Search Results (106)

The concept of “material effort” appears in continuum mechanics wherever the response of a material to the currently existing state of loads and boundary conditions loses its previous, predictable character. However, within the material, which still descriptively remains a continuous medium, new physical structures appear and new previously unused physical features of the continuum are activated. The literature is dominated by a simplified way of thinking, which assumes that all these states can be characterized and described by one and the same measure of effort—for metals it is the Huber–Mises–Hencky equivalent stress. Quantitatively, perhaps 90% of the literature is dedicated to this equivalent stress. The remaining authors, as well as the author of this paper, assume that there is no single universal measure of effort that would “fit” all operating conditions of materials. Each state of the structure’s operation may have its own autonomous measure of effort, which expresses the degree of threat from a specific destruction mechanism. In the current energy sector, we are increasingly dealing with “low-cycle thermal fatigue states”. This is related to the fact that large, difficult-to-predict renewable energy sources have been added. Professional energy based on coal and gas units must perform many (even about 100 per year) starts and stops, and this applies not only to the hot state, but often also to the cold state. The question arises as to the allowable shortening of start and stop times that would not to lead to dangerous material effort, and whether there are necessary data and strength characteristics for heat-resistant steels that allow their effort to be determined not only in simple states, but also in complex stress states. Do these data allow for the description of the material’s yield surface? In a previous publication, the author presented the results of tension and compression tests at elevated temperatures for two heat-resistant steels: St12T and 26H2MF. The aim of the current work is to determine the properties and strength characteristics of these steels in a pure torsion test at elevated temperatures. This allows for the analysis of the strength of power turbine components operating primarily on torsion and for determining which of the two tested steels is more resistant to high temperatures. In addition, the properties determined in all three tests (tension, compression, torsion) will allow the determination of the yield surface of these steels at elevated temperatures. They are necessary for the strength analysis of turbine elements in start-up and shutdown cycles, in states changing from cold to hot and vice versa. A modified testing machine was used for pure torsion tests. It allowed for the determination of the sample’s torsion moment as a function of its torsion angle. The experiments were carried out at temperatures of 20 °C, 200 °C, 400 °C, 600 °C, and 800 °C for St12T steel and at temperatures of 20 °C, 200 °C, 400 °C, 550 °C, and 800 °C for 26H2MF steel. Characteristics were drawn up for each sample and compared on a common graph corresponding to the given steel. Based on the methods and relationships from the theory of strength, the yield stress and torsional strength were determined. The yield stress of St12T steel at 600 °C was 319.3 MPa and the torsional strength was 394.4 MPa. For 26H2MH steel at 550 °C, the yield stress was 311.4 and the torsional strength was 382.8 MPa. St12T steel was therefore more resistant to high temperatures than 26H2MF. The combined data from the tension, compression, and torsion tests allowed us to determine the asymmetry and plasticity coefficients, which allowed us to model the yield surface according to the Burzyński criterion as a function of temperature. The obtained results also allowed us to determine the parameters of the Drucker-Prager model and two of the three parameters of the Willam-Warnke and Menetrey-Willam models. The research results are a valuable contribution to the design and diagnostics of power turbine components. Full article

Micro-fracturing technology is a key approach to enhancing the flow capacity of oil sands reservoirs and improving Steam-Assisted Gravity Drainage (SAGD) performance, whereas heterogeneity in reservoir physical properties significantly impacts stimulation effectiveness. This study systematically investigates the coupling mechanisms of asphaltene content, clay content, and heavy oil viscosity on micro-fracturing stimulation effectiveness, based on the oil sands reservoir in Block Zhong-18 of the Fengcheng Oilfield. By establishing an extended Drucker–Prager constitutive model, Kozeny–Poiseuille permeability model, and hydro-mechanical coupling numerical simulation, this study quantitatively reveals the controlling effects of reservoir properties on key rock parameters (e.g., elastic modulus, Poisson’s ratio, and permeability), integrating experimental data with literature review. The results demonstrate that increasing clay content significantly reduces reservoir permeability and stimulated volume, whereas elevated asphaltene content inhibits stimulation efficiency by weakening rock strength. Additionally, the thermal sensitivity of heavy oil viscosity indirectly affects geomechanical responses, with low-viscosity fluids under high-temperature conditions being more conducive to effective stimulation. Based on the quantitative relationship between cumulative injection volume and stimulation parameters, a classification-based optimization model for oil sands reservoir operations was developed, predicting over 70% reduction in preheating duration. This study provides both theoretical foundations and practical guidelines for micro-fracturing parameter design in complex oil sands reservoirs. Full article

