Search Results (4,264)

Decarbonization of compression-ignition engines requires evaluation of carbon-free and low-carbon fuel alternatives. Ammonia () offers zero direct carbon emissions but faces combustion challenges including low flame speed (7 ) and high auto-ignition temperature (657 °). Methanol provides improved reactivity and bound oxygen content that can enhance ignition characteristics. This computational study investigates diesel–ammonia–methanol ternary fuel blends using validated three-dimensional CFD simulations (ANSYS Forte 2023 R2; ANSYS, Inc., Canonsburg, PA, USA) with merged chemical kinetic mechanisms (247 species, 2431 reactions). The model was validated against experimental in-cylinder pressure data with deviations below 5% on a single-cylinder diesel engine (510 cm³, 17.5:1 compression ratio, 1500 rpm). Ammonia energy ratios were systematically varied (10–50%) with methanol substitution levels (0–90%). Fuel preheating at 530 K was employed for high-alcohol compositions exhibiting ignition failure at standard temperature. Results demonstrate that peak cylinder pressures of 130–145 bar are achievable at 10–30% ammonia with M30K–M60K configurations, comparable to baseline diesel (140 bar). Indicated thermal efficiency reaches 38–42% at 30% ammonia-representing 5–8 percentage point improvements over diesel baseline (31%)-but declines to 30–32% at 50% ammonia due to fundamental combustion limitations. reductions scale approximately linearly with ammonia content: 35–55% at 30% ammonia and 75–78% at 50% ammonia. emissions demonstrate 30–60% reductions at efficiency-optimal configurations. Multi-objective optimization analysis identifies the A30M60K configuration (30% ammonia, 60% methanol, 530 K preheating) as optimal, achieving 42% thermal efficiency, 58% reduction, 51% reduction, and 11% power enhancement versus diesel. This configuration occupies the Pareto frontier “knee point” with cross-scenario robustness. Full article

To evaluate the influence of different surface conditioning protocols—sandblasting (SB), tribochemical silica coating (TBC), CO₂ laser irradiation, and plasma-enhanced chemical vapor deposition (PECVD-Si coating for 49 min) on surface roughness (Ra), surface morphology, and composite-to-zirconia shear bond strength (SBS). Eighty 3Y-TZP plates were randomly allocated into four groups (n = 20) based on surface conditioning protocol: Group 1 (SB), Group 2 (CO₂ laser), Group 3 (TBC), and Group 4 (PECVD-Si coating for 49 min). From each group, five specimens underwent Ra assessment using a contact profilometer, and five specimens were examined for surface morphology via scanning electron microscopy (SEM). The remaining ten specimens received resin composite buildup, followed by artificial aging. Subsequently, SBS testing was performed using a universal testing machine, and failure modes were evaluated under a stereomicroscope. Statistical analysis was conducted using one-way ANOVA with post hoc Tukey test and chi-square for fracture assessment(α = 0.05). Group 1 (SB) demonstrated the lowest Ra (0.844 ± 0.063 µm) and SBS (12.21 ± 4.6 MPa), whereas Group 4 (PECVD-Si coating for 49 min) exhibited the highest Ra (1.388 ± 0.098 µm) and SBS (30.48 ± 2.5 MPa). Intergroup comparison revealed no statistically significant differences between Groups 2 and 3 for both Ra and SBS values (p > 0.05). However, Groups 1 and 4 differed significantly in both parameters (p < 0.05). PECVD-based silica coating for 49 min demonstrated superior surface conditioning efficacy for 3Y-TZP, yielding significantly higher Ra and SBS values compared to sandblasting, tribochemical silica coating, and CO₂ laser irradiation. Full article

