Stress Loading Research Articles

The Load Cycle Amplitude Model: An Efficient Time-Domain Extrapolation Technique for Non-Stationary Loads in Agricultural Machinery

In traditional time-domain extrapolation methods, the peak over threshold (POT) model is unable to accurately identify large load cycles in the load time history, resulting in distorted extrapolation results, particularly when addressing non-stationary loads. To address this problem, this paper proposes a time-domain extrapolation method based on the load cycle amplitude (LCA) model. The core of the method involves using load cycle amplitude features extracted from the measured loads as the basis for modelling, rather than extreme turning points based on threshold extraction. This approach prevents the load’s time-domain characteristics from compromising the accuracy of the extrapolation results. The case analysis results demonstrate that the extrapolation method based on the LCA model achieves more reliable results with both non-stationary and stationary loads. Furthermore, the streamlined modelling process results in reductions of 10.63% and 20.84% in the average computing time for the algorithm when addressing stress and vibration loads, respectively. The LCA model proposed in this paper further facilitates the integration of time-domain extrapolation methods into reliability analysis software.

Experimental study on fatigue performance of TC4 titanium alloy liner carbon fiber composite cylinders in seawater environment

Abstract The corrosive nature of seawater poses significant challenges to the design of gas cylinders in marine environments. Currently, TC4 titanium-alloy cylinders are predominantly used because of their resistance; however, they are costly and challenging to manufacture. To address this issue, this study proposes employing TC4 titanium alloy liner carbon fiber composite cylinders, which can reduce the manufacturing cost and processing difficulty while ensuring excellent protection against seawater corrosion and fatigue resistance. The fatigue life of the cylinders was predicted and analyzed using the finite element method, and a prototype was manufactured for verification. The results show that the composite layer can effectively share the stress load for the liner under the working pressure cycle, which increases the fatigue life of the titanium alloy liner carbon fiber composite cylinders and provides strong support for their application in marine engineering.

New Evidence of Holocene Faulting Activity and Strike-Slip Rate of the Eastern Segment of the Sunan–Qilian Fault from UAV-Based Photogrammetry and Radiocarbon Dating, NE Tibetan Plateau

The eastern segment of the Sunan-Qilian Fault (ES-SQF) is located within the seismic gap between the 1927 M8.0 Gulang earthquake and the 1932 M7.6 Changma earthquake in China. It also aligns with the extension direction of the largest surface rupture zone associated with the 2022 Mw6.7 Menyuan earthquake. Understanding the activity parameters of this fault is essential for interpreting strain distribution patterns in the central–western segment of the Qilian–Haiyuan fault zone, located along the northeastern margin of the Tibetan Plateau, and for evaluating the seismic hazards in the region. High-resolution Google Earth satellite imagery and UAV (Unmanned Aerial Vehicle)-based photogrammetry provide favorable conditions for detailed mapping and the study of typical landforms along the ES-SQF. Combined with field geological surveys, the ES-SQF is identified as a continuous, singular-fault structure extending approximately 68 km in length. The fault trends in the WNW direction and along its trace, distinctive features, such as ridges, gullies, and terraces, show clear evidence of synchronous left lateral displacement. This study investigates the Qingsha River and the Dongzhong River. High-resolution digital elevation models (DEMs) derived from UAV imagery were used to conduct a detailed mapping of faulted landforms. An analysis of stripping trench profiles and radiocarbon dating of collected samples indicates that the most recent surface-rupturing seismic event in the area occurred between 3500 and 2328 y BP, pointing to the existence of an active fault from the Holocene epoch. Using the LaDiCaoz program to restore and measure displaced terraces at the study site, combined with geomorphological sample collection and testing, we estimated the fault’s slip rate since the Holocene to be approximately 2.0 ± 0.3 mm/y. Therefore, the ES-SQF plays a critical role in strain distribution across the central–western segment of the Qilian–Haiyuan fault zone. Together with the Tuolaishan fault, it accommodates and dissipates the left lateral shear deformation in this region. Based on the slip rate and the elapsed time since the last event, it is estimated that a seismic moment equivalent to Mw 7.5 has been accumulated on the ES-SQF. Additionally, with the significant Coulomb stress loading on the ES-SQF caused by the 2016 Mw 5.9 and 2022 Mw 6.7 Menyuan earthquakes, there is a potential for large earthquakes to occur in the future. Our results also indicate that high-resolution remote sensing imagery can facilitate detailed studies of active tectonics.

