Sign in to use this feature.

Years

Between: -

Subjects

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Journals

Article Types

Countries / Regions

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Search Results (455)

Search Parameters:
Keywords = coefficient of friction (COF)

Order results
Result details
Results per page
Select all
Export citation of selected articles as:
30 pages, 8202 KiB  
Article
Structure and Texture Synergies in Fused Deposition Modeling (FDM) Polymers: A Comparative Evaluation of Tribological and Mechanical Properties
by Patricia Isabela Brăileanu, Marius-Teodor Mocanu, Tiberiu Gabriel Dobrescu, Nicoleta Elisabeta Pascu and Dan Dobrotă
Polymers 2025, 17(15), 2159; https://doi.org/10.3390/polym17152159 (registering DOI) - 7 Aug 2025
Abstract
This study investigates the interplay between infill structure and surface texture in Fused Deposition Modeling (FDM)-printed polymer specimens and their combined influence on tribological and mechanical performance. Unlike previous works that focus on single-variable analysis, this work offers a comparative evaluation of Shore [...] Read more.
This study investigates the interplay between infill structure and surface texture in Fused Deposition Modeling (FDM)-printed polymer specimens and their combined influence on tribological and mechanical performance. Unlike previous works that focus on single-variable analysis, this work offers a comparative evaluation of Shore D hardness and coefficient of friction (COF) for PLA and Iglidur materials, incorporating diverse infill patterns. The results reveal that specific combinations (e.g., grid infill with 90% density) optimize hardness and minimize friction, offering practical insights for design optimization in functional parts. Our aim is to provide design insights for enhanced wear resistance and hardness through tailored structural configurations. Carbon Fiber-reinforced PLA (PLA CF), aramid fiber-reinforced Acrylonitrile Styrene Acrylate (Kevlar), and Iglidur I180-BL tribofilament. Disc specimens were fabricated with gyroid infill densities ranging from 10% to 100%. Experimental methodologies included Ball-on-Disc tests conducted under dry sliding conditions (5 N normal load, 150 mm/s sliding speed) to assess friction and wear characteristics. These tribological evaluations were complemented by profilometric and microscopic analyses and Shore D hardness testing. The results show that Iglidur I180-BL achieved the lowest friction coefficients (0.141–0.190) and negligible wear, while PLA specimens with 90% infill demonstrated a polishing-type wear with minimal material loss and a friction coefficient (COF) of ~0.108. In contrast, PLA CF and Kevlar exhibited higher wear depths (up to 154 µm for Kevlar) and abrasive mechanisms due to fiber detachment. Shore hardness values increased with infill density, with PLA reaching a maximum of 82.7 Shore D. These findings highlight the critical interplay between infill architecture and surface patterning and offer actionable guidelines for the functional design of durable FDM components in load-bearing or sliding applications. Full article
(This article belongs to the Collection Mechanical Behavior of Polymer-Based Materials)
Show Figures

Figure 1

19 pages, 9214 KiB  
Article
Tribological Performance of Direct Metal Laser Sintered 20MnCr5 Tool Steel Countersamples Designed for Sheet Metal Forming Applications
by Krzysztof Żaba, Marcin Madej, Beata Leszczyńska-Madej, Tomasz Trzepieciński and Ryszard Sitek
Appl. Sci. 2025, 15(15), 8711; https://doi.org/10.3390/app15158711 - 6 Aug 2025
Abstract
This article presents the results of the tribological performance of 20MnCr5 (1.7147) tool steel countersamples produced by Direct Metal Laser Sintering (DMLS), as a potential material for inserts or working layers of sheet metal forming tools. Tribological tests were performed using a roller-block [...] Read more.
This article presents the results of the tribological performance of 20MnCr5 (1.7147) tool steel countersamples produced by Direct Metal Laser Sintering (DMLS), as a potential material for inserts or working layers of sheet metal forming tools. Tribological tests were performed using a roller-block tribotester. The samples were sheet metals made of materials with significantly different properties: Inconel 625, titanium-stabilised stainless steel 321, EN AW-6061 T0 aluminium alloy, and pure copper. The samples and countersamples were analysed in terms of their wear resistance, coefficient of friction (COF), changes in friction force during testing, and surface morphology after tribological contact under dry friction conditions. The tests were performed on DMLSed countersamples in the as-received state. The largest gain of countersample mass was observed for the 20MnCr5/EN AW-6061 T0 friction pair. The sample mass loss in this combination was also the largest, amounting to 19.96% of the initial mass. On the other hand, in the 20MnCr5/Inconel 625 friction pair, no significant changes in the mass of materials were recorded. For the Inconel 625 sample, a mass loss of 0.04% was observed. The basic wear mechanism of the samples was identified as abrasive wear. The highest friction forces were observed in the 20MnCr5/Cu friction pair (COF = 0.913) and 20MnCr5/EN AW-6061 T0 friction pair (COF = 1.234). The other two samples (Inconel 625, 321 steel) showed a very stable value of the friction force during the roller-block test resulting in a COF between 0.194 and 0.213. Based on the changes in friction force, COFs, and mass changes in friction pair components during wear tests, it can be concluded that potential tools in the form of inserts or working layers manufactured using 3D printing technology, the DMLS method, without additional surface treatment can be successfully used for forming sheets of 321 steel and Inconel 625. Full article
Show Figures

