Search Results (71)

Flexible graphite packing rings are widely employed in high-temperature and high-pressure valve sealing systems owing to their intrinsic lubricity and thermal stability, yet their service reliability is often compromised by low mechanical strength, pronounced creep, and unstable tribological behavior under extreme conditions. Here, we present an interface-engineered strategy to enhance the service performance of graphite packing rings via reinforcement with surface-functionalized PAN-based carbon fibers (PAN-CFs; carbonized fibers derived from polyacrylonitrile precursors). Through controlled oxidative modification of carbon fibers combined with high-temperature graphite expansion, a three-dimensional reinforced graphite network with uniform fiber dispersion was constructed. The influence of PAN-based carbon fiber (PAN-CF) content (0–7 wt%) on compressive strength, thermal stability, friction behavior, and long-term durability was systematically evaluated. An optimal performance was achieved at 5 wt% PAN-CF, featuring a ~58% increase in compressive strength, a stable friction coefficient of 0.15–0.18, and enhanced creep resistance, while retaining over 78% of the initial strength after 1000 h of sustained loading. Microstructural and complementary structural analyses suggest that these improvements are associated with interfacial mechanical anchoring, fiber embedding, and load-transfer reinforcement enabled by fiber surface functionalization and the expanded graphite architecture. This work offers a practical material-level approach to improving the long-term reliability of graphite-based sealing components in demanding industrial environments. Full article

Cemented coal gangue backfill (CCGB) is an important material for the resource utilization of mining solid waste, and its long-term stability is strongly affected by aggregate gradation. In this study, aggregate mass fractal dimension was used to characterize the particle size distribution of coal gangue, and four gradation schemes with different fractal dimensions were designed. Uniaxial compressive strength (UCS) tests, stepwise accelerated creep tests, acoustic emission (AE) monitoring, and scanning electron microscopy (SEM) observations were conducted to investigate strength, creep behavior, crack evolution, and damage mechanisms. The results show that P-wave velocity and UCS exhibit generally non-monotonic variations with fractal dimension, with relatively high values in the intermediate fractal-dimension range. The empirical long-term strengths for $D=2.20$, 2.41, 2.59, and 2.79 are 6.62, 8.83, 7.34, and 7.07 MPa, respectively. AE results indicate that shear cracking first decreases and then increases with fractal dimension, reaching the lowest proportion of 41.8% at $D=2.41$. SEM observations show that an intermediate fractal dimension improves skeleton continuity and interfacial integrity, thereby suppressing shear-related damage and delaying creep instability. These findings demonstrate that aggregate mass fractal dimension is an effective structural parameter for linking gradation characteristics, creep resistance, and damage evolution of CCGB. Full article

Carbon fibre-reinforced polymer (CFRP) composites represent promising lightweight materials for automotive powertrain systems, where increasing demands for weight reduction, energy efficiency, and emission reduction are driving the replacement of conventional metallic components. However, automotive powertrain environments expose CFRP materials to elevated temperatures, cyclic mechanical loading, chemical exposure, and tribological interactions, creating complex degradation conditions that significantly influence long-term durability and reliability. This review systematically analyzes CFRP composites for automotive powertrain applications, focusing on the relationship between operational requirements, material selection, reinforcement architecture, manufacturing technologies, and degradation mechanisms. High-performance thermoplastic systems such as CF/PEEK, CF/PPS, and CF/PEKK are critically compared with conventional thermoset composites. CF/PEEK systems demonstrate superior thermomechanical stability, maintaining significant mechanical performance at temperatures approaching 250 °C and tensile strengths of approximately 1400–1600 MPa, whereas CF/PPS composites provide a more economically efficient compromise between thermal resistance, chemical stability, manufacturability, and recyclability for medium-temperature applications. The review further analyzes dominant degradation mechanisms, including creep deformation, fatigue damage, delamination, fibre–matrix interface degradation, and tribological wear. CFRP degradation is shown to result from the interaction of multiple coupled mechanisms rather than from isolated material failure modes. Tribological wear rates typically range from 10⁻⁶ to 10⁻⁵ mm³/(N·m), while creep–fatigue interactions may reduce component lifetime by up to 40–60% under combined thermomechanical loading. Advanced design strategies, including fibre orientation optimization, laminate architecture tailoring, thickness gradation, and hybrid metal–composite structures, are evaluated together with major manufacturing technologies such as injection moulding, compression moulding, overmoulding, automated fibre placement, and additive manufacturing. The presented review establishes an integrated framework linking material systems, operating conditions, manufacturing processes, and durability requirements for automotive powertrain applications. The analysis demonstrates that no universal CFRP system exists for all powertrain components and that optimal material selection requires balancing thermal stability, fatigue resistance, tribological performance, manufacturability, recyclability, and economic constraints according to the specific operating conditions of each component category. Full article

