Deformation Localization-A Review on the Maximum-Effective-Moment(MEM) Criterion

The essential difference in the formation of conjugate shear zones in brittle and ductile deformation is that the intersection angle between brittle conjugate faults in the contractional quadrants is acute （usually ～60°） whereas the angle between conjugate ductile shear zones is obtuse （usually 110°）. The Mohr-Coulomb failure criterion, an experimentally validated empirical relationship, is commonly applied for interpreting the stress directions based on the orientation of the brittle shear fractures. However, the Mohr-Coulomb failure criterion fails to explain the formation of the low-angle normal fault, high-angle reverse fault, and the conjugate strike-slip fault with an obtuse angle in the ~1 direction. Although it is ten years since the Maximum-Effective-Moment （MEM） criterion was first proposed, and increasingly solid evidence in support of it has been obtained from both observed examples in nature and laboratory experiments, it is not yet a commonly accepted model to use to interpret these anti- Mohr-Coulomb features that are widely observed in the natural world. The deformational behavior of rock depends on its intrinsic mechanical properties and external factors such as applied stresses, strain rates, and temperature conditions related to crustal depths. The occurrence of conjugate shear features with obtuse angles of -110~ in the contractional direction on different scales and at different crustal levels are consistent with the prediction of the MEM criterion, therefore -110° is a reliable indicator for deformation localization that occurred at medium-low strain rates at any crustal levels. Since the strain-rate is variable through time in nature, brittle, ductile, and plastic features may appear within the same rock.

Study on the Criterion of the Correlation between Deformation Precursors and Earthquakes

The relationship between pre-seismic anomalous changes and earthquakes is one of the most basic information to comprehend the process of earthquake preparation and conduct earthquake prediction research.However,few researchers have carried out relevant investigations for a long time.In this paper,the distribution characteristics of deformation anomalies before the Wenchuan earthquake are analyzed,and the widespread distribution area is discussed.Based on previous studies,we improve the relationship between anomaly duration t and magnitude M by introducing distance D.The new model is characterized by lower magnitude fitting error,making it possible to establish the correlation between deformation precursors and earthquakes.The correlation standard between precursors and earthquakes here is defined as Niu's criterion,which is applied to analyze and interpret the relationship between the shortterm anomalies of Hongliuxia fault leveling and the Wenchuan and Jiuzhaigou earthquakes.

Size-dependent thermomechanical vibration characteristics of rotating pre-twisted functionally graded shear deformable microbeams

A three-dimensional(3D)thermomechanical vibration model is developed for rotating pre-twisted functionally graded(FG)microbeams according to the refined shear deformation theory(RSDT)and the modified couple stress theory(MCST).The material properties are assumed to follow a power-law distribution along the chordwise direction.The model introduces one axial stretching variable and four transverse deflection variables including two pure bending components and two pure shear ones.The complex modal analysis and assumed mode methods are used to solve the governing equations of motion under different boundary conditions(BCs).Several examples are presented to verify the effectiveness of the developed model.By coupling the slenderness ratio,gradient index,rotation speed,and size effect with the pre-twisted angle,the effects of these factors on the thermomechanical vibration of the microbeam with different BCs are investigated.It is found that with the increase in the pre-twisted angle,the critical slenderness ratio and gradient index corresponding to the thermal instability of the microbeam increase,while the critical material length scale parameter(MLSP)and rotation speed decrease.The sensitivity of the fundamental frequency to temperature increases with the increasing slenderness ratio and gradient index,and decreases with the other increasing parameters.Moreover,the size effect can suppress the dynamic stiffening effect and enhance the Coriolis effect.Finally,the mode transition is quantitatively demonstrated by a modal assurance criterion(MAC).

Strength and deformation behaviour of coarse-grained soil by true triaxial tests

In order to investigate the influence of intermediate principal stress on the stress-strain and strength behaviour of a coarse-grained soil, a series of true triaxial tests were performed. The tests were conducted in a recently developed true triaxial apparatus with constant minor principal stress σ3 and constant value of intermediate principal stress ratio b=（σ2-σ3）/（σ1-σ3） （al is the vertical stress, and % is the horizontal stress）. It is found that the intermediate principal strain, ε2, increases from negative to positive value with the increase of parameter b from zero to unity under a constant minor principal stress. The minor principal strain, ε3, is always negative. This implies that the specimen exhibits an evident anisotropy. The relationship between b and friction angle obtained from the tests is different from that predicted by LADE-DUNCAN and MATSUOKA-NAKAI criteria. Based on the test results, an empirical equation of g（b） that is the shape function of the failure surface on re-plane was presented. The proposed equation is verified to be reasonable by comparing the predicted results using the equation with true triaxial test results of soils, such as coarse-grained soils in this study, sands and gravels in other studies.