Figure 1

22 pages, 6855 KiB  
Article
Estimation of the Kinetic Coefficient of Friction of Asphalt Pavements Using the Top Topography Surface Roughness Power Spectrum
by Bo Sun, Haoyuan Luo, Yibo Rong and Yanqin Yang
Materials 2025, 18(15), 3643; https://doi.org/10.3390/ma18153643 - 2 Aug 2025
Viewed by 260
Abstract
This study proposes a method for estimating the kinetic coefficient of friction (COF) for asphalt pavements by improving and applying Persson’s friction theory. The method utilizes the power spectral density (PSD) of the top surface topography instead of the full PSD to better [...] Read more.
This study proposes a method for estimating the kinetic coefficient of friction (COF) for asphalt pavements by improving and applying Persson’s friction theory. The method utilizes the power spectral density (PSD) of the top surface topography instead of the full PSD to better reflect the actual contact conditions. This approach avoids including deeper roughness components that do not contribute to real rubber–pavement contact due to surface skewness. The key aspect of the method is determining an appropriate cutting plane to isolate the top surface. Four cutting strategies were evaluated. Results show that the cutting plane defined at 0.5 times the root mean square (RMS) height exhibits the highest robustness across all pavement types, with the estimated COF closely matching the measured values for all four tested surfaces. This study presents an improved method for estimating the kinetic coefficient of friction (COF) of asphalt pavements by employing the power spectral density (PSD) of the top surface roughness, rather than the total surface profile. This refinement is based on Persson’s friction theory and aims to exclude the influence of deep surface irregularities that do not make actual contact with the rubber interface. The core of the method lies in defining an appropriate cutting plane to isolate the topographical features that contribute most to frictional interactions. Four cutting strategies were investigated. Among them, the cutting plane positioned at 0.5 times the root mean square (RMS) height demonstrated the best overall applicability. COF estimates derived from this method showed strong consistency with experimentally measured values across all four tested asphalt pavement surfaces, indicating its robustness and practical potential. Full article
(This article belongs to the Section Construction and Building Materials)
Show Figures