The effects of Mn/RE (Nd, Gd) multi-modification on the microstructure and high-temperature compressive creep properties of Mg–8.0Al alloys were investigated. The dominant intermetallic phases in the as-cast microstructure are β-Mg₁₇4Al₁₂, Al₂(Gd,Nd), Al₁₁(Gd,Nd)₃, Al₈(Gd,Nd)Mn₄, and Al₁₀Mn₂(Gd,Nd). The detailed structures of various intermetallics were revealed by TEM; the results indicate that Mn addition promotes grain refinement and facilitates the precipitation of lath-shaped and spherical β-Mg₁₇Al₁₂ in as-cast Mg–Al–RE alloys, resulting in increases in the tensile strength and elongation of the 1.0Mn alloy by 26.5% and 92.1%, respectively. Additionally, thermally stable micron-scale Al₈(Gd,Nd)Mn₄ and Al₁₂(Gd,Nd)₂Mn₅, along with dynamically precipitated spherical nano-sized AlGd and AlNd particles in the α-Mg matrix, were innovatively observed in compression-crept specimens tested at 200 °C and 60 MPa; these phases play a key role in improving high-temperature creep resistance. A significant finding is that excessive Mn addition deteriorates creep performance, which is attributed to excessive grain refinement and the consequent increase in the contribution of grain boundary sliding during creep. However, the negative effect of grain boundary sliding—caused by grain refinement—on creep performance can be balanced by the strengthening effect of Al–Mn–Gd phases and the dynamic precipitation of nanoscale Al–RE particles. This paper provides new insights for designing Mg–Al–Nd–Gd–Mn alloys with both excellent high-temperature creep resistance and significantly enhanced mechanical properties. Full article

Carbon-fiber reinforced polymer (CFRP) tendons have attracted increasing attention as corrosion-resistant prestressing elements for prestressed concrete and cable-supported structures; however, their practical implementation requires reliable verification of long-term mechanical performance and anchorage reliability. In this study, a 9.5 mm pultruded CFRP tendon and compression-type anchorage system were developed and experimentally evaluated through relaxation, creep rupture, and fatigue tests. The tendon exhibited a tensile strength of 2501 MPa and an elastic modulus of 132.5 GPa. Relaxation tests were conducted at an initial load corresponding to 70% of the ultimate tensile capacity, and the measured relaxation loss after 1000 h was 1.02%. Based on logarithmic regression of the measured data, the relaxation loss at 1,000,000 h was estimated to be 2.11%; however, this value should be interpreted as an extrapolated long-term estimate rather than a directly verified result. Creep rupture tests performed at load ratios of 82.4–100.0% yielded an estimated 1,000,000 h creep rupture load ratio of approximately 80%, although the prediction is subject to uncertainty because of the limited number of specimens and scatter in rupture times. Fatigue tests indicated that the CFRP tendon–anchorage assembly maintained stable performance up to 2,000,000 cycles without measurable degradation in elastic stiffness under the adopted loading conditions. These results suggest that the developed CFRP tendon–anchorage system has promising potential for prestressing applications, while further long-term tests with a larger number of specimens are required to improve the statistical reliability of the extrapolated relaxation and creep rupture predictions. Full article

Salt cavern Compressed Air Energy Storage (CAES) is one of the critical technologies for energy storage and an important infrastructure supporting the construction of new power systems and facilitating the achievement of the dual carbon goals. The salt rock resources in China are primarily composed of continental strata salt rocks, characterized by high heterogeneity, well-developed thin-layer interbedding, dissolution resistance among different lithologies, and significant creep variations. These features, to some extent, limit the improvement of wellbore construction accuracy, the reliability of abandoned well sealing, the safety of natural gas storage operations, and enhancements in gas injection–brine displacement efficiency. This study takes the continental bedded salt rock in the Dawenkou Basin as the research object and adopts a method combining theoretical analysis and field engineering verification to improve the systematic construction technology system, covering the whole process of drilling engineering, abandoned well plugging, the design of an injection and brine extraction device, and gas injection and brine drainage. The research results optimize four key technologies, including precise wellbore trajectory control, dual-section milling, and multi-stage redundant plugging of abandoned wells and long-term anti-corrosion completion with laser cladding, and dual-mode adaptive gas injection and brine drainage, and improve the technical system from wellbore construction to salt cavity formation. This study can provide valuable theoretical references and engineering demonstration guidance for underground space development projects in similar salt basins in China. Full article

