Search Results (1,353)

Mechanical loading of connective tissues is traditionally prescribed by force magnitude. In viscoelastic tissues, a constant external force does not produce a constant internal mechanical environment: stress and strain evolve continuously after load onset, creating a time-varying tissue-level mechanical history relevant to resident cells. This distinction is rarely accounted for in clinical loading protocols or scaffold design. The rate of evolution is governed by the stress relaxation time constant (τ). How τ controls the persistence of mechanical signals under force-controlled sustained loading remains poorly quantified. Thus, we developed a three-dimensional finite element model of the Wistar rat maxillary first molar tooth–periodontal ligament (PDL)–bone complex with a PDL geometry reconstructed from micro-CT imaging by original frame-by-frame manual segmentation and compared outcomes across three τ values spanning two orders of magnitude under identical 0.5 N sustained loading. Under the same applied force, stress retention at 100 s ranged from 68% to 97%, while concurrent deformation creep showed an inverse relationship. These results demonstrate that τ strongly governs the persistence of mechanical signals under sustained force-controlled loading in this model. Supplementary simulations under oblique loading and perturbed PDL modulus confirmed that τ remains the dominant constitutive determinant of stress retention across altered loading directions and stiffness conditions. Full article

This study investigates the effect of Arundodonax L.-derived lignin on the rheological behaviour, mechanical performance and oxidative ageing resistance of bitumen. Arundo donax is a fast-growing invasive grass with high lignin content, representing a promising sustainable biomass source for bitumen modification. Lignin was extracted via the Acid Detergent Lignin method, yielding a fine powder (50–300 μm). The incorporation of 6 wt% lignin into a 35/50 paving-grade bitumen induced significant changes in binder behaviour. Infrared spectroscopy (FTIR) confirmed the polyaromatic and oxygenated nature of lignin and indicated that its interaction with bitumen is primarily physical, involving polar intermolecular interactions rather than chemical bonding. Lignin modification significantly increased stiffness, elasticity, and rutting resistance, as evidenced by higher softening point, complex modulus, and recovery after creep loading. Furthermore, FTIR analysis confirmed a reduced susceptibility to oxidative ageing, demonstrated by lower increases in carbonyl and sulfoxide indexes after ageing. This suggests distinct antioxidant activity associated with the phenolic structures of lignin. Despite these benefits, severe long-term ageing led to a marked reduction in fatigue life, ductility, low-temperature cracking resistance, and adhesive properties. Overall, these results demonstrate that Arundo donax-derived lignin is a promising sustainable modifier for bitumen, though optimisation of the dosage and blending conditions is necessary to balance durability against long-term fracture performance. Full article

A research framework integrating material testing, constitutive fitting, thermo-mechanical coupled simulation, and local refined analysis was developed for 06Cr15Ni25Ti2MoAlVB superalloy bolts. High-temperature tensile and creep tests were performed to establish the Ramberg–Osgood elastic-plastic model and Norton–Bailey creep model. Based on CFD-derived thermal boundary conditions, a thermo-mechanical-creep coupled finite element model was constructed to investigate bolt temperature, global stress response, local thread stress concentration, and fastening-force evolution under rated operating conditions. The results show that the maximum temperature of the exhaust manifold is about 885 °C, while the maximum bolt temperature reaches about 250 °C. The global model predicts a maximum bolt equivalent stress of approximately 513 MPa near the initial threaded contact region. The refined thread model reveals severe stress concentration at the root of the first engaged thread, with a peak stress of about 905 MPa. After 1000 h of high-temperature holding and cooling, bolt fastening force decreases irreversibly by an average of 17.6%, with a maximum reduction of 28.27%. The results provide a reference for fastening design, fastening-force retention evaluation, and life assessment of bolted connections in high-temperature exhaust systems. Full article