During the sintering process of NdFeB bulks, temperature changes and significant temperature differences between the bulk interior and the surface region will produce high residual stress. Temperature field and stress field prediction during the sintering process is one of the key techniques for analyzing residual stress. Therefore, the sintering process simulation and residual stress prediction of NdFeB bulks under different sintering temperatures were conducted based on the modified Drucker–Prager cap (DPC) model in ABAQUS (ABAQUS 2024). The calculated field cloud charts were analyzed against the microstructure of the bulks observed by scanning electron microscope (SEM). The finite element analysis (FEA) results of the sintering process and the residual stress show good agreement with SEM morphologies, which validates the accuracy and predictability of the model. The results indicate that cracks predominantly formed in edge regions. As the sintering temperature increased, longitudinal compressive stress at the edge of the cross-section transitioned into tensile stress. These results indicate that the developed simulation framework effectively identifies crack-prone areas, enabling data-driven optimization to reduce experimental trial-and-error costs in engineering applications. Full article

The Al-Ta energetic structural material (ESM) has significant potential for applications in energetic fragments. To rationally design the hot isostatic pressing (HIP) process for Al-Ta, this paper developed a novel parameter identification method for the modified Drucker–Prager Cap (DPC) model. The identified parameters were subsequently applied to simulate the densification behavior of Al/Ta mixed powders during HIP. Based on the simulation results, the HIP process parameters for fabricating the Al-Ta ESM were determined. Meanwhile, the microstructure, mechanical properties, and impact-induced reaction characteristics of the HIP-fabricated Al-Ta ESM were further analyzed. The main results are as follows. The comparison between the HIP simulations and experiments revealed good agreement, confirming the high accuracy of the identification of the modified DPC model parameters. In addition, the Al-Ta ESM fabricated via HIP at 460 °C/140 MPa/2 h exhibits a dense microstructure and enhanced mechanical properties. Furthermore, it demonstrates effective damage performance during the penetration of double-layered targets. Full article

This study proposes a mechanical model for evaluating the stability of thickened structural walls (TSWs) under complex local loading conditions. The model allows for the calculation of stress distribution and yielding status of TSWs based on the Drucker–Prager (D–P) yield criterion. Compared with two existing theoretical models, the proposed model improves calculation accuracy by approximately 5% and 53%, respectively. The analysis results indicate that the maximum principal stress of TSWs primarily occurs at the midpoint of the left boundary (0, h/2), the center of lateral loading on the bottom boundary (LP, 0), or the center of lateral loading (LP, h/2). As the lateral load position (LP) and width (LW) increase, both the maximum principal stress and the yielding area increase. Increasing the sidewall thickness (ST) and length (SL), while reducing the sidewall height (SH), significantly enhances the overall stability of TSWs. To meet residual ore recovery requirements, it is recommended to increase SL and reduce LP, LW, and SH. In the residual ore recovery project of the Jubankeng tungsten mine, the critical thicknesses of four TSWs were calculated using the proposed mechanical model, yielding values of 4.6 m, 4.2 m, 2.6 m, and 11.9 m. Based on field validation conducted in stopes V3412 and V3301, the discrepancy in maximum principal stress (MPS) between the mechanical model and numerical simulations was within 4% for both cases, further confirming the accuracy and applicability of the proposed model in engineering practice. Full article

