Shear sliding of rough-walled fracture surfaces under unloading normal stress

Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses(1e7 MPa)and numbers of shearing cycles(1 e5).The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies,while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion.The joint friction angle of fractures exponentially increased by 62.22%e64.87%with JRC while decreased by 22.1%e24.85%with shearing cycles.After unloading normal stress,the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity.The surface resistance index(SRI)of fractures decreased by 4.35%e32.02%with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress,but increased by a factor of 0.41e1.64 with JRC.After sliding initiation,the shear displacement of fractures showed an increase in power function.By defining a sliding rate threshold of 5105 m/s,transition from“quasi-static”to“dynamic”sliding of fractures was identified,and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles.The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded,and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities.Dilation was positively related to the shear sliding velocity of fractures.Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation,indicating an increasing shear area ratio by 45.24%e91.02%with normal stress.

Experimental study on the slip evolution of planar fractures subjected to cyclic normal stress

The frictional rupture mechanisms of rock discontinuities considering the dynamic load disturbance still remain unclear.This paper investigates the transitional behaviors of slip events happened on a planar granite fracture under cyclic normal stress with diferent oscillation amplitudes.The experimental results show that the activations of fast slips always correlate with unloading of normal stress.Besides,the intensive normal stress oscillation can weaken the shear strength which is recoverable when the normal stress return to constant.The rupture patterns are quantifed by stress drop,slip length and slip velocity.With the efect of small oscillation amplitudes,the slip events show chaotic shapes,compared to the regular and predictable style under constant normal stress.When the amplitude is large enough,the big and small slip events emerge alternately,showing a compound slip style.Large amplitude of the cyclic normal stress also widens the interval diferences of the slip events.This work provides experimental supports for a convincible link between the dynamic stress disturbance and the slip behavior of rock fractures.

Cyclic shear behavior of en-echelon joints under constant normal stiffness conditions

To reveal the mechanism of shear failure of en-echelon joints under cyclic loading,such as during earthquakes,we conducted a series of cyclic shear tests of en-echelon joints under constant normal stiffness(CNS)conditions.We analyzed the evolution of shear stress,normal stress,stress path,dilatancy characteristics,and friction coefficient and revealed the failure mechanisms of en-echelon joints at different angles.The results show that the cyclic shear behavior of the en-echelon joints is closely related to the joint angle,with the shear strength at a positive angle exceeding that at a negative angle during shear cycles.As the number of cycles increases,the shear strength decreases rapidly,and the difference between the varying angles gradually decreases.Dilation occurs in the early shear cycles(1 and 2),while contraction is the main feature in later cycles(310).The friction coefficient decreases with the number of cycles and exhibits a more significant sensitivity to joint angles than shear cycles.The joint angle determines the asperities on the rupture surfaces and the block size,and thus determines the subsequent shear failure mode(block crushing and asperity degradation).At positive angles,block size is more greater and asperities on the rupture surface are smaller than at nonpositive angles.Therefore,the cyclic shear behavior is controlled by block crushing at positive angles and asperity degradation at negative angles.

Analysis of Stress Concentration Factors due to in-Plane Bending and out-of-Plane Bending Loads on Tubular TY-Joints of Offshore Structures

The aim of this work is to study the stress distributions and the location of hot spots stress in the vicinity of the intersection lines of the tubular elements of the tubular TY-joints.Using the finite element models,we analyze the effects of geometrical parameters on the stress concentration factor in the case of in-plane bending and out-of-plane bending loads,around the weld toe of the tubular joints.Our results reveal the location of the maximum stress concentration factor at the heel or toe in the case of in-plane bending loads and at the saddle point in the case of out-of-plane bending loads.Six parametric equations are established and used to calculate the stress concentration factor at critical locations using the non-linear regression method.The results obtained from the finite element analysis are close to the results of the parametric equations and the experimental data from the previous work.