To give more insight into the microstructural evolution and deformation mechanisms governing the long-term service performance of additively manufactured TiAl-based composites at elevated temperatures, this study investigated the high-temperature compressive creep behavior of a laser powder bed-fused LaB₆ reinforced high-Nb TiAl-based composite after hot isostatically pressing (HIP), with emphasis on the creep response and dynamic recrystallization (DRX) mechanisms under different applied stress levels. The results showed that, as the applied stress increased from 200 MPa to 450 MPa, the steady-state creep rate rose from 2.88 × 10⁻⁸ s⁻¹ to 3.85 × 10⁻⁷ s⁻¹. Stress exponent analysis indicated that creep deformation was predominantly controlled by dislocation climb, and no tertiary creep stage was observed within the investigated stress range. At 200 MPa and 300 MPa, a certain fraction of recrystallized grains formed during prolonged creep exposure. When the stress increased to 400 MPa, the recrystallization process was restricted due to the limited creep duration. In contrast, at 450 MPa, the accelerated accumulation of strain energy significantly promoted recrystallization. Both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) were identified, jointly governing the microstructural evolution. Superior creep resistance can be attributed to multiple synergistic strengthening mechanisms, including the refined α₂/γ lamellar structure induced by HIP treatment, the strong pinning effect of dispersed La₂O₃ nanoparticles on dislocation motion, and the suppression of diffusion-controlled dislocation climb by Nb addition. These combined effects enhance the high-temperature creep performance of the TiAl composite and provide important insights for the application of LPBF-fabricated TiAl-based composites under elevated-temperature service conditions. Full article

The development of cement composites that simultaneously achieve high compressive strength and low density remains a fundamental scientific challenge, particularly because optimizing weight reduction often compromises mechanical performance under sustained high-pressure conditions. In modern construction—especially high-rise buildings, large-span structures, and underground projects—there is an urgent applied need for lightweight materials that can reduce structural self-weight, enhance seismic resilience, simplify foundation design, and improve construction efficiency without sacrificing load-bearing capacity or long-term durability. To address this dual problem, this study investigates high-pressure-resistant lightweight cement composites incorporating hollow glass microspheres (HGMSs) of three different particle sizes as functional fillers, modified with isobutyl triethoxy silane (IBTES) to strengthen interfacial bonding. Ten formulations with varying HGMS types and dosages (5%, 10%, and 15% by volume) were systematically evaluated through creep tests, uniaxial compression experiments, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The scientific results demonstrate marked qualitative and quantitative improvements: the optimal formulation (25 μm HGMS at 5% dosage) exhibited a 22.01% reduction in creep deformation and a 67.85% increase in compressive strength compared to plain cement, while bulk density was reduced by 8.8–19.0%. Enhanced hydration was confirmed by a 23.6% reduction in residual Ca(OH)₂ content and a 31.2% increase in chemically bound water, indicating more complete formation of calcium silicate hydrate (C–S–H) gel. Energy evolution analysis revealed a prolonged elastic energy accumulation stage (increasing from 56% to 95% of total compression duration), signifying a transition toward quasi-ductile failure behavior. From an applied perspective, these quantitative enhancements translate directly into practical construction benefits: the 8.8–19.0% density reduction enables lighter structural components, easing transportation and installation; the 67.85% higher compressive strength ensures reliable performance in high-pressure environments; and the 22.01% lower creep deformation guarantees long-term dimensional stability. Collectively, these findings confirm that the HGMS-IBTES-modified composite offers a scalable, high-performance solution for advanced construction applications where both weight reduction and superior pressure resistance are critical. Full article

