Search Results (220)

The hole expansion process of high-strength steel is influenced by multiple factors, including the deformation path, UTS/YS ratio, uniform elongation, sheet anisotropy, sheet thickness, strain rate, material micro-defects and the work hardening exponent. Based on forming limit curves or instability criteria, the prediction of the hole expansion ratio (HER) often requires extensive initial boundary conditions that complicate the result. In this study, V-Nb bainitic steel was subjected to hot continuous rolling and underwent water quenching with different coiling temperatures, then subsequently followed by thermal simulation and mechanical testing to fit the work hardening exponent (n) and to obtain the necking deformation instability curve. The radial displacement at the hole edge during simulation was predicted with the ratio of ultimate tensile strength to fracture strength. Furthermore, based on the tensile fracture failure criterion, the HER was predicted with the true fracture strain derived from uniaxial tensile tests. Comparison between the simulated results and actual hole expansion tests shows that the crack resistance in the post-uniform stage, strain hardening capacity and deformation compatibility between the microstructure and matrix are critical factors. And the proposed model achieves a prediction accuracy of over 85% for the V-Nb bainitic high-strength steel. Full article

This study employs the fourth-order phase-field method (PFM) to investigate crack propagation. The PFM incurs significant computational costs due to its need for a highly dense node arrangement for accurate crack propagation. This study proposes an adaptive loading step size strategy combined with a scattered node (SCN_var) arrangement with variable spacings. The mechanical and phase-field models are solved using the strong-form meshless local radial basis function collocation method in a staggered approach. The method’s performance is evaluated based on accuracy and computational cost, using regular nodes (RGN) and scattered nodes (SCN_uni) with uniform spacing, as well as SCN_var with variable node spacing. Two benchmark tests are used to analyze the proposed method: a symmetric double-notch tension and a single-edge notch shear test. The analysis shows that the adaptive step size strategy improves numerical stability while the SCN_var significantly reduces computational cost. Using SCN_var, the CPU time is decreased by about thirty times compared to uniform nodes in the tensile case and by approximately three times in the shear case, without sacrificing accuracy. This confirms that directing computational resources to critical regions can significantly reduce CPU time, suggesting that adaptive node redistribution could further enhance computational performance. Full article

Polymethyl methacrylate (PMMA) is widely used in microfluidic device fabrication due to its chemical resistance, low cost, optical transparency, and manufacturing compatibility. However, limited research exists on wall deformations and the minimum achievable wall thickness between machined channels in PMMA via micro-milling. As microfluidic devices require tightly spaced features, identifying the minimum machinable wall thickness is essential for miniaturization and multifunctional integration, enabling rapid and reproducible biomedical testing. This study presents experimental data and finite element modeling on wall deformation characteristics—wall deviation angle, average wall thickness, and minimum machinable wall thickness—between micro-milled PMMA channels. Micro end-milling was performed with varying feed rates, wall thicknesses (50 μm, 100 μm, 150 μm), and milling strategies (direct, radial, axial depth). ANOVA was used to assess parameter influence, and finite element modeling simulated wall bending under the radial depth strategy. Results show that wall thickness, feed rate, and milling strategy significantly affect wall deviation and thickness. Experimental and simulation data revealed consistent trends: 50 μm walls showed cracking, base fractures, and geometric deviations, while 100 μm and 150 μm walls retained structural integrity. A minimum wall thickness of 150 μm is necessary to ensure reliable sealing in microfluidic devices. Full article