Ceramic-on-ceramic (CoC) bearings are widely used in total hip arthroplasty due to their extremely low wear rate, excellent chemical stability, and good biocompatibility. They are considered one of the most reliable long-term friction bearing systems. Although frictional instability, lubrication regime transitions, and microstructural damage mechanisms have been widely reported at the experimental and retrieval-analysis levels, current clinical evidence, limited by follow-up duration and event incidence, has not demonstrated a definitive negative impact on the clinical performance of fourth-generation ceramic components, including BIOLOX® delta. Data from national arthroplasty registries consistently demonstrate excellent survivorship and low complication rates for 4th-generation ceramics in both hard-on-soft and hard-on-hard configurations. The most reported causes for revision, such as infection, dislocation, aseptic loosening, and periprosthetic fracture, are not primarily associated with ceramic-related complications, such as ceramic fracture, excessive wear, squeaking, and revision, related to bearing failure; however, these mechanisms remain highly relevant for the design and evaluation of emerging ceramic materials and next-generation implant systems, where inadequate control may potentially impact long-term clinical performance. This review summarizes recent advances in the tribological research of CoC artificial joints, focusing on clinical tribological challenges, material composition and surface characteristics, lubrication mechanisms, wear and microdamage evolution, and third-body effects. Recent progress in ceramic toughening strategies, surface engineering, biomimetic lubrication simulation, and structural optimization is also discussed. Finally, future research directions are outlined to support the performance optimization and long-term reliability assessment of CoC artificial joint systems. Full article

The present study aimed to evaluate the effect of air-abrasion as a dentin pre-treatment on the bond strength of contemporary adhesive systems. The bonding approaches included etch-and-rinse (ER), self-etch (SE) and universal (UN) adhesive systems, with the latter applied in both ER and SE modes. Twenty-eight third molars were used, each sectioned in four parts. All specimens were embedded in acrylic resin, ground with silicon carbide papers, and divided into eight experimental groups (n = 14) based on the combination of surface pre-treatment (air-abrasion or none) and adhesive approach. Subsequently, a resin cylinder was bonded to each surface following the respective treatment. Shear bond strength (SBS) was evaluated at a cross-head speed of 0.7 mm/min using a shear-testing machine (OM100 Odeme, Luzerna, Brazil). The data were analyzed with one-way ANOVA and Tukey’s post hoc test. No statistically significant increase in SBS after air-abrasion of dentin was found for any of the experimental groups (p > 0.05). Among the adhesive strategies, the ER system presented higher SBS values (32.81 ± 9.04 MPa) than the UN adhesive applied in SE mode (21.68 ± 5.85 MPa) (p < 0.05). Mixed failures were the most common failure type across all groups. In particular, 20.5% of the specimens exhibited adhesive failure, 14.3% cohesive failure within resin composite, 12.5% cohesive failure within dentin and 52.7% specimens demonstrated mixed failure types. Dentin pre-treatment with air-abrasion using 29 μm Al₂O₃ did not significantly increase the SBS of the three tested contemporary adhesive systems; however, the choice of adhesive strategies influenced the SBS outcomes. Full article

To enhance the ductility of coal mine filling materials using recycled asphalt pavement (RAP) and address the limitations in RAP recycling and utilization, this study processed RAP into crushed materials (CMs) and ball-milled materials (BMs). Supplementary with fly ash (FA) and cement, RAP-fly ash cement paste backfill (RFCPB) was prepared. For 1000 g of RFCPB slurry, the composition was 365 g CM, 73 g cement, 270 g water, and a total of 292 g of FA and BM, with an F/B ratio ranging from 1:7 to 7:1. A systematic test program was carried out, including rheological property tests, unconfined compressive strength (UCS) tests combined with deformation monitoring, microstructure analysis, and leaching toxicity tests. Based on these tests, the influence of F/B ratio on the action mechanism, workability, mechanical properties, ductility and environmental compatibility of RFCPB was comprehensively explored. The results show that the rheological behavior of RFCPB slurry conforms to the Herschel–Bulkley (H-B) model; with the decrease in F/B ratio, the yield stress and apparent viscosity of the slurry increase significantly, while the slump and slump flow decrease correspondingly, which is closely related to the particle gradation optimization by BM. For mechanical properties and ductility, the 28-day UCS of RFCPB first increases and then decreases with the decrease in F/B ratio, all meeting the mine backfilling strength requirements; notably, the increase in BM proportion regulates the failure mode from brittle to ductile, which is the key to improving ductility. Microstructural analysis indicates that Dolomite and Albite in BM participate in hydration reactions to generate N-A-S-H and C-A-S-H gels, which fill internal pores, optimize pore structure, and thus synergistically improve UCS and ductility. Additionally, the leaching concentration of toxic ions in RFCPB complies with the environmental protection standards for solid waste. This study provides a theoretical basis for enhancing backfill ductility and advancing the coordinated disposal of RAP and fly ash solid wastes. Full article

