Search Results (288)

The mechanical properties of moraine soil in cold regions are significantly influenced by freeze–thaw cycles (FTCs). However, current understanding of the quantitative characteristics of its shear behavior under the coupled effect of FTCs and confining pressure is still insufficient. To address this, a series of triaxial unconsolidated-undrained shear tests were conducted on saturated moraine soil, with different numbers of FTCs (N = 0, 1, 4, 8, 10, 12, 15, 20) and various confining pressures (σ₃ = 100, 200, 300, 400 kPa). The experimental results reveal that: (1) With an increase in the number of FTCs, the stress–strain curves gradually change from strain-softening to strain-hardening types. Correspondingly, the pore water pressure development shifts gradually from a peak-decay pattern to a growth-stabilization pattern. The peak pore water pressure rises linearly with increasing confining pressure, whereas it decays linearly with an increasing number of FTCs. (2) Both the secant modulus E₅₀ and the shear strength increase with higher confining pressure and decrease with more FTCs. Confining pressure exerts a significant inhibitory and compensatory effect on freeze–thaw-induced damage, markedly reducing the deterioration rate under high confining pressure. (3) Quantitative prediction models for E₅₀ and q_max were established, effectively capturing the coupled effect of confining pressure and FTCs. It can be inferred that confining pressure mitigates structural damage by compressing frost-induced cracks and enhancing interparticle contacts, while FTCs exacerbate the degradation of soil mechanical properties because of ice crystal expansion or contraction and weakening of cementation. This study quantifies the coupled effect of confining pressure and FTCs, and the proposed prediction model provides a useful reference or preliminary estimation for relevant geotechnical engineering designs. Full article

The dissimilar metal welded joints at the safe ends of nuclear primary circuits are highly susceptible to stress corrosion cracking (SCC) initiation in high-temperature, high-pressure water environments. Existing predictive models are predominantly based on homogeneous material assumptions, making it challenging to accurately evaluate the actual failure behavior of welds caused by mechanical property heterogeneity. Consequently, based on the mechanical gradient obtained from hardness tests, this study constructs a finite element model with continuously varying mechanical properties to quantitatively investigate SCC behavior under different crack characteristics. The analysis demonstrates that mechanical heterogeneity significantly influences the crack tip mechanical fields: When the crack is located proximal to the sub-interface (d = 1 mm), the severe mechanical mismatch induces a sharp increase in creep strain, resulting in a peak SCC propagation rate approximately 14.6% higher than those at d = 3 mm. Furthermore, extending the crack length at the weld center (a/W from 0.45 to 0.60) expands the plastic strain zone along the propagation direction, driving an approximately 43.6% increase in the crack growth rate. The heterogeneous model, accounting for the local mechanical gradient, can more accurately reveal the influence laws of crack position and length on SCC propagation behavior, providing theoretical support for improving life prediction accuracy and in-service inspections. Full article

Cemented paste backfill (CPB) is widely used in mining, but its high brittleness, low toughness, and limited ductility can cause it to crack and spall, or even damage the overall structure, thereby limiting its application in deep underground mine excavations. To this end, this study investigates the damage and failure mechanisms of cemented gangue–rubber paste backfill (CGRPB) and analyses its energy evolution characteristics. The aims are to: (i) assess the CGRPB mechanical properties, i.e., toughness, ductility, and brittleness due to incorporating rubber; (ii) analyze the fracture propagation process of CGRPB from an energy evolution perspective. Therefore, monotonic and cyclic compression tests were conducted on CGRPB samples containing 0%, 5%, and 10% recycled rubber powder. This study focuses on analyzing compressive strength, failure modes, stress–strain responses, energy evolution and the damage evolution process. Key findings include: (1)the effect of rubber incorporation on strength is dosage- and curing-age-dependent; a moderate rubber content (5%) improves early-age strength, whereas excessive rubber addition reduces strength due to increased porosity and weakened load-bearing capacity; (2) samples with rubber significantly reduce the length, number, and width of cracks, achieving better structural integrity; (3) introducing rubber improves the pre-peak deformation capacity of the samples; (4) the strain growth magnitude is positively correlated with the rubber content, enhancing their toughness and ductility; (5) adding rubber effectively reduces the damage propagation rate within the sample; (6) under loading, rubber elastic deformation in samples dissipates energy, which describes the approximately linear energy storage and dissipation trend; (7) among the investigated rubber contents, 5% rubber incorporation achieved a favorable balance between mechanical strength, toughness, and ductility. Full article