Figure 1

22 pages, 24500 KiB  
Article
Ambient to Elevated Temperature: Ecotribology of Water-Based Lubricants Incorporating hBN/TiO2 Nanoadditives
by Afshana Morshed, Fei Lin, Hui Wu, Zhao Xing, Sihai Jiao and Zhengyi Jiang
Lubricants 2025, 13(8), 344; https://doi.org/10.3390/lubricants13080344 - 1 Aug 2025
Viewed by 238
Abstract
Ecotribology focuses on both saving energy resources and reducing environmental pollution. Considering environmental concerns, water-based nanolubricants have gained significant attention over conventional oil-based ones. Non-ecotoxic and highly environmentally friendly nanoadditives were chosen for nanolubricant synthesis, especially considering their use at elevated temperatures. In [...] Read more.
Ecotribology focuses on both saving energy resources and reducing environmental pollution. Considering environmental concerns, water-based nanolubricants have gained significant attention over conventional oil-based ones. Non-ecotoxic and highly environmentally friendly nanoadditives were chosen for nanolubricant synthesis, especially considering their use at elevated temperatures. In this study, hexagonal boron nitride nanosheets (hBNNSs) and titanium dioxide nanoparticles (TiO2 NPs) were used to prepare water-based lubricants with glycerol and surfactant sodium dodecyl benzene sulfonate (SDBS) in water under ultrasonication. An Rtec ball-on-disk tribometer was used to investigate the tribological performance of the synthesised water-based lubricants containing different nano-hBN/TiO2 concentrations, with dry and water conditions used as benchmarks. The results indicated that the water-based nanolubricant containing 0.5 wt% hBN and 0.5 wt% TiO2 exhibited the best tribological performance at both ambient (25 °C) and elevated (500 °C) temperatures. This optimal concentration leads to a reduction in the coefficient of friction (COF) by 72.9% and 37.5%, wear of disk by 62.5% and 49%, and wear of ball by 74% and 69% at ambient and elevated temperatures, respectively, compared to that of distilled water. Lubrication mechanisms were attributed to the rolling, mending, tribofilm, solid layer formation, and synergistic effects of hBNNSs and TiO2 NPs. Full article
(This article belongs to the Special Issue Tribology in Manufacturing Engineering)
Show Figures

Figure 1

16 pages, 4508 KiB  
Article
Natural Kelp (Laminaria japonica) Hydrogel with Anisotropic Mechanical Properties, Low Friction and Self-Cleaning for Triboelectric Nanogenerator
by Dongnian Chen, Hui Yu, Jiajia Hao, Qiang Chen and Lin Zhu
Gels 2025, 11(8), 597; https://doi.org/10.3390/gels11080597 - 1 Aug 2025
Viewed by 133
Abstract
Kelp is a natural hydrogel material, which has been widely used in food industry. However, as a natural material, its properties have not been well explored. In this work, the surface and mechanical properties of kelp were investigated. The surface of kelp exhibited [...] Read more.
Kelp is a natural hydrogel material, which has been widely used in food industry. However, as a natural material, its properties have not been well explored. In this work, the surface and mechanical properties of kelp were investigated. The surface of kelp exhibited superoleophobicity and a self-clean property. The friction coefficient (COF) of the kelp surface was also low (<0.1). Interestingly, kelp demonstrated anisotropic mechanical properties either with or without metal ions. The tensile strength and toughness of kelp along with the growth direction (H) were better than those at the direction vertical to the growth direction (V). The adsorption of metal ions would significantly enhance the mechanical properties and ionic conductivity. Triboelectric nanogenerator (TENG) was assembled using kelp with NaCl, which showed excellent output performance (open-circuit voltage of 30 V, short-circuit current of 0.73 μA and charge transfer on contact of 10.5 nC). A writing tablet was prepared to use as the kelp-based self-powered tactile sensor. This work provides a new insight into natural kelp, which may be used as a renewable material. Full article
(This article belongs to the Special Issue Applications of Gels in Energy Materials and Devices)
Show Figures

Figure 1

1887 KiB  
Proceeding Paper
Experimental Evaluation of Coefficient of Friction for Fretting Regimes
by Shumaila Fatima, Shahid Mehmood, Muhammad Awais Hamza, Atta Ur Rahman, Hafiz Samama Sumair, Soban Ullah, Muhammad Ammar Nasir, Muhammad Ehtisham and Husnain Zulfiqar Ali
Mater. Proc. 2025, 23(1), 9; https://doi.org/10.3390/materproc2025023009 - 31 Jul 2025
Abstract
This study investigates the coefficient of friction (COF) and wear behavior in fretting regimes—stick, stick–slip, and gross sliding—under dry and oil-lubricated conditions. Fretting tests were conducted by increasing oscillation amplitude from a few micrometers to 48 µm. In dry conditions, displacement amplitude initially [...] Read more.
This study investigates the coefficient of friction (COF) and wear behavior in fretting regimes—stick, stick–slip, and gross sliding—under dry and oil-lubricated conditions. Fretting tests were conducted by increasing oscillation amplitude from a few micrometers to 48 µm. In dry conditions, displacement amplitude initially rose rapidly, stabilizing after about 5 million load cycles, indicating steady-state behavior. The friction ratio (FR) surged early, peaking between 0.7 and 1.0, before declining to stable values, suggesting a shift from adhesive to stable frictional interaction. The minimal slip amplitude confirmed the predominance of the stick regime. Conversely, in oil-lubricated conditions, displacement amplitude stabilized after an initial increase, achieving higher amplitudes than in dry tests. The FR started below 0.2, gradually increasing to a peak around 10,000 load cycles for higher oscillation amplitudes (e.g., 15 µm), reflecting the lubricant’s role in reducing metal-to-metal contact. COF curves in lubricated tests showed smoother transitions and lower peak values compared to dry tests. These findings highlight the lubricant’s effectiveness in minimizing adhesion and enhancing sliding efficiency, offering insights for optimizing material performance in engineering applications. Full article
Show Figures