Impact of Moisture Absorption on Optical Fiber Sensors: New Bragg Law Formulation for Monitoring Composite Structures

In recent decades, the aviation industry has increasingly adopted composite materials for various aircraft components, due to their high strength-to-weight ratio and durability. To ensure the safety and reliability of these structures, Health and Usage Monitoring Systems (HUMSs) based on fiber optics (FO), particularly Fiber Bragg Grating (FBG) sensors, have been developed. However, both composite materials and optical fibers are susceptible to environmental factors such as moisture, in addition to the well-known effects of mechanical stress and thermal loads. Moisture absorption can lead to the degradation of mechanical properties, posing a risk to the structural integrity of aircraft components. This research aims to quantify and monitor the impact of moisture on composite materials. A new formulation of the Bragg equation is introduced, incorporating mechanical strain, thermal expansion, and hygroscopic swelling to accurately measure Bragg wavelength variations. Experimental validation was performed using both uncoated and polyimide-coated optical fibers subjected to controlled hygrothermal conditions in a climate chamber. The results demonstrate that uncoated fibers are insensitive to humidity, whereas coated fibers exhibit measurable wavelength shifts due to moisture absorption. The proposed model effectively predicts these shifts, with errors consistently below 2.6%. This approach is crucial for improving the performance and reliability of HUMSs in monitoring composite structures, ensuring long-term safety in extreme environmental conditions.

A Modified Bearing Capacity Model for Inclined Shallow Anchor Cable with Experimental Verification

Most theoretical models of shallow anchor cables do not take the effect of anchor inclination into consideration, which is an important factor influencing load distribution, stress concentration, and failure mechanisms. In this paper, a modified bearing capacity was developed for a single anchor cable, taking the anchor inclination into consideration, based on the principle of limit equilibrium. Then, a series of indoor pull-out tests of single anchors with different inclinations were performed, where the effects of the anchor inclination on the bearing capacity and failure mechanisms were carefully analyzed. The experimental bearing capacities were compared to the predicted data of the proposed modified model, as well as other existing experimental results, aiming to verify the applicability and accuracy. The results show that the bearing capacity increases with decreasing anchor inclination because the vertical component of the force acting on the anchor cable increases. The failure models of the anchor cables, pulled out at different angles, exhibit an asymmetric “inverted trumpet” shape, which is caused by the varying stress distributions around the anchor cable during pull-out. In addition, the bearing capacities of the theory differ very little from the experimental and previous results, with a max error of nearly 10%. This study confirms that the proposed model reliably captures the effects of anchor inclination, providing valuable insights for designing inclined anchors in engineering practice.

Challenges of modern work environments and means of overcoming them in the context of psychosocial risk assessments

BackgroundModern work environments constitute an underrepresented part of psychosocial risk assessments at work. Little is known about whether there is an increased stress load at all and what possible improvements could be made in such a case.MethodsModern work environments were assessed in an online questionnaire in 33 companies across a period of more than 4 years. A total of 3431 employees participated in the study. Both quantitative and qualitative data was applied to obtain a differentiated picture.ResultsIncreased stress caused by modern work environments was an issue for around a third of the sample. 31.6% of the participants at least sometimes struggled to balance work and private life. Quite a few of the participants (36.3%) worked sometimes or more outside regular working hours. For 32.4% of participants, the workload has increased due to new technologies, but for 30.4% it has not. The majority (81.4%) feel they can work productively in home offices. The data from 178 completed free text fields on improving modern work environments from the employees’ perspective was analysed. Many named suggestions relate to improvements in time management.ConclusionThis study provides both detailed insights into various aspects of modern work environments and offers solutions to counteract possible negative consequences. Assessing modern work environments in psychosocial risk assessments would be a valuable addition to its completeness.