The multi-objective optimization of multicomponent superalloys has long been impeded by not only the complex interactions among multiple elements but also the low efficiency and high cost of traditional trial-and-error methods. To address this issue, this study proposed a thermodynamic calculation data-driven optimization framework that integrates machine learning (ML) and multi-objective screening based on domain knowledge. The core of this methodology involves introducing a commercial reference alloy and rapidly generating a large-scale thermodynamic dataset through ML models. After training, the ML models were verified to be more efficient at predicting phase transition temperatures and γ′ volume fractions than the CALPHAD methods. Focusing on the mechanical properties, critical strength indices, including solid solution strengthening, precipitation strengthening, and creep resistance based on the calculated γ/γ′ two-phase compositions, were compared with the reference alloy and set as the critical screen criteria. Optimal alloys were selected from the 388,000 candidates. Compared with the reference alloy, two new alloys were experimentally verified to have superior or comparable compressive yield strength and creep resistance at 900 °C at the expense of oxidation resistance and density, while maintaining comparable cost. This work demonstrates the significant potential of combining high-throughput thermodynamic data with intelligent multi-objective optimization to accelerate the development of new alloys with tailored property profiles. Full article

Alfalfa is a high-quality forage crop whose viscoelastic properties strongly influence the performance of baling, pickup, and stacking operations. In this study, small alfalfa block specimens were tested using a universal testing machine to investigate stress relaxation and creep behaviors under different moisture contents (12%, 15%, 18%), densities (100, 150, 200 kg/m³), and maximum compressive stresses (8, 12, 16 kPa). Experimental data were fitted using viscoelastic models for parameter analysis. Results indicated that the relaxation response consisted of a rapid attenuation followed by a slow stabilization phase. The five-element Maxwell model achieved a higher fitting accuracy (coefficient of determination, R² > 0.997) than the three-element model. The creep process exhibited three stages, including instantaneous elastic deformation, decelerated creep, and steady-state deformation, and it was accurately represented by the five-element Kelvin model (R² > 0.998). Increasing moisture content reduced stiffness, while moderate moisture improved viscosity and shape retention. Higher density enhanced blocks compactness, stiffness, and damping characteristics, resulting in smaller deformation. The viscoelastic response to compressive stress showed moderate enhancement followed by attenuation under overload, with the best recovery and deformation resistance observed at 12 kPa. These findings elucidate the viscoelastic behavior of alfalfa blocks and provide theoretical support and engineering guidance for evaluating bale stability and optimizing pickup–clamping parameters. Full article

This study investigates the creep behavior of Wenzhou marine soft soil through 1D and triaxial creep tests, revealing that the secondary consolidation coefficient initially increases then stabilizes with stress level, decreases with OCR, increases with time, and reduces with depth. The e-lgt curves show four-phase deformation (instantaneous, primary consolidation, secondary compression, and accelerated creep), while triaxial tests identify three creep stages (decelerated, steady, and accelerated), with higher confining pressure increasing the deviatoric stress threshold for accelerated creep. Nonlinear stress–strain isochrones shift toward the strain axis with increasing confining pressure. The proposed structural parameter inversely correlates with the secondary consolidation coefficient, demonstrating that enhanced interparticle cementation and soil structure improve long-term creep resistance in coastal soft soil foundations. Full article

γ-TiAl alloy is a lightweight high-temperature structural material, featuring low density, excellent high-temperature strength, creep resistance, etc. It is a key material in the aerospace field. However, the essential defects of γ-TiAl alloys, such as poor room-temperature plasticity and low fracture toughness, have become the biggest obstacles to their practical application. Therefore, in this paper, the physical mechanism of modification of the mechanical properties and electronic structure of γ-TiAl alloys by doping with Sc, V, and Si was investigated by using the first-principles pseudopotential plane wave method. This paper specifically calculates the geometric structure, phonon spectrum, mechanical properties, electron density of states, Mulliken population analysis, and differential charge density of γ-TiAl alloys before and after doping. The results show that after doping, the structural parameters of γ-TiAl have changed significantly, and the doping models all have thermodynamic stability. The B, G, and E values of the doped system are, respectively, within the range of 94–112, 57–69, and 143–170 GPa, indicating that the material’s ability to resist compressive deformation is weakened. Moreover, the B/G values change from 1.5287 to 1.6350, 1.7279, and 1.6327, respectively, and a transformation from brittleness to plasticity occurs. However, it is still lower than the critical value of 1.75, indicating that the doped γ-TiAl alloy material retains its high-strength characteristics while also exhibiting a certain degree of toughness. The total elastic anisotropy index of the doped system increases, and the degree of anisotropy of mechanical behavior significantly increases. The total electron density of states diagram indicates that γ-TiAl alloys possess conductive properties. The covalent interactions between doped atoms and adjacent atoms have been weakened to varying degrees, which is manifested as a significant change in the charge distribution around each atom. The above results indicate that the doping of Sc, V, and Si can effectively tune the mechanical properties and electronic structure of γ-TiAl alloys. Full article