Natural-fracture connectivity substantially influences hydraulic-fracture interaction with pre-existing discontinuities, but its quantitative role in fracture-network propagation remains insufficiently constrained. In this study, a coupled LEFM–cohesive-zone hydraulic-fracture propagation model was developed by combining crack-tip deflection criteria, traction-separation damage evolution and fluid–solid coupling. True triaxial hydraulic-fracturing experiments were conducted on artificial fracture networks with I-, V-, Y- and X-shaped connectivity elements to evaluate the model response. The results show that connected natural fractures redirect hydraulic fractures under low horizontal stress differences, producing deflection angles of 30–50 degrees. When the stress difference exceeds 4 MPa, fracture growth becomes more strongly aligned with the maximum principal stress direction. In the true triaxial tests, the total number of connected natural fractures increased from 14 in the I-shaped network to 17 and 21 in the Y- and X-shaped networks, corresponding to increases of 21.4% and 50.0%, respectively. X-shaped networks showed the strongest sensitivity to stress difference and injection rate, while higher elastic modulus reduced fracture width and promoted longer, narrower fractures. Scale-normalized comparisons based on image-derived experimental measurements showed that the predicted propagation length, fracture width and connected-fracture number followed the experimental trend from I-shaped to Y-shaped and X-shaped networks, with relative errors within 7.1% and a mean absolute percentage error of 4.8%. These findings suggest that fracture topology strongly influences pressure transmission and multidirectional activation in the tested models, whereas field-scale extrapolation requires three-dimensional validation and transport analysis. Full article

Hydrogen energy systems—proton exchange membrane fuel cells (PEMFCs), water electrolyzers, and high-pressure hydrogen storage vessels—are increasingly deployed in transportation, maritime, aerospace, and stationary applications where mechanical vibration is unavoidable. Yet vibration research remains fragmented into single-technology studies whose findings often appear inconclusive or contradictory. This review provides a cross-technology assessment of vibration phenomena in hydrogen energy systems, covering PEMFC performance and degradation, structural dynamics of stacks and storage vessels, water management and two-phase flow, diagnostics and modeling, and application-specific challenges for road, marine, aircraft, and space systems. By organizing the evidence around a small set of shared mechanisms—loss of mechanical preload (bolt loosening), two-phase flow disruption, and fatigue-driven crack growth—we establish a unified framework that reconciles the seemingly case-dependent results of earlier, single-technology reviews. Whether vibration acts as friend or foe is governed by a consistent parameter set: amplitude, frequency, direction, and cumulative exposure time. Short, low-frequency excitation can aid water removal in fuel cells, improve cold-start behavior, and raise electrolyzer hydrogen yield by up to 128%, whereas sustained exposure roughly doubles PEMFC voltage degradation rates, loosens clamping bolts, and drives fatigue in storage-vessel supports. The evidence base is currently dominated by PEMFC studies, and this review accordingly treats fuel cells in the greatest depth. Priority research needs are identified: standardized vibration test protocols, long-duration durability data, vibration characterization of electrolyzers prior to offshore deployment, and coupled multiphysics models supporting vibration-aware design. Full article

This study analyzed the effect of a processing sequence comprising precision casting, heat treatment, and high-temperature plastic deformation on the microstructure and mechanical properties of the Haynes 282 nickel superalloy. The starting material was prepared in an industrial VIM IC induction furnace under vacuum conditions; the quality of the resulting castings, phase composition, thermal effects, and the alloy’s behavior during uniaxial compression were then evaluated. Castings in the form of rods with diameters of 10, 12, and 16 mm were produced at a molten alloy temperature of 1550 °C and a ceramic mold temperature of 1250 °C. The lowest porosity values, ranging from approximately 0.036–0.16%, were obtained for the vacuum furnace cooling variant, which was selected for further testing. DTA analysis revealed characteristic thermal effects in the range of 935.9–1379.8 °C, which enabled the selection of supersaturation parameters and a safe range for deformation tests. After supersaturation and aging, the samples were compressed at temperatures of 700–1200 °C at strain rates of 0.001 s⁻¹ and 0.008 s⁻¹. An increase in temperature caused a systematic decrease in maximum stress and yield stress, with the highest plastic resistance observed at temperatures of 700–800 °C. In this range, the microstructure exhibited characteristics of strong strain hardening, high dislocation density, and strain localization. At temperatures of 850–1000 °C, a transition to conditions of intense dynamic recovery and dynamic recrystallization was observed, whereas above 1050 °C, grain growth following recrystallization dominated. The most favorable compromise between reducing deformation resistance, minimizing the risk of cracking, and maintaining a finer microstructure was achieved in the 900–1000 °C range. The results indicate that the combination of precision casting and controlled thermomechanical working can serve as the basis for further optimization of the manufacturing technology for Haynes 282 superalloy semi-finished products. Full article

