wt.% on the frontal face of the most worn sample. The results provide a quantitative basis for reducing wire consumption during the WEDM of Inconel 718 while recognising the trade-off with cutting productivity. Full article

Burnishing technologies are a cheap and effective means of improving the surface integrity (SI) and performance of metal components. However, there is practically no information about the integral influence of the preceding turning process on the initial (pre-burnishing) SI. This study answers the question of how the white layer resulting from flank wear on the cutting insert in pre-turning affects the SI and fatigue limit, and determines the extent to which subsequent diamond burnishing (DB) is able to improve the SI and rotating bending fatigue limit of normalised, quenched and high-temperature-tempered C45 steel. The (DB)–SI–fatigue limit correlation was investigated using a holistic approach that took into account the effects of the dynamic pattern of flank wear on the initial SI. An explicit relationship was established between the flank wear, the affected surface layer structure and the fatigue limit. Increasing flank wear to the 60th minute intensified the formation of a gradient layer with finer and thinner grains that formed a texture. As a result, a synergistic effect was observed from turning with an insert operating for 60 min and subsequent DB, which maximised the fatigue limit (741 MPa). After 60 min, the structure of the affected layer changed qualitatively towards the formation of a nanostructured (white) layer, which reversed the trend, worsening the fatigue behaviour. As the thickness of the white layer increased, the fatigue limit was sharply reduced to below 560 MPa after the 90th minute. Regardless of the degree of flank wear, DB significantly improved the SI characteristics and increased the fatigue limit after turning with a worn insert, although the absolute dimensions of the positive DB effect depend on the initial SI and fatigue limit due to pre-turning. To achieve a synergistic effect, the cutting insert should be replaced with a new one after every 60 min of operation. Full article

This study presents an analytical–experimental investigation of the mechanical and tribological behaviour of two coating systems applied to deep, internally profiled cylindrical components manufactured via Electrochemical Rifling (ECR): a hard anodised aluminium oxide (AAO) coating on an aluminium alloy and a hard chromium coating on alloy steel. Experimental characterisation includes microhardness measurements, coefficient of friction determination, and controlled sliding wear tests. The chromium coating exhibits approximately 2.5 times higher microhardness and about 15% lower average coefficient of friction compared to the anodised aluminium layer, resulting in significantly improved wear resistance. Acceptable engineering agreement is observed between analytical predictions and experimental results. For chromium-coated steel, analytical predictions yield approximately 67,200–72,600 cycles, while the experimentally estimated value is about 36,200 cycles. For anodised aluminium, analytical predictions range from approximately 1688 to 2803 cycles, compared to an experimental value of about 2012 cycles. A conservative reliability-oriented criterion yields service lives of approximately 12,000 cycles for chromium coatings and 1000 cycles for anodised aluminium. Weibull-based analysis (R = 0.95) indicates service life ranges of approximately 9300–10,000 and 230–390 cycles, respectively. Full article

Two-dimensional (2D) materials are promising candidates for nanoscale wear-protective coatings. The mechanisms governing their tribological behaviour (i.e., friction and wear) are material-dependent. In this work, we use atomistic molecular dynamics simulations to investigate nanoscale sliding, friction, and lithographic tracks in two 2D materials, graphene and MoS₂, both placed on a SiO₂ substrate. Our results reveal fundamentally different deformation mechanisms in the two materials, where deformation comes as a consequence of applied normal load. MoS₂ deforms via the formation of a stable out-of-plane pucker beneath the contact, enabling efficient absorption and elastic redistribution of mechanical energy within the coating as well as simultaneous reduction of plastic deformation of the underlying material. Wear prevention in the substrate comes at the cost of localised damage to the MoS₂ layer along the sliding path once it reaches the rupture point. On the contrary, graphene exhibits strongly localised deformation due to its high in-plane stiffness and atomic thickness, leading to plastic deformation of the underlying material and mitigating layer damage. These findings provide clear design guidelines for 2D coatings in nanotribological applications, and highlight layered materials, such as MoS₂, as particularly effective for wear protection. Full article