Response of Metabolic Gene Panel to Organic Loading Stress in Propionate-Degrading Methanogenic Anaerobic Digesters

Propionate, a critical intermediate in anaerobic digestion, and its syntrophic removal, is sensitive to stress. To our knowledge, this study investigates for the first time the response of a metabolic gene panel to organic loading rate (OLR) stress in propionate-degrading methanogenic consortia in lab-scale upflow anaerobic sludge blanket (UASB) reactors. The experimental phases included stabilisation (1.4–2.8 g COD/L/day), electroactive enrichment, OLR shock (6 g COD/L/day), and early recovery. Quantitative PCR was used to assess the abundance of key functional genes (16SrRNA, mcrA, pilA, and hgtR). During stabilisation, ~200 mLCH₄/h was produced, the mcrA/16SrRNA ratio was 0.78–2.64, and pilA and hgtR abundances were 1.29–2.27 × 105 and 2.12–4.37 × 104 copies/gVS. Following the OLR shock, methane production ceased entirely, accompanied by a sharp decline in the mcrA/16S ratio (0.08–0.24) and significant reductions in pilA (1.43-log) and hgtR (1.34-log) abundance. Partial recovery of pilA and hgtR abundance (1.19 × 105 and 8.57 × 104) was observed in the control reactor after the early recovery phase. The results highlight the utility of mcrA, 16SrRNA, pilA, and associated ratios, as reliable indicators of OLR stress in lab-scale UASB reactors. This study advances the understanding of molecular stress responses in propionate-degrading methanogenic consortia, focusing on direct interspecies electron transfer in process stability and recovery.

Multi-compartment impact of micropollutants and particularly antibiotics on bacterial communities using environmental DNA at river basin-level.

Bacterial communities respond to environmental conditions with diverse structural and functional changes depending on their compartment (water, biofilm or sediment), type of environmental stress, and type of pollution to which they are exposed. In this study, we combined amplicon sequencing of bacterial 16S rRNA genes from water, biofilm, and sediment samples collected in the anthropogenically impacted River Aconcagua basin (Central Chile, South America), in order to evaluate whether micropollutants alter bacterial community structure and functioning based on the type and degree of chemical pollution. Furthermore, we evaluated the potential of bacterial communities from differently polluted sites to degrade contaminants. Our results show a lower diversity at sites impacted by agriculture and urban areas, featuring high loads of micropollution with pesticides, pharmaceuticals and personal care products as well as industrial chemicals. Nutrients, antibiotic stress, and micropollutant loads explain most of the variability in the sediment and biofilm bacterial community, showing a significant increase of bacterial groups known for their capabilities to degrade various organic pollutants, such as Nitrospira and also selecting for taxa known for antibiotic resistance such as Exiguobacterium and Planomicrobium. Moreover, potential ecological functions linked to the biodegradation of toxic chemicals at the basin level revealed significant reductions in ecosystem-related services in sites affected by agriculture and wastewater treatment plant (WWTP) discharges across all investigated environmental compartments. Finally, we suggest transitioning from simple concentration-based assessments of environmental pollution to more meaningful toxic pressure values, measured environmental concentrations normalised by effect information, in order to comprehensively evaluate the role of micropollutants at the ecological (biodiversity) level.