This study investigates hydrogen-assisted fatigue crack growth (FCG) in vintage pipeline steels to quantify grade-dependent degradation under hydrogen–natural gas blending conditions. Fatigue behavior was evaluated using compact-tension specimens extracted from API X52 and X70 pipeline steels and tested in natural gas–hydrogen mixtures at a total pressure of 6.9 MPa and ambient temperature. Hydrogen concentration was systematically varied from 0% to 100% H₂ to assess its influence on crack-length evolution, fatigue crack growth rate, and fracture morphology. Crack propagation was characterized as a function of the stress-intensity-factor range, and scanning electron microscopy was used to examine hydrogen-induced changes in fracture mechanisms. The results demonstrate that FCG accelerates as hydrogen concentration increases, with a strong dependence on steel grade. X70 exhibited substantially greater hydrogen-induced FCG acceleration than X52, despite showing better fatigue resistance under hydrogen-free conditions. Fatigue life reductions approached 60% for X70 at 100% hydrogen, compared with approximately 30% for X52 under the same conditions. Significant early-life sensitivity was observed in X70 even at low hydrogen concentrations, whereas X52 showed more pronounced acceleration during later stages of crack growth. The influence of hydrogen was nonlinear and tended to stabilize at elevated blend fractions, indicating a saturation-type response once hydrogen-assisted crack growth became dominant. Fractographic analyses revealed a transition from ductile tearing in natural gas environments to terrace- and facet-controlled crack propagation in hydrogen-rich environments, accompanied by secondary cracking and river-pattern features. These findings demonstrate that hydrogen–natural gas blending can significantly alter fatigue crack growth behavior and relative material performance in pipeline steels, highlighting the need for grade-specific integrity assessment of existing pipeline infrastructure. Full article

This paper proposes a method for simulating freeze–thaw damage in water-rich sandstone using PFC3D (Particle Flow Code in three dimensions). Water-rich sandstone is idealized as a composite system consisting of rock particles, water particles, and three types of contact surface: rock–rock, rock–water, and water–water. The volume change in water particles is governed by temperature, unfrozen water content, and porosity. During thawing, the volume change in water particles is realized by increasing the porosity after each cycle because the expansion of water particles is reflected by pore enlargement and the accumulation of externally supplied water. The proposed approach is intended for saturated or highly water-rich sandstone under laboratory freeze–thaw conditions with external water replenishment. It represents freeze–thaw damage associated with pore water freezing expansion and porosity-controlled equivalent water replenishment, whereas ice segregation, cryogenic suction, moisture migration, and a moving freezing front are not explicitly considered. A comparison between simulation results and laboratory tests indicates that the proposed method can effectively reproduce the freeze–thaw cycling process in water-rich sandstone. The results show that the mechanical behavior of sandstone after freeze–thaw cycles, including uniaxial compressive strength and elastic modulus, deteriorates significantly. The failure mode changes from shear failure to splitting failure. Freeze–thaw cycling and subsequent uniaxial compression are dominated by tensile damage, with tensile cracks accounting for approximately 90% of the total cracks. The tensile damage rate, Rt, increases exponentially. Crack development induced by freeze–thaw cycling follows an S-shaped trend and can be divided into three stages: slow crack growth from 0 to 10 cycles, rapid crack growth from 10 to 32 cycles, and a reduced growth rate after 32 cycles. The results provide a reference for the freeze–thaw damage analysis of rocks in cold regions and numerical simulations of freeze–thaw cycling processes. Full article