Most existing creep studies on NEPE propellant focus on room and high temperatures, lacking systematic investigation into low-temperature creep damage. In this work, uniaxial creep tests at −10 °C, −30 °C and −50 °C under three stress levels were conducted. All specimens show complete three-stage creep behavior. Higher stress accelerates interface debonding and shortens rupture life, while low temperature restricts molecular chain movement and suppresses damage growth. Combined with continuum damage mechanics and strain-equivalence hypothesis, a modified time-hardening creep model embedded with the Kachanov damage-evolution equation is established. All fitting coefficients of determination exceed 0.989. A FORTRAN UMAT subroutine is developed on ABAQUS (version 2024) for numerical simulation, using SDV1 and SDV8 to output creep strain and damage variables respectively. Simulation strain curves match experimental data well and reproduce full-range creep evolution. Damage remains low for most of the service time and surges only in the final 5–10% of the lifetime. The proposed model and subroutine accurately characterize the low-temperature creep and damage evolution of NEPE propellant, supporting grain structural integrity analysis and long-term storage life prediction. Full article

To elucidate the mechanisms responsible for the low strength, pronounced variability, and long-term deformation of carnallitite, and to provide a basis for stope parameter design in deep potash mines, two carnallitite seams from a potash mine were investigated. Group C carnallitite and Group D halite-dominated rock salt were subjected to short-term compression tests and multiscale comparative analyses, while Groups A and B carnallitite specimens were tested under multistage creep loading. Particle Flow Code (PFC) simulations were conducted to evaluate the influence of particle size distribution. The results indicate the following: (1) The representative Group C specimens exhibited an average uniaxial compressive strength of 7.83 MPa, which was substantially lower than that of Group D. The acoustic emission (AE), scanning electron microscopy (SEM), and computed tomography (CT) analyses revealed greater heterogeneity in damage evolution and failure behavior, mainly associated with polymineralic composition, weak particle–matrix interfaces, local pores, and insufficient particle connectivity. (2) Particle-scale heterogeneity influenced the load-bearing capacity of carnallitite. In the PFC sensitivity analysis, narrowing the prescribed particle-size-distribution range from 0.4–8.0 mm to 4.0–4.0 mm at a mean particle size of 4.0 mm was associated with an increase in simulated strength from 7.82 to 10.40 MPa. Because quantitative contact-network descriptors were not extracted, the corresponding contact-network interpretation is treated as mechanistic rather than direct quantitative evidence. (3) The long-term uniaxial strengths of Groups A and B were estimated as 3.3 MPa and 4.8 MPa, respectively, using the adopted specific-failure-energy method. The modified Burgers model provided a good fit to the creep data within the tested stress levels, yielding coefficients of determination of 0.957 and 0.964 and root-mean-square error (RMSE) values of 0.0803 and 0.0552 percentage points. Based on the long-term strength constraints and the site-specific design assumptions adopted in this study, the calculated inter-room pillar widths were 6 m for Group A and 4 m for Group B. These findings provide insights into the multiscale damage mechanisms and long-term stability assessment of carnallitite stopes in deep potash mines. Full article

In ultra-supercritical (USC) power plants, P92 steel welded joints are continuously subjected to creep-fatigue (CF) loading, rendering them susceptible to premature cracking during service. To investigate the CF interaction behavior, CF tests were performed on P92 steel welded joints at 650 °C under various dwell times. The results indicate that prolonged dwell periods progressively shorten the cycle life. Scanning electron microscopy (SEM) observations reveal that with increasing dwell time, the fracture mechanism of the P92 steel gradually transitions from a fatigue-dominated failure mode to one governed by creep-fatigue interaction damage. Subsequently, nanoindentation was employed to evaluate the hardness (H), elastic modulus (E), and creep deformation, based on which the strain rate sensitivity (m) was estimated and the underlying damage mechanisms were thoroughly discussed. Full article

