Stress Field Research Articles

Nanocomposites of Epoxy with Fe3O4 Featuring Dynamic Disulfide Bonds: Fracture Toughness, Reprocessing, and Functional Properties.

Nanocomposites of epoxy with Fe3O4 featuring dynamic disulfide bonds were fabricated. To facilitate the dispersion of Fe3O4 nanoparticles, we synthesized poly(ε-caprolactone)-grafted Fe3O4 nanoparticles, which were then incorporated into epoxy to generate robust interfacial interactions between epoxy and the inorganic nanoparticles. Through this approach, a fine dispersion of the inorganic nanoparticles in the epoxy matrix was successfully obtained. The incorporation of Fe3O4 nanoparticles with fine dispersion resulted in the epoxy being effectively toughened; the critical stress field intensity factor (KIC) was enhanced twice as the control epoxy. Thanks to the integration of the dynamic covalent bonds (i.e., disulfide bonds), the nanocomposites displayed excellent reprocessable or recyclable properties. Depending on the contents of poly(ε-caprolactone)-grafted Fe3O4 nanoparticles, the nanocomposites can be modulated to have shape recovery with the desired shape transition temperatures. Benefiting from the dynamicity of disulfide bonds, the shape memory behavior featured reconfigurability. Inheriting from the nature of Fe3O4 nanoparticles, the nanocomposites likewise displayed superparamagnetic and photothermal properties. By taking advantage of the photothermal behavior, shape memory can be triggered through infrared laser irradiation and in a noncontact manner.

Study on the evolution law of the ‘Butterfly-type’ plastic zone in the surrounding rock of deep dynamic pressure roadway

The formation and development of plastic zone in the surrounding rock is the essence of large deformation damage to the surrounding rock in deep, highly stressed roadway. The −850 m roadway of the Qujiang mine is laid flat longitudinally under the 805 working face and coal pillar, and under the influence of the mining movement of the upper working face and the pre-stressing pressure of the coal pillar, the periphery of the roadway is no longer a pure non-uniform stress field, but a non-uniform stress field with both vertical and horizontal dynamic pressure. Based on the Hoek–Brown strength criterion, the unified strength theory is modified and the nonlinear unified strength theory of rock is established by comprehensively considering the intermediate principal stress, rock properties and rock structure. The boundary line equation of the plastic zone of the surrounding rock with non-uniform stress field under mining is proposed, and the effects of lateral pressure coefficient, Hoek–Brown parameter and intermediate principal stress as well as dynamic pressure coefficient on the morphology of the plastic zone are investigated. The results show that: (1) When the lateral pressure coefficient λ ≠ 1.0, the plastic zone of the surrounding rock expands in the direction of inclination to the corners of the roadway, and the whole is similar to the “butterfly-type”, and the more the value of λ deviates from l.0, the more the shape of the plastic zone is similar to the “butterfly-type”. (2) Regarding the dynamic pressure coefficient and the change curve of the radius of the plastic zone, whether it is the shallow stress field or the deep stress field, the curve is the first smooth growth, and the dynamic pressure coefficient reaches a certain value (about Di = 2.5), and the radius of the plastic zone starts to show a sharp nonlinear growth, which is a ‘sharp lifting type’. The influence of the dynamic pressure coefficient on the radius of the plastic zone exists Dξ critical dynamic pressure coefficient. (3) The influence of intermediate principal stresses on the extent of the plastic zone and the magnitude of displacements in the pavement enclosure is inter-zonal in nature. The study on the evolution of the “butterfly-type” plastic zone is of great theoretical and practical significance for the development and utilisation of deep underground resources.