Figure 1

25 pages, 2151 KiB  
Article
A Possibility of Tribological Investigation of Physicochemical Processes in a Friction Pair Operating Under Selective Transfer Conditions
by Filip Ilie, Daniel Constantin Cotici and Andrei-Florin Hristache
Lubricants 2025, 13(8), 331; https://doi.org/10.3390/lubricants13080331 - 30 Jul 2025
Viewed by 236
Abstract
The physicochemical processes that occur during selective transfer in the contact area of a bronze/steel friction pair lubricated with glycerin are experimentally studied by the polarization method to observe how they influence the tribological properties (friction and wear) of the pair. The proposed [...] Read more.
The physicochemical processes that occur during selective transfer in the contact area of a bronze/steel friction pair lubricated with glycerin are experimentally studied by the polarization method to observe how they influence the tribological properties (friction and wear) of the pair. The proposed method allows for the study of tribochemical transformations of glycerin and the friction pair materials during the work process with selective transfer. The analysis of the experimental results allows for the establishment of the conditions for a stable and stationary selective transfer during the operation of the bronze/steel pair, by friction, at which the friction coefficient (COF) values and wear are low. This was achieved by implementing continuous lubrication with fresh glycerin in the contact area, choosing the optimal flow rate, and maintaining an optimal ratio between glycerin and the chemical transformation products, within well-established limits, to avoid undesirable consequences. Acrolein, as a product of chemical transformation (resulting from the catalytic dehydration of glycerin), is the most important for the initiation and stability of the selective transfer, and as the main reaction product, also represents a pathway of regeneration. Thus, it was found that the friction relative moments and the acrolein concentration presented conclusive/specific results at loads of 4–15 MPa and a sliding speed of 0.3 m/s. The optimum lubricant entry speed is 15–30 mg/min, for a minimum COF and reduced wear (about 0.028–0.03 at relatively high operating temperatures (45 and 60 °C)), and at low temperatures (30 °C) the minimum COF is about 0.038, but the lubricant inlet entry speed increases considerably, by around 1000 mg/min. Therefore, this paper aims to demonstrate the possibility of moving to another stage of practical use of a friction pair (with greatly improved tribological properties) that operates with selective transfer, much different from the ones still present, using a lubricant with special properties (glycerin). The research method used (polarization) highlights the physicochemical properties, tribochemical transformations of the lubricant, and the friction pair materials present in the contact area, for the understanding, maintenance, and stability of selective transfer, based on experiments, as a novelty compared to other studies. Full article
(This article belongs to the Special Issue Experimental Modelling of Tribosystems)
Show Figures