Effect of lateral stress on frictional properties of a fracture in sandstone

The injection of large volumes of natural gas into geological formations,as is required for underground gas storage,leads to alterations in the effective stress exerted on adjacent faults.This increases the potential for their reactivation and subsequent earthquake triggering.Most measurements of the frictional properties of rock fractures have been conducted under normal and shear stresses.However,faults in gas storage facilities exist within a true three-dimensional(3D)stress state.A double-direct shear experiment on rock fractures under both lateral and normal stresses was conducted using a true triaxial loading system.It was observed that the friction coefficient increases with increasing lateral stress,but decreases with increasing normal stress.The impact of lateral and normal stresses on the response is primarily mediated through their influence on the initial friction coefficient.This allows for an empirical modification of the rate-state friction model that considers the influence of lateral and normal stresses.The impact of lateral and normal stresses on observed friction coefficients is related to the propensity for the production of wear products on the fracture surfaces.Lateral stresses enhance the shear strength of rock(e.g.Mogi criterion).This reduces asperity breakage and the generation of wear products,and consequently augments the friction coefficient of the surface.Conversely,increased normal stresses inhibit dilatancy on the fracture surface,increasing the breakage of asperities and the concomitant production of wear products that promote rolling deformation.This ultimately reduces the friction coefficient.

Unveiling the silent link:Normal-tension glaucoma's enigmatic bond with cardiac blood flow

This comprehensive review embarks on a captivating journey into the complex relationship between cardiology and normal-tension glaucoma(NTG),a condition that continues to baffle clinicians and researchers alike.NTG,characterized by optic nerve damage and visual field loss despite normal intraocular pressure,has long puzzled clinicians.One emerging perspective suggests that alterations in ocular blood flow,particularly within the optic nerve head,may play a pivotal role in its pathogenesis.While NTG shares commonalities with its high-tension counterpart,its unique pathogenesis and potential ties to cardiovascular health make it a fascinating subject of exploration.It navigates through the complex web of vascular dysregulation,blood pressure and perfusion pressure,neurovascular coupling,and oxidative stress,seeking to uncover the hidden threads that tie the heart and eyes together in NTG.This review explores into the intricate mechanisms connecting cardiovascular factors to NTG,shedding light on how cardiac dynamics can influence ocular health,particularly in cases where intraocular pressure remains within the normal range.NTG's enigmatic nature,often characterized by seemingly contradictory risk factors and clinical profiles,underscores the need for a holistic approach to patient care.Drawing parallels to cardiac health,we examine into the shared vascular terrain connecting the heart and the eyes.Cardiovascular factors,including systemic blood flow,endothelial dysfunction,and microcirculatory anomalies,may exert a profound influence on ocular perfusion,impacting the delicate balance within the optic nerve head.By elucidating the subtle clues and potential associations between cardiology and NTG,this review invites clinicians to consider a broader perspective in their evaluation and management of this elusive condition.As the understanding of these connections evolves,so too may the prospects for early diagnosis and tailored interventions,ultimately enhancing the quality of life for those living with NTG.

Nonlinear Elastic Constitutive Model of Soil-Structure Interfaces Under Relatively High Normal Stress

The shear characteristics of soil-structure interfaces with different roughness are studied systematically by us-ing the DRS-1 high normal stress and residual shear apparatus. The experimental results indicate that,under a relatively high normal stress,normal stress and the coefficient of structural roughness are the most important factors affecting the mechanical interface characteristics. The relationship between shear stress and shear displacement of the soil-structure interface is a hyperbolic curve with high regression accuracy. Based on our experimental results,a nonlinear elastic con-stitutive model of the soil-structure interface under relatively high normal stress is established with a definite physical meaning for its parameters. The model can predict the strain hardening behavior of the soil during the shearing process. The results show an encouraging agreement with experimental data from direct shear tests.

Impact of normal stress-induced closure on laboratory-scale solute transport in a natural rock fracture

The impact of normal stress-induced closure on fluid flow and solute transport in a single rock fracture is demonstrated in this study.The fracture is created from a measured surface of a granite rock sample.The Bandis model is used to calculate the fracture closure due to normal stress,and the fluid flow is simulated by solving the Reynold equation.The Lagrangian particle tracking method is applied to modeling the advective transport in the fracture.The results show that the normal stress significantly affects fluid flow and solute transport in rock fractures.It causes fracture closure and creates asperity contact areas,which significantly reduces the effective hydraulic aperture and enhances flow channeling.Consequently,the reduced aperture and enhanced channeling affect travel time distributions.In particular,the enhanced channeling results in enhanced first arriving and tailing behaviors for solute transport.The fracture normal stiffness correlates linearly with the 5th and 95th percentiles of the normalized travel time.The finding from this study may help to better understand the stress-dependent solute transport processes in natural rock fractures.