Deformation and Densification Laws of Powder Cold Forging

The deformation and densification laws of preform upsetting and closed-die forging were researched based on experimental results of cold forging of deoxidized Fe powder sintering porous material under different initial conditions such as friction factor, ratio between height and diameter and relative density. The fracture limit criteria＂ for powder cold-forging upsetting and the limit strain curve were achieved. The effect of friction facto,, ratlt, between height and diameter and relative density on fracture strain limitation was emphatically analyzed. The limit process parameter curves for the deformation of upsetting were also confirmed. Laws of deformation, densification and density distribution for closed-die forging of powder perform during cold-forging were further analyzed and discussed with the help of experimental phase analysis. As a result, this experiment established theoretical foundations for the design of preform and die as well as optimization of technological process parameters.

Limestone mechanical deformation behavior and failure mechanisms： a review

In this paper, several mechanical deformation curves of limestone are reviewed, and the effects of temperature, confining pressure, and fluid are discussed. Generally, Mohr–Coulomb is used for limestone brittle fracture. The characteristic of low temperature cataclastic flow and the conditions and constitutive equations of intracrystal plastic deformation such as dislocation creep,diffusion creep, and superplastic flow are discussed in detail. Specifically, from the macroscopic and microscopic view, inelastic compression deformation(shear-enhanced compaction) of large porosity limestone is elaborated.Compared with other mechanics models and strength equations, the dual porosity(macroporosity and microporosity) model is superior and more consistent with experimental data. Previous research has suffered from a shortage of high temperature and high pressure limestone research; we propose several suggestions to avoid this problem in the future:(1) fluid-rock interaction research;(2) mutual transition between natural conditions and laboratory research;(3) the uniform strength criterion forshear-enhanced compaction deformation;(4) test equipment; and(5) superplastic flow mechanism research.

考虑T应力及裂隙参数的岩体压剪断裂准则

针对压剪作用下裂隙面将发生闭合及摩擦滑移的特点,首先基于Muskhelishvili复变函数理论,建立了压剪作用下裂隙岩体的Kolossoff-Muskhelishvilli应力函数,并求得考虑裂隙3类参数(即几何参数、摩擦强度参数和变形参数)的裂隙尖端应力强度因子K和3个T应力分量的计算公式;其次,将其代入经典的最大周向应力准则,得到考虑裂隙尖端T应力及裂隙3类参数的修正最大周向应力准则;同时该准则认为裂隙法向及切向刚度与裂隙面受力特征密切相关,而非定值,并给出了不同裂隙倾角时的裂隙变形参数.最后,基于压剪作用下翼裂纹起裂角试验结果对该准则的合理性进行了初步验证,结果说明考虑裂隙变形参数是有必要的.

基于CFD方法的民用飞机缩比飞行试验尺度效应研究

缩比飞行试验在民用飞机的研制过程中日益受到重视,其尺度效应影响评估是设计缩比飞行试验工况的基础,也是确认飞行数据适用性的关键。基于几何和动力学相似准则,针对某民用飞机及其缩比验证机设计分析工况组,采用计算流体力学方法研究相似准则参数(马赫数Ma、雷诺数Re、弗劳德数Fr)对气动载荷、典型气动导数及弹性变形的影响。研究结果表明,在动力学相似时,验证机与原型机间的气动特性差异主要来源于马赫数,雷诺数影响较小;当原型机以中低马赫数(Ma<0.5)飞行时,此时马赫数压缩效应不明显,验证机与原型机具有近似的展向与弦向载荷分布特征,典型稳定导数及操纵导数差异约10%,在控制律设计鲁棒性范围内;进一步保持质量与刚度分布相似时,机翼翼尖扭转变形差异不超过0.5°,挠度差异不超过0.5%,在工程上属于可接受的范围。

