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.

An anisotropic constitutive model of geomaterials based on true triaxial testing and its application

Series of testing on coarse grained soils were carried out with a true triaxial testing apparatus. The loads were applied from the major principal and minor principal directions, respectively, to simulate the construction and water impounding process of a rock fill dam. The stress and strain relationships induced by the different loading methods were investigated. A remarkable stress-induced anisotropy under complex stress state was observed. Contrary to popular assumptions in traditional numerical analysis and constitutive models, it was found that different elastic modulus and Poisson ratio exist in different principal directions in rock fill dams. From the testing results, an anisotropic constitutive model based on Duncan-Chang nonlinear model is presented to overcome the limitations of axi-symmetric assumptions in conventional triaxial experiments and constitutive models. Both models were then applied in FEM analysis of an under-construction earth core high rock soil filled dam with the focus on hydraulic fracturing. The study reveals the major biases that exist when numerical analysis and constitutive models do not give serious consideration to the intermediate principal stress and anisotropy effects in soil rock built structures.

Intermittent disturbance mechanical behavior and fractional deterioration mechanical model of rock under complex true triaxial stress paths

Mechanical excavation,blasting,adjacent rockburst and fracture slip that occur during mining excavation impose dynamic loads on the rock mass,leading to further fracture of damaged surrounding rock in three-dimensional high-stress and even causing disasters.Therefore,a novel complex true triaxial static-dynamic combined loading method reflecting underground excavation damage and then frequent intermittent disturbance failure is proposed.True triaxial static compression and intermittent disturbance tests are carried out on monzogabbro.The effects of intermediate principal stress and amplitude on the strength characteristics,deformation characteristics,failure characteristics,and precursors of monzogabbro are analyzed,intermediate principal stress and amplitude increase monzogabbro strength and tensile fracture mechanism.Rapid increases in microseismic parameters during rock loading can be precursors for intermittent rock disturbance.Based on the experimental result,the new damage fractional elements and method with considering crack initiation stress and crack unstable stress as initiation and acceleration condition of intermittent disturbance irreversible deformation are proposed.A novel three-dimensional disturbance fractional deterioration model considering the intermediate principal stress effect and intermittent disturbance damage effect is established,and the model predicted results align well with the experimental results.The sensitivity of stress states and model parameters is further explored,and the intermittent disturbance behaviors at different f are predicted.This study provides valuable theoretical bases for the stability analysis of deep mining engineering under dynamic loads.

Microdynamic mechanical properties and fracture evolution mechanism of monzogabbro with a true triaxial multilevel disturbance method

The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters.However,the mechanical properties and damage/fracture evolution mechanisms of deep rock induced by microdynamic disturbance under three-dimensional stress states are unclear.Therefore,a true triaxial multilevel disturbance test method is proposed,which can completely simulate natural geostress,excavation stress redistribution(such as stress unloading,concentration and rotation),and subsequently the microdynamic disturbance triggering damaged rock failure.Based on a dynamic true triaxial test platform,true triaxial microdynamic disturbance tests under different frequency and amplitudes were carried out on monzogabbro.The results show that increasing amplitude or decreasing frequency diminishes the failure strength of monzogabbro.Deformation modulus gradually decreases during disturbance failure.As frequency and amplitude increase,the degradation rate of deformation modulus decreases slightly,disturbance dissipated energy increases significantly,and disturbance deformation anisotropy strengthens obviously.A damage model has been proposed to quantitatively characterize the disturbance-induced damage evolution at different frequency and amplitude under true triaxial stress.Before disturbance failure,the micro-tensile crack mechanism is dominant,and the micro-shear crack mechanism increases significantly at failure.With the increase of amplitude and frequency,the micro-shear crack mechanism increases.When approaching disturbance failure,the acoustic emission fractal dimension changes from a stable value to local large oscillation,and finally increases sharply to a high value at failure.Finally,the disturbance-induced failure mechanism of surrounding rock in deep engineering is clearly elucidated.