Figure 1

18 pages, 6673 KiB  
Article
Tribological Properties of MoN/TiN Multilayer Coatings Prepared via High-Power Impulse Magnetron Sputtering
by Jiaming Xu, Ping Zhang, Jianjian Yu, Puyou Ying, Tao Yang, Jianbo Wu, Tianle Wang, Nikolai Myshkin and Vladimir Levchenko
Lubricants 2025, 13(8), 319; https://doi.org/10.3390/lubricants13080319 - 22 Jul 2025
Viewed by 370
Abstract
To address the limitations of single-layer nitride coatings, such as poor load adaptability and low long-term durability, MoN/TiN multilayer coatings were prepared via high-power impulse magnetron sputtering (HiPIMS). HiPIMS produces highly ionized plasmas that enable intense ion bombardment, yielding nitride films with enhanced [...] Read more.
To address the limitations of single-layer nitride coatings, such as poor load adaptability and low long-term durability, MoN/TiN multilayer coatings were prepared via high-power impulse magnetron sputtering (HiPIMS). HiPIMS produces highly ionized plasmas that enable intense ion bombardment, yielding nitride films with enhanced mechanical strength, durability, and thermal stability versus conventional methods. The multilayer coating demonstrated a low coefficient of friction (COF, ~0.4) and wear rate (1.31 × 10−7 mm3/[N·m]). In contrast, both TiN and MoN coatings failed at 5 N and 10 N loads, respectively. Under increasing loads, the multilayer coating maintained stable wear rates (1.84–3.06 × 10−7 mm3/[N·m]) below 20 N, and ultimately failed at 25 N. Furthermore, the MoN layer contributes to COF reduction. Grazing-incidence X-ray diffraction analysis confirmed the enhanced crystallographic stability of the multilayer coating, thereby revealing a dominant (111) orientation. The multilayer architecture suppresses crack propagation while effectively balancing hardness and toughness, offering a promising design for extreme-load applications. Full article
Show Figures

Figure 1

24 pages, 4796 KiB  
Article
Comprehensive Experimental Optimization and Image-Driven Machine Learning Prediction of Tribological Performance in MWCNT-Reinforced Bio-Based Epoxy Nanocomposites
by Pavan Hiremath, Srinivas Shenoy Heckadka, Gajanan Anne, Ranjan Kumar Ghadai, G. Divya Deepak and R. C. Shivamurthy
J. Compos. Sci. 2025, 9(8), 385; https://doi.org/10.3390/jcs9080385 - 22 Jul 2025
Viewed by 290
Abstract
This study presents a multi-modal investigation into the wear behavior of bio-based epoxy composites reinforced with multi-walled carbon nanotubes (MWCNTs) at 0–0.75 wt%. A Taguchi L16 orthogonal array was employed to systematically assess the influence of MWCNT content, load (20–50 N), and sliding [...] Read more.
This study presents a multi-modal investigation into the wear behavior of bio-based epoxy composites reinforced with multi-walled carbon nanotubes (MWCNTs) at 0–0.75 wt%. A Taguchi L16 orthogonal array was employed to systematically assess the influence of MWCNT content, load (20–50 N), and sliding speed (1–2.5 m/s) on wear rate (WR), coefficient of friction (COF), and surface roughness (Ra). Statistical analysis revealed that MWCNT content contributed up to 85.35% to wear reduction, with 0.5 wt% identified as the optimal reinforcement level, achieving the lowest WR (3.1 mm3/N·m) and Ra (0.7 µm). Complementary morphological characterization via SEM and AFM confirmed microstructural improvements at optimal loading and identified degradation features (ploughing, agglomeration) at 0 wt% and 0.75 wt%. Regression models (R2 > 0.95) effectively captured the nonlinear wear response, while a Random Forest model trained on GLCM-derived image features (e.g., correlation, entropy) yielded WR prediction accuracy of R2 ≈ 0.93. Key image-based predictors were found to correlate strongly with measured tribological metrics, validating the integration of surface texture analysis into predictive modeling. This integrated framework combining experimental design, mathematical modeling, and image-based machine learning offers a robust pathway for designing high-performance, sustainable nanocomposites with data-driven diagnostics for wear prediction. Full article
(This article belongs to the Special Issue Bio-Abio Nanocomposites)
Show Figures