Quantitative 3-D investigation of faulting in deep mining using Mohr–Coulomb criterion and slip weakening law

Assessing the risk of fault-slip rockburst is crucial for ensuring the safety of mining operations and effectively mitigating potential disasters. In this study, we propose an integrated 3-D numerical modeling framework combining the virtual fault (VF), 3-D Mohr–Coulomb criterion model (MC), and slip weakening model (SW) to investigate the dynamics of fault failure and coseismic slip induced by mining activities near faults. Our research focuses on the fault stress ratio (k) and how it responds to variables such as fault dip angle (φ), mining distance (Dm), fault frictional parameters (μs, μd, and Dc), and panel length (Wm) within a depth-dependent stress field. Our findings demonstrate that the k serves as a critical indicator of fault reactivity, with its sensitivity to φ and Dm, significantly heightening the potential for seismic activities. We found that footwall mining, in particular, affects fault stability more than hanging wall mining, often causing greater instability. Additionally, decreases in normal stress due to mining activities are found to be crucial in triggering fault reactivation and coseismic slip. The SW model reveals that k initially decreases with increasing slip and stabilizes as slip progresses, highlighting the critical role of evolving frictional properties in fault stability. Additionally, this study confirms that mining-induced fault slips exhibit self-similar behaviors analogous to natural faulting, with a proportional relationship between slip distribution and static stress drop, validated through robust numerical analysis. This study enhances the understanding of fault mechanics in mining-induced conditions and provides a robust framework for assessing seismic risks, offering practical insights for improving safety and stability in deep mining operations.

On the stresses associated with heterointerfaces

ABSTRACT Considering the formation of misfit dislocations in systems with both high and low lattice mismatch, the Peierls–Nabarro mechanism is first introduced to deal with periodic dislocations. The effect of interfacial misfit dislocations on the interior of the crystal is then investigated using exact elasticity solutions. The core structure of the misfit dislocation is then given, and it is emphasised that the stress field inside the crystal can be determined under certain combinations of material constants so as to determine the atomic configuration of the material. An application of the theoretical results to interfacial dislocations of a BN/AlN heterojunction is shown, and the reliability of theory is verified by first-principles calculations.

Comparative Study of the Effects of Different Surface States During the Laser Sealing of 304 Steel/High-Alumina Glass

Laser welding (sealing) is a promising technology for joining metal to glass, but it shows poor joint strength in existing studies. This study conducted the laser sealing of a 304 stainless steel alloy to high-alumina glass using pre-oxidation and laser surface melting as an interlayer. The present investigation aimed to determine the influence of this surface modification strategy on the mechanical behavior of glass-to-metal sealing joints made via laser welding. An experimental campaign was conducted on 304 stainless steel and high-alumina glass. Pre-oxidation and laser surface melting treatment were performed on the 304 steel alloy surface before joining to improve the mechanical interlock and chemical bonding between the substrates. The microstructures of the 304 steel alloy/glass interface were investigated by using scanning electron microscopy (SEM) and an energy-dispersive spectrometer (EDS), and the interface evolution mechanism and the correlation between the steel/glass joining strength and the interface morphology were discussed. Finite element analysis software simulated the temperature field and stress field in the welding process, and the reasons for the differences in the welding strengths of different surface treatment samples were analyzed in depth. The results showed that the laser surface melting strategy used significantly influenced the mechanical behavior of the joints and the failure mode. Adopting a higher number of scans improved the mechanical interlock and, consequently, the mechanical behavior of the joints.

Neural network-based ground stress field inversion and fault influence study in south Sichuan shale gas reservoirs

Neural network-based ground stress field inversion and fault influence study in south Sichuan shale gas reservoirs

Refined Inversion Analysis of 3D Ground Stress Field Based on Random Field

Refined Inversion Analysis of 3D Ground Stress Field Based on Random Field

Numerical Study to Analyze the Influence of Process Parameters on Temperature and Stress Field in Powder Bed Fusion of Ti-6Al-4V.