Experimental study of the dynamic mechanical responses and failure characteristics of coal under true triaxial confinements

Investigations on the dynamic mechanical properties and failure mechanisms of coal under in-situ stress is essential for the prevention of dynamic disasters in deep coal mines.Thus,a modified true triaxial Hopkinson bar was employed to explore the dynamic mechanical behaviors of coal at different confining pressures(0–20 MPa)and strain rates(40–220 s^(-1)).The results show that the dynamic peak stress is positively correlated with lateral static pre-stressσy andσz,but negatively correlated with axial static prestressσx.At approximate strain rates,increasing the lateral static pre-stress facilitates increasing the dynamic peak stress,but the minimum lateral static pre-stress is the primary factor limiting a significant increase in dynamic peak stress of coal.Furthermore,the dynamic differential stress is linearly related to the logarithm of strain rate,and the peak strain varies linearly with strain rate.However,there is no significant correlation between confining pressure and peak strain.Moreover,X-ray CT images and photographic fracture observations of coal samples show the failure patterns under uniaxial and triaxial conditions are splitting failure and shear failure,respectively.The device provides a viable approach for fully comprehending the dynamic mechanical behaviors of rock-like material in complex stress conditions.

New artificial neural networks for true triaxial stress state analysis and demonstration of intermediate principal stress effects on intact rock strength

Simulations are conducted using five new artificial neural networks developed herein to demonstrate and investigate the behavior of rock material under polyaxial loading. The effects of the intermediate principal stress on the intact rock strength are investigated and compared with laboratory results from the literature. To normalize differences in laboratory testing conditions, the stress state is used as the objective parameter in the artificial neural network model predictions. The variations of major principal stress of rock material with intermediate principal stress, minor principal stress and stress state are investigated. The artificial neural network simulations show that for the rock types examined, none were independent of intermediate principal stress effects. In addition, the results of the artificial neural network models, in general agreement with observations made by others, show （a） a general trend of strength increasing and reaching a peak at some intermediate stress state factor, followed by a decline in strength for most rock types; （b） a post-peak strength behavior dependent on the minor principal stress, with respect to rock type; （c） sensitivity to the stress state, and to the interaction between the stress state and uniaxial compressive strength of the test data by the artificial neural networks models （two-way analysis of variance; 95% confidence interval）. Artificial neural network modeling, a self-learning approach to polyaxial stress simulation, can thus complement the commonly observed difficult task of conducting true triaxial laboratory tests, and/or other methods that attempt to improve two-dimensional （2D） failure criteria by incorporating intermediate principal stress effects.

Shear failure behaviors and degradation mechanical model of rockmass under true triaxial multi-level loading and unloading shear tests

The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stress σ_(n) and lateral stressσ_(p)to investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσ_(n)and σ_(p),the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσ_(n),while they first increase and then gradually decrease asσ_(p)increases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσ_(n),but shows no significant change withσ_(p).Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion c_(jp),friction angleφ_(jp),and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσ_(n)andσ_(p),G first rapidly decreases and then tends to stabilize;cjp,φ_(jp),andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.

Study on fracture propagation behavior in ultra-heavy oil reservoirs based on true triaxial experiments

As the ultra-heavy oil reservoirs developed by steam assisted gravity drainage(SAGD)in the Fengcheng oilfield,Xinjiang have problems such as huge steam usage,long preheating period,low production,and inaccessible reserve in local parts.Based on the rock mechanics and porosity/permeability characteristics of heavy oil reservoir and interlayer,a series of true triaxial experiments and CT tests considering the fracturing fluid injection rate,viscosity,perforation density and location of fracture initiation were conducted to disclose the propagation behavior of micro-and macro-fractures in the reservoirs and mudstone interlayers.These experiments show that fracturing in the heavy oil reservoirs only generates microfractures that cannot break the interlayer.In contrast,when fracturing in the interlayer,the higher the injection rate(greater than 0.6 m^3/min),the lower the viscosity,the easier it is to form macro-fractures in the interlayers,and the further the fractures will propagate into the reservoirs.Also,increasing perforation density tends to create complex macro-fracture network in the interbedded reservoirs and mudstone interlayers.The findings of this study can provide scientific guidance for the selection of fracturing layer and the optimization of parameters in the interlayer fracturing of heavy oil reservoirs.

