Level Of Stress Concentration Research Articles

Micro-Scale Fracture Characteristics of Emulsified Asphalt Cold Recycled Mixture Based on Discrete Element Method

Asphalt pavement often experiences structural failure due to repeated vehicle loading. The discrete element method (DEM) model was established based on the semicircle bending test (SCB) to investigate the fracture damage mechanism of emulsified asphalt cold recycled mixture (CRME) under loading. The micro-mechanical parameters of CRME were determined through a reliable validation process using the uniaxial compression static creep test. The microscopic fracture characteristics of CRME were investigated through the load-displacement curve, stress distribution, and force chain distribution. The fracture energy was used as the evaluation index to analyze the influence of prefabricated notch length and aggregate gradation on the fracture performance of CRME. The results indicate that the emulsified asphalt mortar-aggregate interface was the critical weak position of the mixture fracture; the failure of the tension chain was the main destructional form of the SCB test. The development of cracks affected the stress concentration phenomenon and stress concentration level of the mixture. Fine-grained mixture exhibited crack resistance. The number and length of cracks were affected by gradation. As the prefabricated notch length increased, the influence gradually diminished. The research results could provide theoretical and data support for the design of CRME.

Oméga-3 et psychiatrie : que dit la littérature ?

Psychiatry is faced with a lack of new treatments despite a great deal of research and is re-exploring the use of old molecules and dietary supplements. Our aim here is to present a narrative review of the indications for omega-3 supplementation in various psychiatric disorders. Omega-3s belong to the family of polyunsaturated fatty acids (PUFAs). The 3 important omega-3 PUFAs in psychiatry are α-linolenic acid (ALA): C18:3n-3, eicosapentaenoic acid (EPA) C20:5n-3 and docosahexaenoic acid (DHA) C22:6n-3. In psychosis, a distinction must be made between 3 categories of patients: patients who have chronic schizophrenia (SCZ), patients with a first psychotic episode (FEP) and patients at ultra-high risk of psychosis (UHR).The data in the literature indicate that omega-3 supplementation is well tolerated. However, there is an increased risk of atrial fibrillation at doses over 4g/d, mainly in people over the age of 65.Omega-3 supplementation is not recommended for eating disorders, attention deficit hyperactivity disorder or autism spectrum disorders. Omega-3 supplementation could be beneficial in borderline personality disorder and psychotic disorders, particularly in patients at ultra-high risk of psychotic transition (UHR) to prevent psychotic transition and FEP to improve remission, and in bipolar disorder. It is now recommended for unipolar depression by the World Federation of Societies of Biological Psychiatry (WFSBP) and the Canadian Network for Mood and Anxiety Treatments (CANMAT) Taskforce. There are a large number of clinical trials of omega-3 supplementation. However, these trials use different types of supplementation (EPA alone, DHA alone, EPA+DHA, etc.) with different dosages and EPA/DHA ratios and over variable durations. In addition, the origin of the omega-3s may vary, although most of the studies used omega-3s of marine origin (fish). Finally, it has not been studied whether the time of day (fasting, during a meal, morning, evening, etc.) impacts the efficacy of the treatment.Confounding factors are often not taken into account. For example, some studies suggest a link between the response to omega-3 supplementation and the inflammation or oxidative stress level. Omega-3 supplementation acts on numerous biological pathways: inflammation, oxidative stress, monocarbon metabolism (vitamin B9, B12, homocysteine), myelination,... For psychotic disorders, meta-analyses tend not to distinguish between UHR, PEP and schizophrenic patients.There have not been enough studies to validate the doses and duration of supplementation. The doses and durations in the recommendations are based solely on incomplete data from published studies. Further studies are needed to optimize these recommendations. Except for UHR patients and those with borderline personality disorder, omega-3 supplementation is always used as a complement to psychotropic treatment.In conclusion, the results of clinical trials, meta-analyses and recommendations are heterogeneous and may be divergent. Omega-3 supplementation in psychiatry is still extensively studied, with numerous studies and meta-analyses published recently. Omega-3 supplementation could be part of the goal of personalized medicine, as some studies are already suggesting. In the future, the efficacy of omega-3 supplementation could be improved by targeting sub-groups of patients: patients with inflammatory profiles, high levels of oxidative stress and low blood omega-3 concentrations. Due to the increasing number of studies published on omega-3 supplementation in psychiatric disorders, the conclusions of this review are provisional and will need to be updated.