This paper presents a comprehensive numerical investigation to simulate heat transfer and residual stress formation of Ti-6Al-4V alloy during the Laser Powder Bed Fusion process, using a finite element model (FEM). The FEM was developed with a focus on the effects of key process parameters, including laser scanning velocity, laser power, hatch space, and scanning pattern in single-layer scanning. The model was validated against experimental data, demonstrating good agreement in terms of temperature profiles and melt pool dimensions. The study elucidates the significant impact of process parameters on thermal gradients, melt pool characteristics, and residual stress distribution. An increase in laser velocity, from 600 mm/s to 1500 mm/s, resulted in a smaller melt pool area and faster cooling rate. Similarly, the magnitude of residual stress initially decreased and subsequently increased with increasing laser velocity. Higher laser power led to an increase in melt pool size, maximum temperature, and thermal residual stress. Hatch spacing also exhibited an inverse relationship with thermal gradient and residual stress, as maximum residual stress decreased by about 30% by increasing the hatch space from 25 µm to 75 µm. The laser scanning pattern also influenced the thermal gradient and residual stress distribution after the cooling stage.

Design and Applications of a Continuously Tunable Bragg Reflector for the Visible Spectrum

Bragg reflectors have become fundamental in optical technologies, providing wavelength-specific reflection in fields like telecommunications and photonic devices. Based on the visible band as well as its application, this paper describes the concept and possible implementation of a frequency-tunable Bragg reflector. Applying the method of alternating the thin film of Titanium dioxide (TiO) and silicon oxide (SiO) with a soft PDMS substrate and a liquid crystal layer, the system allows for direct tuning of the reflected wavelengths. A dual-tuning mechanism, combining an electric field and mechanical stress tuning, significantly enhances the performance of the static Bragg reflectors. The inclusion of such modifications creates an optimal design for advanced optical systems with varied applications, including tunable lasers, adaptive optics, and high-end imaging systems. This paper also addresses the challenges of tunable fabrication and the current their limitations, exploring alternative ways of integrating new materials and the future of multifunctional optical systems. Therefore, the ongoing adjustment of Bragg reflectors presents novelties in telecommunication systems, biomedical imaging, and photonic devices.

Evaluation of the Zirconium Hydride Morphology at the Flaws in the CANDU Pressure Tube Using a Novel Metric

The Zr-2.5%Nb alloy used to manufacture the pressure tubes for the CANDU 600 power plant experiences continual corrosion when the reactor’s fuel channels are functioning normally. Analysis of the hydrogen accumulation circumstances, the creation of zirconium hydride platelets, evaluation of the platelets’ reorientation in the thermo–mechanical field at volumetric flaws, and determination of the hydrogen morphology are therefore significant goals of the worldwide research being conducted in this field. In this paper, pressure tube alloy samples with artificial V flaws were hydrided by the technique of electrolytic deposition of a hydrogen film layer, followed by a specific thermal treatment. Micrographs of the Zr-2.5%Nb alloy samples in the radial cross-section were taken to examine the hydride reorientation phenomenon that occurred when the samples were heated under mechanical stress. The complex stress field around a tip flaw promoted the formation of some circles from hydride filaments. To characterize the zirconium hydride morphology in the reorientation zone at the volumetric flaw tip, image analysis and processing techniques were applied. To better characterize the reorientation zone from the point of view of embrittlement and mechanical behavior, this paper proposes a novel metric for the morphology of hydrides located in the reorientation zone. This work’s findings are beneficial for the investigation of CANDU fuel channels’ structural integrity.

Collaborative control technology and application of support and modification for soft-rock roadway in a kilometer-deep coal mine

The soft-rock roadways in kilometer-deep coal mines are often damaged by large deformation and have to be periodically expanded and repaired, which seriously restricts the safe and efficient production of coal mines. A typical soft-rock roadway in a kilometer-deep coal mine is selected as the engineering, and the main reasons for roadway deformation are analyzed, and the ground stress and mechanical characteristics are obtained. The Flac3D numerical model, which can accurately reflect the deformation characteristics of surrounding rock in kilometer-deep soft-rock roadway, has been constructed, and the evolution laws of stress field and its damage mechanism have been analyzed with the vertical stress, vertical displacement and plastic zone. The damage range of roadway surrounding rock is elucidated by endoscopic observation, and the synergistic control technology of support and modification is proposed. The on-site engineering application is carried out in Qianyingzi Coal Mine, and the results show that the collaborative control technology of support and modification ensures the safety and stability of deep soft-rock roadway. The results provide important and preliminary technical references for realizing safe and intelligent mining in coal mines.