This study presents an experimental and numerical investigation into the mechanical behavior of corrugated steel–concrete composite bridge decks with composite dowel shear connectors. Four full-scale specimens were fabricated and subjected to flexural tests to obtain and analyze the load–deflection and load–strain curves. A finite element model was developed and validated against the experimental results. The validated model was subsequently applied to analyze the load-carrying process and to perform parametric sensitivity analysis. The effects of the concrete strength grade, steel strength, corrugated steel plate thickness, concrete slab thickness, and corrugated steel plate height on the ultimate bearing capacity were evaluated. The results indicate that corrugated steel–concrete composite bridge decks were subjected to concrete shear failure. The ultimate bearing capacity of the bridge deck reached approximately 3.36 times the design value, demonstrating a high safety reserve. Throughout the entire flexural failure process, the shear connectors performed effectively, with only minimal relative slip observed at the steel–concrete interface. At the instance of failure, only partial areas of the corrugated steel plate yielded. To fully exploit the structural potential, the key design parameters require rational coordination. Full article

Wellbore integrity maintenance constitutes a fundamental safety and technological challenge throughout the entire lifecycle of oil and gas wells (including production, injection, and CO₂ sequestration operations). As a critical completion phase, perforation generates a high-temperature, high-pressure shaped charge jet that impacts and compromises wellbore structural integrity. This process may induce failure in both the cement sheath body and its interfacial zones, potentially creating fluid migration pathways along the cement-casing interface through perforation tunnels. Current research remains insufficient in quantitatively evaluating cement sheath damage resulting from perforation operations. Addressing this gap, this study incorporates dynamic jet effects during perforation and establishes a numerical model simulating high-velocity jet penetration through casing–cement target–formation composites using a rock dynamics-based constitutive model. The investigation analyzes failure mechanisms within the cement sheath matrix and its boundaries during perforation penetration, while examining the influence of mechanical parameters (compressive strength and shear modulus) of both cement sheath and formation on damage characteristics. Results demonstrate that post-perforation cement sheath aperture exhibits convergent–divergent profiles along the tunnel axis, containing exclusively radial fractures. Primary fractures predominantly initiate at the inner cement wall, whereas microcracks mainly develop at the outer boundary. Enhanced cement compressive strength significantly suppresses fracture initiation at both boundaries: when increasing from 55 MPa to 75 MPa, the undamaged area ratio rises by 16.6% at the inner wall versus 11.2% at the outer interface. Meanwhile, increasing the formation shear modulus from 10 GPa to 15 GPa reduces cement target failure radius by 0.4 cm. Cement systems featuring high compressive strength and low shear modulus demonstrate superior performance in mitigating perforation-induced debonding. Full article

While carbon fiber strength is typically characterized through single-fiber tensile tests, these isolated measurements do not account for the local mechanical constraints present within a composite architecture. This study employs a synergistic computational micromechanics approach combining finite element analysis (FEA) and analytical modeling to investigate how the surrounding matrix influences the Stress Intensity Factor (SIF) and the apparent ultimate strength of embedded fibers. By calculating the J-integral, we demonstrate that the matrix provides a significant shielding effect, constraining crack opening displacements and substantially reducing the SIF. This mechanism results in a marked increase in in situ fiber tensile strength relative to dry fibers. Incorporating this matrix-adjusted Weibull distribution into a longitudinal failure model significantly improves the prediction of fiber-break density accumulation, showing closer correlation with experimental benchmarks than traditional models. Full article

This study evaluated the ballistic performance and failure mechanisms of epoxy-based hybrid laminates reinforced with abaca/UHMWPE and pineapple leaf fiber (PALF)/UHMWPE fabrics fabricated by using vacuum-assisted hand lay-up. Ballistic tests utilized 9 mm full metal jacket (FMJ) rounds (~426 m/s impact velocity) under NIJ Standard Level IIIA conditions (44 mm maximum allowable BFS). This experimental test was complemented by finite element analysis (FEA) incorporating an energy-based bilinear fracture criterion to simulate matrix cracking and fiber pull-out. The results showed that abaca/UHMWPE composites exhibited lower backface signature (BFS) and depth of penetration (DOP) values (~23 mm vs. ~42 mm BFS; ~7 mm vs. ~9 mm DOP) than PALF/UHMWPE counterparts, reflecting superior interfacial adhesion and more ductile failure modes. Accelerated weathering produced matrix microcracking and delamination in both systems, reducing overall ballistic resistance. Scanning electron microscopy confirmed improved fiber–matrix bonding in abaca composites and interfacial voids in PALF laminates. The FEA results reproduced major failure modes, such as delamination, fiber–matrix debonding, and petaling, and identified stress concentration zones that agreed with experimental observations, though the extent of delamination was slightly underpredicted. Overall, the study demonstrated that abaca/UHMWPE hybridcomposites offer enhanced ballistic performance and durability compared with PALF/UHMWPE laminates, supporting their potential as sustainable alternatives for lightweight protective applications. Full article