Optimization design of support structure based on 3D printing technology

Parts are often warped and deformed when they are molded using selective laser melting (SLM) technology. Thus, it is necessary to study the addition support modes of parts molded using SLM. Consequently, we designed dendritic, E-stage and conical supports, having different structural parameters and different partitions using Magics, and then, we analyzed their performances using the finite element software Abaqus. The structural parameters of the supports were optimized and finally tested using SLM molding technology. The maximum stress concentration was found for dendritic supports, followed by E-stage supports, and then conical supports. The stress concentration and deformation level of Scheme 2 were less than those of Scheme 1. The stress intensity and deformation levels for two partitions were less than those for three partitions. For parts molded by SLM, the deformation was maximum for conical supports, followed by dendritic supports, and then E-stage supports. When gradient supports of similar volumes were added, additional partitions did not effectively improve the molding quality. When supports of similar volumes were added, adding gradient supports did not effectively improve the molding quality. The results provide a basis for the application of SLM in molding high-precision parts.

Study of the Effect Launching System using Airbags on the Hull Structures of Pinisi Ship

Using airbags for ship launching is a technological innovation with promising implications for the shipbuilding industry. Considering the inefficiency and time consumption of the traditional Pinisi ship launching method, an airbags system is considered an alternative technology. This research involves a simulation of applying airbag technology for ship launch on the Pinisi Ship to assess stress concentration and magnitude. The Pinisi ship, airbags, and skates are designed in three dimensions on a real-size scale for analysis and then analysed using Finite Element Analysis (FEA) in ANSYS software. During the launch, the keel of the ship and airbags were subjected to a compressive force with a 3-millisecond analysis time. The stress and stress concentration levels in the Pinisi ship's structure vary between using airbags and the traditional launch method during launch. The ship's engine room bulkhead and the bow collision bulkhead structure underwent considerable tensile and compressive stresses in longitudinal and transverse orientations. The average maximum compressive stress and maximum tensile stress that occur in the longitudinal direction of the ship are around 50.2 MPa and 87.3 MPa, respectively. Compared to the maximum compressive stress, which accounts for 36% of the overall maximum stress encountered, the highest tensile stress experienced by the ship's structure is 64%.

Fatigue lifetime predictions of notched specimens based on the critical distance and stress concentration factors

The theory of critical distances is used for evaluation of effects of notches on load-bearing capacity of notched components under static or cyclic fatigue loading. The theory can also be used to predict the fatigue life of notched components. One of the assumptions for a reliable prediction is that the critical distance is independent of the notch geometry and its stress concentration level. The study shows that the critical distance depends not only on the number of cycles to failure (under fatigue loading), but also on the notch radius. In this case, direct use of the critical distance leads to unreliable predictions. The study quantifies the relation between the model notch (from which the critical distance is determined) and the predicted notch by means of the ratio of their stress concentration factors. The predictions modified by the ratio of stress concentration factors provide results that are in satisfactory agreement with the experimental data. The predictions were made and verified on the basis of fatigue data measured on two stainless steels 1.4306 and 1.4307, and high strength structural steel S690QL. Smooth and notched specimens were tested on an ultrasonic fatigue machine in a symmetrical tension–compression mode. The results were evaluated in the regions of high cycle and very high cycle fatigue.

Identification of structural defects and their impact on the magnetic memory, static and cyclic strength of VNS9-SH thin sheet trip-steel