The rapid expansion of island and reef infrastructure has intensified the demand for sustainable concrete materials, yet the scarcity of conventional aggregates and freshwater severely constrains their supply. More critically, the fundamental bonding mechanism between steel reinforcement and coral aggregate concrete (CAC) remains poorly understood due to the highly porous, ion-rich nature of coral aggregates and the complex interfacial reactions at the steel–cement–coral interface. Moreover, the synergistic effect of polyoxymethylene (POM) fibers in modifying this interfacial behavior has not yet been systematically quantified. To fill this research gap, this study develops a C40-grade POM-fiber-reinforced CAC and investigates the composition–property relationship governing its bond performance with steel bars. A comprehensive series of pull-out tests was conducted to examine the effects of POM fiber dosage (0, 0.2%, 0.4%, 0.6%, 0.8%, and 1.0%), protective layer thickness (32, 48, and 67 mm), bar type, and anchorage length (2 d, 3 d, 5 d, and 6 d) on the interfacial bond behavior. Results reveal that a 0.6% POM fiber addition optimally enhanced the peak bond stress and restrained radial cracking, indicating a strong fiber-bridging contribution at the micro-interface. A constitutive bond–slip model incorporating the effects of fiber content and c/d ratio was established and experimentally validated. The findings elucidate the multiscale coupling mechanism among coral aggregate, POM fiber, and steel reinforcement, providing theoretical and practical guidance for the design of durable, low-carbon marine concrete structures. Full article

To investigate the seepage and deformation failure characteristics of deep unloaded rock mass under cyclic loading and unloading disturbance, a series of triaxial cyclic loading and unloading tests were conducted on granite. These tests were performed under varying seepage pressures and unloading conditions to analyze the mechanical properties, seepage behavior, and fracture failure characteristics of the material. The findings indicate the following: (1) An increase in seepage pressure and unloading magnitude results in pronounced radial expansion characteristics in the rock specimens following cyclic loading and unloading. Additionally, the axial, radial, and volumetric residual strains exhibit a nonlinear acceleration in growth as the number of cyclic loading and unloading applications increases. (2) The elastic modulus of rocks exhibits two distinct phases: an initial rapid decline followed by a steady-state decrease. Concurrently, Poisson’s ratio demonstrates an initial decrease, which is subsequently followed by a consistent increase. Furthermore, when considering the effects of unloading, the inflection point of the Poisson’s ratio curve will occur earlier. (3) The interplay between seepage pressure and unloading conditions markedly exacerbates the damage and degradation of the rock. Specifically, under conditions of 70% unloading and a seepage pressure of 4 MPa, the peak stress of the rock specimen is reduced by 21.90%, and the peak intensity permeability increases by 446.70%. (4) Under conditions of high confining pressure and elevated seepage pressure, V-shaped conjugate shear fracture surfaces are likely to develop during the cyclic loading failure of granite, accompanied by a limited number of secondary shear cracks. Concurrently, tensile failure surfaces that are parallel to the maximum principal stress are also observed under the influence of unloading. Full article

The miscible process of virgin and aged asphalt in rejuvenated asphalt was studied by molecular dynamics (MD) simulation. In this paper, we used MD software to establish a molecular model of asphalt, and the model of aged asphalt was established by adding ketone and sulfoxide functional groups to the original asphalt. Wood tar rejuvenator (WTR) was selected for rejuvenation of aged asphalt, and parameters such as density, surface free energy, cohesion energy density, and Young’s modulus were used to verify the molecular model. The density, relative concentration, interaction energy, mean square displacement of molecules, diffusion coefficient, mixing free energy, and radial distribution function were used to analyze the action mechanism of the rejuvenator in the rejuvenation process and the suitable service temperature and optimal amount of WTR. The results demonstrated that the WTR with 373 K and 15% mass ratio has the best rejuvenation effect on aged asphalt. The addition of WTR can increase the interaction energy between original and aged asphalt by 12.9%, reduce the Van der Waals potential energy of aged asphalt by 13.85%, and thus ensure the uniform distribution of internal molecules in rejuvenated asphalt. A 15 wt% WTR can reduce the intermolecular distance of asphaltenes from 9.4 Å to 5.2 Å, thereby alleviating the displacement effect during the asphalt aging process. The diffusion coefficients of WT-rejuvenated asphalt at 298 K and 373 K are 28.6% and 44.6% higher than those of extracted oil-rejuvenated asphalt, respectively; thus, WT-rejuvenated asphalt has better crack resistance. Full article