新华滑坡变形演化规律与预警判据

为揭示四川省泸定县新华滑坡在水库蓄水、库水位波动以及季节性降雨综合作用下的变形演化规律,探讨其在多因素耦合作用下滑坡岩土体强度劣化的渐进累积效应。基于对水电工程库区新华滑坡的现场调查及多源长序列监测数据分析,并结合滑坡累计位移-时间(S-t)曲线3阶段演化特征与新华滑坡实测S-t曲线,对该滑坡3个阶跃性变形周期的演化阶段进行了判识与划分,同时采用改进的切线角方法进行了计算与分析,构建了以改进切线角预警阈值为依据的新华滑坡分级预警定量划分标准。研究结果表明,水库蓄水初期水位的短期大幅度上升、水库运行期的水位快速下降及季节性强降雨影响是新华滑坡变形加速的主要诱因。根据分析与探讨,改进切线角预警阈值能在一定程度上为辨别新华滑坡现阶段的稳定状态与潜在风险提供指导,但仍应考虑多重预警指标并综合滑坡体宏观变形破坏迹象进行判定。

Health diagnosis of ultrahigh arch dam performance using heterogeneous spatial panel vector model

Currently,more than ten ultrahigh arch dams have been constructed or are being constructed in China.Safety control is essential to long-term operation of these dams.This study employed the flexibility coefficient and plastic complementary energy norm to assess the structural safety of arch dams.A comprehensive analysis was conducted,focusing on differences among conventional methods in characterizing the structural behavior of the Xiaowan arch dam in China.Subsequently,the spatiotemporal characteristics of the measured performance of the Xiaowan dam were explored,including periodicity,convergence,and time-effect characteristics.These findings revealed the governing mechanism of main factors.Furthermore,a heterogeneous spatial panel vector model was developed,considering both common factors and specific factors affecting the safety and performance of arch dams.This model aims to comprehensively illustrate spatial heterogeneity between the entire structure and local regions,introducing a specific effect quantity to characterize local deformation differences.Ultimately,the proposed model was applied to the Xiaowan arch dam,accurately quantifying the spatiotemporal heterogeneity of dam performance.Additionally,the spatiotemporal distri-bution characteristics of environmental load effects on different parts of the dam were reasonably interpreted.Validation of the model prediction enhances its credibility,leading to the formulation of health diagnosis criteria for future long-term operation of the Xiaowan dam.The findings not only enhance the predictive ability and timely control of ultrahigh arch dams'performance but also provide a crucial basis for assessing the effectiveness of engineering treatment measures.

缓倾软岩隧道底部结构劣化因素及影响机制分析

【目的】探明缓倾软岩隧道底部结构劣化的影响因素及影响机制,研究在不同围岩强度、岩层产状、地应力作用下的缓倾软岩隧道底部变形及塑性区发展趋势。【方法】基于Hoek-Brown强度准则和遍布节理本构模型确定数值模拟的力学参数并构建开挖模型,通过改变Hoek-Brown参数、岩层产状、地应力状态分析隧道的变形规律。【结果】深埋缓倾软岩隧道拱底两侧具有明显非对称变形,随着Hoek-Brown参数和围岩强度的提高,隧道拱底隆起量不断降低,且拱底两侧的非对称变形有所减弱并趋向于对称变形。当围岩强度较低时,围岩混合剪切型塑性区主要分布在拱底,基体剪切破坏主要分布在边墙,且剪切破坏范围随围岩强度的提高呈不断减小趋势。在倾角为0°~30°条件下,随着岩层倾角的增大,隧道底部隆起呈不断减小趋势,且拱底塑性区分布深度逐渐减小。随着岩层倾向角增大,隧道底部非对称变形和变形量增加,且拱底混合剪切塑性破坏区不断向深处延伸。随着侧压力系数和隧道埋深的增大,隧道仰拱处的变形量和变形速率比其他位置的大,且埋深的改变主要影响围岩塑性区体积和分布深度,而侧压力系数的改变还影响塑性区的分布形态。【结论】缓倾软岩隧道的变形发展趋势和塑性区破坏模式均与岩层产状有关,缓倾角条件下的拱底变形较大,且围岩节理剪切破坏主要发生在岩层倾斜方向上。该研究结果可为类似工程在施工过程中确定不利变形位置及优化支护方案提供参考。

Deformation control criterion of shield tunnel under lateral relaxation of soft soil