Regulatory mechanisms of retinal ganglion cell death in normal tension glaucoma and potential therapies

Normal tension glaucoma(NTG)is a multifactorial optic neuropathy characterized by normal intraocular pressure,progressive retinal ganglion cell(RGC)death,and glaucomatous visual field loss.Recent studies have described the mechanisms underlying the pathogenesis of NTG.In addition to controlling intraocular pressure,neuroprotection and reduction of RGC degeneration may be beneficial therapies for NTG.In this review,we summarized the main regulatory mechanisms of RGC death in NTG,including autophagy,glutamate neurotoxicity,oxidative stress,neuroinflammation,immunity,and vasoconstriction.Autophagy can be induced by retinal hypoxia and axonal damage.In this process,ischemia can cause mutations of optineurin and activate the nuclear factor-kappa B pathway.Glutamate neurotoxicity is induced by the over-stimulation of N-methyl-D-aspartate membrane receptors by glutamate,which occurs in RGCs and induces progressive glaucomatous optic neuropathy.Oxidative stress also participates in NTG-related glaucomatous optic neuropathy.It impairs the mitochondrial and DNA function of RGCs through the apoptosis signal-regulating kinase-JUN N-terminal kinase pathway.Moreover,it increases inflammation and the immune response of RGCs.Endothelin 1 causes endothelial dysfunction and impairment of ocular blood flow,promoting vasospasm and glaucomatous optic neuropathy,as a result of NTG.In conclusion,we discussed research progress on potential options for the protection of RGCs,including TANK binding kinase 1 inhibitors regulating autophagy,N-methyl-D-aspartate receptor antagonists inhibiting glutamate toxicity,ASK1 inhibitors regulating mitochondrial function,and antioxidants inhibiting oxidative stress.In NTG,RGC death is regulated by a network of mechanisms,while various potential targets protect RGCs.Collectively,these findings provide insight into the pathogenesis of NTG and potential therapeutic strategies.

Viscosity and Normal Stress Difference of Aggregating Colloid

Following a sticky particle model and Its computer simulation scheme proposed In the previous papers, the viscosity and normal stress difference are cakulated when the aggregating colloid is being sheared. The plotting of the viscosity vs shear strain shows a sigmoidal shape, which Is also observed in experimental results. The normal stress difference is plotted vs shear strain, which has not been reported in the literatures till now.

Emotions and Stressing Situations Adaptation of Nursing Students in the New Normality

Background: New normality is uncertain in every sense, specifically in education and for many health disciplines. Being immersed in COVID-19 pandemics brought serious consequences for mental health, and is very important to handle emotions and stress coping strategies to obtain positive outcomes. Objective: To identify the most frequent emotions, as well as the adaptation strategies to the new normality faced by the students of nursing. Methods: Qualitative and phenomenological research, with the participation of 20 students from both genders in the middle term of nursing career at Faculty of Higher Studies Iztacala, National Autonomous University of Mexico, from August to November 2021. Information was collected from a focal group for ten sessions;analysis was according to De Souza Minayo, and there was a signed informed consent letter from participants. Results: Four categories emerged with sub-categories. Category I Maximized emotions. Sub-categories: 1) Frustration, anger, disappointment;2) Personal disappointment, hopelessness, uncertainty;3) Depression. Category II Support elements close to the new normality. Sub-categories: 1) Family communication;2) Education for mental and physical health. Category III Stressing situations that exceeded the student. Sub-category: Disease in lovely ones. Category IV Stress coping strategies. Sub-categories: 1) Friends and relatives that help to get better;2) Family values. Informers pointed out to have maximized emotion, and having no self-control on its negative outcomes occurred;in addition, the situation was not favorable at home with several losses of loved ones, as well as a poor economy that threatened students to give up studies. Conclusion: Emotions facing this new normality are very important and should be attended to, their proper handling will result in a new learning of socio-emotional abilities, stress coping strategies development, better adaptation and informed decisions taken.

