Areas Of High Stress Concentration Research Articles

Synergy in bio-inspired hybrid composites with hierarchically structured fibrous reinforcements

In response to the global energy crisis, high-performance transportation sectors are rapidly embracing lightweight materials to enhance energy efficiency and sustainability, while grappling with the persistent challenges of developing structural materials that meet stringent safety standards with robust mechanical performance and ease of scalability. Thus, this work presents a combined experimental and theoretical framework to develop a profound understanding of the synergistic effect in hybrid composites with bio-inspired fibrous reinforcements, by elucidating the interfacial interactions across multiple length-scales, encompassing atomic covalent bonding to micro-morphology. A model hybrid composite system, containing a self-assembled fibrous reinforcement consisting of nano-sized Graphene Nanoplatelets (GnP) covalently bonded onto chemically-modified micro-sized Glass Fibers (GF), was utilized to showcase the synergistic effect and highlight its associated mechanisms. The interfacial interactions of the reinforcement were optimized by obtaining the maximum density of covalent bonds, which was achieved with 0.5 wt% GnP for the hybrid composites containing 10 wt% GF, increasing the work of adhesion by 33 %, compared to the biphasic GF composites. The composite’s morphology contains minimal agglomeration with ∼68 % of GnPs oriented with the melt flow, supressing high-stress concentration areas, while the formed crystalline microstructure, with ∼18 % β-crystals, allows the matrix to absorb substantial energy. Furthermore, the increased trans-crystallization encapsulating the hierarchical reinforcement induced nanoscale stiffness variations, increasing rigidity, and forming an ∼16 µm gradient interphase that facilitates load transfer. The greatest synergistic effect observed was ∼54 %, ∼37 %, and ∼75 % for the tensile modulus, tensile strength, and impact strength, respectively. Additionally, a theoretical framework accounting for the synergistic effect was formulated, using a two-step core/shell homogenization model, which shows great potential in expediting the design and optimization of innovative hybrid composite materials.

Characteristics and mechanisms of near-surface negative atmospheric electric field anomalies preceding the 5 September 2022, Ms 6.8 Luding earthquake in China

Abstract. A magnitude 6.8 strike-slip earthquake (EQ) struck Luding, Sichuan Province, China, on 5 September 2022, resulting in significant damage to nearby Ganzi Prefecture and the city of Ya'an. In this research, the near-surface atmospheric electric field (AEF) recorded at four sites 15 d before the Luding EQ was analyzed and differentiated, and multisource auxiliary data including precipitation, cloud base height, and low cloud cover were used at the same time. Nine possible seismic AEF anomalies at four sites were obtained preliminarily. Accordingly, microwave brightness temperature (MBT) data, which are very sensitive to the surface dielectrics and are closely related to the air ionization, together with surface soil moisture, lithology, and a 3D-simulated crustal stress field, were jointly analyzed to confirm the seismic relations of the obtained negative AEF anomalies. The geophysical environment for crustal high-stress concentration, positive charge carrier transfer, and surface accumulation was demonstrated to exist and to meet the conditions necessary to generate local negative AEF anomalies. Furthermore, to deal with the spatial disparities in sites and regions with potential atmospheric ionization, near-surface wind field data were employed to scrutinize the reliability of the AEF anomalies by comprehensively analyzing the spatial relationships among surface charges accumulation areas, wind direction and speed, and the AEF sites. Finally, four negative AEF anomalies were deemed to be closely related to the Luding EQ, and the remaining five possible anomalies were ruled out. A possible mechanism of negative AEF anomalies before the Luding EQ is proposed: positive charge carriers were generated from the underground high-stress concentration areas and then transferred to and accumulated on the ground surface to ionize the surface air, thus disturbing the AEF above the ground. This study presents a method for identifying and analyzing seismic AEF anomalies and is also beneficial for the examination of the pre-earthquake coupling process between the coversphere and the atmosphere.

