Search Results (561)

Hot-fluid injection in thermal-enhanced oil recovery (thermal-EOR, TEOR) imposes temperature-driven volumetric strains that can substantially alter in situ stresses, fracture geometry, and wellbore/reservoir integrity, yet existing TEOR modeling has not fully captured coupled thermo-poroelastic (thermo-hydro-mechanical) effects on fracture aperture, fracture-tip behavior, and stress rotation within a displacement discontinuity method (DDM) framework. This study aims to examine the influence of sustained hot-fluid injection on stress redistribution, hydraulic-fracture deformation, and fracture stability in thermal-EOR by accounting for coupled thermal, hydraulic, and mechanical interactions. This study develops a fully coupled thermo-poroelastic DDM formulation in which fracture-surface normal and shear displacement discontinuities, together with fluid and heat influx, act as boundary sources to compute time-dependent stresses, pore pressure, and temperature, while internal fracture fluid flow (Poiseuille-based volume balance), heat transport (conduction–advection with rock exchange), and mixed-mode propagation criteria are included. A representative scenario considers an initially isothermal hydraulic fracture grown to 32 m, followed by 12 months of hot-fluid injection, with temperature contrasts of ΔT = 0–100 °C and reduced pumping rate. Results show that the hydraulic-fracture aperture increases under isothermal and modest heating (ΔT = 25 °C) and remains nearly stable near ΔT = 50 °C, but progressively narrows for ΔT = 75–100 °C despite continued injection, indicating potential injectivity decline driven by thermally induced compressive stresses. Hot injection also tightens fracture tips, restricting unintended propagation, and produces pronounced near-fracture stress amplification and re-orientation: minimum principal stress increases by 6 MPa for ΔT = 50 °C and 10 MPa for ΔT = 100 °C, with principal-stress rotation reaching 70–90° in regions adjacent to the fracture plane and with markedly elevated shear stresses that may promote natural-fracture activation. These findings show that temperature effects can directly influence injectivity, fracture containment, and the risk of unintended fracture or natural-fracture activation, underscoring the importance of temperature-aware geomechanical planning and injection-strategy design in field operations. Incorporating these effects into project design can help operators anticipate injectivity decline, improve fracture containment, and reduce geomechanical uncertainty during long-term hot-fluid injection. Full article

Background: Elastography is a non-invasive technique used to assess tissue stiffness. There are two main types of elastography: shear-wave elastography and strain imaging. Both are useful for evaluating the degree of liver fibrosis (LF). Shear-wave imaging is influenced by fibrosis and hepatic congestion, whereas strain imaging primarily reflects fibrosis progression and is less affected by congestion. We previously reported the clinical usefulness of combinational elastography in patients with heart failure (HF). However, its prognostic significance in this population remains unclear. Accordingly, in this prospective study, we aimed to evaluate the prognostic impact of combinational elastography in patients with HF. Methods: We included 77 patients with HF (median age: 79 years). Shear-wave imaging was used to obtain shear-wave velocity (Vs), whereas the liver fibrosis index (LF index) was derived from strain imaging. The Vs/LF index (V/L) was used as a prognostic indicator based on combinational elastography. Cardiac events were defined as cardiac death or hospitalization due to HF. Results: During a median follow-up of 716 days, 17 cardiac deaths or hospitalizations for HF were observed. The V/L demonstrated a cut-off value of 1.2 for predicting cardiac death or hospitalization for HF, with an area under the curve of 0.80, sensitivity of 0.82, and specificity of 0.68. Kaplan–Meier analysis demonstrated that patients with a high V/L (≥1.2) had significantly higher rates of hospitalization for HF than those with a low V/L (<1.2; log-rank test, p < 0.001). Conclusions: Combinational elastography demonstrated prognostic utility in patients with HF and may serve as a novel, non-invasive tool for assessing hepatic congestion. Full article

This study first heat-treats the surface of plain-woven carbon fibers to remove the surface sizing. The treated carbon fibers were then hot-pressed with polypropylene films to produce a carbon fiber/polypropylene prepreg. The resulting prepreg was subjected to uniaxial and off-axis tensile tests, providing fundamental data for constructing a constitute model for the carbon fiber/polypropylene prepreg. The relative error between the model predictions and experimental data is maintained within ±10%. Based on the experimental results, a temperature-dependent viscoelastic–hyperelastic constitutive model for carbon fiber/polypropylene is proposed. This model decomposes the unit volume strain energy function into four components: matrix isochoric deformation energy, fiber tensile strain energy, fiber–fiber shear strain energy, and fiber-matrix shear strain energy. The matrix energy is strain rate-dependent, exhibiting viscoelastic mechanical behavior. The material parameters of the constitutive model were identified by fitting the experimental data. The model was implemented in MATLABR2024a, and off-axis tensile tests were performed at temperatures ranging from 423 K to 453 K. Numerical simulations were compared with experimental results to validate the model. This work provides guidance for the development and validation of constitutive models for thermoplastic polypropylene prepregs. Full article