Quality and mechanical resilience are crucial for reducing losses in fruit production and for supporting food chains. Indeed, integrating empirical data with rheological models bridges gaps in fruit processing equipment design. Therefore, the objective of this research is to analyze the relationship between the mechanical and physical properties of seven economically important fruits—nectarine, kiwi, cherry, apple, peach, pear, and apricot—to assess their mechanical behavior and post-harvest quality. Standardized compression, creep, and puncture tests were conducted to establish mechanical parameters, such as rupture force, elasticity, and deformation energy. Physical characteristics including size, weight, density, and moisture content were also measured. The results indicated significant differences among the various categories of fruits; apples and pears were most suitable for mechanical harvesting and long storage periods, whereas cherries and apricots were least resistant and susceptible to injury. Correlations were high among the physical measurements, tissue firmness, and viscoelastic properties, thereby confirming structural properties’ contribution in influencing fruit quality and handling efficiency. The originality of this research is in its holistic examination of physical and mechanical properties under standardized testing conditions, thus offering an integrated framework for enhancing post-harvest operations. These findings offer practical insights for optimizing harvesting, packaging, transportation, and quality monitoring strategies based on fruit-specific mechanical profiles. Full article

This paper reviews the applications and performance advantages of ultra-high-performance concrete (UHPC), engineered cementitious composite (ECC), and recycled aggregate concrete (RAC) in composite flexural members. UHPC is characterized by its ultra-high strength, high toughness, excellent durability, and microcrack self-healing capability, albeit with high costs and complex production processes. ECC demonstrates superior tensile, flexural, and compressive strength and durability, yet it exhibits a lower elastic modulus and greater drying shrinkage strain. RAC, as an eco-friendly concrete, offers cost-effectiveness and environmental benefits, although it poses certain performance challenges. The focus of this review is on how to enhance the load-bearing capacity of composite beams or slabs by modifying the interface roughness, adjusting the thickness of the ECC or UHPC layer, and altering the cross-sectional form. The integration of diverse concrete materials improves the performance of beam and slab elements while managing costs. For instance, increasing the thickness of the UHPC or ECC layer typically enhances the load-bearing capacity of composite beams or plates by approximately 10% to 40%. Increasing the roughness of the interface can significantly improve the interfacial bond strength and further augment the ultimate load-bearing capacity of composite components. Moreover, the optimized design of material mix proportions and cross-sectional shapes can also contribute to enhancing the load-bearing capacity, crack resistance, and ductility of composite components. Nevertheless, challenges persist in engineering applications, such as the scarcity of long-term monitoring data on durability, fatigue performance, and creep effects. Additionally, existing design codes inadequately address the nonlinear behavior of multi-material composite structures, necessitating further refinement of design theories. Full article

Textile-reinforced alkali-activated mortar (TRAAM) is a composite material that is characterized by a strain- or deflection-hardening response under tension or flexure, respectively, as well as by a good bond with concrete and masonry substrates. Owing to comparable or even superior mechanical performance compared to “conventional” cement- or lime-based textile-reinforced mortar (TRM) systems and its potentially eco-friendly energy and environmental performance, TRAAM has been incorporated to retrofitting schemes. The current article reviews the studies that investigate TRAAM as a strengthening overlay for masonry and concrete members. This article focuses on the mechanical performance of the strengthened members, which, where possible, is also compared with that of members strengthened with conventional TRM systems. It is concluded that TRAAM can enhance the flexural and shear capacity of masonry and concrete members, while it can also upgrade the compression strength and seismic response of concrete members. In addition, it is concluded that the effectiveness of TRAAM can be comparable with that of “conventional” TRM systems. The combination of TRAAM with thermal insulation boards has also been proposed for structural and energy upgrading of masonry walls. Furthermore, TRAAM can be a promising solution for increasing the fire resistance of strengthened masonry members. However, research on the long-term performance of TRAAM, including durability, creep, and shrinkage, is still limited. Finally, the lack of established standards for TRM retrofitting is more evident for TRAAM applications. Full article