In this article, we propose a new numerical approach, abbreviated as Cos-SDA, for analyzing flexural deformation problems of geomaterials. The Cos-SDA is achieved by implanting the strong discontinuity approach (SDA) into the computational framework of the Cosserat continuum finite element approach (Cos-FEA). Most of the Cos-FEA is based on the Mohr–Coulomb (M-C) criterion at present. However, the M-C yield surface is not smooth because of hexagonal corners, which can cause numerical difficulties in the Cos-FEA. The Drucker–Prager (D-P) criterion can be viewed as a smooth approximation to the M-C criterion. Meanwhile, the M-C criterion does not take into account the influence of the intermediate principal stress on strength, but D-P criterion is able to reflect the combined effect of the three principal stresses. Therefore, based on the MATLAB system, an improved three-dimensional (3D) Cos-FEA is proposed by using the D-P criterion. Through a numerical example of three-dimensional flexural deformation analysis of an excavation in layered rock, it is demonstrated that the improved Cos-FEA can effectively simulate flexural deformation and the entire progressive failure process. The improved Cos-FEA inherits the advantages of both the Cos-FEA and D-P criterion and neutralizes their mechanical responses, so it is more reasonable in simulating the progressive failure process occurring in an alternating rock mass. Most importantly, the D-P criterion-based Cos-FEA is observed to have a higher convergence speed and stability. Full article

Current construction puts forward new requirements for the construction of important buildings and structures every year. In this regard, new approaches to the design of buildings and structures using modern types of structural elements should take priority, which includes the vibrocentrifuged tube concrete columns. The purpose of this study is to evaluate the efficiency of manufacturing tube concrete columns using vibration (V), centrifugation (C), and vibrocentrifugation (VC) technologies and to perform a comparative analysis with the bearing capacity of solid tube concrete columns. Compositions of concrete grades B25, B30 and B40 were developed and manufactured using V, C and VC technologies. The greatest compressive strength was recorded for vibrocentrifuged concrete. Three samples of solid tube concrete columns and nine samples of hollow tube concrete columns were made from these concrete types. It was found that VC tube concrete columns have the highest bearing capacity values, which are up to 30.4% greater than those of vibrated columns, up to 15.1% greater than those of centrifuged hollow tube concrete columns, and up to 12.9% greater than those of vibrated solid tube concrete columns. It was proven that the use of vibrocentrifugation technology allows for the reduction in the weight of concrete pipe structures because of the hollow concrete core and the increase in the load-bearing capacity because of the high compression of the concrete core by the steel casing pipe. Full article

Electronic devices play an extremely important role in the aerospace field. Aluminum nitride (AlN) is a promising ceramic material for high-reliability electronic packaging structures that are subjected to impact loads during service. Quasi-static and dynamic flexural tests were conducted to determine the rate-dependent flexural strengths of AlN ceramics. The impact response of the AlN substrates was investigated using experimental tests and a smeared fixed-crack numerical model. The critical velocity of the impactor and the failure mode of the ceramic plate can be accurately predicted using the Drucker–Prager criterion with the scaled fracture-strength parameter. The radial cracks on the ceramic plate upon impact were well reproduced via the proposed novel numerical technique, showing better accuracy compared to the widely used Johnson–Holmquist II (JH-2) model. The effect of impactor nose shape and deflection angles were further investigated to better illustrate the low-velocity impact response of AlN ceramic substrates. Based on the dynamic flexural-strength testing results, this study achieves the prediction of low-speed impact response for AlN ceramic structures, thereby providing technical support for the impact reliability analysis of aerospace ceramic-packaging devices. Full article

Rock failure, which causes instability in rock engineering, is an engineering accident that generally occurs through the coalescence of the preexisting cracks in rocks. Therefore, it is very important to research the coalescence of rock cracks to prevent rock engineering accidents. Based on the mechanical theories of elastoplastic mechanics and fracture mechanics (the generalized Drucker–Prager (D-P) yield criterion and the core concept of the Kachanov method), the propagation of the plastic zones at rock crack tips affected by far-field uniform pressures is theoretically researched considering the interaction of two collinear cracks of unequal length. Moreover, for two cases of two cracks of equal length and unequal length in rocks, the basic laws of crack coalescence by the propagation of the plastic zones at rock crack tips are first studied, and the suggested threshold values of crack spacing for crack coalescence in rocks are provided. The results show that, for equal-length cracks, as the crack spacing decreases, the cracks propagate by a quadratic polynomial function, and the threshold is 0.2 of the ratio of crack spacing to crack length. Moreover, for unequal-length cracks, as the crack spacing decreases, the cracks propagate by a linear function, and the threshold is 0.3 of the ratio of crack spacing to secondary crack length. Finally, using the numerical simulation of a rock slope including equal-length and unequal-length cracks, and a laboratory test with a rock-like material specimen including unequal-length cracks, the main conclusions of the abovementioned theoretical studies have been verified. In this study, although the basic law of crack coalescence is first studied and the threshold value of crack coalescence is suggested first, the researched crack morphology and rock properties are relatively simple. Full article