This study investigates the development of adiabatic shear bands (ASBs) in AISI 1045 carbon steel under high-strain-rate uniaxial compression, emphasizing the conditions governing their onset and growth. Split Hopkinson pressure bar (SHPB) experiments were carried out at strain rates of 1000, 2000 and 4000 s⁻¹ with controlled displacement/strain interruption to capture gradual ASB formation throughout the process. Stress–strain data were analyzed alongside optical microscopy to determine the critical strain for ASB initiation, document ASB morphology, dimensions and type, and connect ASB formulating stages to material macroscopic mechanical behavior. The observations clarify how deformation evolves from homogenous plastic flow to localized shear instability as the strain and strain rate increase, linking mechanical response to microstructural features. Integrating these results, the effects of strain rate and strain progress on ASB formation and evolution characteristics are investigated. These findings enhance our understanding of shear localization phenomena under dynamic loading and provide a basis for predicting failure modes in structural applications. Full article

The present work studies the developing network of adiabatic shear bands (ASBs) during dynamic plane strain compression of orthogonal AISI 1045 steel billets, aiming to investigate the ASB trajectories and their evolution mechanism. This paper conducts a finite element (FE) numerical analysis in LS-DYNA software, developing a doubly coupled analysis by combining both structural–thermal and structural–damage couplings. The Modified Johnson–Cook (MJC) formulas are considered for modeling both the material plasticity and damage law, implementing thermo-viscoplastic numerical approaches, while a critical temperature for material failure is further adjusted. Finally, the case study relates to a parametric analysis of specimen aspect ratio, aiming to reveal its effect on the developing ASB network and its propagating characteristics. Full article

The growing demand for miniature mechanical components has increased the importance of ultra-precision micro machine tools and real-time monitoring. This study examines acoustic emission (AE) sensing for the intelligent control of an ultra-precision micro lathe. AE signals were measured while brass and aluminum alloys were turned with cermet and diamond tools at different spindle speeds and cutting depths. Finite element simulations were performed to clarify the AE generation mechanisms. The AE waveform amplitude changed stepwise corresponding to tool–workpiece contact, elastoplastic deformation, and chip formation, enabling precise contact detection at the 0.1 μm level. The AE amplitude increased with increasing spindle speed and increasing depth of cut except during abnormal conditions (e.g., workpiece adhesion). Frequency analysis revealed a dominant peak near 0.2 MHz during normal cutting, as well as high-frequency (>1 MHz) components linked to built-up edge formation. Simulations confirmed that these AE features reflect variations in the strain rate in the shear zone and on the rake face. They also confirmed that cutting force spectra under high friction reproduce the experimentally observed high-frequency peaks. These findings demonstrate the feasibility of using AE sensing to identify the cutting state and support the development of self-optimizing micro machine tools. Full article

In deep coal mining, fault slip-type rockbursts occur frequently. Understanding the shear mechanical properties of bedded coal seams and their intrinsic mechanisms is crucial. This study used PFC^2D7.0 numerical simulation to systematically investigate the shear mechanical behavior and micro-mechanisms of bedded coal under different normal stresses (1, 2, 3, 4 MPa). The research results show that: (1) The shear stress-displacement curves of bedded coal show three stages: elastic rise, strain softening, and residual stability. Both peak and residual shear strengths increase with the rise in normal stress. The peak strength shows nonlinear growth, while the residual strength exhibits a good linear relationship. Higher normal stress significantly reduces the strength reduction rate and effectively inhibits the brittleness of coal. (2) The failure mode consistently manifests as shear failure along the preset weak bedding plane, forming a distinct shear zone. Crack evolution analysis shows that shear cracks within the bedding are the primary form of damage, with minimal contribution from tensile cracks. (3) Force chain analysis shows that an increase in normal stress significantly enhances the density and connectivity of compressive force chains within the shear zone. It also effectively inhibits tensile force chains, with the bedding plane consistently serving as the primary area for stress concentration and transfer. This study provides important theoretical references for understanding the shear instability mechanism of bedded coal, predicting its mechanical response, and preventing fault slip-type rockbursts in deep coal mines. Full article

