Effect Of Stress Release Research Articles

High capacity amorphous GeO2/C composite anodes for improved long cycle stability of lithium-ion batteries

Although GeO2 has a high theoretical capacity, its poor cyclic stability limits its application. In this work, amorphous GeO2/C composite anode materials were prepared by hydrothermal and sintering methods to improve the long-term cycle stability of Ge based anodes. The reversible specific capacity of the anode was 1300 mAh g−1 after 200 stable cycles at a current density of 0.2 A g−1, and it was 1002 mAh g−1 after 1000 long cycles at a high current density of 1 A g−1. The capacity retention rates of the amorphous GeO2/C-24 composite electrode were 84 % for the 2nd to the 200th discharge, being significantly higher than that of the commercial GeO2 electrode (10 %). C doping changed the structure of GeO2 atomic bonds and made C and O combine preferentially, resulting in Li+ intercalating to the GeO2/C interface and the increase in the number of lithiation reaction sites, Li+ diffusion coefficient, lithium-storage capacity and electrode capacity. The volume expansion rate of GeO2 was reduced from 12.84 % to 2.51 % by C doping, resulting in the high structure stability of the anode in long cycles for LIBs. The reason was the stress release effect of the amorphous C coating, and the formation of a stable and appropriate thickness of the SEI film.

Improving thermal stability and reliability of power chips by sintering foam structure layer

In order to ensure the high-temperature reliability of device in high temperature service, a new sintered structure layer, nano-Ag paste filling graphene reinforced Ni foam, was designed to realize the chip packaging in this work. This layer had excellent reliability and high-temperature heat dissipation stability, which benefit from the higher proportion of low-angle grain boundaries, finer grains and excellent heat dissipation capacity of graphene. The foam structure had favorable stress release effect, which made the sintered layer had high service reliability. The excellent heat dissipation ability of graphene overcomes the inherent defect of slow heat dissipation of the device under high temperature environment.

Study on microstructure and thermal shock resistance of plasma sprayed Cr2O3/8YSZ composite coating

In order to explore the high temperature performance of Cr2O3/8YSZ composite coating, four kinds of Cr2O3/8YSZ composite coatings were prepared on the surface of Q235 steel by using the plasma spraying technology (the content of 8YSZ is 50%, 30%, 20% and 0%, respectively). The morphology of the coating was characterized through thermal field emission scanning electron microscopy, and the distribution of elements in the section of the coating was scanned by using EDS line. The phase composition of the composite coating was analyzed by using X-ray diffractometer, and the surface roughness of the composite coating was measured by using surface profilometer. The microhardness of the coating was measured by using automatic micro-Vickers hardness tester, and the scratch resistance of the coating was compared by using scratch tester. The thermal shock resistance of the coating was tested in Gleeble-3800 thermal physical simulator, and the cross section morphology after thermal shock was observed and analyzed. The results show that when the ratio of Cr2O3 to 8YSZ is 7∶3, the sample coating has good thermal shock resistance due to the deflection effect of 8YSZ on the vertical cracks and the thermal stress release effect of the pores and cracks in the coating.

Reasonable vertical position of the advanced center drift in super deep buried soft rock tunnel

In super deep-buried soft-rock tunnels, significant deformation disasters often accompany high-ground stress. Advanced center drift stress release technology to release some in-situ stress in advance can effectively solve many problems caused by large deformation. Therefore, based on the Haba Snow Mountain Tunnel in the Lijiang Section of the Yunnan-Tibet Railway, the research on the vertical reasonable position of the advanced center drift is carried out. Using literature research, numerical simulation, and on-site experiments, the deformation of surrounding rock, the stress distribution of support, and the distribution of the plastic zone of surrounding rock at different vertical positions of the advanced center drift are studied. The application effect of the advanced center drift is analyzed through on-site monitoring data. The results show that different advanced center drift vertical positions have a stress-release particular impact. When the arch top of the advanced center drift is 2 m away from the main tunnel arch top, the stress release effect and support stress are relatively ideal, and the on-site measured tunnel deformation can reduce by an average of 44.52%. The research results can provide a reference for the design of advanced center drift in similar projects.