In recent years, a kind of novel cellular concrete, fabricated by spherical saturated superabsorbent polymers, was developed. Its compressive behavior under high strain rate loadings has been studied by split Hopkinson pressure bar equipment in previous research, which revealed an obvious strain rate effect. It has been found by many researchers that the dynamic increase factor (DIF) of compressive strength for concrete-like materials measured by SHPB includes considerable structural effects, which cannot be considered as a genuine strain rate effect. Based on the extended Drucker–Prager model in Abaqus, this paper uses numerical SHPB tests to investigate structural effects in dynamic compression for this novel cellular concrete. It is found that the increment in compressive strength caused by lateral inertia confinement decreases from 5.9 MPa for a specimen with a porosity of 10% to 2 MPa for a specimen with a porosity of 40% at a strain rate level of 70/s, while the same decreasing trend was found at other strain rate levels of 100/s and 140/s. The lateral inertia confinement effect inside the cellular concrete specimen can be divided into the elastic development stage and plastic development stage, bounded by the moment dynamic stress equilibrium is achieved. The results obtained in this research can help to obtain a better understanding of the enhancement mechanism of the compressive strength of cellular concrete. Full article

In order to reveal the intrinsic mechanism of the mechanical properties of lime-treated sandy soil from a microscopic perspective, triaxial tests were conducted to analyze the macroscopic mechanical characteristics of sandy soil with different lime contents (0%, 5%, 8%, and 12%). The changes in the microstructure of the lime-treated sandy soil were studied through scanning electron microscopy, energy-dispersive spectroscopy, and mercury intrusion tests, combined with fractal theory for quantitative characterization. The results indicate that the stress–strain curve of lime-treated sandy soil can be divided into four stages: linear elastic, non-linear, failure, and residual strength. With the increase in lime content, the peak stress and cohesion first increase and then decrease, while the internal friction angle first decreases and then increases, suggesting the presence of an optimal threshold for lime content between 5% and 12%. The failure mode transitions from diagonal shear failure to bulging failure, significantly enhancing stability; both the fitted Mohr–Coulomb and Drucker–Prager failure criteria effectively reflect the failure patterns of the specimens in principal stress space. The results based on the three fractal dimensions demonstrate that lime-treated sandy soil exhibits clear fractal characteristics, with the highest fractal dimension value at a lime content of 8%, corresponding to the highest overall strength. In addition, the fractal dimension shows a binomial relationship with pore characteristic parameters and shear strength parameters; it can effectively characterize the complexity of the microstructure and accurately predict changes in shear strength parameters. Full article

In the process of long-barrel coring, the improper selection of operating parameters can easily cause blocked deformation, violent vibration of the core, core fracture, and impact crushing, which lead to a reduction in the stability of the core and core harvesting rates. Accurate knowledge of the influence of relevant factors on core stability is the key to improving core harvesting rates. Therefore, in this study, a numerical calculation model for tight and fractured cores in a barrel was constructed based on the Drucker–Prager criterion, using the finite element method. A numerical calculation model of a core broken into a barrel was constructed using the discrete element method. A study was conducted on the influence law of core stability under different core lengths, rotational speeds, weights on bit, and well inclination angles. The influence of each factor on core stability was analysed based on the vibration displacement and stress distribution characteristics of the core. The calculations show that increasing the weight on bit and reducing the rotation speed can effectively reduce the radial vibration displacement and local stress in tight and fractured cores, reduce the possibility of core fracture or breakage, and improve core stability. When the well inclination angle is large, it can easily cause core deformation and wall sliding, generating large contact stress and radial vibration displacement, significantly reducing the core stability. A broken core has the worst stability and is easily compacted in the core barrel, producing secondary crushing and plugging effects. Increasing the core barrel length resulted in a more unstable core. Compared with single-barrel coring, the distortion of the core column under double-barrel coring was more evident. In addition, the coring process, cuttings distribution, and drill bit hydraulic characteristics were studied based on the CFD-DPM method. The conclusions of this study are of great significance for optimising coring operation parameters to further improve core stability and coring harvest rate. Full article