To address the technical challenge of balancing formability and strength in automotive aluminum alloys, this study examined an Al-4.35Mg-3.6Zn-0.2Cu alloy subjected to a combined heat-treatment schedule consisting of a two-step solution treatment (470 °C for 24 h followed by 460 °C for 30 min) and a subsequent two-step aging process (T4P: 80 °C for 12 h, followed by BH: 180 °C for 30 min). Microstructural evolution was characterized using transmission electron microscopy, and uniaxial tensile tests were performed in accordance with the GB/T 228.1-2021 standard at a strain rate of 0.2 mm/min. In the T4P condition, the matrix contained both GPI zones (~0.9 nm) and GPII zones (~1.2 nm), with no detectable T-phase precipitation. The presence of GPII zones enhanced ductility by promoting dynamic recovery after dislocation shearing, resulting in a yield strength (YS) of 178 MPa, an ultimate tensile strength (UTS) of 310 MPa, and an elongation (El) of 9%. After BH treatment, the GPII zones transformed into semi-coherent T′-Mg₃₂(AlZnCu)₄₉ precipitates (~2.4 nm), which strengthened the alloy through their semi-coherent interfaces. The retained GPII zones mitigated the loss of ductility, and the final mechanical properties reached a YS of 275 MPa, a UTS of 340 MPa, and an El of 8.5%, corresponding to a BH response of 97 MPa. Strengthening-mechanism calculations indicated that GP zones contributed approximately 120 MPa to the yield strength in the T4P state, whereas T′ precipitates contributed about 169.64 MPa after BH treatment. The calculated values agreed well with the experimental results, with a deviation of less than 3%. This study clarifies the precipitation sequence in the alloy—supersaturated solid solution → GPI zones → GPII zones → T′ phase—and establishes the relationship between microstructure and strength–ductility behavior. The findings provide theoretical guidance for the design and optimization of high-strength, high-formability aluminum alloys for automotive outer-panel applications. Full article

This study investigates the influence of dynamic perturbation on gelation behavior in a model colloidal system composed of hydrophobic silica particles dispersed in dioctyl phthalate. Contrary to the prevailing assumption that gelation is independent of oscillatory frequency, particularly at small strain amplitudes within the linear viscoelastic regime, our results reveal a pronounced dependence of gelation dynamics on the frequency of applied shear. In contrast, variations in strain amplitude and shear rate amplitude exert minimal effects. This observed behavior deviates significantly from classical gelation theory, which typically predicts frequency-independent rheological properties at the gel point. The results uncover a previously unrecognized viscoelastic phenomenon in soft colloidal materials, wherein microstructural rearrangements near the gelation threshold appear to be modulated by the timescale of mechanical excitation. As a result, traditional criteria for identifying gelation become less effective. The liquid-to-solid transition in these colloidal systems aligns more closely with the physics of particle jamming, rather than polymer network formation. Full article

This work examines how rolling speed, feeding rate, and pass schedule—with a constant total reduction—affect the stress–strain fields, rolling force, and texture evolution of Al–Cu–Sc alloy sheets. A coupled finite element (FEM) and viscoplastic self-consistent (VPSC) framework is employed and compared with EBSD measurements to connect macroscopic fields with microscale texture changes. Results indicate that increasing rolling speed raises the effective strain rate and deformation heating, which lowers peak rolling force and improves in-plane stress homogenization on the RD–ND plane, while enhancing surface–core incompatibility and residual-stress gradients along the ND–TD direction. A higher feeding rate mainly intensifies work hardening, slightly elevates rolling force, and promotes near-surface stress/strain localization; in contrast, multi-pass schedules redistribute deformation between passes and reduce macroscopic stress concentration. Texture analyses show a speed-induced rotation from $⟨001⟩$ toward $⟨111⟩$ orientations, strengthening shear-related components; KAM maps suggest increased local orientation gradients consistent with higher stored energy. The simulations capture the principal experimental trends across conditions, supporting the use of the combined framework for trend-level process guidance. Overall, the findings clarify parameter–microstructure relationships and provide a basis for designing rolling routes that balance force reduction, stress uniformity, and texture control in Al–Cu–Sc sheets. Full article

Carbon-Fiber-Reinforced Plastic (CFRP) is a typical lightweight material used in the aerospace industry. However, the automotive industry has focused on the application of composite materials in vehicle components for weight reduction. In particular, hybrid parts consisting of CFRP reinforcement and a steel outer have been investigated in many studies as a solution to satisfy weight reduction and high strength. In this paper, a steel/CFRP hybrid part was evaluated by impact analysis using several material models, such as the Johnson–Cook model, progressive damage analysis (PDA), and cohesive zone model (CZM). First, the mechanical properties of the steel were determined under different strain rates to assess collision effects. Subsequently, the material properties of the CFRP were evaluated to predict the failure of composite material in the tensile and compressive directions. In addition, the cohesive properties of adhesive film were evaluated under normal and shear modes. Finally, impact analysis using the obtained material properties was conducted to predict the behavior and strength of the steel/CFRP hybrid part under collisions, and the results were compared with the experimental results for verification. Full article