Asphalt serves as the core binder for heavy-load high-modulus pavements, and its viscoelasticity across a wide temperature range directly governs pavement-rutting resistance, low-temperature crack resistance and service life. Virgin asphalt contains abundant light fractions and exhibits insufficient stiffness at high temperatures. Modification with single styrene–butadiene–styrene block copolymer (SBS) fails to meet the anti-deformation requirements under heavy loads, while separate incorporation of nano-silica (nano-SiO₂) aggravates low-temperature brittleness. Existing studies lack comprehensive investigations into the rheological evolution laws and synergistic microscopic mechanisms of asphalt modified by combined SBS and nano-SiO₂. In this paper, virgin asphalt was adopted as raw material to prepare composite modified asphalt with gradient dosages. Integrated macroscopic performance tests and multi-scale microscopic characterizations were conducted for systematic analysis. High-temperature, low-temperature and fatigue performances were evaluated via conventional physical property tests, temperature sweep tests, multiple stress creep recovery (MSCR), linear amplitude sweep (LAS) and bending beam rheometer (BBR) tests. Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC) and thin-layer chromatography–flame ionization detection (TLC-FID) were utilized to analyze variations in functional groups, molecular weight and four fractions, to elaborate the two-phase synergistic modification mechanism. The results demonstrate that the combined incorporation of SBS and nano-SiO₂ synchronously optimizes the comprehensive performances of asphalt. Compared with single-SBS-modified asphalt, the sample with optimal dosages achieves elevated high-temperature modulus and rutting factor, reduced permanent deformation, improved low-temperature stress relaxation capacity and remarkably decelerated fatigue damage accumulation rate. Microscopic characterizations verify that only physical interactions occur during modification without generating new substances. The nano-filler facilitates the aggregation of small molecules and increases the proportion of macromolecules; meanwhile, it physically adsorbs light fractions and induces apparent redistribution of asphalt components, raising the relative proportion of resins and asphaltenes in the organic asphalt phase, realizing moderate heavy-fraction enrichment of the asphalt system. This study clarifies the internal correlation between molecular fraction evolution characteristics and macroscopic rheological performances of asphalt co-modified by nano-SiO₂ and SBS, which can provide theoretical references for formula design and engineering application of modified asphalt materials. Full article

Background: Neurodynamic techniques are commonly used to improve neural mobility and musculoskeletal function, but their effects on muscle mechanical properties remain unclear. This study investigated the acute effects of femoral nerve slider, femoral nerve tensioner, and static stretching interventions on the rectus femoris and vastus medialis muscles. Methods: Thirty healthy adults (18–35 years) were non-randomly allocated using a predetermined alternating sequence to a femoral nerve slider (n = 10), femoral nerve tensioner (n = 10), or static stretching group (n = 10). No sham or no-intervention control group was included. Muscle mechanical properties were assessed before and immediately after the intervention using the MyotonPRO (Myoton AS, Tallinn, Estonia). Outcomes included muscle tone, stiffness, logarithmic decrement, relaxation time, and creep. A three-way mixed repeated-measures ANOVA was performed. Results: No statistically significant differences in pre–post changes were detected among the three intervention groups for any of the examined mechanical parameters. Significant main effects of time were found for stiffness (p = 0.026) and creep (p = 0.005), indicating overall reductions from pre- to post-assessment. Significant time × muscle interactions were identified for relaxation time (p = 0.029) and creep (p = 0.002), indicating different temporal patterns between the rectus femoris and vastus medialis. Following Holm adjustment of the follow-up comparisons, the pre–post reduction in the vastus medialis remained statistically significant for creep but not for relaxation time. The rectus femoris demonstrated greater stiffness and logarithmic decrement values, whereas the vastus medialis exhibited greater relaxation time values. Conclusions: No statistically significant differences in immediate pre–post changes in quadriceps muscle mechanical properties were detected among the femoral nerve slider, femoral nerve tensioner, and static stretching groups. Temporal and muscle-specific patterns were observed for selected mechanical parameters; however, these findings should not be interpreted as evidence of equivalence between the interventions. Full article

In order to provide a theoretical framework for the synergistic optimization of the “rigid backbone-flexible network” in the molecular design of polyimides with high Young’s modulus, high toughness, and excellent creep resistance for wearable electronics applications, the effects of sequence structure on the mechanical properties of siloxane-containing polyimides were investigated by molecular dynamics simulations. A series of poly(siloxane-imide) block copolymer models with distinct sequence structures were constructed via molecular dynamics (MD) simulations based on 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2′-bis(trifluoromethyl)benzidine (TFDB) as hard segment A, and 6FDA and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (SiDA) as soft segment B. The results indicate that extending hard segment length enhances Young’s modulus and suppresses creep because of the enhancement of chain rigidity and formation of stable physical aggregates. Appropriately extending soft segment sequence length can improve the failure strain through rapid conformational adjustment, while excessively long soft segments lead to stress concentration, thereby reducing the failure strain. The (A₅B₅)₂ model structure exhibits superior comprehensive performance among all systems, with a relatively high Young’s modulus, failure strain, and creep recovery rate. This is attributed to the synergistic balance between the rigidity of the hard segment and the mobility of the soft segment. Full article