Effect of PyC/BN interfacial phases on mechanical behavior of SiC/SiC composites

AbstractPyC/BN multiphase interfacial phases were prepared on the surface of SiC fiber preform, then the near stoichiometric ratio SiC fiber reinforced SiC ceramic matrix composites were obtained by polymer impregnation and pyrolysis (PIP) process. The mechanical behavior of SiC/SiC composites was characterized by three‐point bending tests and fracture toughness tests. The stress release and load transfer effects of the interfaces under external loads were analyzed by scanning electron microscope (SEM). Results showed that with the increasing of PyC component thickness from .10 to.30 µm in the PyC/BN multiphase interfacial phases, the bending strength and fracture toughness both increased first and then decreased. The results occurred due to the competition between load transfer and stress release of the interfaces. The relatively optimized interfacial phase structure was that the thickness of the PyC interfacial phase and BN interfacial phase were .20 and.30 µm. The bending strength and fracture toughness of the optimized SiC/SiC composites reached 660.65 MPa and 29.01 MPa•m1/2. Respectively, many matrix cracks appeared in the horizontal and vertical directions, occupying almost the entire fracture section. The growth path of the matrix crack was significantly increased with many long fibers pulled out and broken, which was conducive to the strengthening and toughening of SiC/SiC composites.

Regulatory effects of stress release from decellularized periosteum on proliferation, migration, and osteogenic differentiation of periosteum-derived cells.

Bone injury is often associated with tears in the periosteum and changes in the internal stress microenvironment of the periosteum. In this study, we investigated the biological effects of periosteal prestress release on periosteum-derived cells (PDCs) and the potential mechanisms of endogenous stem cell recruitment. Decellularized periosteum with natural extracellular matrix (ECM) components was obtained by a combination of physical, chemical, and enzymatic decellularization. The decellularized periosteum removed immunogenicity while retaining the natural network structure and composition of the ECM. The Young's modulus has no significant difference between the periosteum before and after decellularization. The extracted PDCs were further composited with the decellularized periosteum and subjected to 20% stress release. It was found that the proliferative capacity of PDCs seeded on decellularized periosteum was significantly enhanced 6 h after stress release of the periosteum. The cell culture supernatant obtained after periosteal prestress release was able to significantly promote the migration ability of PDCs within 24 h. Enzyme-linked immunosorbnent assay (ELISA) experiments showed that the expression of stroma-derived factor-1α (SDF-1α) and vascular endothelial growth factor (VEGF) in the supernatant increased significantly after 3 h and 12 h of stress release, respectively. Furthermore, periosteal stress release promoted the high expression of osteogenic markers osteocalcin (OCN), osteopontin (OPN), and collagen type I of PDCs. The change in stress environment caused by the release of periosteal prestress was sensed by integrin β1, a mechanoreceptor on the membrane of PDCs, which further stimulated the expression of YAP in the nucleus. These investigations provided a novel method to evaluate the importance of mechanical stimulation in periosteum, which is also of great significance for the design and fabrication of artificial periosteum with mechanical regulation function.