复杂应力条件下粗粒料的剪胀性研究进展

粗粒料的剪胀性是其强度和变形研究的重要问题之一,它取决于颗粒排列、粒间压力等细微观作用;在宏观层面,受相对密度与应力状态的影响。围绕复杂应力条件下粗粒料的剪胀问题,从粗粒料力学特性的试验研究、粗粒料的剪胀性强度准则以及临界状态与剪胀性方面,对国内外的研究进展进行了系统论述。在此基础上,提出该领域呈现如下发展态势:①通过大型真三轴试验开展粗粒料剪胀率的试验研究与理论分析,能够促进粗粒料本构理论的发展进步;②结合应力路径试验中的应力变形规律研究,可实现从常规三轴条件下向复杂应力条件下的剪胀方程的进一步发展,从而体现强度与变形问题的统一;③采用状态参量去评价土体的松密状态与剪胀性,能够耦合应力状态与孔隙比,尽量避免“一种材料,多组参数”。研究结果表明状态参量和应力路径相结合的方法,使得粗粒料的力学特性研究更加具有科学性和系统性。

基于真三轴试验装置的岩石渗流密封方式改进及实验研究

国内现有的非常规油气储层的渗透性测试大多采用圆柱试样,通过假三轴试验装置进行测试,而真三轴条件下立方体试件棱边大多存在棱边串流与端面密封不严的缺陷。基于现有真三轴试验装置,以及大量的实验经验,针对现有的立方体试件单橡胶套渗流密封方式进行改进。介绍了嵌套式“上下密封套”结构特征,特别对棱边区的密封进行了设计,提出了密封套顶-底端面凹陷型内嵌“单孔网槽导流板”结构设计,并对顶部传压板的尺寸进行了讨论。对100 mm×100 mm×100 mm立方体煤样进行了真三轴渗流试验分析,得到了不同入口渗透压力真三轴围压条件下的渗透率。该密封方法的改进有助于提高科研单位及测试中心对原位地应力条件下非常规油气储层渗透性测试精度,并提高高端科研人才的实践创新能力与科研素养。

基于真三轴卸载试验不同倾角组合煤岩力学特性研究

为深入研究煤炭开采过程中顶板结构面倾角对煤岩力学特性的影响,通过自主研发的地声过程模拟试验系统,开展不同结构面倾角条件下组合煤岩真三轴加卸载试验,并利用声发射探测系统进行监测。研究结果表明:随着结构面倾角的增大,试样的破坏强度逐步下降,裂隙发展也逐渐减弱,其破坏形态从张拉剪切破坏逐渐向剪切破坏转变,直至倾角达到40°时,试样整体发生滑移破坏;在卸载破坏前,倾角<30°的试样发生充分的塑性变形,其承载力得到充分发挥,而倾角≥30°的试样达到临界破坏极限时迅速破坏,出现部分或完全滑移破坏;声发射信号集中于卸载破坏阶段,试样的结构面倾角越大,声发射累计计数越少,当倾角达到40°时发生滑移破坏,最大振铃计数大幅下降,对其累计计数略有影响。研究成果可为深入认识顶板结构面倾角引起的卸载破坏机制及矿山安全开采提供参考。

A generalized nonlinear three-dimensional Hoek‒Brown failure criterion

To understand the strengths of rocks under complex stress states,a generalized nonlinear threedimensional(3D)Hoek‒Brown failure(NGHB)criterion was proposed in this study.This criterion shares the same parameters with the generalized HB(GHB)criterion and inherits the parameter advantages of GHB.Two new parameters,b,and n,were introduced into the NGHB criterion that primarily controls the deviatoric plane shape of the NGHB criterion under triaxial tension and compression,respectively.The NGHB criterion can consider the influence of intermediate principal stress(IPS),where the deviatoric plane shape satisfies the smoothness requirements,while the HB criterion not.This criterion can degenerate into the two modified 3D HB criteria,the Priest criterion under triaxial compression condition and the HB criterion under triaxial compression and tension condition.This criterion was verified using true triaxial test data for different parameters,six types of rocks,and two kinds of in situ rock masses.For comparison,three existing 3D HB criteria were selected for performance comparison research.The result showed that the NGHB criterion gave better prediction performance than other criteria.The prediction errors of the strength of six types of rocks and two kinds of in situ rock masses were in the range of 2.0724%-3.5091%and 1.0144%-3.2321%,respectively.The proposed criterion lays a preliminary theoretical foundation for prediction of engineering rock mass strength under complex in situ stress conditions.