Refractory high-entropy and compositionally complex alloys are routinely compared by nominal composition and as-processed phase, yet processing changes the material that is actually tested. This is a critical, mechanism-led narrative review rather than a systematic review; the databases, complete search strings, screening sequence, inclusion and exclusion criteria, and evidence-grading rubric are reported so that coverage and selection bias can be assessed independently. This review synthesizes 186 publications around the NbTaV compositional core and compares alloys through directly measurable features of the processed state: interstitial content, local chemical order, grain-boundary chemistry, defect and grain architecture, phase morphology, compositional gradients and surfaces. Every source is assigned to a compositional tier and graded along four evidence axes: 96 of the 186 sources report Nb–Ta–V-containing states (Tier I), 58 are body-centered cubic refractory comparators (Tier II) and 32 are transferred-mechanism analogues (Tier III), and only 14 Tier I sources supply direct tensile, fracture or tensile-creep measurements. This asymmetry, rather than any disagreement between compositions, is the field’s binding evidence constraint. Direct tensile, fracture, and creep measurements are kept separate from compression, hardness, calculation, and screening evidence. This separation reconciles observations that otherwise appear to conflict: oxygen can strengthen or embrittle; lattice distortion can raise strength while lowering dislocation mobility; local order can harden the alloy, redirect defects or precede decomposition; and second phases help only within morphology- and service-specific compatibility windows. The strongest tensile behavior is obtained when mobile plasticity carriers are preserved, and interstitials, interfaces and phase continuity are simultaneously controlled. High-temperature, environmental, and irradiation performance depend additionally on the transition from the as-manufactured condition to the state that evolves during service. Quantitative matching tolerances for the convergent-state falsification test, service-condition-specific validation hierarchies, ordinal scoring rules for the phase-compatibility map, and a source-level audit of every quantitatively compared value are provided so that the framework can be tested and the synthesis independently checked. Full article

Fully grouted rock bolts have been extensively utilized in underground reinforcement. Numerous experimental and theoretical studies have been performed to examine the short-term strength of the fully grouted rock bolts under the normal pullout test. However, the creep behavior closely associated with the long-term strength of the rock-bolting system has been rarely examined. Here, we proposed a fractional-derivative-based constitutive model to simulate the observed creep stages of the fully grouted rock bolts under the confined pullout creep condition. The model leveraged the Abel dashpot to capture the nonlinear creep and an exponentially decaying damage function to represent the accumulated deterioration in the bolt–grout interfacial strength during creep. The proposed constitutive model was validated against a series of laboratory confined pullout creep tests. The tests covered confining pressures up to 3.0 MPa and sustained pullout loads ranging from 37 to 279 kN. The analytical curves agreed closely with the measurements (R² > 0.98), indicating that the model can characterize the time-dependent pullout response of the tested bolt–grout system. Our study facilitates the underground reinforcement system design in the fields of civil and mining engineering where long-term rock-bolting service is required. Full article

TiAl alloy exhibits excellent strength, oxidation resistance and creep resistance, making it a preferred candidate material to replace high-temperature alloys. Currently, TiAl alloy has been widely applied in aerospace, the marine industry and other fields involving high-stress contact or highly corrosive environments. Selective laser melting (SLM) technology provides a brand-new approach for the fabrication of TiAl alloys, which enables direct forming of workpieces with complex structures and significantly reduces manufacturing cycles. However, the quality and performance of SLM fabricated TiAl alloys are highly dependent on laser energy input. Therefore, this study fabricated TiAl4822 alloy under different SLM process parameters, and systematically conducted investigations on its tribological properties and electrochemical corrosion behavior. The experimental results show that the SLM process did not alter the basic phase composition of TiAl4822 alloy, with Ti_0.6Al_0.4 as the dominant phase. TiAl4822 alloys fabricated under the parameter combinations of 1000 mm/s + 140 W exhibited outstanding wear resistance, and the wear mechanism transformed from severe adhesion and abrasive wear to mild oxidative wear. When the laser power was 100 W and the scanning speed was 1200 mm/s, the alloy achieved the highest corrosion resistance, with the corrosion potential reaching the maximum value of −390.065 mV and the corrosion current density decreasing to the minimum value of 8.73 × 10⁻⁶ A/cm². Thus, different parameter combinations can realize the optimization of tribological properties and electrochemical corrosion performance respectively. This study lays a theoretical foundation for promoting the high-performance engineering application of this alloy in harsh wear-resistant and corrosion-resistant environments. Full article