Experimental Study on Spectral Response Characteristics and Mechanical State of Coal Based on Artificial Acoustic Signals

With the increase in coal mining depth, the stress and strain state of coal and rock mass affects the formation of dangerous zones of dynamic phenomena. In order to study the relationship between the frequency spectrum characteristics of artificial acoustic signals and the stress state of coal and gas pressure, a test device and system that can generate acoustic signals by mechanical vibration excitation are developed by using the design idea of the unit module. Firstly, the basic mechanical parameters of coal under uniaxial compression are analyzed. On this basis, we use the test device to study the qualitative and quantitative relationships between the relative stress coefficient K value of the coal body and the axial loading stress, whether it contains gas, and the mechanical vibration force. The test results show that when the gas-containing coal and the gas-free coal are subjected to the same external mechanical vibration knocking force to stimulate the artificial acoustic signal test, the relative stress coefficient K value increases first and then decreases with the increase in axial loading stress. The relationship between the relative stress coefficient K and the axial loading stress σ can be expressed in the form of exponential function K=e−Cσ. When the axial loading stress and the external mechanical vibration force are both fixed values, the relative stress coefficient K value of the coal body with gas is smaller than that without gas. When the axial loading stress and gas-bearing pressure of the coal body are both fixed values, the relative stress coefficient K value decreases with the increase in the impact force of the external mechanical vibration. This experimental study can provide a reference for the identification and prediction of dynamic disasters based on artificial acoustic signals.

QUEUE MANAGEMENT SYSTEM FOR COMMUNITY HEALTH CENTRE (CASE STUDY: PUSKESMAS UMBAN SARI)

The Community Health Center Queue Management System is an Android and website-based online queuing system. The purpose of this research is to help Puskesmas Umban Sari who faces difficulty in managing patient queues. The main process handled by the system is registration and data recapitulation. The system has two queuing features that can be activated or not as needed, namely the priority queue and linear queue. The development method in this research is done by using the Rational Unified Process (RUP). The tests carried out are black box testing, usability testing, and performance testing. Based on the outcomes obtained from black box testing, it can be determined that the system is functioning very well. The Usability testing with a total of 50 respondents shows a score of 84%, which means that this system is quite satisfactory and useful for users. Whereas in performance testing, the Load Testing and Stress Testing processes were obtained by 67%, which means that the performance of this system is quite good when given heavy pressure and many users access simultaneously. The system successfully reduced waiting times and improved service efficiency.

Bio‐Inspired Graded and Uniform Cylindrical Lattices Fabricated by Material Extrusion 3D Printing: An Experimental and Numerical Investigation

ABSTRACTThe main requirements of the biomedical and aerospace industries are new and innovative lightweight materials. Bio‐inspired structures, which are inspired by various biological designs, have demonstrated notable advancements over traditional lightweight structures. In this study, bioinspired uniform and graded cylindrical triply periodic minimal surface (TPMS) and strut‐based lattice structures were studied for their mechanical qualities and energy absorption capacities fabricated by material extrusion 3D printing using PLA material. It was found that the cylindrical TPMS diamond lattice achieved maximum stress of 78.5 MPa and absorbed 19.14 MJ/m3 of energy, outperforming strut‐based designs with a 48% higher energy absorption than cylindrical BCC lattice structure. Graded designs further improve energy absorption through a better stress distribution. The findings validated the Gibson–Ashby model, highlighting the enhanced load distribution and stress transfer in the strut‐based and TPMS diamond structures. The finite element (FE) model results closely matched the experimental data, confirming its predictive reliability with a maximum error of energy absorption of 7.7%, elastic modulus of 6.9%, and plateau stress of 4.7%. These insights underscore the superior energy absorption and mechanical stability of cylindrical TPMS diamond lattices, indicating their potential for satisfying stringent industrial and technical performance requirements. The novelty of these designs lies in their bioinspired structures and significant enhancements in mechanical performance and energy absorption. Future research should build on these results to design efficient materials tailored to specific needs using FE models to optimize development processes before experimental testing.