Temper embrittlement (TE) degrades the toughness of high-strength Ni-Cr-Mo steels, typically driven by competing mechanisms of impurity segregation and carbide precipitation. To decouple these effects, this study investigates the influence of prior austenite grain size (PAGS) on TE kinetics in a low-phosphorus (0.0038 wt.%) steel. Varying PAGS microstructures were subjected to isothermal aging and characterized using impact testing and atom probe tomography (APT). APT confirmed negligible phosphorus segregation, proving TE is driven primarily by M₂₃C₆ carbide precipitation. Compositional profiling revealed that carbide growth is kinetically governed by chromium (Cr) diffusion. Kinetic modeling via the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation demonstrated that coarse-grained steel exhibits a higher initial embrittlement rate due to continuous intergranular carbide networks that facilitate crack propagation. Conversely, fine-grained structures promote discontinuous precipitation, delaying early-stage embrittlement, although both microstructures reach comparable degradation after prolonged exposure. By isolating precipitation kinetics from impurity effects, this research demonstrates that PAGS critically dictates the rate of carbide-driven TE, providing predictive insights for the microstructural design and lifetime optimization of high-strength structural alloys. Full article

High-nickel NCA/Si–C 21700 cells exhibit strongly condition-dependent degradation, but the coupled influence of temperature and rate on electrochemical, thermal, and structural evolution remains insufficiently resolved. Here, Samsung INR21700-50E cells were aged under a 3 × 3 matrix of ambient temperatures (0, 23, and 40 °C) and C-rates (0.5C, 1C, and 2C). Periodic reference performance tests were used to track capacity, 10 s direct-current internal resistance, electrochemical impedance, pseudo-open-circuit voltage, differential voltage/incremental capacity behavior, heat generation, and post-mortem morphology. Guided by the hypothesis that temperature and rate history change not only the speed but also the dominant pathway of aging, the results show that both ambient temperature and the charge/discharge rate program govern the aging trajectory. Low-temperature cycling accelerates capacity loss and resistance growth through severe polarization and lithium plating, indicating dominant loss of lithium inventory. High-temperature operation promotes interfacial side reactions, impedance rise, and cathode structural degradation, leading to stronger loss of active material at later stages. An increasing C-rate amplifies these effects by raising overpotential and thermal load. Heat generation power increases markedly with aging and depends strongly on temperature–rate history. Scanning electron microscopy confirms cathode cracking, anode surface film thickening, and separator degradation under severe conditions. These experimental indicators are integrated into a mechanism-aware diagnostic framework that maps capacity retention, DCIR/EIS parameters, ICA/DVA indices, and heat generation metrics to dominant aging modes, supporting BMS state-of-health estimation, lifetime prediction, thermal management, and second-life screening of high-nickel NCA cells. The condition-averaged trajectories are further converted into a semi-empirical aging law that links capacity loss, resistance growth, and heat generation increase for BMS-oriented lifetime prediction. Full article

Titanium alloys have been extensively employed in the aerospace industry, and their service performance is largely governed by high-temperature low-cycle fatigue damage. However, investigations into the fatigue behavior of TC25 titanium alloy subjected to corrosion in a marine atmospheric environment remain limited. In this study, high-temperature low-cycle fatigue tests were conducted on TC25 titanium alloy before and after corrosion. It was found that, after corrosion, the proportion of the structural failure stage increased by approximately 10%. The corrosion pits on the surface led to local stress concentration, resulting in an increase in the number of fatigue crack sources and an acceleration of the fatigue crack growth rate, thus reducing the fatigue life of the material. These findings provide important theoretical and experimental support for the application of TC25 titanium alloy in marine environments. Full article

The use of the stress intensity factor K to characterize the severity of crack tip stress fields is widespread throughout engineering. The relationship between K and the crack growth rate is then usually represented empirically by a straight line Paris law relationship on logarithmic axes. This study develops an analytical relationship between the two by linking crack growth to the accumulation of fatigue damage ahead of the moving crack tip. A stress-based fatigue model was used, with inputs from plastic 2D plane stress FE analyses representing an edge crack by a sharp semi-circular notch. Stress–distance profiles ahead of the crack tip were extracted at the maximum and minimum points of a range of fatigue loading cycles. These were then used with data from smooth specimen LCF tests to predict the build-up of fatigue damage at regularly spaced locations ahead of the crack tip and hence crack growth rates. Full da/dN–ΔK curves were generated for the nickel-based superalloy RR1000 at 20 °C with loading R-ratios of 0, −1 and 0.5. The R = 0 and R = −1 crack growth rate predictions agreed well with experimental data, as did the steeper growth rate slope calculated at R = 0.5. The method was then extended to predict overload behaviour. Full article