New Insights on the Seismic Activity of Ostuni (Apulia Region, Southern Italy) Offshore

On 23 March 2018, an event of magnitude ML 3.9 occurred about 10 km from the town of Ostuni, in the Adriatic offshore. It was the most energetic earthquake in South–Central Apulia ever recorded instrumentally. On 13 February 2019, in the same area, a second ML 3.3 event was recorded. The analysis of the 2018 event shows that the ambiguity of the solution of the fault plane reported by INGV (Istituto Nazionale di Geofisica e Vulcanologia) on the Italian National Earthquake Centre website can be solved considering existing seismic profiles, exploration well logs and the Quaternary activity of faults in the epicentral area. A seismogenic source was identified in the rupture of a small portion of a 40 km length structure with strike NW-SE, dipping at a high angle toward the south. In this work, we have relocated the recent earthquakes by using the seismic stations managed by the University of Bari (UniBa), one of which is quite close to the event’s epicenter (about 20 km), together with data coming from the RSN (Rete Sismica Nazionale). Furthermore, we have determined the focal mechanism of some events, with implications on stress field of the area. Our results show right-lateral transtensional kinematics of the seismogenic faults along approximately E-W striking planes, with a tension, T, with a trend of about 60° (NE-SW direction) and a plunge of 20°. Finally, we have tried to correlate the location of the four best constrained earthquakes with their seismogenic structures.

Croatian catalogue and database of focal mechanism solutions, characteristic mechanisms, and stress field properties in the Dinarides and the surrounding regions

This report presents the CroFMS catalogue and database of focal mechanism solutions (FMS). It is based on the first-motion polarity data for earthquakes in Croatia and the neighbouring regions, collected over last four decades. The current catalogue version contains FMS for 410 earthquakes that were computed consistently, using the same programs, velocity models, and sets of parameters. Its content is described in terms of distributions of the time and origin of polarity picks, magnitudes, epicentral distances of stations, the quality marks, the phases used, azimuthal gap and distance to the closest station. It was also shown that solutions from the CroFMS catalogue and those independently obtained from the moment tensor inversions are generally consistent.Comparison of observed FMS with the latest European model of active fault sources (EFSM20) revealed several inconsistencies, most notably in the Zagreb and Petrinja epicentral areas, the greater Rijeka region, the Central Adriatic archipelago, and in the zone of surface traces of the thrust fronts of the East-Bosnian–Durmitor and Drina–Ivanjica nappes in Bosnia and Herzegovina.Spatial averaging of FMS over the whole study area produced maps of characteristic focal mechanisms, which may be found useful in the seismic hazard assessment in the areas where active faults are not identified or characterised.A formal stress inversion of the focal mechanism solutions produced a map of maximum horizontal stress orientations across the study area, revealing localized lateral variations that had not been identified in previous studies.

Reconstruction of the Temperature Conditions of Burial-Related Pressure Solution by Clumped Isotopes Validates the Analysis of Sedimentary Stylolites Roughness as a Reliable Depth Gauge

Rough surfaces known as stylolites are common geological features that are developed by pressure solution, especially in carbonate rocks, where they are used as strain markers and as stress gauges. As applications are developing in various geological settings, questions arise regarding the uncertainties associated with quantitative estimates of paleostress using stylolite roughness. This contribution reports for the first time a measurement of the temperature at which pressure solution was active by applying clumped isotopes thermometry to calcite cement found in jogs linking the tips of the stylolites. This authigenic calcite formed as a redistribution of the surrounding dissolved material by the same dissolution processes that formed the extensive stylolite network. We compare the depth derived from these temperatures to the depth calculated from the vertical stress inversion of a bedding parallel stylolite population documented on a slab of the Calcare Massiccio formation (early Jurassic) formerly collected in the Umbria-Marches Arcuate Ridge (Northern Apennines, Italy). We further validate the coevality between the jog development and the pressure solution by simulating the stress field around the stylolite tip. Calcite clumped isotopes constrain crystallization to temperatures between 35 and 40 °C from a common fluid with a δ18O signature around −1.3‰ SMOW. Additional δ18O isotopes on numerous jogs allows the range of precipitation temperature to be extended to from 25 to 53 °C, corresponding to a depth range of 650 to 1900 m. This may be directly compared to the results of stylolite roughness inversion for stress, which predict a range of vertical stress from 14 to 46 MPa, corresponding to depths from 400 to 2000 m. The overall correlation between these two independent depth estimates suggests that sedimentary stylolites can reliably be used as a depth gauge, independently of the thermal gradient. Beyond the method validation, our study also reveals some mechanisms of pressure solution and the associated p,T conditions favouring their development in carbonates.