Analysis of a stepped shaft in a rubber cracker machine

This paper presents a comprehensive failure analysis study of a stepped shaft in a rubber recycling factory. The investigation aims to identify the underlying cause of the shaft's failure and provide insights for enhancing the reliability and durability of industrial machinery. Through visual examination, scanning electron microscopy (SEM), mechanical characterization, elemental composition analysis using X-ray fluorescence (XRF), and finite element analysis (FEA), the study reveals the presence of low-cycle fatigue, primarily attributed to small surface imperfections. The macroscopic inspection indicates a high-stress concentration area where the shaft diameter changes. FEA results corroborate stress concentration in the failure region. Safety factor analysis suggests premature failure of the shaft. Further inspection reveals that misalignment of the shaft with respect to the ground leads to excessive vibration, potentially contributing to the low-cycle fatigue failure. To address this, a solution is proposed and implemented, involving correct alignment of a new shaft, reinforced fixation of the machine to the ground, and construction of a steel-reinforced concrete base. Subsequent operation of the rubber cracker machine with the implemented solution demonstrates successful prevention of shaft failures. The study highlights the importance of proper design, material selection, and operational considerations in enhancing the reliability of industrial machinery.

Stresses in Teeth with External Cervical Resorption Defects Restored with Different Biomimetic Cements: A Finite Element Analysis

IntroductionThis study compared the stress distributions in teeth with simulated external cervical resorption defects restored with different restorative materials and identified areas of high stress concentration. MethodsA maxillary central incisor created in a scanned model using HyperWorks software (Altair Engineering Inc, Troy, MI) served as the control. External cervical resorption defects based on Shanon Patel’s classification were created (1Bd/2Bd/3Bd) in the scanned model. The defects were restored using mineral trioxide aggregate, Biodentine, glass ionomer cement, and Bioaggregate. On all the models, a force of 100 N was applied on the palatal aspect 2 mm incisal to the cingulum directed at 45° along the long axis of the tooth. ResultsThe stresses generated in dentin and cementum are less, with a restorative material having a high Young’s modulus. For the 1Bd defect, MTA and Bioaggregate showed least stresses in dentin and cementum, respectively, whereas Biodentine had consistently lower stresses in dentin and cementum. Larger defects like 2Bd and 3Bd restored with Bioaggregate exhibited minimum stresses in dentin and cementum. ConclusionsBioaggregate and Biodentine replace dentin with maximum stress and maximum strain. Elastic moduli similar to or higher than dentin are preferred for restoring cervical third resorptive lesions of the tooth.

Damage Analysis of Segmental Dry Joint Full-Scale Prestressed Cap Beam Based on Distributed Optical Fiber Sensing.

Distributed fiber optic sensors (DFOS) can detect structural cracks and structural deformation with high accuracy and wide measurement range. This study monitors the segmental prestressed bent cap, assembled with a large key dry joint, based on optical fiber technology, and it allows the comparison of its damaging process with that of a monolithic cast in place counterpart. The obtained results, comprising cross-section strain distributions, longitudinal strain profiles, neutral axis location, crack pattern, and the damage process, show that the DFOS technology can be successfully used to analyze the complex working stress state of the segmental beam with shear key joints, both in the elastic range and at the ultimate load, and to successfully identify the changing characteristics of the stress state of the segmental capping beam model when elastic beam theory no longer applies. The DFOS data confirm that the shear key joint, as the weak point of the segmental cap beam, results in the high stress concentration area, and the damage rate is higher than that of the cast-in-place beam. The accurate monitoring by the DFOS allows for the realization that the damage occurs at the premature formation of a concentrated compression zone on the upper part of the shear key.

Theoretical analysis of drilling cuttings considering stress zoning of surrounding rock and its application in stress detection