Figure 1

22 pages, 6390 KiB  
Article
Exploring the Tribological Potential of Y2BaCuO5 Precursor Powders as a Novel Lubricant Additive
by Shuo Cheng, Longgui He and Jimin Xu
Lubricants 2025, 13(7), 315; https://doi.org/10.3390/lubricants13070315 - 19 Jul 2025
Viewed by 308
Abstract
Friction leads to substantial energy losses and wear in mechanical systems. This study explores the tribological potential of the high-temperature superconductor precursor Y2BaCuO5 (Y211), synthesized via chemical co-precipitation, as a novel additive to PAO6 base oil. A 0.3 wt.% Y211/PAO6 [...] Read more.
Friction leads to substantial energy losses and wear in mechanical systems. This study explores the tribological potential of the high-temperature superconductor precursor Y2BaCuO5 (Y211), synthesized via chemical co-precipitation, as a novel additive to PAO6 base oil. A 0.3 wt.% Y211/PAO6 lubricant (CD) was formulated using ultrasonic dispersion. Tribological performance was evaluated using a custom end-face tribometer (steel-on-iron) under varying loads (100–500 N) and speeds (300–500 rpm), comparing CD to neat PAO6. The results indicate that the Y211 additive consistently reduced the coefficient of friction (COF) relative to neat PAO6, maintaining a stable value around ~0.1. However, its effectiveness was strongly load-dependent: a significant friction reduction was observed at 100 N, while the benefit diminished at higher loads (>200 N), with the COF peaking around 200 N. Rotational speed exerted minimal influence. Compared with neat PAO6, the inclusion of 0.3 wt.% Y211 resulted in a reduction in the coefficient of friction by approximately 50% under low-load conditions (100 N), with COF values decreasing from 0.1 to 0.045. Wear depth measurements also revealed a reduction of over 30%, supporting the additive’s anti-wear efficacy. Y211 demonstrates potential as a friction-reducing additive, particularly under low loads, but its high-load performance limitations warrant further optimization and mechanistic studies. This highlights a novel tribological application for Y211. The objective of this study is to evaluate the tribological effectiveness of Y2BaCuO5 (Y211) as a lubricant additive, investigate its load-dependent friction behavior, and explore its feasibility as a multifunctional additive leveraging its superconductive precursor structure. Full article
(This article belongs to the Special Issue Novel Lubricant Additives in 2025)
Show Figures

Figure 1

11 pages, 4974 KiB  
Article
Effect of Modulation Period on the Microstructure and Tribological Properties of AlCrTiVNbN/TiSiN Nano Multilayer Films
by Hongjuan Yan, Haoran Wang, Xiaona Li, Zhaoliang Dou and Fengbin Liu
Coatings 2025, 15(7), 839; https://doi.org/10.3390/coatings15070839 - 17 Jul 2025
Viewed by 275
Abstract
The impact of modulation periods on the microstructure, as well as the tribological and mechanical characteristics of the AlCrTiVNbN/TiSiN nano multilayer films, was investigated. The films were prepared with modulation periods ranging from 4 nm to 7 nm, and their properties were explored [...] Read more.
The impact of modulation periods on the microstructure, as well as the tribological and mechanical characteristics of the AlCrTiVNbN/TiSiN nano multilayer films, was investigated. The films were prepared with modulation periods ranging from 4 nm to 7 nm, and their properties were explored using X-ray diffraction (XRD), scanning electron microscope (SEM), nanoindentation, and a tribological tester. All nano multilayer films revealed a face-centered cubic (FCC) structure with a preferred planar direction of (200). As the modulation period increased, the XRD peak moved to higher angles, and the interplanar distance decreased. Also, the mechanical properties deteriorated, and the COF rose monotonically as a result. The nano multilayer film with a modulation period equal to 4 nm exhibited a smooth surface with minimal small particles, the highest hardness of 15.51 ± 0.16 GPa and elastic modulus of 182.89 ± 2.38 GPa, the highest values for the ratios of H/E and H3/E2, the lowest average friction coefficient of 0.73, and a wear rate equal to (8.2 9 ± 0.18) × 10−8 mm3·N−1·m−1. The improvement in the properties of the film was ascribed to the coherent growth and alternating stress field between the AlCrTiVNbN and TiSiN layers. Full article
(This article belongs to the Special Issue Surface Protection for Metal Materials)
Show Figures