Identification of microstructure defects, which are stress concentrators (SC) during the operation of mechanical engineering products, is an important scientific and practical task relevant for manufacturing enterprises. This problem becomes especially urgent and difficult for critical helicopter parts made of sheet TRIP steel VNS9-Sh (23Kh15N5AM3-Sh) and operating under cyclic loads due to the complex microstructure of the steel and small thickness of strips and sheets. To assess the impact of structural defects on the cyclic strength of products made of the steel under study, the specimens were preliminary sorted proceeding from the results of their testing using the method of metal magnetic memory (MMM) and metallographic studies. The MMM method is a structure-sensitive procedure which provides information about the presence of structural defects that arise during the manufacture. Magnetic anomalies in the form of sharp local changes in the intrinsic stray magnetic field (SSMF) (H) and its gradient |ΔH| along the length of the controlled section Δx, were identified on the surface of sheets cut from five different batches. A conventional classification of the identified anomalies was made according to the magnitude of the magnetic field gradient. The specimens of two types were cut in zones of magnetic anomalies and outside them: type 1 — for cyclic tests and type 2 — for metallographic studies. The geometric parameters and field gradient values of magnetic anomalies on specimens of type 1 and type 2 were the same. Metallographic studies in zones of maximum magnetic field gradient on type 2 specimens revealed defects in the form of a strip at the boundary of different structures, which is a structural stress concentrator (SSC) and a source of the inhomogeneity and changes in the magnetic properties. Type 1 specimens with similar magnetic anomalies and Type 1 specimens cut from sheets outside zones of magnetic anomalies were then selected for cyclic testing. Comparative tests for cyclic strength of the specimens with and without specified SSC were carried out. It is shown that the presence of SSC zones in the specimens reduces the number of cycles to failure during cyclic tests by 1 – 2 orders of magnitude compared to the specimens free of SSC. Based on cyclic tensile tests of specimens, a limiting value of the magnetic field gradient was determined that corresponds to the acceptable level of stress concentration on structural defects. This value is recommended for use as a rejection criterion when examining a new tape by the MMM method.

The evolution of carbides during long-term creep/aging of nickel based superalloy K444

In K444 alloy, the evolution of carbides during stress aging (creep) and stress-free aging at 900 °C for 5000 h, and interrupted at 3000 h were investigated, combining microstructure characterization and quantitative statistics method. After stress-free aging for 5000 h, the volume fraction of intragranular MC and M6C carbides decrease from 0.48 % to 0.66 %–0.26 % and 0.48 %, respectively, while that of M23C6 carbides increase to 0.28 %. The two degradation behaviors can be concluded as MC + γ → M6C + M23C6 + γ′ and M6C + γ → M23C6 + γ′ respectively. The former controlled by the diffusion of Ti occurred earlier, while the latter determined by the diffusion of W and Mo mainly happened later. The applied stress did not change degradation reactions while accelerate the degradation rate slightly. During stress-free aging, the morphology of grain boundaries (GBs) changed from discrete distribution to semi-continuous and then to continuous chain, and the content of MC and M6C carbides decreases while that of M23C6 carbides increases. The applied stress markedly promotes above behaviors. Especially, the completed continuous chain formed before 3000 h. Moreover, the applied stress induced the formation of cavitation on the GBs, which is attributed to the following reasons. First, it can accelerate the degradation of GBs and decline the GBs strength. What's more, dislocations pile up on the GBs and cause a high level of stress concentration. Finally, the new generated phase interfaces have a greater deviation with its adjacent carbides, weakening the binding force of GBs.

Quasi-3D dynamic photoelastic analysis of stress distribution during preparation of simulated canals with 13 mechanical preparation systems.

The aim of this study is to compare the stress produced on the internal walls of simulated canals by nine rotary and four reciprocating systems. Sixty-five isotropic transparent blocks containing a 60° curved and tapered simulated canal were selected and distributed into 13 groups (n = 5) according to the preparation system: BioRace, HyFlex EDM, iRaCe, Mtwo, One RECI, ProTaper Next, RaCe EVO, Reciproc, Reciproc Blue, R-Motion, VDW.ROTATE, XP-Endo Rise Shaper, and XP-Endo Shaper. Each resin block was mounted in a vice and a digital camera recorded the entire sequence of each preparation system through a circular polariscope set for dark field analysis. The video frames when each instrument reached the end of the coronal, middle, and apical thirds of the canal were extracted from the recordings and analysed by two independent observers regarding the stress generated on the canal walls using a semi-quantitative evaluation on a 0-5 scale. Intra- and inter-observer agreement were subjected to the Cohen's Kappa coefficient test, whilst the experimental results were compared using Kruskal-Wallis test post hoc pairwise comparisons with Bonferroni correction (α = 5%). The inter- and intra-observer agreement were 0.98 and 1, respectively. Most instruments demonstrated acceptable performance (scores ≤ 2) in all thirds. Other instruments, such as the HyFlex EDM 25.12 (coronal and middle thirds), Reciproc Blue R25 and Reciproc R25 (coronal and apical thirds), R-Motion 30.04 (apical third), and VDW.ROTATE 20.05 (apical third) showed scores higher than 3. Statistical analysis revealed a significant difference amongst the tested systems at the coronal, middle, and apical thirds (p < .05). None of the canal instrumentation protocols were stress-free, showing varying levels of stress concentrations. Various factors seemed to influence the magnitude of stress and its distribution pattern on the canal walls. Overall, instruments characterized by a larger taper, lower speed, reciprocating motion, and made of heat-treated NiTi alloy exhibited higher patterns of stress distribution.