AbstractDrilling cuttings method is a commonly used method to detect the risk of rockburst, which has been widely recognized and applied in coal mines. However, in the current theoretical research on the relationship between drilling cuttings method and coal stress, it is generally considered that the mechanical parameters of coal at different positions of roadway are unchanged, and the influence of surrounding rock plastic zone and elastic zone is not considered. Therefore, according to the secondary distribution characteristics of roadway side stress, the theoretical calculation formula of drilling cuttings in the plastic zone and elastic zone of the roadway side is established in this paper. The example shows that the distribution of cuttings on the roadway side is obviously consistent with the abutment pressure. The cuttings in the plastic zone and the elastic zone are in linear and power function with the coal stress, respectively, and the cuttings in the plastic zone are greater than those in the elastic zone. With the increase of the hole diameter, the slope of the relationship curve between the drill‐cutting weight and stress gradually increases, and the response of the drill‐cutting weight with a large hole diameter to the change of coal stress is more obvious. The numerical simulation results show that the error of the theoretical calculation formula of the drilling cuttings method is less than 9%, which can meet the engineering application needs of estimating the drill‐cutting weight in coal and the stress of coal. Using the theoretical formula, the stress field in the leading area of the working face is measured, and the leading influence range and the accurate position of the high stress concentration area are determined, which provides more comprehensive stress information for the early warning of impact danger and pressure relief.

Punching shear code provisions examination against the creation of an opening in existed RC flat slab of various sizes and locations

Punching shear is a critical problem in flat slabs directly supported at columns resulting in a high-stress concentration area, increasing the probability of brittle punching shear failure. However, the capacity is reduced by creating an opening that affects the overall behavior of the slab based on its size and location with respect to the loaded area. Furthermore, the design and analysis of the various structural elements are based on international regulations that have major differences in their basis and executions. In this study, the different code provisions in punching shear of RC two-way flat slab without shear reinforcement are examined under various opening sizes and locations using the Nonlinear Finite Element Analysis (NLFEA) procedure using ABAQUS software. A total of twenty-one model has been simulated for examining the prediction accuracy by the ACI318-19, MC2010, and EC2 under the effect of opening size (100, 200, and 300) mm, and locations (zero, 0.25d, 0.50d, 2.0d, 4.0 h, 5.5d, and 6.0d) under two main categories; the critical punching perimeter, and the critical opening location. However, it has been revealed that the proposed value of 0.50d as the critical punching perimeter is the most reliable one; besides, the value of 4 h is enough for defining the position where the effect of an opening could be neglected regardless of its size. Furthermore, it has been found that the column-to-opening ratio (C/O) is a very significant factor in controlling the punching shear capacity prediction accuracy by the different codes. Predictions get more overestimated under larger (C/O) values where increasing the C/O ratio by half increases the ultimate deflection percentage by an average of 22 %, except for those with smaller C/O values of less than 0.5, where it only reaches a maximum value of 13 %. Moreover, code prediction of the ACI318-19 and the MC2010 was found to be overestimated in all cases. In contrast, the EC2 was underestimated with an accurate prediction for an opening location of 2.0d from the column's face. However, it has been found that ACI318-19 is the most accurate one regarding the critical punching perimeter (0.5d) and critical opening location (4.0d).

Corrosion of Low Carbon Steel in Chloride Containing Environment

This research aims to investigate the corrosion of low-carbon steel in a chloride-containing environment. The investigation started by preparing and studying the surface condition of the specimens. The mechanical properties, microstructures and chemical compositions were also comparatively investigated between standard and corroded specimens. The results showed that the surface of the corroded samples was rough and peeling, different from the standard specimens, which were relatively smooth and non-corrosive. The average ultimate tensile strength and average yield strength of normal specimens were higher than those of corroded specimens at 5.39% and 2.32%, respectively. The corrosion products developed on the surface of corroded specimens caused a high-stress concentration area. The specimen is more prone to cracks and breaks when subjected to tensile stress. The surface of the normal specimen was composed of iron, oxygen, carbon, and silicon. In contrast, the surface of the corroded specimen contained the same elements as the normal specimen except chlorine which was detected. The film layer of the corroded specimen was cracked in contrast with the normal specimen, where the film still covered the metal substrate. The chemical composition analysis found that the corroded specimen's film layer contained chlorine, which is not detected in the film layer of the normal specimen. This is because the film layer of hot-rolled steel remains porous even passing the hot-rolling process. These pores allow chloride ions to diffuse and react with the film layer and the metal substrate. This makes the film layer of the corroded specimen thicker and initiates cracks. When stable alpha-iron-oxyhydroxide is formed on the steel surface, it can help to suppress corrosion.