Composite laminates designed for additive manufacturing require efficient material distribution to minimize weight while maintaining structural integrity. Traditional topology optimization methods, however, produce continuous density fields incompatible with layer-based fabrication. This work presents Selective Reinforcement Optimization (SRO), a stress-driven methodology that converts uniformly loaded laminate layers into localized reinforcement regions, or “patches”, at critical stress concentrations. The approach employs layer-wise statistical analysis of Tsai–Wu failure indices to identify high-variance layers; applies DBSCAN clustering to extract spatially coherent stress regions while rejecting artificial concentrators; and generates CAD-compatible and manufacturing-ready boundary geometries through a custom concave hull algorithm. The method operates iteratively in dual modes: lightweighting progressively removes full layers and replaces them with localized regions when the structure is safe, while strengthening adds reinforcement without layer removal when failure criteria are approached. Case studies demonstrate weight reductions of 10–30% while maintaining failure indices below unity, with typical convergence achieved within 100 iterations. Unlike classical topology optimization, which requires extensive post-processing, SRO directly outputs discrete patch geometries compatible with composite additive manufacturing, offering a computationally efficient and production-oriented framework for the automated design of layered composite structures. Full article

Cracking occurred in the surface coating of a screw rotor during shale gas well operations. To determine whether the coating cracks could contribute to the failure of the 42CrMo substrate, the microstructure and morphology of surface cracks and local corrosion pits were examined and analyzed using a metallographic microscope, an SEM, and an EDS. To investigate the cross-sectional morphology and elemental distribution of corrosion pits, EDS mapping was performed. The composition of the corrosion products was characterized using Raman spectroscopy and XPS. In addition, four-point bend stress corrosion tests were conducted on screw rotor specimens under simulated service conditions. The results indicate that the P and S contents in the screw rotor substrate exceeded the specified limits, whereas its tensile and impact strengths satisfied the standard requirements. The microstructure consisted of tempered sorbite and ferrite, along with a small amount of sulfide inclusions. The corrosion products on the fracture surface were primarily identified as FeOOH, Fe₃O₄, and Cr(OH)₃. All specimens failed during the four-point bend tests. The chlorine (Cl) content in the corroded regions reached up to 8.05%. These findings demonstrate that the crack resistance of the 42CrMo screw rotor was markedly reduced under the simulated service conditions of 130 °C in a saturated, oxygenated 25% CaCl₂ solution. The study concludes that stress concentration induced by sulfide inclusions in the screw rotor, together with the combined effects of chloride ions, dissolved oxygen, and applied load, promotes the initiation and propagation of stress corrosion cracking. Therefore, it is recommended to strictly control the chemical composition and inclusion content of the screw rotor material and to reduce the oxygen content of the drilling fluid, thereby mitigating the risk of corrosion-induced cracking of the rotor. Full article

Carbon–metal composite NiCrFeC coatings, prepared with and without controlled oxygen addition, were investigated to evaluate the influence of oxygen on the structure, mechanical response, and tribological performance. X-ray diffraction revealed that oxygen-containing films (NiCrFeC + O₂) exhibit a mixed metallic–oxide microstructure with CrNi, CrO, and NiO phases, whereas oxygen-free coatings show only CrNi crystalline peaks. The incorporation of oxygen led to a substantial increase in nano-hardness, from 0.84 GPa for NiCrFeC to 1.59 GPa for NiCrFeC + O₂. Scratch testing up to 100 N indicated improved adhesion and higher critical loads for the oxygen-rich coatings. Tribological measurements performed under dry sliding conditions using a sapphire ball showed a significant reduction in friction: NiCrFeC + O₂ stabilized at ~0.20, while NiCrFeC exhibited values between 0.25 and 0.35 at 0.5 N and 0.4–0.5 at 1 N, accompanied by non-uniform sliding due to coating failure. Wear-track analysis confirmed shallower penetration depths and narrower wear scars for NiCrFeC + O₂, despite similar initial roughness (~35 nm). These findings demonstrate that oxygen incorporation enhances hardness, adhesion, and wear resistance while substantially lowering friction, making NiCrFeC + O₂ coatings promising for low-friction dry-sliding applications. Full article