Shale is a common rock in oil and gas extraction, and the study of its nonlinear mechanical behavior is crucial for the development of engineering techniques such as hydraulic fracturing. This paper establishes a new coupled elastic–plastic damage model based on the second law of thermodynamics, the strain equivalence principle, the non-associated flow rule, and the Drucker–Prager yield criterion. This model is used to describe the mechanical behavior of shale before and after peak strength and has been implemented in ABAQUS via UMAT for numerical computation. The model comprehensively considers the quasi-brittle and anisotropic characteristics of shale, as well as the strength degradation caused by damage during both the elastic and plastic phases. A damage yield function has been established as a criterion for damage occurrence, and the constitutive integration algorithm has been derived using a regression mapping algorithm. Compared with experimental data from La Biche shale in Canada, the theoretical model accurately simulated the stress–strain curves and volumetric–axial strain curves of shale under confining pressures of 5 MPa, 25 MPa, and 50 MPa. When compared with experimental data from shale in Western Hubei and Eastern Chongqing, China, the model precisely fitted the stress–strain curves of shale at pressures of 30 MPa, 50 MPa, and 70 MPa, and at bedding angles of 0°, 22.5°, 45°, and 90°. This proves that the model can effectively predict the failure behavior of shale under different confining pressures and bedding angles. Additionally, a sensitivity analysis has been performed on parameters such as the plastic hardening rate b, damage evolution rate B_ω, weighting factor r, and damage softening parameter a. This research is expected to provide theoretical support for the efficient extraction technologies of shale oil and gas. Full article

To investigate the fracture mechanism of rock–concrete (R–C) systems with an interface crack, Brazilian splitting tests were conducted, with a focus on understanding the influence of the interface crack angle on failure patterns, energy evolution, and RA/AF characteristics. The study addresses a critical issue in rock–concrete structures, particularly how crack propagation differs with varying crack angles, which has direct implications for structural integrity. The experimental results show that the failure paths in R–C disc specimens are highly dependent on the interface crack angle. For crack angles of 0°, 15°, 30°, and 45°, cracks initiate from the tips of the interface crack and propagate toward the loading ends. However, for angles of 60°, 75°, and 90°, crack initiation shifts away from the interface crack tips. The AE parameters RA (rise time/amplitude) and AF (average frequency) were used to characterize different failure patterns, while energy evolution analysis revealed that the highest percentage of energy consumption occurs at a crack angle of 45°, indicating intense microcrack activity. Moreover, a novel tensile strength prediction model, incorporating macro–micro damage interactions caused by both microcracks and macrocracks, was developed to explain the failure mechanisms in R–C specimens under radial compression. The model was validated through experimental results, demonstrating its potential for predicting failure behavior in R–C systems. This study offers insights into the fracture mechanics of R–C structures, advancing the understanding of their failure mechanisms and providing a reliable model for tensile strength prediction. Full article

A growing number of scholars are drawn to using numerical approaches powered by computer simulations as a potential solution to industrial problems. Replicating the compaction process in powder metallurgy with accuracy is one such issue. The Drucker-Prager-Cap model requires parameter calibration as the most used method for simulating powder compaction. This paper addresses this issue and presents a new technique for doing so. Utilizing Abaqus software 2020, the compaction process was simulated for the benchmark powder, which is the alloy Ag57.6-Cu22.4-Sn10-In10. The difference between simulation results and experimental data was reduced by applying the Particle Swarm Optimization technique in Python. The suggested approach may accurately forecast the Drucker-Prager-Cap model parameters, as demonstrated by comparing the optimized parameters utilizing the research’s method with their experimental values. The findings revealed how well the suggested approach in this study calibrated the DPC model, yielding three parameters—Young’s modulus, material cohesion, and hydrostatic pressure yield stress—with respective RMSEs of 1.95, 0.12, and 324.64 concerning their experimental values. Full article