Metro shield tunnels under the lateral relaxation of soil(LRS)are susceptible to significant lateral deformations,which jeopardizes the structural safety and waterproofing.However,deformation control standards for such situations have not been clearly defined.Therefore,based on a specific case,a model test is conducted to realize the LRS of a shield tunnel in a sandy stratum to reveal its effect on segment liners.Subsequently,a deformation control criterion is established.The LRS is simulated by linearly reducing the loads applied to the lateral sides of the segment structure.During lateral unloading,the lateral earth pressure coefficient on the segment decreases almost exponentially,and the structural deformation is characterized by horizontal expansion at the arch haunches and vertical shrinkage at the arch vault and arch bottom.Based on the mechanical pattern of the segment structure and the acoustic emission,the deformation response of a segment can be classified into three stages:elastic and quasi-elastic,damage,and rapid deformation development.For a shield tunnel with a diameter of approximately 6 m and under the lateral relaxation of sandy soil,when the ellipticity of the segment is less than 2.71%,reinforcement measures are not required.However,the segment deformation must be controlled when the ellipticity is 2.71%to 3.12%;in this regard,an ellipticity of 3%can be used as a benchmark in similar engineering projects.

The Hoeke-Brown failure criterion and GSI-2018 edition

The HoekeBrown criterion was introduced in 1980 to provide input for the design of underground excavations in rock.The criterion now incorporates both intact rock and discontinuities,such as joints,characterized by the geological strength index(GSI),into a system designed to estimate the mechanical behaviour of typical rock masses encountered in tunnels,slopes and foundations.The strength and deformation properties of intact rock,derived from laboratory tests,are reduced based on the properties of discontinuities in the rock mass.The nonlinear HoekeBrown criterion for rock masses is widely accepted and has been applied in many projects around the world.While,in general,it has been found to provide satisfactory estimates,there are several questions on the limits of its applicability and on the inaccuracies related to the quality of the input data.This paper introduces relatively few fundamental changes,but it does discuss many of the issues of utilization and presents case histories to demonstrate practical applications of the criterion and the GSI system.

A Generalized Yield Criterion

A generalized yield criterion is proposed based on the metai plastic deformation mechanics and the fundamental formula in theory of plasticity. Using the generalized yield criterion, the reason is explained that Mises yield criterion and Tresca yield criterion do not completely match with experimental data. It has been shown that the yield criteria of ductile metals depend not only on the quadratic invariant of the deviatoric stress tensor J2, but also on the cubic invariant of the deviatoric stress tensor J3 and the ratio of the yield stress in pure shear to the yield stress in uniaxial tension κ/σs. The reason that Mises yield criterion and Tresca yield criterion are not in good agreement with the experimental data is that the effect of J3 and κ/σs is neglected.

Anisotropy of strength and deformability of fractured rocks

Anisotropy of the strength and deformation behaviors of fractured rock masses is a crucial issue for design and stability assessments of rock engineering structures, due mainly to the non-uniform and non- regular geometries of the fracture systems. However, no adequate efforts have been made to study this issue due to the current practical impossibility of laboratory tests with samples of large volumes con- taining many fractures, and the difficulty for controlling reliable initial and boundary conditions for large-scale in situ tests. Therefore, a reliable numerical predicting approach for evaluating anisotropy of fractured rock masses is needed. The objective of this study is to systematically investigate anisotropy of strength and deformability of fractured rocks, which has not been conducted in the past, using a nu- merical modeling method. A series of realistic two-dimensional （2D） discrete fracture network （DFN） models were established based on site investigation data, which were then loaded in different directions, using the code UDEC of discrete element method （DEM）, with changing confining pressures. Numerical results show that strength envelopes and elastic deformability parameters of tested numerical models are significantly anisotropic, and vary with changing axial loading and confining pressures. The results indicate that for design and safety assessments of rock engineering projects, the directional variations of strength and deformability of the fractured rock mass concerned must be treated properly with respect to the directions of in situ stresses. Traditional practice for simply positioning axial orientation of tunnels in association with principal stress directions only may not be adequate for safety requirements. Outstanding issues of the present study and su^zestions for future study are also oresented.