A new approach (CSA-Score) to assessing the cumulative overall stress load in the case of animal experiments and even beyond

In laboratory animal science, severity assessment has been mandatory by European law since 2013. Various severity assessments have been created for many single manipulations. However, when multiple harmful interventions or stressors occur simultaneously or repeatedly, the cumulative overall severity is difficult to capture objectively, often leading to significant underestimation. We propose a new scoring system (CSA-Score) that makes it possible to visualise cumulative stress loads. The main features of the CSA-Score are, that severity measures of multiple stressors must not be simply added together. Moreover, the highest individual stress load forms the basis for the cumulative score. All further stressors must be added in a weighted manner. The developed scoring system is based on four different aspects, namely the definition of the (1) highest individual stress load, the assessment of (2) parallel and (3) serial occurring stress loads and the consideration of a (4) baseline stress load. From these four different aspects, a cumulative overall stress load can then be determined through score allocations. We propose that this scoring system will be highly effective in objectively depicting cumulative stress load and covert burden and therefore leading to a more realistic overall severity assessment.

The association between subjective sleep and stress in recreational athletes

Subjective sleep and stress are strongly associated, at multiple levels, and the current body of evidence highlights a bi-directional association. Previous research has highlighted that issues with sleep can impact on several stress responses. On the other side of this relationship, research has shown that stress-inducing factors can significantly impact sleep. The present study examined this association in a sample of recreational athletes, a population that has received little to no research focus to date Recreational athletes are defined as individuals who exercise >4 hours per week for health, fitness, or unofficial competitions. Recreational athletes (n = 34) completed online measures of subjective sleep, subjective stress, subjective anxiety/depression and training load (PSQI, PSS, HADS and DALDA). Pearson correlations were carried out to examine associations between variables. There was a significant positive correlation between subjective sleep quality and subjective stress. There was a significant positive correlation between subjective stress and training load. There was a significant positive correlation between subjective sleep quality and training load. The positive associations between sleep, stress and training load are consistent with previous research, but the present study adds to the literature by highlighting the associations in recreational athletes. Recreational athletes should proactively manage their sleep and stress, as due to the bi-directional relationship, improving sleep may benefit stress, and improving stress may benefit sleep quality. This is also likely to benefit overall mood and reduce the likelihood of overtraining in recreational athletes.

The Evaluation of Mechanical Properties of Commercial Composite Bones and 3D-Printed Bones Produced Using the CJP Technology

Cadaver bones and artificial bones are utilized to perform preoperative studies and education purposes. Cadaver bones are hard to find, require ethical permissions, and have infection hazards. Therefore, commercial artificial bones are preferred in practice. Nonetheless, since these commercial alternatives are standardly produced in an average size and geometry, it is almost impossible to adapt them to a specific surgical simulation. In addition, these artificial bones have relatively high costs, which limits their accessibility. On the other hand, ColorJet printing (CJP), one of the three-dimensional printing technologies, offers a rapid and cost-effective alternative. However, whether the printed 3D-printed models can mechanically comply with artificial bones is unclear. In this study, 3D-printed bones and artificial commercial composite bones were compared in terms of mechanical properties. Compression tests were applied over 14 printed and 14 composite bones using the ISO 5833 standard. Mechanical properties including stress-strain, load to failure, and elastic modulus were calculated, and these results were compared using the two-sample independent t-test, which is one of the statistical analysis methods. Consequently, there was no significant difference between the bone models in terms of stress and failure load values (p

Digital Twin-based Online Structural Optimization? Yes, It's Possible!