Pupillometry to show stress release during equine sports massage therapy

Anecdotal reports state that wellness treatments for horses, such as massage therapy, relaxes the treated animal. Massage therapists and horse owners typically report an ”improvement” without verifying or quantifying the treatment results. This paper shows that the effect of wellness treatment and stress release can be measured with pupillometry. One of the horse’s pupils was photographed at the beginning and end of the treatment to determine the changes in the balance between the sympathetic and parasympathetic system activities. The owners assigned horses to two experimental groups: animals receiving a massage (N = 18) and horses standing with a person next to the horse for the time of a massage in the stable lane (N = 10). Six animals in the experimental group were excluded from the analysis because the pupils could not be traced. We opened the images of the pupil with Fiji (ImageJ) and used the elliptical selection tool to measure the pupils’ and iris’ areas. The ratio between the pupils’ aperture and the iris’ area was a normalized measure for pupil size. At the end of the experiment, we compared the normalized size of the pupils with a two-tailed paired t-test within groups and a two-tailed t-test between groups. For the experimental group, it was before and after the treatment, and for the control group, before and after the horse was placed in the stable lane. Comparisons between the experimental and control groups were made at the procedure's beginning and end. The treatment significantly decreased the normalized pupil area in the experimental group, on average, by a factor of 0.78 ± 0.15 (P = 0.042). For the horses in the control group, the pupil size increased, on average, by a factor of 1.14 ± 018. Changes were statistically not significant (P = 0.19). The initial pupil size of the horses in the experimental group was 1.88 times larger than that in the control group. After the treatment, the difference was reduced to a factor of 1.25. At the beginning of the experiment, the horses in the experimental group had, on average, larger pupil sizes than the horses in the control group, indicating that the horses in the experimental group were more stressed before the treatment than the control animals. The observed changes in pupil size in the experimental group likely resulted from enhanced parasympathetic and diminished sympathetic activity resulting from the treatment. Observed changes in pupil size agree with the anecdotal horse owner reports and the therapist’s treatment notes.

Viscos-elastic-plastic solution for deep buried tunnels considering tunnel face effect and sequential installation of double linings

Tunnels excavated in soft rock under high in situ stress are usually accompanied by large time-dependent deformation, slow convergence, and long periods of increased support load due to the strong rheological properties of the surrounding rock. This paper presents a time-dependent solution for deeply buried supported circular tunnels excavated in viscoelastic-plastic strain-softening rock masses, in which both the whole process of longitudinal excavation and the sequential installation of two elastic linings are considered. In the solution, the surrounding rock obeys a Burger-creep viscous elastic–plastic strain-softening model and two stages, referring to the “tunnel face influence stage” and the “creep stage”, are divided to derive the explicit expressions of the time-dependent tunnel convergences and support loads, in which the former stage accounts for the effect of stress release based on the elastic–plastic analysis, and the latter concentrates on the long-term response induced by the viscous behavior of the ground. To account for the different rock qualities, tunnel face advance rates, and lining tunnel support locations, the elastic–plastic strain-softening solution in the former stage is divided into three cases and the viscos-elastic–plastic solution in the creep stage includes two sub-solutions depending on the evolutions of stress paths being considered or not. For validation purposes, the provided analytical solutions are compared with the numerical results by finite-difference simulations and previous solutions. Following that, parametric studies are conducted to compare the stresses, deformations, and support loads under different stages and solutions. Finally, to further verify the applicability of the solutions in practical tunnels, the convergences, support loads and lining stresses of a typical tunnel cross-section in the Saint Martin La Porte access adit are successfully predicted. Overall, the proposed solutions in this study provide a profitable idea for deriving various viscoelastic-plastic or elasto-viscoplastic explicit solutions that can simultaneously account for both the rock rheology and tunnel face effect.

Understanding the synergistic impact of stress release and cementation on sandstone using sound waves — Implications for exhumation estimation