Uncertainty measurement and research of Finite element analysis of Water Jet data based on Internet of Things

Nowadays, the concept of energy saving and water saving is deeply rooted in people’s minds, so it is necessary to promote efficient water-saving irrigation technology. Sprinkler irrigation is an efficient water-saving method, which is relatively uniform and does not affect the structure of the soil. It saves time and labor to irrigate fields, and has been used in more and more areas in China. The Internet of things technology is used to establish monitoring sites, collect and transmit water information, study and analyze crop fertilization and irrigation water volume, and achieve the purpose of saving water, fertilizer and labor. In test site traffic and sprinkler relationship between speed and pressure test, flow and in different pressure conditions were measured under different conditions of running speed, observe the fluid flows through the three links of pipe head loss and energy loss of the tee to the role of the internal pressure and axial force and other force, high stress concentration areas vulnerable to damage. The hydraulic characteristics in the process of water spraying are studied. The numerical simulation in this paper is completed by finite element software, and the hydraulic characteristics of the three-way pipe are analyzed by finite element to optimize the structure of the three-way pipe.

Macro/mesofracture and instability behaviors of jointed rocks containing a cavity under uniaxial compression using AE and DIC techniques

To better understand the macro/mesofracture and instability behaviors of the jointed surrounding rock of a cavity, a series of uniaxial compression tests on jointed granite samples with openings were conducted using acoustic emission (AE) and digital image correlation (DIC) techniques. The experiments indicated that with increasing joint angle, the peak strength and elastic modulus first decreases and subsequently increases, reaching a minimum as the joint angle approaches 45°. The linear transition point of the AE cumulative count before the peak stress is related to crack initiation or interpenetration, while each instantaneous increase in the AE count after the peak stress is associated with the stress drop caused by the localization of high strain or the formation or further development of visible cracks. The accelerated release of AE energy probably has a better early warning ability for the prediction and forecast of rock instability and failure. Moreover, the prominent strain localization bands indicate crack initiation, and the crack extension behavior signifies the gradual evolution of the strain localization bands. The existence of joints changes the stress distribution patterns in the samples, and the high stress concentration areas formed at the joint tips and around the cavities interact and jointly dominate the fracturing process, eventually leading to complex failure modes. The unstable failure of the specimens is mainly induced by tensile cracks around the caverns and the joint tips, accompanied by local shear failure.

Evaluation of Clinical Outcome of Subtrochanteric & Proximal Femur Fracture treated by Interlocking Intramedullary Nail with Side plate

Fractures of the subtrochanteric region and proximal femur can be especially challenging to manage, and they warrant special consideration to obtain consistently satisfactory results. The subtrochanteric zone of the femur is generally considered to include the area extending 5 cm distally from the inferior border of the lesser trochanter, or the junction of the proximal one third and middle third of the femoral shaft. Fractures that have their major displacement in this area are considered subtrochanteric fractures despite the possibility that some of them may extend into the trochanteric area proximally or the distal femoral shaft. The management of fractures of the subtrochanteric region and proximal femur has always held a particular interest for orthopedic surgeons. Biomechanically, the subtrochanteric area of the proximal femur is an area of high stress concentration, which has led to high rates of implant failures in the treatment of these fractures. Current evidence suggested that interlocking intramedullary nail with side plate offer better outcome.
 Objectives: To evaluate the operative efficacy and clinical outcome of interlocking intramedullary nail with side plate in the treatment of subtrochanteric & proximal femur fracture.
 Methods: This prospective cross sectional study was conducted in Cumilla General Hospital and private Clinics, Cumilla, from April 2018 to November 2019 among the 62 cases of subtrochanteric femur fractures. Objective of this study was to find out a safe, effective management of fracture, early mobility of patient, functional joint motion and short stay in hospital. All patients were treated by interlocking intramedullary nail with side plate. Routine follow up was carried out and outcomes were assessed. Radiographic examination was used to evaluate callus formation and fracture healing in postoperative 1, 3, 6 and 12 months follow-up. Functional recovery was evaluated by Harris Hip Scoring (HHS) system.
 Result: In this study, the mean age was 49.3±8.5 years. Among 62 cases 52 cases (83.9%) were male and 10 cases (16.1%) were female. The male and female ratio was 5.2:1. Regarding the causes of injury, out of 62 patients 50 (81%) had a history of fall from height. In 12 (19%) cases, motor vehicle accident was the cause of fracture. Average time of healing was 18 weeks. According to Harris hip score findings, 46 cases were considered as excellent in functional recovery, 11 good, 4 fair and 1 poor. The proportion of the patients with excellent and good recovery was 91.8%.
 Conclusion: Study showed interlocking intramedullary nail with side plate provides better functional outcome with early mobility of patients, and fracture unites without joint stiffness and less complication.
 Central Medical College Journal Vol 5 No 2 Jul 2021 PP 88-93