The article deals with the study of stress corrosion cracking (SCC) of X70 steel using corrosion-mechanical testing that simulates the operating conditions of underground pipelines. The tests were carried out under cyclic four-point bending at stresses close to the yield point, in electrolytes with various hydrogen charging capacities. The following model environments were used: NS4 solution and citrate buffer (pH 5.5). Hydrogen charging was controlled by the addition of thiourea and by varying the potential. It was shown that microcracks initiated at corrosion defects (pits) and then emerged at the surface to form narrow cracks. The incubation period depends on the environment: under corrosive conditions it is approximately two times shorter than in the air. The size and nature of stress concentrators play a significant role: natural pits (~hundreds of μm) lead to crack formation within 24–28 days, whereas artificial holes (0.6–1 mm) lead to crack formation within 5–7 days. The effect of hydrogen was established: the acceleration is insignificant under moderate hydrogen charging, whereas the incubation period decreases sharply at high hydrogen charging. Critical hydrogen concentrations where its effect becomes significant were determined. Methods for inhibiting stress corrosion cracking by means of organosilicon films (vinyl- and aminosilanes, as well as their mixtures with inhibitors—benzotriazole and amines) were considered. The most effective composition is vinylsilane + benzotriazole: the time to crack initiation increases from 5 to 36 days, and the crack growth rate decreases. Full article

Titanium alloy welded joints are key parts of deep-sea pressure hulls, which are subjected to fatigue loadings in service. In this study, axial fatigue tests, mode I fatigue crack growth tests, and mixed-mode I–II fatigue crack growth tests were conducted on the Ti-6Al-4V ELI titanium alloy welded joint, and its fatigue failure mechanism and crack growth behavior is investigated and compared with the base material. The results show that the S–N curve of Ti-6Al-4V ELI titanium alloy welded joints has a very similar slope as the base material, but its fatigue performance is lower than the base material. However, the welded joints exhibit a higher resistance in the near-threshold region under mode I loading compared to the base material. Scanning electron microscope observation indicates that the fatigue crack mainly initiates from gas pores during welding for the Ti-6Al-4V ELI titanium alloy welded joints. Under mixed-mode I–II loading, the stress intensity factor range component $\mathsf{\Delta }{K}_{\mathrm{I}}$ of welded joints is higher than that of the base material, and an equivalent stress intensity factor range model is proposed to describe the crack growth rate under both mode I and mixed-mode I–II loadings. The new model incorporates a parameter dependent on the mode mixity ratio defined by $\mathsf{\Delta }{K}_{\mathrm{I}\mathrm{I}}/\mathsf{\Delta }{K}_{\mathrm{I}}$ in this paper, and it unifies the crack growth data well under mode I and mixed-mode I–II loadings. The paper indicates that the gas pores during welding are an important factor for the poor fatigue performance of Ti-6Al-4V ELI titanium alloy welded joints. Full article

Composite laminates experience static and fatigue delamination, presenting significant challenges for failure prediction. This is critical in curved composites, where delamination behavior is complex to predict. In this study, fatigue tests were conducted on curved composite laminates under non-constant mixed-mode conditions. The testing setup involved a four-point bending test using L-shaped, unidirectional carbon-fiber-reinforced polymer curved beam specimens. A Teflon insert placed at the bend was used to initiate delamination. Experimental data acquisition included digital image correlation (DIC) to monitor delamination length during testing. This is important since it enhances subsequent model correlation. A virtual crack closure technique (VCCT)-based method for simulating fatigue-driven delamination under variable mixed-mode conditions was validated against experiments. Delamination growth was modeled using a Paris-like power–law relationship based on the strain energy release rate. The approach was implemented in Abaqus as a user subroutine, incorporating load ratio and mode mixity effects through VCCT-based mode separation. This study demonstrates accurate fatigue delamination prediction and highlights the role of optical measurements in experiments. The model improves our understanding of delamination propagation under varying mode mixity and contributes to structural integrity analysis. The results show how mode mixity influences delamination, impacting the performance and lifecycle of composite structures. Full article