真三轴单面卸荷条件下中间主应力对深埋洞室岩爆影响特征

岩爆灾害已成为国内外深埋洞室建设的重大安全隐患。利用新型真三轴岩爆试验系统,开展了不同中间主应力下“单面侧向卸荷-三向五面受力-竖向持续加载”的室内物理模拟试验,对比分析了不同中间主应力下岩样的弹射破坏过程、破坏形态特征、声发射特性、碎块特征以及弹射动能等变化规律;基于三维离散元理论和多晶建模技术(随机生成Voronoi矿物晶粒),研究了真三轴单面卸荷条件下岩爆“孕育—发生—发展—破坏”全过程及能量演化特征。研究结果表明:不同中间主应力下岩爆弹射破坏过程可概括为颗粒局部弹射、岩石劈裂成板、板折断裂成块及块片全面弹射;其中,岩石劈裂成板是岩爆孕育过程中必然经历的破坏现象。岩样临空面破坏形态具有相似的多元分区破坏特征,即邻近临空面区域产生以张拉破坏为主的劈裂裂缝,远离临空面区域产生以剪切破坏为主的贯穿性斜裂缝。声发射撞击数演化过程可分为相对平稳阶段、快速上升阶段、整体破坏阶段及平静期阶段。随着中间主应力的不断增大,碎块的弹射动能呈增大的变化趋势。岩爆碎块多以粗粒、中粒与细粒碎块为主,且随中间主应力的增加,微粒碎块质量基本不变,细粒、中粒与粗粒碎块质量则呈平稳增加的趋势。利用考虑颗粒矿物成分的晶体尺度精细仿真模型(CSFM)模拟了岩爆“孕育—发生—发展—破坏”全过程,获得了岩样的应力-应变曲线,其变化趋势与室内试验测试结果基本一致且曲线吻合度较好。弹性应变能的演化曲线大致可分为早期增长速率递增阶段、近似线性增长阶段、屈服平台期间增长速率递减阶段及峰后急剧下降阶段。

考虑中间主应力效应的修正Hoek-Brown真三轴强度准则

为改善Hoek-Brown强度准则未考虑中间主应力对岩石强度的影响,通过岩石真三轴试验结果分析了岩石强度的演化规律,引入中间主应力系数,量化分析主应力系数对岩石真三轴强度的影响,考虑Hoek-Brown强度准则中的参数和岩石应力水平间的关联性,提出了基于拉格朗日插值方法的修正岩石真三轴Hoek-Brown强度准则,分析了其空间包络特征。最后,利用7种岩石的真三轴试验数据与其它3种真三轴强度准则进行最优拟合误差分析,探讨了修正强度准则的合理性。研究结果表明:岩石强度随着最小主应力的增加逐渐增大,随着中间主应力的增加则呈现先增大后减小的变化规律,表现出显著的区间效应;修正强度准则不仅能够继承Hoek-Brown强度准则在子午面上的非线性优点,且能够表征岩石强度在应力空间中的基本特性;线性和非线性插值形式的修正强度准则空间包络面分别为非等边的六棱锥面以及能够满足拉压子午面区间连续光滑要求的圆锥面;修正强度准则能够较好地预测岩石真三轴试验强度,较为合理地反映中间主应力对岩石强度的影响;相比于线性插值形式强度准则,二次插值形式强度准则能够提高岩石强度的预测精度1.2~2.0倍;相较于其他真三轴强度准则,修正强度准则对不同硬脆性岩石的真三轴试验结果均具有良好的强度预测精度,体现了修正强度准则的适用性和可靠性。