Research on behavior of underground pressure in shallow coal seam with three-face goaf working face

During the mining process of coal mines, coal pillars are often formed in the goaf on three sides, and the stress behavior of coal seams has a significant impact on the safety of coal mines. The upper part of panel 3104 of Xinwang Coal Mine is the room-pillar goaf of the 2# coal seam, and the lower part is the goaf of the 7# coal seam. The same coal seam is adjacent to the goaf of panel 3102. Therefore, there are hidden dangers for safe mining in panel 3104 affected by the goaf on three sides. Through FLAC3D numerical simulation, on-site Pasat-M detection, microseismic monitoring, and support resistance measurement, the stress distribution law of surrounding rock in the working face is analyzed. The following conclusions are obtained. There are several high wave velocity stress concentration areas in the coal body of 3104 working face. During the mining of the working face, the mining influence 90m in front of the working face began to spread to the area of the left coal pillar, and the vertical stress at the left coal pillar began to increase. Stress concentration appears in 0–20m strata at the top of 3# coal seams. At the top of a 3# coal seam, the vertical stress concentration coefficient can reach 2 in the range of 4–12m. The influence range of 3104 working face mining advance can reach 200m. Under the influence of mining, a large number of microseismic events occurred at 160m above and 150m below 3# coal seam. This law has reference value for the mining strata behaviors of coal seams under similar conditions.

Rock burst mechanism induced by stress anomaly in roof thickness variation zone: a case study

The variation of hard roof thickness is an essential contributor in triggering rock bursts during longwall mining. Case analysis and numerical modeling were used to study the stress and energy characteristics of the coal and rock mass and its fracture behaviour in the roof thickness variation zone (RTVZ). The results show that the coal seam has higher initial stress if overlain by a thicker hard roof, whose stress monitoring value is 1.8–2.6 times that of the thin zone. The increasing variation in the roof thickness or the roof properties causes a greater initial stress change in the coal seam. In the thick roof zones, the superposition of the advanced abutment pressure and the increased initial stress will result in a high-stress concentration area, where the stress mutation coefficient value can be up to 1.08–1.15. A higher rock burst risk might thus present in the roadway near the longwall in the thick roof zone, where more intensive elastic energy was released in the coal/rock mass. Also, it is more likely to have a significant dynamic load in the thin roof zone due to the higher possibility of roof breakage, and the total microseismic energy can reach 1.8–3.2E + 08J. Highlights Case analysis and numerical modelling were used to study the formation mechanism of stress anomaly in coal seams, energy evolution characteristics of the coal/rock mass and its fracture behaviour in the RTVZ. The mechanism of rock bursts induced by coal mining in the RTVZ is determined. The thick roof zone has high-stress concentration, where more intensive elastic energy is released in the coal/rock mass. Due to easier roof breakage, it is more likely to have a significant dynamic load in the thin roof zone. The prevention and control method of rock bursts in the RTVZ is put forward. The rock bursts can be relieved by reducing the initial stress increased in the thick roof zone. Strengthening roadway support can reduce the influence of dynamic load on the roadway.

Biomechanical Comparison Between Porous Ti6Al4V Block and Tumor Prosthesis UHMWPE Block for the Treatment of Distal Femur Bone Defects.