Experimental study on the splitting tensile failure of a carbon nanotube-modified fly ash foamed concrete filler

To study the enhancement effect of carbon nanotubes (CNTs) on the splitting tensile properties of foamed concrete backfill in which cement and fly ash were used as the cementitious materials and natural sand was used as the aggregate, specimens of CNT-modified foamed concrete backfill were prepared. Brazilian splitting tests were used to investigate the splitting tensile strength of the CNT-modified foamed concrete backfill, and the digital speckle correlation method was used to analyze the stress field characteristics and crack expansion law of the specimens during splitting tensile testing. The stress–strain characteristics and energy dissipation laws of the backfill were studied at various static loading rates, and a relationship between the splitting tensile strength, ultimate strain, and loading rate was established. The results showed that at the optimum CNT content of 0.05%, the peak strength and ultimate strain of the modified foamed concrete backfill increased by an average of 67.2% and 21.7%, respectively. Moreover, after modification with CNTs, the foamed concrete backfill was less likely to develop strain concentration areas before reaching peak strength. The triangular stable loadbearing structure formed by the modified foamed concrete backfill after splitting caused the end of the stress–strain curve to exhibit varying degrees of “backlash”. For the CNT-modified foamed concrete backfill, the peak strength correlated logarithmically with the loading rate, while the ultimate strain correlated as a power function of the loading rate. At a low loading rate, the CNT-modified foamed concrete backfill dissipated less energy, and the reverse was true for higher rates.

Modeling the Stress Field in MSLA-Fabricated Photosensitive Resin Components: A Combined Experimental and Numerical Approach

This study presents an experimental and numerical investigation into the stress field in cylinders manufactured from photosensitive resin using the Masked Stereolithography (MSLA) technique. For material characterization, tensile and bending test data from resin specimens were utilized. The stress field in resin disks was experimentally analyzed using photoelasticity and Digital Image Correlation (DIC) methods, subjected to compressive loads, according to the cylinder–plane contact model. Images were captured during the experiments using polarizing film and a low-cost CPL lens, coupled to a smartphone. The experimental results were compared with numerical and analytical simulations, where the formation of fringes and regions indicating the direction and magnitude of normal and shear stresses were observed, with variations ranging from 0.6% to 8.2%. The convergence of the results demonstrates the feasibility of using parts produced with commercially available photosensitive resin on non-professional printers for studying contact theory and stress fields. In the future, this methodology is intended to be applied to studies on stress in gears.

Numerical analysis of the hydraulic fracture propagation behavior encountering gravel in conglomerate reservoirs

Hydraulic fracturing, which forms complex fracture networks, is a common technique for efficiently exploiting low-permeability conglomerate reservoirs. However, the presence of gravel makes conglomerate highly heterogeneous, endowing the deformation, failure, and internal micro-scale fracture expansion mechanisms with uniqueness. The mechanism of fracture expansion when encountering gravel in conglomerate reservoirs remains unclear, challenging the design and effective implementation of hydraulic fracturing. This paper utilizes the Abaqus platform and adopts the maximum circumferential strain fracture criterion to establish a two-dimensional fluid-solid-structure coupled fracture expansion model. The study investigates the impact of permeability, Young’s modulus, in-situ stress difference, and incidence angle on the fracture expansion behavior in the presence of gravel. The results indicate that low-permeability gravel induces pressure changes near the fracture tip, like 13% pore pressure increase and stress reductions. Shear stress on the gravel surface rises by 28.3%, and choosing layers with a smaller permeability gap between matrix and gravel can reduce complex near-well fractures. High Young’s modulus gravel has a stress shielding effect around fractures, which is direction-dependent, with over tenfold stress variations. It causes a 60.7% increase in peak shear stress on the gravel surface, exacerbating fracture complexity and reducing extension distance, and a greater strength disparity between gravel and matrix enhances this effect. A high in-situ stress difference (over 8 MPa) weakens gravel-caused stress shielding, leading to stable fracture propagation with a single morphology and increased extension distance, though not favoring complex network formation. As the incidence angle rises, the gravel’s impact on stress and seepage fields weakens, but the risk of shear failure on the cementation interface increases. The findings provide a basis for optimizing operations in such reservoirs considering the various properties of gravel and their effects on fluid flow and fracture behavior.