Conventional building materials predominantly rely on non-renewable resources, while the exploration of high-performance and renewable alternatives exhibits the potential for sustainability. Bamboo offers excellent renewability, mechanical properties, and eco-friendliness; however, the susceptibility to cracking impedes its application, especially for long-term structural requirements. The cracking primarily occurs when tangential tensile stresses on inner/outer surfaces exceed the transverse tensile strength of bamboo. This study addresses the issue of transverse cracks in Moso bamboo (Phyllostachys edulis) by proposing and validating a tangential stress prediction model based on the theoretical model of transverse stress in standard circular rings. A correction factor K was determined through finite element analysis to account for the non-standard circular ring shape of bamboo and the presence of the bamboo culm base. Using Moso bamboo samples aged 1 to 7 years, experiments were conducted under varying temperatures (35 °C, 45 °C, and 55 °C) and humidity levels (30%, 50%, and 60%) to measure the initiation and propagation of cracks under tangential stress. Based on experimental data, a functional relationship was established between the internal and external surface strains of bamboo and factors such as bamboo age, geometric dimensions of the bamboo ring, temperature, and humidity. This model can calculate the tangential stress of bamboo based on bamboo age, geometric dimensions of the bamboo ring, temperature, humidity, tangential/radial elastic modulus ratio, and water loss time. It provides a theoretical foundation and engineering reference for predicting and preventing cracking in Moso bamboo. Full article

Natural rock materials, containing micro-cracks and pore defects, significantly alter their mechanical behavior. This study investigated fracture interactions of red sandstone containing double close-round holes (diameter: 10 mm; bridge angle: 30°, 45°, 60°, 90°) using acoustic emission (AE) monitoring and the discrete element simulations method (DEM), which was a novel methodology for revealing dynamic failure mechanisms. The uniaxial compression tests showed that hole geometry critically controlled failure modes: specimens with 0° bridge exhibited elastic–brittle failure with intense AE energy releases and large fractures, while 45° arrangements displayed elastic–plastic behaviors with stable AE signal responses until collapse. The quantitative AE analysis revealed that the fracture-type coefficient k had a distinct temporal clustering characteristic, demonstrating the spatiotemporal synchronization of tensile and shear crack initiation and propagation. Furthermore, numerical simulations identified a critical stress redistribution phenomenon, that axial compressive force chains concentrated along the loading axis, forming continuous longitudinal compression zones, while radial tensile dispersion dominated hole peripheries. Crucially, specimens with 45° and 90° bridges induced prominently symmetric tensile fractures (85° to horizontal direction) and shear-dominated failure near junctions. These findings can advance damage prediction in discontinuous geological media and offer direct insights for optimizing excavation sequences and support design in cavern engineering. Full article

Undetected cracks in railroad wheels pose significant safety and economic risks, while current inspection methods are limited by cost, coverage, or contact requirements. This study explores the use of passive, air-coupled ultrasonic acoustic (UA) sensors for detecting wheel damage on stationary or moving wheels. Two controlled datasets of wheelsets, one with clear damage and another with early, service-induced defects, were tested using hammer impacts. An automated system identified high-energy bursts and extracted features in both time and frequency domains, such as decay rate, spectral centroid, and entropy. The results demonstrate the effectiveness of UAE (ultrasonic acoustic emission) techniques through Kernel Density Estimation (KDE) visualization, hypothesis testing with effect sizes, and Receiver Operating Characteristic (ROC) analysis. The decay rate consistently proved to be the most effective discriminator, achieving near-perfect classification of severely damaged wheels and maintaining meaningful separation for early defects. Spectral features provided additional information but were less decisive. The frequency spectrum characteristics were effective across both axial and radial sensor orientations, with ultrasonic frequencies (20–80 kHz) offering higher spectral fidelity than sonic frequencies (1–20 kHz). This work establishes a validated “ground-truth” signature essential for developing a practical wayside detection system. The findings guide a targeted engineering approach to physically isolate this known signature from ambient noise and develop advanced models for reliable in-motion detection. Full article