In structural design, simulation technology has been extensively applied. However, simulation-based offline optimization methods encounter two primary limitations: (1) they typically optimize parameters based on a structure's mechanical properties under extreme, static conditions, and (2) they involve complex, time-consuming performance calculations. To address these challenges, this paper introduces a structural online optimization framework driven by shape-performance integrated digital twins (SPI-DTs), which breaks the connection barrier between the real-time dynamics of digital twins and the offline characteristics of traditional optimization under dynamic operating conditions. Initially, the structure's remaining life is calculated online using real-time performance data from the digital twin, with the constraint stress and equivalent load derived via the static load equivalent method. A hierarchical radial basis function is then proposed, which integrates multi-source data for rapid calculation of the structure's target performance under the equivalent load. Finally, structural optimization parameters, determined through topology optimization, are solved using the multi-objective genetic algorithm. The feasibility of the proposed method is demonstrated through typical case studies: the wing cantilever beam and a three-dimensional flat plate. The results show that the weight of the wing cantilever beam case based on size optimization is reduced by 12.07%, and the weight of the flat plate case based on combined topology optimization and size optimization is reduced by 66.66%. In conclusion, the proposed framework offers a viable approach to achieving lightweight design and extending the operational life of structures under real-world conditions.

Multi-stage load partitioning in additively manufactured Al6061+TiC nanocomposite characterized by in-situ neutron diffraction

Metal matrix composites (MMCs), combining metal matrix and ceramic particles, exhibit high mechanical strength and stiffness compared to conventional metallic materials. During fusion-based additive manufacturing (AM), MMCs undergo a rapid heating and cooling thermal history, which affects the interfacial bonding, thermal misfit stress and mechanical load transfer behavior between the metal matrix and particles, thus impacting the bulk mechanical performance. Here, we investigate the deformation dynamics and phase-specific load transfer in fusion-based AMed Al6061+TiC MMCs through in-situ neutron diffraction. By calculating the phase-specific lattice strains, a multi-stage load transfer and deformation behavior during uniaxial compression is revealed: (1) elastic deformation in Stage I for both phases; (2) sudden stress rebalance between two phases in Stage II, evidenced by a sudden decrease in Al lattice strain and increase in TiC; (3) active load carrying by both phases in Stage III, with both phases experiencing an increase in lattice strains. The deformation mechanism of each stage is deducted by correlating the evolutions of the interphase stresses and peaks’ broadening and intensity of the Al matrix. The local plastic deformation of the Al matrix near the phase interface is triggered and leads to stress rebalancing in Stage II. The global plastic deformation subsequently propagates throughout the Al matrix in Stage III, and the composite is further hardened through both dislocation multiplication and load transfer. The findings offer valuable insights into deformation and load-sharing behavior in AMed MMCs.

Effects of Beads and Shot Peening Intensity on the Surface Integrity and Fatigue Performance of a Stainless Gear Steel

Shot peening was performed on stainless gear steel using multiple kinds of beads at multiple intensities. The effects of shot peening on surface integrity and the rotational bending fatigue performance were tested with the crack origin location observed. The results showed that the average surface roughness increases from Sa0.408 μm to Sa1.165 μm as the shot peening intensity increases, which does not necessarily lead to an increase in surface stress concentration coefficient. The compressive residual stress profile and the depth of the hardened layer increase with the increase of shot peening intensity. During ceramic bead peening, the fatigue improvement, with a maximum of 25 times, increases with the raise of intensity (0.06–0.20 mmA), while the fatigue improvement decreases when intensity (0.2–0.30 mmA) increases using cast steel shot. Based on ceramic shot peening, a method was proposed to predict the origin location of rotational bending fatigue cracks of gear stainless steel, in which the effects of surface stress concentration, compressive residual stress, and external load introduced were all considered. By using the superposition method of external load and residual stress, the maximum actual stress corresponding depth is obtained, which is the origin position of the rotational bending fatigue crack.