ROLE OF SODIUM CHANNELS IN THE DEVELOPMENT OF OXIDATIVE STRESS IN ISCHEMIA/REPERFUSION MODEL

Ischemic and reperfusion injury is a critical condition, as it is necessary to control cell death and maintain tissue function. Restoration of nutrient and oxygen flow causes secondary damage to ischemic cells and is called reperfusion injury. Reperfusion injury causes, on the one hand, fluctuations in ion concentration inside cells, in particular sodium ions, due to changes in the conductivity of voltage-dependent ion channels, and, on the other hand, activation of the antioxidant system as a response to oxidative stress, in which the key role is given to reactive oxygen species and nitric oxide. Thus, the effect of ion channel inhibitors on the progression of oxidative stress, apoptosis and necrosis during reperfusion is of particular interest.&#x0D; The aim of the study is to examine the impact of sodium channels on oxidative stress under ischemic and reperfusion injury and sodium channel blockers action.&#x0D; Materials and Methods. The authors studied the influence of the synthesized peptide toxin, an inhibitor of voltage-gated sodium channels, under modelled ischemia/reperfusion in CHO-K1 culture on the level of apoptosis, necrosis, and oxidative stress (concentration of reactive oxygen species, nitric oxide, and glutathione) using fluorescent dyes and fluorescence microplate reader.&#x0D; Results. Data obtained indicate a decreased level of apoptosis and necrosis, and a control level of nitric oxide under toxin at a nanomolar concentration. At the same time, the concentrations of reactive oxygen species and glutathione did not change. Thus, the inhibitor toxin acted as a protective agent by preventing a decrease in the nitric oxide concentration, which favorably affected the survival of the cell culture during reperfusion after ischemia.

The effect of size and shape of pores on the prediction model of compressive strength of foamed concrete

The Balshin’s model is the most well-known of the models used to predict the compressive strength of aerated concrete. Among the pore characteristics such as the amount of porosity, the size of the pores, and their shape, Only the amount of porosity is placed as a specific parameter in the Balshin’s model. The impact of the other two characteristics, on the other hand, is included in the power value of the Balshin’s equation. Compressive strength tests and identifying the characteristics of air voids using microscopic imaging were performed on the mixtures produced in this study, which had weight ratios of sand to the cement of 1, 1.5, and 2, and the percentage of foam volumes of 0, 15, 25 and 35. In this study, a review of some of the factors influencing the change in the pore characteristics was performed, including the porosity of the foamed mixture and the size of sand used, in addition to the effect of the pore characteristics such as size and shape on the compressive strength of the foamed mixture. This study aims to conduct a comparative analysis of the models introduced in previous research to determine the effect of the pore characteristics of semi-structural and structural foamed mixtures (with sand) caused by mixture porosity and the sand size on the Balshin’s model. Among the types of relationships presented for the Balshin’s model, the relationship based on the paste fraction porosity was used. According to the findings of this study, foam porosity is the most important factor influencing pore size change, followed by sand size. The increase in the size of the pores and their non-sphericality decreased the relative compressive strength and, as a consequence, increased the power of the Balshin’s model because the maximum level of stress concentration was created adjacent to the middle diameter of the pores at the period of concrete rupture.