Exhumation is the process that encompasses uplift and erosion, leading to the removal of overburden and the release of effective stress exerted on rocks. When estimating exhumation magnitude using the compaction trend method, it is commonly assumed that the physical properties of rocks are insensitive to stress reduction. However, recent laboratory evidence has indicated that porosity exhibits weaker sensitivity to stress release compared with velocity that can be significantly affected by stress release. This raises questions regarding the validity of irreversible compaction assumed by compaction trend method. It remains unclear whether the impact of stress release can be observed in real rocks in exhumed areas because there is a lack of methods to directly measure the impact of stress release on field data. In addition, studying real rocks is further complicated by the presence of rock diagenesis and its interaction with stress release. To address these knowledge gaps, this study uses stress-dependent burial and uplift modeling and interprets an extensive well-log data set using the modeling-derived evaluation metrics. Conceptual modeling suggests that methods that neglect the combined effect of cementation and stress release tend to underestimate the exhumation magnitude. Furthermore, we discover that the disparity between porosity sensitivity and velocity sensitivity to stress release can be leveraged to derive a metric we call “porosity inconsistency” that can serve as a qualitative and quantitative measure for identifying and evaluating stress release in sandstone using geophysical field measurements. We gather a significant amount of sonic velocity and porosity data from normally compacted and uplifted clean sandstones in the Norwegian Sea and the Barents Sea. Notably, we observe significant porosity inconsistency in the exhumed well 6510/2-1 in the Norwegian Sea. In the Barents Sea, which has experienced extensive Cenozoic exhumation, the well data reveal a varying pattern of porosity inconsistency increasing toward the north and decreasing toward the west. This distribution of porosity inconsistencies in the Barents Sea wells not only aligns with the spatial variation of exhumation reported in various studies but also exhibits a positive correlation with the magnitude of exhumation. Furthermore, the exhumation magnitude derived from velocity-depth trends is considerably lower than the magnitude obtained from porosity/density-depth trends for wells displaying significant porosity inconsistency. These observations provide support for the predictions made by the conceptual modeling. The results of this study enhance our understanding of the synergistic impact of stress release and cementation on sandstone. Moreover, these findings have implications for pore pressure prediction and core evaluation in exhumed areas. They also provide insights into the feasibility and interpretation of time-lapse data of reservoir injection, for which the effective stress is likely to decrease due to pore pressure buildup.

Short-Range Graphitic Nanodomains in Hypocrystalline Carbon Nanotubes Realize Fast Potassium Ion Migration and Multidirection Stress Release.

Defect-rich carbon materials are considered as one of the most promising anodes for potassium-ion batteries due to their enormous adsorption sites of K+ , while the realization of both rate capability and cycling stability is still greatly limited by unstable electrochemical kinetics and inevitable structure degradation. Herein, an Fe3+ -induced hydrothermal-pyrolysis strategy is reported to construct well-tailored hybrid carbon nanotubes network architecture (PP-CNT), in which the short-range graphitic nanodomains are in-situ localized in the pea pod shape hypocrystalline carbon. The N,O codoped hypocrystalline carbon region contributes to abundant defect sites for potassium ion storage, ensuring high reversible capacity. Meanwhile, the short-range graphitic nanodomains with expanded interlayer spacing facilitate stable K+ migration and fast electron transfer. Furthermore, the finite element analysis confirms the volume expansion caused by K+ intercalation can be availably buffered due to the multidirection stress release effect of the unique porous pea pod shape, endowing carbon nanotubes with superior structural integrity. Consequently, the PP-CNT anode exhibits superior potassium-storage performance, including high reversible capacity, exceptional rate capability, and ultralong cycling stability. This work opens a new avenue for the fabrication of advanced carbon materials for achieving durable and fast potassium storage.

Fabrication of perovskite solar cells with PCE of 21.84% in open air by bottom-up defect passivation and stress releasement

The archetypical n-type semiconductor material, tin oxide (SnO2), is common and well-known electron transport layer (ETL) material in regular perovskite solar cells (PSCs) due to the superior electron mobility and suitable energy level alignment with perovskite. However, plentiful detrimental defects concentrated at perovskite/SnO2 ETLs interface and unfavorable residual stress within perovskite films, compromise and dampen the photovoltaic performance and shelf stability of PSCs. Herein, alkali metal salts (i.e., 2, 2′-biquinoline-4, 4′-dicarboxylic acid alkali metal salts (BCA-2H, BCA-2Na, and BCA-2K)) are employed as pre-buried modifiers in SnO2 films to achieve a holistic amelioration of ETLs, perovskite photoactive layer, and their interface heterojunction. The BCA modification facilitates crystal orientation and crystalline of SnO2 nanocrystals, instrumental in decreasing trap state densities within functional layers, releasing interfacial residual tensile strain, and upgrading perovskite film performance. In comparison to BCA-2H- and BCA-2Na-doped ETLs, the BCA-2K decoration corroborate better defect passivation and stress release effect originating from preferable interface enhancement and desirable surface chemical properties. Consequently, the PSCs based on SnO2-BCA-2K ETL fabricated under open-air conditions deliver the champion efficiency of 21.84% accompanied by negligible hysteresis. Moreover, the unpacked devices maintain 81.2% of its original value after 1200 h storage under an ambient condition of 55 ± 5% (relative humidity, RH) and 25 ± 5 ℃ with open-circuit conditions.