This study examined whether short water rinsing after hydrofluoric acid (HF) etching achieves comparable total bond strength (TBS) to more advanced cleaning protocols. Ninety-six lithium disilicate specimens were etched with 5% HF and then assigned to one of six post-etch cleaning methods: a 15 s water spray, 60 s water spray, brushing with a toothbrush, an ultrasonic bath with distilled water, an ultrasonic bath with 99% isopropanol, or a 37% phosphoric acid followed by an ultrasonic bath. The specimens were then bonded to acrylic tubes filled with composite resin. Half of the specimens were stored in water at 37 °C for three days, and the other half were stored for 150 days with 37,500 thermal cycles (5 °C/55 °C). TBS testing, failure mode evaluation, and microleakage testing were performed. Two-way ANOVA and Tukey’s test were used for statistical evaluation. Aging for 150 days significantly reduced TBS in all groups. Cleaning with a 60 s water spray resulted in significantly higher TBS than phosphoric acid plus ultrasonic cleaning, regardless of storage time. No significant differences were found among the other cleaning methods. There was no change in microleakage among the different groups; the failure was predominantly cohesive. A 15 s water spray after HF etching was as effective as more complex cleaning protocols in terms of TBS and SEM-observed surface characteristics. Full article

This study examines the influence of build orientation on the mechanical behavior of 316 stainless steel components fabricated by selective laser melting (SLM). Additively manufactured tensile specimens produced in different build orientations were experimentally analyzed and compared with reference specimens obtained from conventionally hot-rolled material and laser-cut to identical geometries. Uniaxial tensile testing combined with digital image correlation (DIC) was employed to evaluate the mechanical response and full-field strain evolution. Microstructural features were investigated using scanning electron microscopy (SEM), while phase composition was assessed by X-ray diffraction (XRD). The results reveal a pronounced orientation-dependent mechanical anisotropy in the SLM specimens, reflected in variations in yield strength, ultimate tensile strength, and ductility. Specimens loaded perpendicular to the build directions exhibited higher strength but reduced ductility compared to those loaded parallel to the build direction, whereas the rolled material showed a more isotropic mechanical response. Although the XYZ and XZY samples feature similar deposition patterns, the XRD analysis revealed a the existence of a $\left[220\right]$ texture. Thus, the mechanical performances of XZY specimens are about $10\%$ lower compared to XYZ printed samples. The stress maximum–strain curves were extrapolated from the true data using the Swift model. The section dedicated to numerical modeling includes a failure model based on the traixility. The numerical models were validated for the range $\eta \in \left[0.33\dots 0.45\right]$ specific to uniaxial tension. Fractographic observations further confirmed the correlation between build orientation, microstructural features, and fracture behavior. The present study provides a multiscale experimental framework linking processing conditions, microstructure, and mechanical response in additively manufactured stainless steel. Full article

In accelerated bridge construction, precast concrete girders are connected to cast-in-place concrete slab using shear transfer reinforcement across the interface plane to ensure the composite action. The steel transverse reinforcement is prone to severe corrosion due to the extensive use of de-icing salts and severe environmental conditions. As glass fiber-reinforced polymer (GFRP) reinforcement has shown to be an effective alternative to conventional steel rebars as flexural and shear reinforcement, the present research work is exploring the performance of GFRP reinforcements as shear transfer reinforcement between precast and cast-in-place concretes. Experimental testing was carried out on forty large-scale push-off specimens. Each specimen consists of two L-shaped concrete blocks cast at different times, cold joints, where GFRP reinforcement was used as shear friction reinforcement across the interface with no special treatment applied to the concrete surface at the interface. The investigated parameters included the GFRP reinforcement shape (stirrups and headed bars), reinforcement ratio, axial stiffness, and the concrete compressive strength. The relative slip, reinforcement strain, ultimate strength, and failure modes were reported. The test results showed the effectiveness and competitive shear transfer performance of GFRP compared to steel rebars. A shear friction model for predicting the shear capacity of as-cast, cold concrete joints reinforced by GFRP reinforcement is introduced. Full article