Experimental and Numerical Study on the Shear Strength and Strain Energy of Rock Under Constant Shear Stress and Unloading Normal Stress

Excavation and earth surface processes(e.g.,river incision)always induce the unloading of stress,which can cause the failure of rocks.To study the shear mechanical behavior of a rock sample under unloading normal stress conditions,a new stress path for direct shear tests was proposed to model the unloading of stress caused by excavation and other processes.The effects of the initial stresses(i.e.,the normal stress and shear stress before unloading)on the shear behavior and energy conversion were investigated using laboratory tests and numerical simulations.The shear strength of a rock under constant stress or under unloading normal stress conforms to the Mohr Coulomb criterion.As the initial normal stress increases,the cohesion decreases linearly and the tangent of the internal friction angle increases linearly.Compared with the results of the tests under constant normal stress,the cohesions of the rock samples under unloading normal stress are smaller and their internal friction angles are larger.A strength envelope surface can be used to describe the relationship between the initial stresses and the failure normal stress.Shear dilatancy can decrease the total energy of the direct shear test under constant normal stress or unloading normal stress,particularly when the stress levels(the initial stresses in the test under unloading normal stress or the normal stress in the test under constant normal stress)are high.The ratio of the dissipated energy to the total energy at the moment failure occurs decreases exponentially with increasing initial stresses.The direct shear test under constant normal stress can be considered to be a special case of a direct shear test under unloading normal stress with an unloading amount of zero.

Parameter Estimations of the TFR Model Under Exponential Distribution at a Normal Stress

The TFR（Tampered Failure Rate） model was proposed by Bhattacharyya and Soejoeti（1989） for step-stress accelerated life tests, On step-stress completely accelerated test occasions, the paper gives a method of estimating parameters under a normal stress.

Normalized fatigue properties of asphalt mixture at various temperatures

This study normalized the mixture's fatigue behavior at various temperatures,and the strength and fatigue tests of the mixture were conducted.The stress state of the asphalt mixture includes direct tensile,uniaxial compression,and indirect tensile.The Desai yield surface and fatigue path were proposed.And a normalized fatigue characteristics model of the mixture was established.The following conclusions were obtained.With the increases in the loading rate,the strength of the asphalt mixture increased.As the temperature increases,the strength of the mixture is reduced.At various temperatures and rates,the strength forms a closed curved surface.The Desai strength yield surface was established,which forms a closed curved surface.When the loading rate and temperature are below a certain critical line,the asphalt mixture will not undergo strength damage.At a fixed stress state,the fatigue damage path of the mixture was determined.The stress ratio was determined considering the influence of the loading rate.In this way,a normalized model can be described to express the asphalt mixture fatigue properties at various temperatures and stress levels.For the asphalt mixture in an indirect tensile state,the normalized fatigue equation parameter is 4.09.This model is more suitable for reflecting the viscous-elastic behavior of the mixtures than the fatigue equation determined by the notional stress ratio.

Finite element analysis on stresses field of normalized layer thickness within ceramic coating on aluminized steel

Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA) and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for describing thickness ratios of HDA/PEO coatings. Then, the effect of thickness ratio on stresses field of HDA/PEO coatings subjected to uniform normal contact load was investigated by finite element method. Results show that the surface tensile stress is mainly affected by the thickness ratio of Al layer when the total thickness of coating is unchanged. With the increase of Al layer thickness, the surface tensile stress rises quickly. When Al2O3 layer thickness increases, surface tensile stress is diminished. Meanwhile, the maximum shear stress moves rapidly towards internal part of HDA/PEO coatings. Shear stress at the Al2O3 /Al interface is minimal when Al2O3 layer and Al layer have the same thickness.

考虑弯曲空间效应影响的箱梁强迫振动分析

选取附加挠度为剪力滞广义位移,箱梁体系总动能中计入剪力滞附加变形的影响,综合运用薄壁结构弹性理论和Hamilton原理,建立考虑弯曲空间效应影响的箱梁强迫振动控制微分方程及边界条件,并给出任意简谐荷载作用下简支和连续箱梁的强迫振动解析解。引入振动频率影响的应力和挠度放大系数,详细分析简支、连续箱梁剪切剪力滞效应在初等梁结果中的占比及放大系数分布规律。算例分析表明:考虑弯曲空间效应影响的箱梁截面纵向动应力与有限元结果吻合良好;振动频率越大,应力和挠度放大系数、剪切效应占比越大,剪力滞效应占比越小;同频率振动时,简支箱梁放大系数远大于两跨连续箱梁(单跨长等于简支跨长),且频率越高,差值比越大;基频内振动时,箱梁纵向应力计算可忽略剪力滞效应,挠度计算需考虑剪切变形的影响。