Effect of Synchronized Laser Shock Peening on Decreasing Defects and Improving Microstructures of Ti-6Al-4V Laser Joint.

Repairing processing is a significant method for damaged high-cost Ti-6Al-4V components to decrease economic loss, which usually utilizes a welding technique. For a large-size structural component, welding processing is commonly completed in air conditioning, which makes it difficult to avoid welding defects. To this end, an appropriate matching technique is important for improving welding performance. In the present research, asynchronized laser shock peening (ALSP) and synchronized laser shock peening (SLSP) techniques were utilized to decrease the influence of macro welding defects on laser-welded Ti-6Al-4V joints. The results show that SLSP has a greater effect on inducing surface plastic deformation on Ti-6Al-4V joints with a pitting depth of more than 25 microns while ALSP can lead to a pitting depth of about 15 microns. Through micro-CT observation a long hot crack exists in the central area of as-welded joints with a length of about 2.24 mm, accompanied by lots of pores in different sizes on double sides. After ALSP processing, some pores are eliminated while others are enlarged, and one-side crack tips present closure morphology. However, some microcracks exist on the side-wall of hot cracks. With the influence of SLSP, significant shrinkage of pores can be observed and both sides of crack tips tend to be closed, which presents a better effect than ALSP processing. Moreover, greater effects of grain refinement and thermal stress release could be achieved by SLSP processing than ALSP, which can be ascribed to dynamic recrystallization. For the as-welded joint, the ultimate tensile strength (UTS) and elongation (EL) values are 418 MPa and 0.73%, respectively. The values of UTS and EL in the ALSP processed joint are increased to 437 MPa and 1.07%, which are 4.55% and 46.48% higher than the as-welded joint, respectively. Such values after SLSP processing are 498 MPa and 1.23%, which are 19.14% and 68.49% higher than the as-welded joint, respectively.

Effects of thermal history of in-situ thermal management on as-built property heterogeneity of plasma arc additively manufactured Inconel 625

In-situ thermal management (ISTM) is one of the most prospective approaches to alleviating heat accumulation and achieving progressive forming for arc-based additive manufacturing. The aim of this study was to investigate the influences of thermal history, i.e., the cooling rate and the intrinsic heat treatment (IHT), of ISTM on as-built property heterogeneity of plasma arc additively manufactured Inconel 625 thin-wall deposit. The thermal history is obtained from numerical simulation. Results show that the variation of the thermal history of ISTM results in the bottom-up varied cooling rate and IHT, which together lead to the location-heterogeneous primary dendrite arm spacing, interdendritic phases and grain size. IHT of each layer is quantified by temperature-time integration (TTI), and Gaussian distributed TTI (above 600 °C) indicates the middle region of the deposit with ISTM is subjected to the most intense IHT. Compared with the counterpart of the conventional interlayer cooling strategy, the intensified high-temperature IHT of ISTM contributes to significant mitigation of micro-segregation, i.e., the brittle-hard interdendritic phases reduce 61.9%. Furthermore, a weighted value of cooling rate and TTI is innovatively introduced to depict the heterogeneity of mechanical property, which presents an exponential growth of ultimate tensile strength with the weighted value. Moreover, the layer-by-layer decreased heat input and the high-temperature preheating between layers of ISTM contribute to a certain residual stress release effect along the building direction.