Energy absorption performance of the auxetic arc-curved honeycomb with thickness and arc angle gradient based on additive manufacturing

Auxetic arc-curved honeycomb has attracted extensive attention due to its lower stress concentration level. The energy absorption capacity of the arc-curved honeycomb can be further enhanced by the gradient design. In this paper, on the basis of the auxetic arc-curved honeycomb, thickness gradient honeycombs and arc angle gradient honeycombs are designed. The effects of different gradient configurations on the energy absorption of auxetic arc-curved honeycomb are discussed. The finite element model verified by experiments is used to study the compression behavior. The results show that the specific energy absorption of the gradient honeycombs increased by 11.0 % and 16.8 %, respectively. Compared with the uniform honeycomb, when the wall thickness is arranged alternately between layers and the arc angle decreases from both sides to the middle. This work systematically studies the effects of different gradient configurations on the deformation mode and energy absorption capacity of auxetic arc-curved honeycomb, which can provide guidance for the design of gradient honeycomb.

Correlation between micro-structure and acoustic emission characteristics of granite by split tests

The mesoscopic structure of rocks determines their strength and deformation characteristics. The grain and pore size distribution of granite samples buried depth of 1600 m to 1900 m in a goldmine of Shandong Province are measured by polarizing microscope and low-field nuclear magnetic resonance. The splitting test is carried out and the acoustic emission signal is obtained in real time by using an electro-hydraulic servo press and PCI-2 acoustic emission collector. The relationship between meso-mechanics and acoustic emission characteristics of split granite is analyzed. The experimental result shows that there is no clear correlation between meso-grain size and pore size distribution. Rocks with larger mineral grains easily form inter-embedded structures between grains and grains, the bearing effect of grains is enhanced, and the tensile strength of rocks is improved. The level of stress concentration in the rock is closely related to the pore size of the rock, and the acoustic emission ringing count before the main rupture in the large aperture (0.1~10 mm) of the rock is more active than that of the small aperture rock (0.01~1 mm), and a large number of high frequency acoustic signals are induced by the penetration between the pores in the unstable failure stage and post-peak failure stage, the stress concentration is higher, and the energy release frequency is increased, however the energy released strength by a fracture is weak.

The effect of a single dose of selenium with vitamin E on oxidative stress and fertilization indicators of ram sperm over the course of spermatogenesis

The aim of the experiment was to determine the effect of a single subcutaneous administration of selenium (Se) + vitamin E on the ejaculate volume, sperm count and viability, level of apoptosis and oxidative stress (OS) and Se concentration in ejaculates and blood of rams with respect to the time course of the spermatogenic cycle. The experimental group (EG; n = 6) was treated with a single injection of Selevit at a dose of 5 ml per animal (11 mg of sodium selenite and 125 mg of vitamin E/per animal). The control group (CG; n = 4) was treated in the same way, only with saline. Samples of blood and ejaculates were collected from each ram prior to application of Se and on the 1st, 14th, 26th, 38th, 50th and 62nd day after injection. Results showed that the Se concentration in the blood of EG was significantly higher only 24 h after application. Selenium concentration in the ejaculates of the EG was higher during the whole duration of the experiment (62 days), but significantly so only until day 14. The level of OS was significantly reduced on day 1, 14, and 62 after application of Selevit. There were no significant differences in the other analysed indicators. The results showed that one subcutaneous injection of Selevit had a positive effect on Se concentration and OS level in ejaculates, but was not sufficient to improve other monitored sperm quality indicators.

Вплив включення із функціонально-градієнтного матеріалу на концентра-цію напружень в тонких пластинах та циліндричних оболонках з круговим отвором