Angle crack defects significantly affect compressor blade radial deformation characteristics, posing critical challenges for reliability assessment under operational uncertainties. This study proposes a novel osprey optimization algorithm (OOA)-optimized Kriging and radial basis function (RBF) method (OOA-KR) for the efficient reliability evaluation of blade radial clearance with angle crack defects. The approach integrates Kriging’s uncertainty quantification capabilities with RBF neural networks’ nonlinear mapping strengths through an adaptive weighting scheme optimized by OOA. Multiple uncertainty sources including crack geometry, operational temperature, and loading conditions are systematically considered. A comprehensive finite element model incorporating crack size variations and multi-physics coupling effects generates training data for surrogate model construction. Comparative studies demonstrate superior prediction accuracy with RMSE = 0.568 and R² = 0.8842, significantly outperforming conventional methods while maintaining computational efficiency. Reliability assessment achieves 97.6% precision through Monte Carlo simulation. Sensitivity analysis reveals rotational speed as the most influential factor (S = 0.42), followed by temperature and loading parameters. The proposed OOA-KR method provides an effective tool for blade design optimization and reliability-based maintenance strategies. Full article

The ridged cutter, a highly representative non-planar PDC cutter known for its strong impact resistance and wear durability, has demonstrated significant effectiveness in enhancing the rate of penetration (ROP) in hard, highly abrasive, and interbedded soft–hard formations. Understanding the crack evolution is fundamental to revealing the rock-breaking mechanism of ridged PDC cutters. To date, studies on rock breaking with ridged cutters have largely focused on macroscopic experimental observations, lacking an in-depth understanding of the crack evolution characteristics during the rock fragmentation process. This study employs the Finite–Discrete Element Method (FDEM) to establish a three-dimensional numerical model for simulating the interaction between the ridged cutter and the rock. By analyzing crack propagation paths, stress distribution, and the stiffness degradation factor (SDEG), the initiation, propagation patterns, and sequence of cracks around the cutter are investigated. The results indicate the following outcomes: (1) The ridged cutter breaks rock mainly by tensioning and shearing, while the conventional planar cutter breaks the rock by shearing. (2) The rock-breaking process proceeds in three stages: compaction, micro-failure, and volumetric fragmentation. (3) Crack evolution around the cutter follows the rule of “tension-initiated and shear-propagation”; that is, tensile damage first generates at the front of the crack due to tensile stress concentration, whereas shear damage subsequently occurs at the rear under high shear stress. Finally, mixed tensile–shear macro-cracks are generated. (4) The spatial distribution of cracks exhibits strong regional heterogeneity. The zone ahead of the cutter contains mixed tensile–shear cracks, forming upward-concave cracks, horizontal cracks, and oblique cracks at 45°. The sub-cutter zone is dominated by tensile cracks; the zone on the flank side of the cutter consists of a radial stress field, accompanied by oblique 45° cracks. The synergistic evolution mechanism and distribution law of tensile–shear cracks revealed in this study elucidate the rock-breaking advantages of ridged cutters from a micro-crack perspective and provide a theoretical basis for optimizing non-planar cutter structures to achieve more efficient volumetric fracture. Full article

Dynamic behavior of coaxial axisymmetric planar cracks in the transversely isotropic magneto-electro-elastic (MEE) material in transient in-plane magneto-electro-mechanical loading is studied. Magneto-electrically impermeable as well as permeable cracks are assumed for crack surfaces. In the first step, considering prismatic and radial dynamic dislocations, electric and magnetic jumps are obtained through Laplace and Hankel transforms. These solutions are utilized to derive singular integral equations in the Laplace domain for the axisymmetric penny-shaped and annular cracks. Derived Cauchy singular type integral equations are solved to obtain the density of dislocation on the crack surfaces. Dislocation densities are utilized in computation of the dynamic stress intensity factors, electric displacement, and magnetic induction in the vicinity tips of crack tips. Finally, some numerical case studies of single and multiple cracks are presented. The effect of system parameters on the results is then discussed. Full article