基于离散元的颗粒材料中应变局部化形成与演化研究

岩土颗粒材料的应变局部化失效问题广泛存在于工程设计应用中,主要表现为介观尺度上的应变局部化现象和宏观尺度上的剪切带产生,目前在微观尺度上的形成机理尚不明确。为了系统研究颗粒集合体的应变局部化的形成与演化过程,通过使用离散单元法(Discrete Element Method,DEM)模拟了指定平面应变加载路径的真三轴试验,获取了宏观和微观尺度上的颗粒材料几何、运动以及力学信息。为了找出表征应变局部化特性的最佳特征量,比较了颗粒温度、波动位移和局部剪胀角等微观指标,发现波动位移在表征应变局部化方面与其他参数相比相关性更好,并选定其作为应变局部化表征变量。为了量化颗粒集合体从应变局部化开始产生到发育完成的具体应变区间,采用莫兰指数对波动位移的空间分布特征进行统计和分析,确定了颗粒集合体在弹塑性转换阶段的发育区间。进一步对颗粒集合体应变局部化发育区间内的波动位移空间分布进行探究,并统计不同空间区域内波动位移的概率密度函数,发现研究区域外部的局部塑性在过渡阶段停止演化,而内部塑性以逾渗模式发展。最终,通过波动位移的空间分布进行聚类分析,获得了描述介观尺度上应变局部化的团簇体模型。该模型可以将颗粒集合体宏观剪切带的形成与发育和单个颗粒的微观塑性发展相联系,刻画颗粒集合体从介观尺度上的应变局部化出现到宏观尺度上剪切带完全形成的演化过程。

弱动力扰动作用下岩石微裂隙演化特征及灾害防控

【目的】高应力叠加弱动力扰动是诱发冲击地压的关键因素,但不同扰动幅值、频率、卸载范围下的岩石微裂纹扩展特征和能量耗散规律尚不明确,无法为冲击地压防治提供技术支撑。【方法】基于真三轴卸载动力扰动试验,分析了不同扰动幅值(5、10 MPa)、频率(4、10 Hz)、三向应力卸载(0、12MPa)下深部围岩失稳破坏规律,并结合SEM扫描分析了岩石微裂隙特征。通过锚杆拉拔试验,优化了锚杆肋间距和肋高,提高了其吸能支护作用,提出了“吸能锚杆-低阻抗混凝土注浆-喷浆-挂网”组合支护技术。利用传感器对巷道进行长期监测,得到治理前后压力与振动数据。【结果和结论】研究表明:(1)随着扰动幅值和频率的增加,裂纹增加显著且不规则,岩石断口的方向分形维数降低。当扰动为10MPa、10Hz时,分形维数降至最低值0.62,孔隙方向角80°~120°孔隙定向频率达到最大值的52%,约为原始岩石的1.68倍。说明岩石受扰动后颗粒的应力不均匀,导致应力集中,断裂方向明显。(2)随着扰动幅值和频率的增加,SEM图像的微孔隙面积先快速增加,后缓慢增加且增加趋势越来越小。扰动频率每增加2 Hz,岩石微裂隙面积增加约24.13%。(3)现场测试表明随着锚杆肋间距和肋高增加,拉拔曲线形态由“弹塑性阶段-破坏失效阶段-残余阶段”逐渐过渡为“弹塑性阶段-微量屈服阶段-大量强化阶段-破坏失效阶段-残余阶段”,肋间距48mm、肋高2mm的螺纹钢锚杆吸能效果最好。经现场监测可将巷道压力稳定在36 N左右,峰值加速度控制在8000mm/s^(2)以内。研究揭示了卸载动力扰动作用下围岩破坏及能量释放规律,提出的“吸能锚杆-低阻抗混凝土注浆-喷浆-挂网”支护技术,可为类似深部工程提供理论指导。