The processing of bulk amorphous alloys is typically realized through superplastic deformation in the supercooled liquid region, and current research efforts predominantly focus on enhancing formability by optimizing processing parameters such as temperature and duration. However, excessive temperatures or prolonged exposure times can induce crystallization, which severely compromises the mechanical and functional properties of the alloy. This study presents the design of an ultrasonic vibration (UV)-assisted metal hot-forming apparatus that integrates an ultrasonic vibration field into the superplastic flow deformation of amorphous alloys. High-temperature compression experiments were conducted on Zr₅₅Cu₃₀Al₁₀Ni₅ amorphous alloy, and finite element simulations were performed to model the experimental process. Results show that ultrasonic vibration reduces the flow stress of the amorphous alloy, thereby enhancing its superplastic deformation capability. Simulation analysis reveals that surface effects arise from periodic interface separation between the pressure plate and the specimen caused by ultrasonic vibration, leading to a cyclic disappearance of friction forces, which manifest macroscopically as a reduction in effective friction. On the other hand, vibration introduces additional strain rates. Since the undercooled liquid of amorphous alloys exhibits non-Newtonian fluid behavior characterized by shear-thinning, ultrasonic vibration assistance can effectively reduce the apparent viscosity, thereby improving their filling capacity. Full article

The study of mechanical response and crack propagation behavior of layered composite rock mass is helpful for the efficient extraction of geological energy and the safety and stability of underground space structures. The shale is a heterogeneous rock, which is often mixed with mudstone and sandstone. Studying the propagation law of cracks in layered composite rock mass can better serve underground engineering. In this paper, three different strength rock materials (coarse sandstone, red sandstone, and gray sandstone) were spliced together to make three-point bending specimens with prefabricated cracks in the middle, and three-point bending experiments under different loading rates were carried out. The digital image correlation method was used to visualize the strain distribution in the three-point bending experiment, and the difference in crack propagation in different layered composite rock masses was studied. The numerical simulation is established by the cohesive element, and the correctness of the simulation is verified by the displacement-load data. Then the crack propagation speed under different conditions is studied. The results show that there are differences and similarities in the crack propagation process in different strength gradient composite rock masses. When the crack propagates from strong to weak, the crack tip receives more complex tensile shear force, which facilitates the crack crossing the interface. As the loading speed increases, the earlier the prefabricated crack initiates, the shorter the time it stays at the joint surface. When the crack propagates from strong to weak, the crack propagation is more penetrating. Full article

This study quantitatively investigates the influence of inter-particle rotation moment transition and mesoscopic friction on the macroscopic mechanical behavior of frozen sand by integrating plane strain tests with discrete element simulations. Two distinct contact models were employed under different temperatures and loading rates. The numerical results demonstrate that the parallel bond model, which accounts for particle rotation, accurately reproduces the full-range stress–strain response, including the strain-softening stage, whereas the contact bond model underestimates post-peak strength due to its inability to transmit moments. It is revealed that taking the influence of rotation moment transition into consideration promotes the uniformity of the local deformation distribution, thereby enhancing the material’s ductility, while mesoscopic friction parameters directly govern the shear band inclination angle at failure. Discrepancies in shear band morphology between experiments and simulations—single versus X-shaped bands—are explained by the inclination of loading plates in physical tests. This study establishes quantitative links between mesoscopic interaction mechanisms and macroscopic responses, offering valuable insights for developing advanced constitutive models for frozen soil in engineering applications. Full article

Elastomeric materials exhibit complex time-dependent behaviour under mechanical loading, necessitating accurate constitutive models for industrial applications. This study investigates the hyperelastic and viscoelastic responses of two carbon black-filled natural rubber compounds (50 ShA and 60 ShA) through cyclic shear/compression tests and stress relaxation experiments. The Arruda–Boyce model captures equilibrium behaviour, while the Bergström–Boyce model predicts transient viscoelasticity without relying on Prony series. Considering the results obtained it can be concluded that quantitative hysteresis analysis shows 7–26% energy dissipation, dependent on hardness and strain rate. Relaxation rates (10⁻⁶–10⁻⁷ s⁻¹) inversely correlated with hysteresis, validated by FEM simulations. A deviation of <3.5% between experiments and simulations confirms the model’s robustness for long-term viscoelastic predictions. This framework enables the efficient design of rubber components (e.g., seismic isolators, seals) requiring prolonged durability under load. Full article