Background: Functional appliance therapy is widely employed for the management of skeletal Class II malocclusion in growing patients. However, treatment outcomes are influenced by multiple biological and behavioural variables, including genetic background, craniofacial growth pattern, neuromuscular adaptability, orofacial resting postures, and patient adherence. These factors often limit direct comparison of different appliance systems. Monozygotic twin studies provide a unique biological model by minimizing genetic and environmental variability, allowing more accurate evaluation of appliance-specific effects. Methods: This case report presents a comparative evaluation of a clear functional jaw corrector and a conventional twin block appliance in two 11-year-old female monozygotic twins at cervical vertebral maturation index stage 3. Both patients exhibited similar skeletal Class II patterns, vertical growth tendencies, proclined maxillary incisors, and convex soft tissue profiles. Twin A was treated with a removable clear functional jaw corrector fabricated using mandibular advancement blocks incorporated into a 1.5-mm Essix retainer sheet, while Twin B received a conventional twin block appliance. Treatment objectives, wear protocol, and duration were identical. Neither patient received orofacial myofunctional therapy. Results: Post-treatment clinical and cephalometric evaluation demonstrated improvement in sagittal jaw relationships, facial profile, and occlusal relationships in both patients. However, differences were observed in the magnitude of skeletal correction, dentoalveolar effects, vertical control, and the extent of molar and canine relationship correction. Conclusions: Both appliance designs were effective in improving sagittal relationships under similar biological conditions, with minor differences favoring the clear functional jaw corrector. However, the findings also highlight that orthodontic appliance therapy alone does not address underlying orofacial myofunctional factors, emphasizing the importance of incorporating functional assessment and adjunctive myofunctional therapy for optimal and stable outcomes. Full article

The fast drainage of surface water from road pavements is essential to ensure both driving safety and adequate infrastructure service life. For close-graded asphalt mixtures, surface runoff relies on sufficient longitudinal and transverse slopes that convey water toward hydraulic drainage devices. However, construction defects, surface distress, or inadequate placement of drainage systems may compromise this process and reduce pavement durability. When water infiltrates beneath the wearing course and saturates the underlying layers, heavy traffic loads can accelerate deterioration through erosion, pumping, interlayer delamination, and subgrade overstress. This work investigates the joint use of Ground Penetrating Radar (GPR) and Mobile Laser Scanning (MLS) to evaluate drainage deficiencies and detect signs of layer delamination in bituminous pavements. A highway section in Salerno (Italy) was selected as a case study due to known hydraulic-related issues. MLS data were used to reconstruct pavement geometry and model surface runoff patterns, while GPR surveys assessed the condition of the bonding between asphalt and base layers. The results revealed ineffective runoff management and identified multiple areas affected by delamination, confirming a relationship between surface drainage behaviour and subsurface damage. These findings highlight the broader potential of the integrated GPR–MLS framework as a scalable and transferable approach for proactive drainage assessment and structural monitoring in pavement management practices. Full article

Aluminium alloys are extensively considered in aviation and automobiles owing to their lightweight properties and favourable specific strength-to-weight ratio. Generally, the poor surface properties of these alloys limit their application, particularly in sliding conditions. To enhance the surface qualities, particularly the material’s wear resilient features, a unique surface modification process using electro-discharge coating (EDC) has been employed. This work investigates the optimisation of coating variables produced by the EDC technique utilising green compact electrodes composed of 50 wt.% tungsten disulfide (WS₂) and 50 wt.% copper (Cu) powder. The substrate material utilised was AA7075 alloy. The Taguchi–TOPSIS approach was employed to determine optimal EDC process variables, with pulse-on time (T_on), current (I_p), and pulse-off time (T_off). Wear rate (WR), surface roughness (SR), and friction coefficient (CoF) were used to assess the coating features. A wear study was performed with a pin-on-disc device with an undeviating sliding speed (0.25 m/s) and a 25 N load. The results revealed that the supreme features derived from the linear plots were I_p (4 A), T_on (80 µs), and T_off (5 µs). The ANOVA found that I_p had the utmost significant impact, accounting for 44.09%; T_off, 28.01%; T_on, 20.33%; and minimum error, 8.58%. A validation trial with perfect parameters returned values of 0.000179 mm³/Nm (WR), 0.204 (CoF), and 2.818 µm (SR). These findings are significantly better than those of the other coatings. The discrepancy among the estimated and experimental relative closeness in optimal settings is 6.34%, demonstrating that the Taguchi–TOPSIS method is more appropriate for multi-criteria optimisation. Full article

Three-dimensional printed polymers produced using Fused Deposition Modelling (FDM) exhibit directional microstructures resulting from filament paths, layer interfaces, and cellular infill, leading to mechanical and tribological responses distinct from those of homogeneous bulk materials. This study presents a comparative tribomechanical evaluation of polypropylene (PP) bulk inserts and 3D-printed polyethylene terephthalate glycol (PETG) inserts with a 30% hexagonal infill, relevant for robotic gripping applications. Progressive scratch tests were performed under loads from 5 to 100 N (150 N for PP), and profilometry was applied to quantify groove morphology, ridge formation, and displaced-volume ratios. An elasto-plastic conical indentation model was used to derive indentation pressures and elastic–plastic transition radii from groove geometry. The PETG inserts exhibited heterogeneous groove depth, intermittent ridge tearing, and friction fluctuations associated with the internal infill structure, consistent with previous findings on anisotropy and architecture-dependent behaviour in additively manufactured polymers. In contrast, bulk PP demonstrated smoother friction profiles and more stable plastic flow under increasing loads. Two functional indices—specific frictional work and ridge-to-trace volumetric ratio—are introduced to support material selection for robotic gripping systems. The results show that local contact mechanics in 3D-printed inserts are governed by print-induced structural features and can be effectively evaluated through a scratch-based elasto-plastic analysis. The methods and results presented in this work support the rational selection and design of polymer inserts for robotic gripper fingertips. The proposed scratch-based elasto-plastic evaluation framework enables manufacturers and automation engineers to compare 3D-printed and conventional materials based on friction stability, wear response, and deformation resistance. This approach can be directly applied to optimise gripping performance in industrial handling, packaging, and collaborative robotics. Full article