Purpose: The management of bone defects is a crucial content of total knee revision. This study compared the biomechanical performance of porous Ti6Al4V block and tumor prosthesis UHMWPE block in treating distal femoral bone defects. Methods: The finite element models of AORI type 3 distal femoral bone defect treated with porous Ti6Al4V block and UHMWPE block were established. Sensitivity analysis was performed to obtain the appropriate mesh size. The biomechanical performance of treatment methods in bone defects were evaluated according to the peak stress, the Von Mises stress distribution, and the average stresses of regions of interest under the condition of standing on one foot and flexion of the knee. Statistical analysis was conducted by independent samples t-test in SPSS (p < 0.05). Results: In the standing on one-foot state, the peak stress of the porous Ti6Al4V block was 12.42 MPa and that of the UHMWPE block was 19.97 MPa, which is close to its yield stress (21 MPa). Meanwhile, the stress distribution of the UHMWPE block was uneven. In the flexion state, the peak stress of the porous Ti6Al4V block was 16.28 MPa, while that of the UHMWPE block was 14.82 MPa. Compared with the porous Ti6Al4V block group, the average stress of the region of interest in UHMWPE block group was higher in the standing on one foot state and lower in the flexion state (p < 0.05). Conclusion: More uniform stress distribution was identified in the porous Ti6Al4V block application which could reserve more bone. On the contrary, uneven stress distribution and a larger high-stress concentration area were found in the UHMWPE block. Hence, the porous Ti6Al4V block is recommended for the treatment of AORI type 3 distal femoral bone defect.

Concept design of a digital twin architecture for ship structural health management

Ocean-going vessels frequently experience severe weather conditions. Occasionally, the actual environmental loads are much larger than design values, resulting in deviations from design conditions that may cause serious structural damage. A structural digital twin can enhance predictability and reliability of marine structures, and thus provide vessel operators, owners, and stakeholders with a more accurate overview of a vessel’s condition. It can also help reduce lifecycle costs through proposing rational and optimal inspection, maintenance, repair programs, and assist on maximizing service life and mission availability. This paper uses a benchmark vessel to investigate structural behaviors of the vessel through dynamic loading approach. The correlation between structure members and critical responses are established, and high stress concentration areas have been identified. Subsequently, this paper develops a conceptual digital twin architecture. The proposed digital twin predicts responses of the entire structure to measured or predicted environmental conditions with a hybrid model combining numerical simulations with measurements. While the traditional structural monitoring system focuses on the health condition of typical hot spots, the proposed digital twin may improve structural health awareness of the entire hull structure based on a limited number of sensors.

Statistical Characterization of Stress Concentrations along Butt Joint Weld Seams Using Deep Neural Networks

In order to ensure high weld qualities and structural integrity of engineering structures, it is crucial to detect areas of high stress concentrations along weld seams. Traditional inspection methods rely on visual inspection and manual weld geometry measurements. Recent advances in the field of automated measurement techniques allow virtually unrestricted numbers of inspections by laser measurements of weld profiles; however, in order to compare weld qualities of different welding processes and manufacturers, a deeper understanding of statistical distributions of stress concentrations along weld seams is required. Hence, this study presents an approach to statistically characterize different types of butt joint weld seams. For this purpose, an artificial neural network is created from 945 finite element simulations to determine stress concentration factors at butt joints. Besides higher quality of predictions compared to empirical estimation functions, the new approach can directly be applied to all types welded structures, including arc- and laser-welded butt joints, and coupled with all types of 3D-measurement devices. Furthermore, sheet thickness ranging from 1 mm to 100 mm can be assessed.

Distribution Law of Deep Complex In Situ Stress and Influence of Underground Engineering in Huanghuai Area