ology, in particular, space-rocket engineering, oil-and-gas engineering, power engineering, construction, etc. The presence of openings in their plate and shell components leads to a sharp increase in local stresses, which, under certain conditions, may trigger destructive processes. The use of functionally graded materials (FGMs) with certain mechanical properties can significantly reduce the stress concentration in the vicinity of local concentrators in the form of openings, cutouts, fillets, grooves, etc. This paper presents the results of computer simulation and finite element analysis of the stress and strain fields of thin plates and thin-walled cylindrical shells with a circular opening and an annular FGM inclusion surrounding it. The effect of the dimensions of the FGM inclusion and the law of variation of its elastic modulus on the stress and strain concentration in the vicinity of the opening was studied. The stress and strain intensity distribution in local stress concentration zones was obtained. It was found that an annular FGM inclusion with certain mechanical properties can reduce the stress concentration factor by more than 30%. In this case, a proportional decrease in strain intensity in the vicinity of the opening is also observed. The law of variation of the elastic modulus of the FGM inclusion and the inclusion width have a significant effect not only on the level of stress and strain concentration, but also on the stress and strain pattern. The results of the large-scale computational experiments show that an FGM annular inclusion reduces both the stress and the strain intensity around the opening. Therefore, the use of annular FGM reinforcements in plates and cylindrical shells with openings makes it possible to control the distribution and magnitude of the stress and strain intensities in local stress and strain concentration zones.

Improved lightweight corrugated network design to auxetic perforated metamaterial

Auxetic metamaterials with peanut-shaped perforations are superior for durable morphing control applications due to its extremely low stress concentration level and controllable auxetic capability. However, there are some issues to be concerned for such metamaterials with complex cellular features, including (1) improving structure topology for higher material efficiency, (2) tunable Poisson's ratio from positive to negative, (3) characterization of full elastic properties. To this end, an improved lightweight design with orthogonal corrugated beams is proposed in this study to approximate the perforated auxetic structure and then its full anisotropic elastic constants are characterized by a distinctive computational homogenization model based on the eigenfunction expansion variational theory with simple implementation technique of periodic displacement constraints. The numerical model is verified by the experimental tests of three specimens with different geometrical topologies. Subsequently, the dependence of structural elastic responses on the microstructural configuration is highlighted towards an elevated understanding of cell-structure-property relationship. It is demonstrated that the local in-plane rotation of interconnected regions in unit cell under uniaxial loading contributes to the structural auxetic behavior. Also, it is feasible to achieve tailorable mechanical properties through flexible microstructural adjustment and a design criterion of the crucial zero Poisson's ratio is given by a polynomial in terms of the normalized amplitude and thickness of the curved beam. The results pave a way to the design and analysis of novel metamaterials with tunable mechanical properties.

In silico evaluation of additively manufactured 316L stainless steel stent in a patient-specific coronary artery

Additive manufacturing (AM) is an emerging method for the fabrication of stents, which is cost-saving and capable of producing personalised stent designs. However, poor surface finish and dimension discrepancy in the manufactured stents can significantly affect not only their own mechanical behavior but also mechanical response of arteries. This study investigates the effects of surface irregularities and dimension discrepancy of a 316L stainless steel stent, manufactured using laser powder bed fusion (LPBF), on its biomechanical performance, in comparison with the original design and a commercial stent. In silico simulations of stent deployment in a patient-specific coronary artery, based on intravital optical coherency tomography imaging, are conducted to assess the stent deformation as well as arterial stress and damage. Severe plastic strain concentrations (with a maximum value of 1.93) occur in the LPBF stent after deployment due to surface irregularities, suggesting a high risk of stent fracture. The LPBF stent is harder to expand due to its thicker struts and closed-cell design (diameter of 4.14 mm at the peak inflating pressure during deployment, compared to 4.58 mm and 4.65 mm for the designed and MULTI-LINK RX ULTRA stents, respectively). Also, the LPBF stent induces a higher level of stress concentration (with a maximum value of 23.04 MPa) to the arterial layers, suggesting a higher risk of tissue damage and in-stent restenosis. This study demonstrates a clear need for further development of the AM process for manufacturing medical implants, especially the surface finish and dimension accuracy.