天然裂缝产状对水力压裂施工压力的影响

天然裂缝产状是影响裂缝壁面法向应力及切向应力的重要参数,而天然裂缝应力状态是决定地面施工压力大小的重要因素,准确计算、预测施工压力大小对水力压裂设计与施工有着重要的作用。根据天然裂缝产状和地层地应力状态,基于裂缝起裂与延伸准则,建立地面施工压力计算模型,并利用实际裂缝型储层进行计算分析。研究发现:正断层与走滑断层中,倾角越小施工压力越小,正断层中方位角越趋近于0°、180°、360°时施工压力越小;走滑断层中方位角越趋近于90°、270°时施工压力越小。逆断层中,当方位角为0°~45°、135°~225°、315°~360°时,倾角越大施工压力越大,当方位角为45°~135°、225°~315°时,倾角越大施工压力越小;同一倾角下,方位角在0°~90°、180°~270°范围内时,施工压力随方位角增大而减小,方位角在90°~180°、270°~360°范围内时,施工压力随方位角增大而增大。根据天然裂缝产状准确计算施工压力大小,可为现场压裂施工参数选择与优化提供理论依据。

储粮仓仓壁动态侧压力的树模型预测方法

针对储粮仓卸料时仓壁动态侧压力难以准确预测的问题,利用机器学习方法中的树模型建立了仓壁动态侧压力预测模型。首先,分析了仓壁动态侧压力的主要影响因素为筒仓的结构尺寸、贮料的物理参数及测点位置。利用收集的496组仓壁动态侧压力数据,构建机器学习预测模型的数据集。然后,基于树模型,建立了仓壁动态侧压力的决策树(decision tree,DT)预测模型,在此基础上,利用Bagging算法和Boosting算法,建立了仓壁动态侧压力的随机森林(random forest,RF)预测模型和梯度提升树(gradient boosting decision tree,GBDT)预测模型。通过对比3种预测模型在测试集的均方误差(mean-square error,MSE)、决定系数和相对误差,表明GBDT预测模型的泛化性能最优。最后,通过开展模型试验和数值模拟,对GBDT预测模型进行验证,结果表明拟合良好。同时,根据树模型的分枝原理,判断出仓壁动态侧压力影响因素的重要性,得到对于贮料的物理参数,密度的重要性排第一;对于筒仓的结构尺寸,卸料口尺寸排第一。因此,在进行储粮仓设计时,建议优先考虑仓内散体物料的密度和仓的卸料口尺寸。

土工格室加筋正常固结粉质黏土应力应变响应

土工格室加筋正常固结粉质黏土对工程建设意义重大。基于土工格室与填土的相互作用机制和增量法,采用弹塑性理论、邓肯-张双曲线模型、修正剑桥屈服函数以及剪胀方程,推导了土工格室加筋正常固结黏土的应力应变响应计算模型,进行了土工格室加筋正常固结黏土的三轴固结排水剪切试验,实测不同围压下的应力应变关系,采用三轴试验结果验证了所提理论模型的正确性和可靠性。此外,采用所提理论模型进行了参数敏感分析,研究了填土的力学性质参数、格室的网格尺寸和力学性质参数对于加筋土应力应变响应的影响。研究结论表明,与砂砾料相似,土工格室约束作用对于正常固结黏土的内摩擦角影响较小,而黏聚力有所增加;随着轴向应变的增加或围压的减小,加筋效果逐渐明显;加筋正常固结黏土的强度和刚度随着非线性弹性常数k的增加、强度参数φ的增加和Rf的减小而增大,常数n对于加筋土应力应变响应影响较小。本研究成果可为工程建设提供理论借鉴。

Behavior of interfacial stresses between RC beams and GFRP sheets

Seven reinforced concrete （RC） beams with epoxy-bonded glass fiber reinforced plastic （GFRP） sheets and two control RC beams were experimentally tested to investigate the bond behavior of the interfaces between RC beams and GFRP sheets. The variable parameters considered in test beams are the layers of GFRP sheets, the bond lengths and the reinforcement ratios. The results indicate that the flexural strength of the repaired beams is increased, but the ultimate load of beams with GFRP sheets debonding failure is reduced relatively. The bond length is the main factor that results in bonding failure of the strengthened beams. An experimental method of interfacial shear stress is proposed to analyze the distribution of shear stress according to experimental results. The analytical method of shear and normal stresses and a simple equation are proposed to predict the peeling loads. The proposed model is applied to experimental beams. The analytical results show a good agreement with the experimental results.