Huanghuai area is rich in coal resources, but due to the increasingly complex geological environment faced by coal mining, the complexity of structural stress is one of the main problems. In order to find out the distribution law of deep in situ stress in the Huanghuai area, the in situ stress measurement data of 81 effective measuring points in 24 mines with depths ranging from −100 m to −1200 m are analyzed in the present study base on the in situ stress measurement data. Furthermore, numerical simulation and field observation are used to analyze the deformation and failure characteristics of the surrounding rock. The research results show that the deep mining area of Huanghuai exhibited a high stress level, and the vertical and horizontal principal stress increases with increasing depth. The ratio of the lateral pressure coefficient ranges from 0.90 to 2.70, and the in situ stress field presented a trend of transition to the quasihydrostatic pressure field type as the depth extended, in which 80.23% of the measuring points are distributed between 1.20 and 2.10, belonging to the typical tectonic stress field type in which tectonic stress is absolutely dominant. The observation results of the surrounding rock and numerical simulation reveal that when the layout axis of the roadway is approximately perpendicular to the direction of the maximum horizontal principal stress, a high stress concentration area is present on the roof and floor of the roadway, the deformation increases sharply, and the support pressure of the roof and floor increases.

Optimum Selection of Mining Plans for Pillars Containing Interlayers Based on Numerical Simulation

A reasonable selection of the pillar mining plan is the key to ensure smooth mining in the goaf group, which plays an important part in safe production. In formulating and optimizing the pillar mining plan, the influence of the ground pressure evolution law should be fully considered. This paper first introduces two mining plans for pillars, and then, numerical simulations were used to analyze the two mining plans from four perspectives such as stress evolution law, stress concentration degree, force state of pillars, and weak marble layers. The results show that the mining plan 1 that retreats from the middle of the ore body to the two wings is the optimal as it can realize sequential mining in high-stress concentration areas at the middle section. This effectively alleviates the stress on the surrounding rock during mining and will not aggravate the collapse of the marble-interbedded area.

Mechanism and Prevention of Rockburst in Deep Multipillar Gob-Side Entry

Abstract Rockburst frequently occurs in deep multipillar gob-side entry in Inner Mongolia and Shaanxi, China. A case study of the Hongqinghe coal mine was analyzed to reveal the occurrence mechanism of rockburst in deep multipillar gob-side entry through theoretical and applied research. And new control methods were put forward. The results show that there is an essential difference between the surrounding rock load characteristics of multipillar gob-side entry and single-pillar gob-side entry. Within the influence area of the lateral goaf, more coal pillars will promote stress concentration, and the high stress concentration area will migrate to the coal pillar of mining roadway. The hanging roof of the working face can cause the stress concentration in the area of leading coal pillar to reach 5 times. The multipillar gob-side entry is less affected by the dynamic load of the roof of the lateral goaf. The ‘F-shaped and L-shaped’ stress source structure model of the deep gob-side multipillar entry was established, and the occurrence mechanism of rockburst is revealed. On the one hand, the static load of rockburst start foundation is formed under the superposition of lateral goaf, rear goaf, and multicoal pillar. On the other hand, the superposition of the foundation static load and the opportune static load induces the start of rockburst. Aiming at the two types of load sources, the fracturing method of kilometer bedding drilling in the roof of coal pillar area is proposed to reduce the foundation static load. The treatment method of periodic tendency blasting fracture of leading roadway roof in a working face reduces opportune static load. The field test has been carried out, and the effect was good.

On the Compression Instability during Static and Low-Cycle Fatigue Loadings of AA 5083 Welded Joints: Full-Field and Numerical Analyses

The aim of this scientific work was to evaluate the compression instability effects during static and low-cycle fatigue loadings of AA 5083 welded joints, commonly used in marine structures. Low-cycle fatigue assessment in marine structures is of utmost importance since high levels of plastic deformation can arise in the proximity of high-stress concentration areas. Displacement ratios equal to minus one and zero were used to perform experimental low-cycle fatigue tests. The tests were monitored by means of the Digital Image Correlation technique in order to detect the strain patterns, with particular attention paid to stress concentration areas, indicating that a specimen tends to buckle during high compression loads, for tests with a displacement ratio of minus one. The tests at displacement ratios equal to −1 showed a lowering of the strain–life curve revealing a considerable effect on compression instability. A nonlinear finite element modelling procedure, depending only on hardness measurements, was developed. The hardness measurements were used in order to assess the distinct mechanical properties of the different zones that were included in the finite element model. The finite element model results were compared to the data achieved by means of the digital image correlation technique, demonstrating that hardness measurements can help predict the low-cycle fatigue behaviour of welded joints and consider compression instability phenomena.