Investigations on the macro‐meso mechanical properties and energy dissipation mechanism of granite shear fracture under dynamic disturbance

AbstractTo explore the mechanical characteristics and failure mechanisms of rock shear fracture under dynamic disturbance, the laboratory shear test and numerical simulation based on particle flow code (PFC) were carried out, and the mesoscopic degradation characteristics and energy dissipation mechanisms of rock shear fracture were analyzed. The results show that: (1) The crack initiation stress of rock under the disturbance condition is relatively reduced by 20%–29%, and there is a “shear fracture weakening effect.” The frequent alternating effect of stress concentration and release at the post‐peak failure stage is more obvious. (2) The number of cracks in rock under shear action shows the evolution of “calm → low speed growth → rapid increase → decrease of amplification → stabilization” with the increase of shear displacement. Compared with the conventional shear test, more cracks, and wider debris zones are formed. The number of cracks increases by 53%–106%, and the number of debris increases by 31%–138%. (3) The energy change trend of disturbance shear fracture test is basically consistent with that of conventional shear test. With the increase of normal stress, the input energy, elastic strain energy and dissipation energy of rock failure point show a certain linear growth feature. Compared with the conventional shear test, the input energy and stored strain energy of the failure point in the disturbance shear test are smaller, with relative reduction of 16.5% and 22.1%. Namely, the normal frequent disturbance reduces the energy storage capacity and failure resistance of rock.

Impacts of Water and Stress Transfers from Ground Surface on the Shallow Earthquake of 11 November 2019 at Le Teil (France)

The 4.9 Mw earthquake of 11 November 2019 at Le Teil (France) occurred at a very shallow depth (about 1 km), inducing the surface rupture of La Rouvière fault. The question was raised shortly after about the potential impact of a nearby surface quarry. Thanks to satellite differential interferometry, here, we revealed the existence of a secondary surface rupture of the quasi-parallel Bayne Rocherenard fault. A newly processed seismic cross-section allowed us to shape the three-dimensional geometry of the local three-fault system. Assuming that the earthquake was triggered by the impact of meteoric water recharge, our numerical simulations show that the hydraulic pressure gradient at depth was at a maximum during the period of 2010–2019, just before the seismic event. The estimated overpressure at the intersection of the two faults, which is the most probable place of the hypocenter, was close to 1 MPa. This hydraulic effect is about two and a half times larger than the cumulative effect of mechanical stress release due to the mass removal from the surface quarry over the two past centuries. This work suggests a rapid hydraulic triggering mechanism on a network of faults at a shallow depth after a heavy rainfall episode.

Thermoelastoplastic Finite Element Analysis of TiAl6V4 Thin-walled Ring Parts Based on Laser Metal Deposition Processing

Based on the simulation theory of stress field and temperature field in additive manufacturing, this paper numerically simulates and analyzes the laser metal deposition process of thin-walled ring, optimizes the simulation results by setting different process parameters, and analyzes the possible problems in the process of laser metal deposition and the corresponding optimization scheme. The comparison results of temperature field simulation results show that the phenomenon of temperature superposition and slow heat dissipation will occur in the printing process. Set a certain cooling time between the two adjacent layers, the temperature will gradually increase from layer by layer, and the heat dissipation will also improve, which plays an optimization role in preventing excessive temperature and remelting to a certain extent. The results of stress field analysis show that under the influence of temperature change, the upper material has a certain stress release effect on the lower material during welding, which makes the stress change between the middle layers in the printing process show a wavy trend, and large residual stress will be generated in the cooling process of the formed parts after printing. Through the deformation analysis results of the formed parts, it is concluded that the deformation of the formed parts increases gradually from bottom to top, and with the increase of printing speed, the maximum deformation caused by welding decreases gradually, but the area of high deformation area on the formed parts increases gradually.

Relieving Residual Stress of 316L Stainless Steel by Acoustic/Thermal Composite Treatment

The influence of temperature, vibration time, amplitude, and other factors on the residual stress release effect was studied using the method of low-temperature heating and high-frequency ultrasonic vibration, and excellent control parameters were obtained. In addition, the influence of cutting weld reinforcement on the residual stress release was also studied. The results demonstrate that the highest relative residual stress release rate was 280.29%, the average release was over 150 MPa, and the efficiency was higher than that of the general stress release methods. After cutting the reinforcement, only a small part of residual stress was released, influencing the overall residual stress distribution relatively little. The experimental material was a butt-welded 316L stainless steel plate μ-X360s diffractometer, and this was used for measuring the residual stress.

Effect of experimental stress and cortisol release induced by ACTH administration on expression of key genes related to milk synthesis and apoptosis during mammary involution of Saanen goats.