Figure 1

17 pages, 4068 KiB  
Article
Mechanical Properties and Tribological Behavior of Al2O3–ZrO2 Ceramic Composites Reinforced with Carbides
by Jana Andrejovská, Dávid Medveď, Marek Vojtko, Richard Sedlák, Piotr Klimczyk and Ján Dusza
Lubricants 2025, 13(7), 310; https://doi.org/10.3390/lubricants13070310 - 17 Jul 2025
Viewed by 368
Abstract
To elucidate the key material parameters governing the tribological performance of ceramic composites under dry sliding against steel, this study presents a comprehensive comparative assessment of the microstructural characteristics, mechanical performance, and tribological behavior of two alumina–zirconia (Al2O3–ZrO2 [...] Read more.
To elucidate the key material parameters governing the tribological performance of ceramic composites under dry sliding against steel, this study presents a comprehensive comparative assessment of the microstructural characteristics, mechanical performance, and tribological behavior of two alumina–zirconia (Al2O3–ZrO2) ceramic composites, each reinforced with a 42 vol.% carbide phase: zirconium carbide (ZrC) and tungsten carbide (WC). Specifically, tungsten carbide (WC) was selected for its exceptional bulk mechanical properties, while zirconium carbide (ZrC) was chosen to contrast its potentially different interfacial reactivity against a steel counterface. ZrC and WC were selected as reinforcing phases due to their high hardness and distinct chemical and interfacial properties, which were expected to critically affect the wear and friction behavior of the composites under demanding conditions. Specimens were consolidated via spark plasma sintering (SPS). The investigation encompassed macro- and nanoscale hardness measurements (Vickers hardness HV1, HV10; nanoindentation hardness H), elastic modulus (E), fracture toughness (KIC), coefficient of friction (COF), and specific wear rate (Ws) under unlubricated reciprocating sliding against 100Cr6 steel at normal loads of 10 N and 25 N. The Al2O3–ZrO2–WC composite exhibited an ultrafine-grained microstructure and markedly enhanced mechanical properties (HV10 ≈ 20.9 GPa; H ≈ 33.6 GPa; KIC ≈ 4.7 MPa·m½) relative to the coarse-grained Al2O3–ZrO2–ZrC counterpart (HV10 ≈ 16.6 GPa; H ≈ 27.0 GPa; KIC ≈ 3.2 MPa·m½). Paradoxically, the ZrC-reinforced composite demonstrated superior tribological performance, with a low and load-independent specific wear rate (Ws ≈ 1.2 × 10−9 mm3/Nm) and a stable steady-state COF of approximately 0.46. Conversely, the WC-reinforced system exhibited significantly elevated wear volumes—particularly under the 25 N regime—and a higher, more fluctuating COF. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) of the wear tracks revealed the formation of a continuous, iron-enriched tribofilm on the ZrC composite, derived from counterface material transfer, whereas the WC composite surface displayed only sparse tribofilm development. These findings underscore that, in steel-paired tribological applications of Al2O3–ZrO2–based composites, the efficacy of interfacial tribolayer generation can supersede intrinsic bulk mechanical attributes as the dominant factor governing wear resistance. Full article
Show Figures

Figure 1

25 pages, 5042 KiB  
Article
Surface Topography-Based Classification of Coefficient of Friction in Strip-Drawing Test Using Kohonen Self-Organising Maps
by Krzysztof Szwajka, Tomasz Trzepieciński, Marek Szewczyk, Joanna Zielińska-Szwajka and Ján Slota
Materials 2025, 18(13), 3171; https://doi.org/10.3390/ma18133171 - 4 Jul 2025
Viewed by 392
Abstract
One of the important parameters of the sheet metal forming process is the coefficient of friction (CoF). Therefore, monitoring the friction coefficient value is essential to ensure product quality, increase productivity, reduce environmental impact, and avoid product defects. Conventional CoF monitoring techniques pose [...] Read more.
One of the important parameters of the sheet metal forming process is the coefficient of friction (CoF). Therefore, monitoring the friction coefficient value is essential to ensure product quality, increase productivity, reduce environmental impact, and avoid product defects. Conventional CoF monitoring techniques pose a number of problems, including the difficulty in identifying the features of force signals that are sensitive to the variation in the coefficient of friction. To overcome these difficulties, this paper proposes a new approach to apply unsupervised artificial intelligence techniques with unbalanced data to classify the CoF of DP780 (HCT780X acc. to EN 10346:2015 standard) steel sheets in strip-drawing tests. During sheet metal forming (SMF), the CoF changes owing to the evolution of the contact conditions at the tool–sheet metal interface. The surface topography, the contact loads, and the material behaviour affect the phenomena in the contact zone. Therefore, classification is required to identify possible disturbances in the friction process causing the change in the CoF, based on the analysis of the friction process parameters and the change in the sheet metal’s surface roughness. The Kohonen self-organising map (SOM) was created based on the surface topography parameters collected and used for CoF classification. The CoF determinations were performed in the strip-drawing test under different lubrication conditions, contact pressures, and sliding speeds. The results showed that it is possible to classify the CoF using an SOM for unbalanced data, using only the surface roughness parameter Sq and selected friction test parameters, with a classification accuracy of up to 98%. Full article
(This article belongs to the Section Metals and Alloys)
Show Figures