Strain manipulation of spin-polarized topological phase in WSe2/CrI3 heterostructure

Here, based on first-principles calculations and topological analysis, we show that the spin-polarized topological phase is present in a van der Waals (vdW) heterostructure WSe2/CrI3. We reveal that magnetism induced by proximity effects in the heterostructure breaks the time-reversal symmetry (TRS) and thus induces gapped topological edge states, exhibiting the TRS-breaking quantum spin Hall (QSH) effect. By applying a stress field, the WSe2/CrI3 heterostructure manifests enhanced spin polarization, Rashba splitting, and tunable bandgap. The TRS-breaking QSH effect observed in the WSe2/CrI3 heterostructure exhibits remarkable robustness against interlayer shearing. The distinct anisotropy associated with in-plane strain provides precise manipulation strategies for bandgap engineering. Notably, in-plane tensile strain can significantly increase the nontrivial bandgap by up to 98 meV, suggesting the magnetic WSe2/CrI3 heterostructure represents an outstanding platform for achieving the TRS-breaking QSH effect at room temperature. Our findings provide a theoretical foundation for the development of low-dissipation spintronic nanodevices.

Size effect on Raman measured stress and strain induced phonon shifts in ultra-thin silicon film

The fabrication of complex nano-scale structures, which is a crucial step in the scaling of (nano)electronic devices, often leads to residual stress in the different layers present. This stress gradient can change many of the material properties, leading to changes in device performance, especially in the active part of the transistor, the channel. Measuring, understanding, and, ultimately, controlling the stress fields is hence crucial for many design steps. The level of stress can in principle be measured by micro-Raman spectroscopy. This, however, requires a priori knowledge of the mechanical properties of the material. However, mechanical properties start to deviate from the bulk values when film dimensions become thinner than 5 nm. If this effect is ignored, errors of up to 400% can be introduced in the extracted stress profile. In this work, we illustrate this effect for a range of Si (001) slabs with different silicon film thicknesses, ranging from 5 to 0.7 nm and provide best practices for the proper interpretation of micro-Raman stress measurements.

Energy Dissipation during Crack Growth in Rubbers with Mullins Softening

The modulus and toughness of rubbers can be improved by incorporating fillers into the rubber matrix. Filled rubbers exhibit a strain‐induced softening phenomenon known as the Mullins effect. Upon deformation, filled rubbers can dissipate strain energy, which results in enhanced resistance to crack growth. An in‐depth understanding of the energy dissipation accompanying crack growth is important for the predictive modeling of rubber fracture. Herein, an experimental study on the fracture toughness of filled and unfilled rubbers with a focus on characterizing the energy dissipation caused by the Mullins effect during crack growth is presented. A particle tracking method is used to measure the nonlinear deformation fields in notched rubber specimens when subjected to monotonic tensile loading. Using the measured deformation fields and an independently calibrated constitutive model, the evolution of stress fields during crack growth is quantitatively evaluated, based on which the energy dissipation and intrinsic toughness are determined with the assumption of steady‐state crack growth. It is found that the filled rubber exhibits more energy dissipation during crack growth than the unfilled rubber. More importantly, the intrinsic toughness of the filled rubber (5000–8000 J m−2) is also much higher than that of the unfilled rubber (150–300 J m−2).