In situ observation on fracture behavior of the three-phase zone of the L415/N08825 bimetallic composite pipe welded joint

In this study, the fracture behavior of the three-phase zone of the L415/N08825 bimetallic composite pipe welded joint was investigated by in-situ tensile test and EBSD observation. According to the results of the tensile tests, the fracture occurs in the heat-affected zone (HAZ). There, the interface between the cladding and the base layer first separated, the N08825 layer fractures, and then the L415 layer finally fractures. The results of the in-situ tensile test show that the crack initiated in the unmixed zone of the interface between the L415 and N08825 layers, and then multiple crack initiation points appeared on the N08825 side, eventually merging and rapidly propagating. The crack propagation path is approximately straight, and the interface has little effect on the propagation path. The dominant fracture mechanism is microporous aggregated ductile fracture. The results of EBSD observation revealed that the high frequency of low angle grain boundaries (LAGBs) concentrated in the unmixed zone originated from the substructure. The CSL grain boundaries of the BCC structure crystal are mainly Ʃ3, Ʃ11, and Ʃ17b, and the CSL grain boundaries of the FCC structure crystal are mainly Ʃ3, Ʃ5, and Ʃ17b, which increase fracture resistance and improve toughness. In addition, the unmixed zone and its interface with L415 have a high level of stress concentration.

Numerical analysis of the influence of coal pillar size on auxiliary tunnel stability

It is very important to study the stability of the tunnel in the area affected by mining activities. In particular, the choice of coal pillar size has a direct influence on the stability of these tunnels. The authors of this study used the Flac3D program to model a mining face LC1 with various coal pillar sizes. The 220 m-long mining face known as LC1 has 20 degrees rock mass layers. The studied coal pillars are various widths at 5 m, 8 m, 10 m, 15 m, 20 m, and 30 m. The highest vertical stress and maximum horizontal stress are placed at different locations along the lower mining face (LC2), as shown by the results of the numerical simulation. The pressure distribution of the rock mass on the tunnel's top and the level of stress concentration on its two sides are asymmetrical for inclined seam conditions. The position of the maximum vertical tension is expected to change from the left hip to the side of the coal pillar as the coal pillar widens. This change essentially marks the system's transition from one stable state to another. Due to the rock mass's weak stability during this transition, the support must be strengthened in order to improve the rock stability.

Real-Time Stress Analysis Affecting Nurse during Elective Spinal Surgery Using a Wearable Device.

Successful spinal surgery demands high levels of concentration and cooperation from participating health care workers. The intraoperative stress levels and concentration levels of surgeons have been studied previously; however, those of nurses are rarely studied. Therefore, the purpose of this study is to understand the stresses affecting surgical nurses by their participating role during spinal surgery. A total of 160 surgical stress records were obtained during 40 surgeries, including electroencephalography (EEG) signals and heart rate variability (HRV) from three orthopedic spinal surgeons and six nurses; concentration, tension level and physical stress were analyzed. Levels of both concentration and tension were significantly higher in circulating nurses during all surgical stages (p < 0.05). Both beats per minute and low frequency/high frequency ratios, which reflect physical stress, were higher in scrub nurses (p < 0.05). As the surgical experience of scrub nurses increased, the key parameters related to stress tended to decrease (p < 0.01). These results will contribute to understanding the pattern of intraoperative stress of surgical nurses, and therefore help in enhancing the teamwork of the surgical team for optimal outcomes.

The characteristics and mechanism of microwave-induced borehole fracturing of hard rock under true triaxial stress

High stress induced by excavation disturbance in deep hard rock engineering can cause rockburst accidents. Microwave-induced borehole fracturing of hard rock is a promising technique for preventing rockbursts, the principle of which is to reduce energy and stress concentration levels in rock mass through microwave heating. The characteristics and mechanism of microwave-induced borehole fracturing of hard rock under different true triaxial stresses were experimentally investigated. After microwave-induced borehole fracturing under different σ1 and σ2 conditions, a complex crack network dominated by tensile cracks was generated in the rock specimen, which is consistent with the results obtained by AF and RA. According to the P-wave velocity before and after the test, the degree of thermal fracture is positively linearly correlated with σ1 and σ2 as a whole, and has good consistency with the length and number of thermal cracks. The results show that the technique will have better applicability and higher fracturing efficiency in high-stress areas. The thermal fracture process of basalt specimens under different σ1 and σ2 conditions is similar, which can be divided into a silent period, quiet period, dense period, and persistent period. In addition, thermal fracture exerts a significant threshold temperature effect, and fracture rate increases rapidly when the temperature reaches 150–192 °C (average about 172 °C). The relationship between thermal fracture and stress provides guidance for parameter design.