Figure 1

19 pages, 4790 KiB  
Article
A Comprehensive Investigation on Shell Hydroforming of AA5052 Through Numerical Modeling and Experimental Analysis
by Arun Achuthankutty, Karthik Narayanan, Ajith Ramesh and Ratna Kishore Velamati
Symmetry 2025, 17(7), 989; https://doi.org/10.3390/sym17070989 - 23 Jun 2025
Viewed by 276
Abstract
This study investigates the shell hydroforming of 1.2 mm-thick AA5052 aluminum alloy sheets to produce hemispherical domes which possess inherent spatial symmetry about their central axis. Shell hydroforming is widely used in fabricating lightweight, high-strength components for aerospace, automotive, and energy applications. The [...] Read more.
This study investigates the shell hydroforming of 1.2 mm-thick AA5052 aluminum alloy sheets to produce hemispherical domes which possess inherent spatial symmetry about their central axis. Shell hydroforming is widely used in fabricating lightweight, high-strength components for aerospace, automotive, and energy applications. The forming process was driven by a spatially symmetrical internal pressure distribution applied uniformly across the blank to maintain balanced deformation and minimize geometrical distortion. Experimental trials aimed at achieving a dome depth of 50 mm revealed wrinkle formation at the blank periphery caused by circumferential compressive stresses symmetrical in nature with respect to the dome’s central axis. To better understand the forming behavior, a validated 3D finite element (FE) model was developed, capturing key phenomena such as material flow, strain rate evolution, hydrostatic stress distribution, and wrinkle development under symmetric boundary conditions. The effects of the internal pressure (IP), blank holding force (BHF), coefficient of friction (CoF), and flange radius (FR) were systematically studied. A strain rate of 0.1 s−1 in the final stage improved material flow, while a symmetric tensile hydrostatic stress of 160 MPa facilitated dome expansion. Although tensile stresses can induce void growth, the elevated strain rate helped suppress it. An optimized parameter set of IP = 5.43 MPa, BHF = 140 kN, CoF = 0.04, and FR = 5.42 mm led to successful formation of the 50 mm dome with 19.38% thinning at the apex. Internal pressure was identified as the most critical factor influencing symmetric formability. A process window was established to predict symmetric failure modes such as wrinkling and bursting. Full article
(This article belongs to the Section Engineering and Materials)
Show Figures

Figure 1

12 pages, 3201 KiB  
Article
Experimental and Numerical Analysis of Friction Effects in the Forming of Thin EN AW 8006-O Aluminum Sheets
by Gianluca Parodo, Luca Sorrentino, Sandro Turchetta and Giuseppe Moffa
Metals 2025, 15(7), 695; https://doi.org/10.3390/met15070695 - 22 Jun 2025
Viewed by 405
Abstract
This work investigates the role of friction in the numerical prediction of formability for ultra-thin aluminum sheets made of the EN AW 8006-O alloy. Nakazima-type hemispherical punch stretching tests were conducted under lubricated conditions to assess the influence of interface tribology on thickness [...] Read more.
This work investigates the role of friction in the numerical prediction of formability for ultra-thin aluminum sheets made of the EN AW 8006-O alloy. Nakazima-type hemispherical punch stretching tests were conducted under lubricated conditions to assess the influence of interface tribology on thickness distribution and failure behavior. The experimental activity included tensile testing for material parameter identification and coefficient of friction (COF) measurements according to ASTM D1894 to characterize interface friction. These parameters were then implemented into a finite element model developed in PAM-STAMP. The simulation results were compared with experimental thickness profiles, and showed good agreement when calibrated friction coefficients were used. The analysis highlights the sensitivity of sheet deformation to frictional conditions, and demonstrates that accurate tribological input significantly improves predictive accuracy. The proposed workflow offers a reliable and efficient methodology for simulating forming processes involving ultra-thin aluminum foils, with potential applications in the food packaging industry. Full article
(This article belongs to the Special Issue Advances in Lightweight Alloys, 2nd Edition)
Show Figures

Figure 1

Back to TopTop