Accurate and efficient modeling of thermomechanical failure in critical structures under extreme conditions remains a great challenge. Traditional local methods struggle with discontinuities, such as fractures, while peridynamics (PD) is computationally intensive. This study presents a rapid prediction framework that combines sequential PD thermomechanical coupling simulations with a deep learning (DL) surrogate model. The framework adopts bond-based PD to solve the deformation field, accounting for thermal expansion, whereas the temperature field is handled using the peridynamic differential operator to address boundary effects and enhance transient accuracy. The validation results show that the PD thermomechanical coupling model achieved high accuracy. For example, the cooling simulation results of a 2D plate using PD and FEM show that the results had a global error in temperature and displacement of less than 0.7%. In the Al₂O₃ ceramic quenching simulations, the crack propagation path is accurately reproduced using the PD model, which matches the experimental data well. To improve the computational efficiency, the DL surrogate model was trained on a large dataset generated by PD simulations. The inputs include the crack geometries and loads, and the outputs are the predicted crack openings, average radial displacement/strain, and circumference change rates. The optimized deep neural network (DNN) consisted of two hidden layers, each with nine neurons. The DNN model predicted complex multi-output responses in approximately 0.5 s, about 1200 times faster than direct PD simulation, maintaining high accuracy. The PD-DL framework offers a new direction for assessing the thermomechanical damage and structural integrity in engineering applications. Full article

This in vitro study aimed to evaluate the fatigue behavior of occlusal veneers (OVs) made of lithium disilicate and composition-gradient multilayered zirconia at different thicknesses, incorporating both experimental and theoretical analyses to predict long-term performance. Seventy-two OVs with ceramic layer thicknesses of 0.5 mm, 1.0 mm, and 1.5 mm were fabricated and adhesively bonded to dentin analog composite abutments. All specimens underwent thermomechanical fatigue testing, involving cyclic loading (49 N, 1.6 Hz, 1.2 million cycles) and thermocycling (5–55 °C), simulating five years of clinical function. Fracture patterns were analyzed using light microscopy and scanning electron microscopy. A fatigue lifetime model based on plate-on-foundation theory and slow crack growth was applied to estimate cycles to radial failure. No complete fractures or debonding occurred. However, 50% of 0.5 mm zirconia OVs developed flexural radial cracks from the intaglio surface, while all lithium disilicate and zirconia veneers ≥1.0 mm remained intact. Theoretical predictions closely matched the experimental outcomes, indicating that 0.5 mm zirconia performance aligned with the lower-bound fatigue estimates for 5Y-PSZ. Results suggest that lithium disilicate offers superior fatigue resistance at minimal thickness, while thin zirconia is prone to subsurface cracking. A minimum thickness of 0.7 mm is recommended for zirconia-based OVs. Full article

Chromizing layers are widely employed in industrial applications due to their superior wear resistance and corrosion resistance. In this study, GCr15 bearing steel was chromized by a solid powder pack chromizing method, and the influence of chromizing time on the microstructure and mechanical properties of the chromized layers was systematically investigated. The results reveal the presence of fine pores dispersed both on the surface and at the chromized layers/substrate interface. The concentration of the Cr and Fe elements displays a gradient distribution throughout the layers. The chromized layers are primarily composed of (Cr,Fe)₂₃C₆ and (Cr,Fe)₇C₃ phases. With an increase in the chromizing time, the thickness and hardness of the chromized layers are gradually increased. A large number of radial and circumferential cracks are observed both within and around the indentation regions, accompanied by spalling at the edge. The brittleness of the chromized layer is increased, and the spalling phenomenon becomes more pronounced with prolonged chromizing time. The chromizing treatment significantly improves the tribological performance of GCr15 steel, reducing its wear rate to approximately one fifth of that of the untreated substrate. Full article