基于DEFORM-3D的微型螺钉冷成形过程有限元分析

典型的螺钉头部成形过程包括镦粗(预成形)和冲槽(最终成形)两个工步,是个比较复杂成形过程。特别是冲槽阶段,镦粗和反挤压同时进行的,情况更为复杂。利用非线形有限元分析软件DEFORM-3D对微型螺钉冷塑性成形过程进行仿真,可以获得成形过程中的应变、应力、材料流动情况,同时还可以对成形过程中的缺陷如折叠、裂纹,进行预测,从而为工艺的设计和改进提供信息。

基于约束收敛法的Hoek-Brown岩体巷道大变形分析

轴对称圆形巷道的弹塑性理论分析是深部软岩巷道施工过程的基础问题和重要问题。基于约束收敛法、有限变形次弹塑性理论、Hoek-Brown破坏准则、应变软化本构模型等基本理论,开展了深埋软弱围岩圆形巷道开挖诱致挤压大变形现象的基础研究。在相关大变形研究的基础上,以巷道开挖后围岩脆塑性解析解来表征岩体应变软化区划分圆环岩体响应解析解的方法,简述Hoek-Brown岩体深埋软岩巷道围岩各分区应力与变形解析解求解思路。通过现场监测数据和不同力学模型的计算结果分别进行模型有效性对比验证,并对m、s、a等岩体强度相关参数进行了影响分析。基于大变形和小变形理论下围岩特征曲线差别,提出软弱破碎岩体的支护建议,为深部不利赋存条件下软弱围岩支护工程设计提供理论分析手段和指导。

冻结硫酸钠粉质黏土强度与本构模型研究

为了研究冻结硫酸钠粉质黏土的变形规律和强度特征,在1 MPa围压下,对-2、-6、-10℃三组温度下不同硫酸钠含量的粉质黏土进行负温三轴剪切试验研究。基于实验数据,计算了冻结硫酸钠粉质黏土的切线模量,研究了轴向应变与偏应力的非线性关系,推导了试样的p-q平面强度准则,提出了冻结硫酸钠盐粉质黏土强度公式,建立了含参数的冻结含盐粉质黏土的修正Duncan-Chang本构模型,并拟合了相关参数,验证了模型精度及适用性。结果表明:试样的偏应力在应变后期趋于稳定,处于向应变硬化过渡的阶段,切线模量E随含盐量的增加呈现先减小再增大再减小的变化规律,切线模量E变化幅度较小,p、q呈明显的线性关系,在0℃至-15℃温度范围内,修正Duncan-Chang本构模型对含盐量小于2.5%的冻结硫酸钠粉质黏土强度具有良好的预测效果。

高面板砂砾石坝堆石料力学变形特性及坝体分区研究

随着高混凝土面板砂砾石坝坝高的突破,坝体内部高应力区和坝坡、坝顶低应力区的应力差别增大,而不同应力条件下砂砾石料和块石料的力学特性存在较大差异,将影响着坝体分区及变形安全。开展砂砾石料和块石料三轴力学试验,研究不同应力条件对其力学变形特性的影响;在此基础上根据坝体应力分布特征,研究高混凝土面板砂砾石坝坝体分区。研究表明,在低围压条件下,块石料的模量系数大于砂砾石料;随着围压增加到一定程度,块石料颗粒破碎导致模量系数大幅降低,远小于砂砾石料的模量系数;为充分利用两种堆石料的力学变形特性,加强高面板砂砾石坝坝体变形控制,坝体内高、低应力区应分别采用砂砾石料和块石料填筑,提出一种基于坝体应力分布特征的坝体分区准则和优化调整方法;最终推荐一种块石料半包砂砾石料的坝体分区型式,提高了高混凝土面板砂砾石坝的综合安全性。

对称X型裂隙类岩体的力学特性及破坏机制研究

为了研究对称X型裂隙对岩石力学特性及破坏机制的影响,对预制对称X型裂隙类岩体试件进行单轴压缩试验和数值模拟分析。结果表明:1)预制裂隙角度影响裂隙尖端的受力状态,是试件裂纹起裂特征和破坏模式的主要因素;2)对比完整试件,裂隙试件的应力-应变曲线峰前出现应力下降现象,峰后表现为延性下降,且峰值强度、弹性模量和弹性应变能明显下降,表明试件的力学特性和能量特征对预制裂隙的敏感性高;3)当0°<α<90°时,随着预制裂隙角度α的增大,Ke和T应力值减小,裂纹尖端抵抗开裂的能力增强,裂隙试件峰值应力增大,且裂尖抵抗Ⅰ和Ⅱ型断裂能力的强弱是造成裂隙试件破坏模式差异的主要原因。