The severe early-age shrinkage of alkali-activated slag is a primary bottleneck restricting its engineering application. In this work, a novel shrinkage control strategy is proposed, dominated by the physical control of vacuum dehydration and assisted by the chemical compensation of MgO. The synergistic mechanism of this strategy in the AAS system was revealed by multi-scale characterization methods (XRD, FTIR, TG, NMR, BSE, and pore solution analysis). Firstly, vacuum dehydration greatly advances the development window of capillary pressure to the early stage (<6 h) of the material in the significant viscoelastic stage by forcibly removing free water between the interlayer and capillary pores. Most of the shrinkage strain energy can be dissipated through the early creep behavior of the slurry, and the strong negative pressure induces the conversion of mesopores to macropores, thereby effectively reducing the equilibrium capillary cracking driving force. Secondly, the late hydration of an appropriate amount of MgO generates magnesium silicate and hydrotalcite phases, which provide a continuous chemical micro-expansion for the matrix to compensate for residual shrinkage and moderately optimize the local pore defects induced by dehydration. The results show that in the sodium silicate solution and sodium hydroxide activating system, the synergistic effect reduces the total shrinkage rate of 28 days by 37.86% and 29.26%, respectively. Additionally, the compressive strength of hardened samples increases by about 20%. This study provides a new theoretical basis for the design of low-shrinkage and high-performance alkali-activated materials based on the physical–chemical coupling mechanism. Full article

Ultra-supercritical (USC) steam turbines combine severe steam conditions with increasingly frequent start-up, shutdown, and load-following operations. Their main steam valves must preserve pressure boundary integrity, sealing, and rapid actuation while non-uniform heating, creep, cyclic plasticity, oxidation, wear, and contact redistribution alter component geometry. However, the relevant evidence remains fragmented across alloy development, component thermo-mechanics, valve aerodynamics, and lifetime monitoring. This short, mechanism-oriented review integrates these domains through a material structure–function framework in which deformation relative to assembly clearance governs jamming risk. It synthesizes evidence on heat-resistant body and surface materials, 9–12% Cr steel stability, weldability and repair sensitivity, and cold, warm, and hot start-up histories. It also evaluates creep–fatigue interaction, contact, flow-induced vibration, multi-physics modeling, validation, uncertainty, monitoring, and digital twins. The synthesis shows that neither peak equivalent stress nor steady-state temperature alone can establish functional reliability. Credible assessment requires temperature-dependent material data, realistic steam-side heat transfer, cyclic constitutive behavior, initial and residual clearances, manufacturing and assembly tolerances, state-dependent friction, uncertainty analysis, and corroborating plant or inspection evidence. The most consequential research needs are valve-level validation datasets, thermal contact testing, function-oriented life criteria, and uncertainty-aware digital twins that jointly inform materials, geometry, and transient operation. Full article

Cast irons are extensively used in high-temperature applications such as cylinder heads of heavy-duty diesel engines, where sustained exposure to high stresses and temperatures can initiate creep-related failure mechanisms, impacting their long-term durability and efficiency. Our previous experimental research demonstrated significant differences in creep mechanisms and behaviour of compacted graphite iron (CGI) under tensile and compressive loading. In situ analysis of the microstructural effects defining these differences during long-term high-temperature experiments is hardly possible. An alternative way to study these effects is to develop advanced micromechanical models using a finite-element method. The aim of this paper is to study the local responses at microscale (considering local distributions of stresses and strains) to macroscale long-term loading at high temperature employing direct introduction of microstructural features into numerical models. The models consider elasto-visco-plastic behaviour of the CGI material under tensile and compressive loading regimes. The novel results presented in this paper are applicable to cast irons as well as other heterogeneous materials such as metal matrix composites and the models presented can be used as a tool in the development of materials with microstructures customised for high-temperature applications. Full article