Incorporating TiAl alloys in engine applications offers benefits including reduced fuel consumption and improved efficiency. However, understanding the wear behaviour of these materials is an important consideration due to their use in harsh environments involving movable parts. This study investigated the wear behaviour and mechanisms of Ti–48Al–2Nb–0.3Si-1Sn (TiAl–S1) together with Ti–48Al–2Nb–0.3Si (TiAl–S0) as a reference alloy against an alumina ball. Scanning electron microscopy (SEM) analysis showed that the addition of Sn refined the lamellar structure from 216 $\mu \mathrm{m}$ to 130 $\mu \mathrm{m}$ and promoted more uniform deformation. SEM observations also indicated that abrasive wear is the dominant mechanism in the TiAl alloys. The TiAl–S1 exhibited lower hardness, resulting in deformation of wear debris and promoting third body acting as a lubricant. SEM-EDS revealed that the tribo-layer and wear debris originated from the TiAl materials rather than the counterpart alumina material. Both alloys demonstrated noble wear resistance, with a wear rate of 7.542 × 10⁻⁶ mm³/Nm for TiAl–S1 and 6.729 × 10⁻⁶ mm³/Nm for TiAl–S0. Even though both TiAl alloys experienced abrasive wear mechanisms, the addition of Sn emerges as a promising alloying strategy, for enhancing ductility without significantly increasing material loss. Full article

The present study investigates the dry sliding wear behaviour of pure Zn, Zn–3Mg, and Zn–3Mg–0.5Y biodegradable alloys using mass loss measurements, friction torque monitoring on an Amsler tribometer, and optical profilometry of wear tracks. The microstructure of the Zn–Mg–Y alloy exhibited an α-Zn matrix comprising Zn–Mg intermetallic constituents and dispersed Y-rich phases. Tribological testing at 20 N and 30 N revealed a marked enhancement in wear resistance for Zn–3Mg in comparison to pure Zn, attributable to matrix strengthening by intermetallic phases. Despite the stabilising effect of Y on the friction response, there was no consistent reduction in wear volume under higher loads. Surface investigations have revealed a multifaceted wear mechanism, characterised by a combination of abrasion, oxide tribolayer formation, and localised adhesion. The measured wear rates were found to fall within the range documented in the available literature concerning biodegradable Zn-based alloys, thereby confirming the experimental validity of the findings. In summary, Zn–3Mg exhibited the optimal equilibrium between friction stability and wear resistance under the examined dry sliding conditions. However, further research in physiological environments is necessary to evaluate its biomedical applicability. Full article

Dental resin composites are routinely exposed to chemically aggressive beverages that may compromise long-term functional performance. This study investigated the structure–property–tribology relationships of four restorative composites (Filtek Z250, Filtek Z550, Herculite, and Herculite Ultra) subjected to cyclic immersion in beverages with different pH values. A total of 120 cylindrical specimens (7 mm diameter, 2 mm thickness; n = 5 per material per condition) were fabricated and exposed to mineral water, tea, coffee, Coca-Cola^®, Cola Light^®, and red wine for 28 days under cyclic conditions. Microhardness, surface roughness (Ra), steady-state coefficient of friction (COF), and mass variation were evaluated. All composites exhibited significant microhardness reduction after acidic exposure (p < 0.05), with the greatest decrease observed for Herculite Ultra in red wine (−47.4%) and Coca-Cola^® (−35.3%). Filtek Z250 demonstrated the highest baseline hardness and the lowest degradation susceptibility. Surface roughness changes were formulation-dependent, with Herculite Ultra showing pronounced roughening (ΔRa up to +0.074 µm), whereas Filtek Z550 exhibited erosion-driven smoothing (ΔRa down to −0.068 µm). Tribological behaviour was primarily governed by matrix softening rather than roughness alterations, with softened systems displaying unstable frictional responses (COF range: 0.127–0.697; p < 0.05). The results indicate that polymer matrix stability plays a more critical role in long-term functional performance than surface roughness or mass variation alone. Clinically, frequent exposure to acidic and solvent-containing beverages may accelerate mechanical and tribological degradation of susceptible composite formulations. Full article