A deformation-diffusion interactive model to study crack-tip behaviour and predict crack growth rate under fatigue and hydrogen-embrittlement conditions

Hydrogen is accepted as a cleaner and more sustainable energy source, since it carries abundant energy and does not produce any effluent gas from burning when compared to fossil fuels. However, long-term degradation in mechanical properties, attributed to hydrogen embrittlement, is reported for metallic materials exposed to gaseous hydrogen, leading to accelerated crack growth behaviour under fatigue. In this paper, a visco-plastic deformation-diffusion interactive model is developed to study fatigue crack growth behaviour in a nickel-based superalloy under hydrogen-embrittlement condition. In the model, cyclic deformation is described by visco-plasticity constitutive model, while hydrogen diffusion is simulated by a modified form of Fick’s first law of diffusion which can address hydrogen diffusion driven by the hydrostatic stress gradient. In particular, trapped hydrogen, expressed as dependent on both diffusible hydrogen concentration and inelastic strain, is considered in the modelling of hydrogen diffusion. The model also describes the effects of hydrogen concentration on mechanical deformation by considering its influence on the evolution of isotropic hardening as well as on the strain state. Interaction between cyclic deformation and hydrogen diffusion is therefore studied for a crack tip in a compact tension specimen subjected to fatigue and hydrogen attack, showing a strong dependency on both loading frequency and stress intensity factor range. Subsequently, a two-parameter criterion is proposed for fatigue crack growth prediction, which accounts for the contributions of both cyclic deformation and hydrogen diffusion. The predictions show a good agreement with experimental data in terms of crack growth rate under fatigue and hydrogen-embrittlement conditions.

Multi-stage evolution characteristics and particle size effect of sandstone granules subjected to cyclic loads

Broken granules of different sizes and poor bearing capacities produced by repeated mining of coal seams contribute to natural disasters, such as rock strata movement. In this study, mechanical tests were performed on broken sandstone granules to explore their compaction and recrushing characteristics under repeated mining. The change characteristics of the relevant mechanical parameters of sandstone granules with different particle sizes and changes in energy density were examined, and compaction and recrushing mechanisms of sandstone granules under cyclic loading were identified. The results show that an increase in the initial particle size of sandstone granules has a significant effect on the increase in the strain under load. The cumulative dissipation energy corresponding to final crushing was greater for granules with larger initial sizes. The particle size of sandstone was found to be proportional to the fractal dimension after compaction and crushing. The probability of granular particles with larger initial particle sizes being broken into smaller particles is greater, resulting in the porosity attenuating most rapidly during the stress loading process of granular particles under repeated mining. Therefore, the degree of sample breakage was relatively severe. Particles were rearranged after compaction and crushing. Repeated mining results in dynamic evolution of the pore compaction, deformation, and fractur of the rock mass, as well as stable recombination. The study results provide important theoretical support for understanding of the movement mechanism of rock strata in the goaf under repeated mining.

Investigation of Acid-Etching Evolution in Natural Fractures of Carbonate Reservoirs Under High Closure Stress

Summary The acid-etching evolution of local natural fractures in high-stress carbonate rocks is a complex, multifield coupled phenomenon, governed primarily by closure stress loading, acid flow, and mass transfer reaction. To unravel the characteristics of this evolution and the impact of closure stress and acid injection rate on acid-etching effectiveness, a set of numerical models that integrate fluid flow, chemical reaction, and mechanical deformation within local natural fractures is established, and numerical simulations of fracture deformation and fracture acid-etching are conducted. The results show that continuous closure stress loading fosters the emergence of dominant flow channels by means of acid flow and acid-rock reaction. These channels guide most of the acid flow, continuously dissolving and etching the fracture walls, ultimately forming channelized acid-etching fractures. When closure stress ranges between 10 MPa and 15 MPa, a coupling balance between high closure stress and flow reaction enables the acid-etching fractures to attain greater widths and flow channels, significantly enhancing their long-term conductivity and deformation resistance. As the acid injection rate increases, the dominant flow channels merge into a single channelized acid-etching fracture due to competitive propagation and preferential dissolution. The dominant flow channel expands both vertically and horizontally under the scouring effect of high injection rates, leading to an increase in both the width of the channelized acid-etching fracture channel and the overall acid-etching fracture width.