单面卸载条件下深埋圆形洞室围岩岩爆的试验模拟研究

为深入研究深部洞室开挖诱发邻近既有洞室围岩岩爆的发生过程和机制,采用真三轴电液伺服诱变试验系统对具有强岩爆倾向性的花岗岩开展试验研究,模拟500 m的三维应力状态。通过卸载洞室围岩单侧荷载模拟邻近洞室开挖,在围岩应力重分布作用下最终诱发岩爆,试验中借助监测设备实时观测洞壁的破坏现象。试验结果表明:(1)在单面卸载条件下,岩爆过程可分为6个阶段,即卸载后的应力重分布、准备期、第1轮岩屑弹射和剥落、平静期、第2轮岩屑弹射和剥落、剧烈破坏;(2)在卸荷作用的影响下,洞壁岩爆呈现出明显的时空特征和非对称性,表现为卸荷后洞室顶底部率先出现明显裂纹,在随后的持续加载过程中,远离卸载面一侧发生剧烈岩爆并形成沿轴向贯通的V型槽;(3)基于定义的滞后效应系数可知,与三向加载岩爆相比,单面卸载下的洞室岩爆具有更强的突然性,且极易导致洞室的整体垮塌。为预防该类型岩爆,邻近洞室开挖时应及时对既有洞室远离卸载面一侧进行支护和加固处理。

含层理砂岩真三轴条件下力学特性研究

为了研究层状砂岩的力学特性与各向异性特征,开展了不同层理倾角与不同中间主应力下的砂岩力学试验。对7种不同倾角(0。、15。、30。、45。、60。、75。、90。)的砂岩进行了3个不同中间主应力水平(10、100、160 MPa)的真三轴试验研究,探讨了层理面倾角对砂岩变形、强度和破坏模式的影响。结果表明,随着中间主应力的增加,砂岩的各向异性逐渐减弱,并趋于各向同性;在高中间主应力的条件下,杨氏模量和破坏角均随各向异性角的增加逐渐增大;峰值强度也受到中间主应力和层面倾角耦合作用的影响;在中间主应力较低的条件下,峰值强度表现出典型的U型变化,随着中间主应力的增加,U型曲线逐渐变得平坦。该研究结果对于指导深埋硬岩工程的设计和施工具有一定的参考意义。

110 kV复合绝缘横担结构设计及工程应用研究

为在输电线路中推广复合绝缘横担,以110 kV输电线路改造工程为背景,提出了一种线路用复合绝缘横担设计方法。从复合绝缘横担的大风、覆冰、安装及断线四种工况荷载计算着手,对复合绝缘横担开展结构设计。采用有限元软件建立两拉-两压结构形式的力学分析模型,在四种工况下对横担进行力学计算,通过力学真型实验验证了复合绝缘横担结构的稳定性和安全性。该方法设计的复合绝缘横担满足该线路安全运行要求,并成功挂网多条110 kV输电线路;针对不同线路塔型设计工作量大、生产周期长的问题,开展典型化设计工作是未来发展的趋势。

高强度螺栓材料全过程真实应力-应变关系研究

对极限状态下螺栓杆会发生较大变形的高强度螺栓连接节点进行模拟分析时,需考虑螺栓材料的真实应力-应变关系。为此,以10.9级M20,M24,M30高强度螺栓为研究对象,探讨单轴拉伸状态下高强度螺栓材料的全过程真实应力-应变关系。首先制作高强度螺栓材料拉伸试件并通过开展单轴拉伸试验获得材料的全过程工程应力-应变曲线。然后采用有限元方法对单轴拉伸试验进行模拟,通过比较有限元分析和实测工程应力-应变曲线,讨论描述材料真实应力-应变关系的Ludwik,Hollomon,Voce,Swift表达式的适用性。最后基于归一化的颈缩前真实应力-应变关系以及归一化的硬化阶段真实应力-应变关系,提出两种改进的Ramberg-Osgood表达式描述螺栓材料的全过程真实应力-应变关系。结果表明:基于颈缩前硬化阶段真实应力-应变曲线拟合的Ludwik,Hollomon,Voce,Swift表达式中,Ludwik,Hollomon,Swift表达式会高估螺栓材料颈缩后的真实应力,而Voce表达式会低估螺栓材料颈缩后的真实应力;本研究提出基于归一化颈缩前真实应力-应变关系的Ramberg-Osgood表达式可较为准确地描述高强度螺栓材料的全过程真实应力-应变关系,其在强化阶段会略高估螺栓材料的真实应力;提出的基于归一化硬化阶段真实应力-应变关系的Ramberg-Osgood表达式可更准确地描述高强度螺栓材料的全过程真实应力-应变关系。