This research paper addresses the hypothesis that stress, induced by ACTH administration and cortisol release increases somatic cell count (SCC) in mammary secretion, and improves the effectiveness of dry off in goats. We report indicators of milk synthesis and mammary gland involution during dry off. Thirty Saanen goats were subjected to abrupt dry off and treatments: (1) ACTH administration (ACTH) or (2) placebo (Control) on days 1, 3, 6, 9, 12, 15, 30, and 60 of dry off. The expression of target genes in mammary tissue that are related to milk synthesis and cell survival such as insulin-like growth factor 1 receptor (IGF1R), phosphatidylinositol-3-kinase (PIK3CA), protein kinase B (AKT1) and mechanistic target of rapamycin (MTOR), casein (CSN2), lactalbumin (LALBA) and lactoferrin (LF) were evaluated, and plasma cortisol concentration, SCC, leucocyte count, and microbiological analyses in milk and mammary secretions were assessed. ACTH significantly downregulated the expression of IGF1R and upregulated the expression of PIK3CA in mammary tissue, increased lactoferrin concentration and SCC, and changed immune cell levels in mammary secretions compared to Control. Furthermore, ACTH administration increased the percentage of dry goats compared to the Control (73 vs. 46%, respectively). We conclude that the effect of stress via ACTH administration and cortisol release accelerated mammary involution during the early dry-off period.

Elastoplastic Solutions for Deep Tunnel Excavation in Weak Rocks with High Geostress Considering Different Stress Release Measures

The Deformation Reserved (DR) method and the Pilot Heading (PH) method are two commonly used stress release methods in the construction of weak rock tunnel under high geostress. The ground pressure exerted on the support would be reduced to a certain extent with the stress release measures according to the Convergence–Confinement principle. The elastoplastic solutions of tunneling with DR method and PH method are derived, respectively, considering the support delay. By introducing the concept of stress release ratio, the equivalent relationship between two methods is studied. The effects of these two methods on reducing the contact pressure between surrounding rock and support are compared. Furthermore, the stress release effects of DR method and PH method under different conditions are explored. The results show that DR method is much more suitable when the geostress is not very high and surrounding rock is intact with high strength. Contrarily, if the geostress is quite high and the surrounding rock is very weak, PH method is suggested. For DR method, the stress release effect abates gradually with the increase of initial geostress, but the effect of stress release by PH method is much better under high geostress. Though both DR method and PH method are effective in reducing the contact pressure between surrounding rock and lining, the reserved deformation and the radius of the pilot tunnel are not suggested to be as large as possible.

Revealing Steric‐Hindrance‐Dependent Buried Interface Defect Passivation Mechanism in Efficient and Stable Perovskite Solar Cells with Mitigated Tensile Stress

AbstractInterface engineering is one feasible and effective approach to minimize the interfacial nonradiative recombination stemming from interfacial defects, interfacial residual stress, and interfacial energy level mismatch. Herein, a novel and effective steric‐hindrance‐dependent buried interface defect passivation and stress release strategy is reported, which is implemented by adopting a series of adamantane derivative molecules functionalized with CO (i.e., 2‐adamantanone (AD), 1‐adamantane carboxylic acid (ADCA), and 1‐adamantaneacetic acid (ADAA)) to modify SnO2/perovskite interface. All modifiers play a role in passivating interfacial defects, mitigating interfacial strain, and enhancing device performance. The steric hindrance of chemical interaction between CO in these molecules and perovskites as well as SnO2 is determined by the distance between CO and bulky adamantane ring, which gradually decreases from AD, ADCA, and ADAA. The experimental and theoretical evidences together confirmed steric‐hindrance‐dependent defect passivation effect and interfacial chemical interaction strength. The interfacial chemical interaction strength, defect passivation effect, stress release effect and thus device performance are negatively correlated with steric hindrance. Consequently, the ADAA‐modified device achieves a seductive efficiency up to 23.18%. The unencapsulated devices with ADAA maintain 81% of its initial efficiency after aging at 60 °C for 1000 h.