Evolution of mechanical parameters of Shuangjiangkou granite under different loading cycles and stress paths

Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation.In this study,to reveal the mechanical parameters of deep surrounding rock under different stress paths,a new cyclic loading and unloading test method for controlled true triaxial loading and unloading and principal stress direction interchange was proposed,and the evolution of mechanical parameters of Shuangjiangkou granite under different stress paths was studied,including the deformation modulus,elastic deformation increment ratios,fracture degree,cohesion and internal friction angle.Additionally,stress path coefficient was defined to characterize different stress paths,and the functional relationships among the stress path coefficient,rock fracture degree difference coefficient,cohesion and internal friction angle were obtained.The results show that during the true triaxial cyclic loading and unloading process,the deformation modulus and cohesion gradually decrease,while the internal friction angle gradually increases with increasing equivalent crack strain.The stress path coefficient is exponentially related to the rock fracture degree difference coefficient.As the stress path coefficient increases,the degrees of cohesion weakening and internal friction angle strengthening decrease linearly.During cyclic loading and unloading under true triaxial principal stress direction interchange,the direction of crack development changes,and the deformation modulus increases,while the cohesion and internal friction angle decrease slightly,indicating that the principal stress direction interchange has a strengthening effect on the surrounding rocks.Finally,the influences of the principal stress interchange direction on the stabilities of deep engineering excavation projects are discussed.

Stress Path Analysis of Deep-Sea Sediments Under the Compression-Shear Coupling Load of Crawler Collectors

The mechanical properties of deep-sea sediments during the driving process of crawler collectors are essential factors in the design of mining systems.In this study,a crawler load is divided into a normal compression load and a horizontal shear load.Then,the internal stress state of sedimentary soil is examined through a theoretical calculation and finite element numerical simulation.Finally,the driving of crawlers is simulated by changing the relative spatial position between the load and stress unit,obtaining the stress path of the soil unit.Based on the calculation results,the effect of the horizontal shear load on the soil stress response is analyzed at different depths,and the spatial variation law of the soil stress path is examined.The results demonstrate that the horizontal shear load has a significant effect on the rotation of the principal stress,and the reverse rotation of the principal stress axis becomes obvious with the increase in the burial depth.The stress path curve of the soil is different at various depths.The spatial variation rule of the stress path of the shallow soil is complex,whereas the stress path curve of the deep soil tends to shrink as the depth increases.The stress path of the corresponding depth should be selected according to the actual research purpose and applied to the laboratory test.

EFFECT OF NON-PROPORTIONAL OVERLOADING ON FATIGUE CRACK GROWTH

The effect of proportional and non-proportional overloading on mode l fatigue crack growth have been studied,and the influences of crack tip plastic zone,crack tip blunting as well as crack closure were discussed.Proportional(model I)overloading may cause more serious crack growth retardation than non-proportional(mixed mode)overloading.Therefore,for estimating the fatigue life of engineering structures to simplify a real overload which may of- ten be non-proportional as a proportional one is not always safe.

Experimental Study on Non-proportional Multiaxial Strain Cyclic Characteristics and Ratcheting of U71Mn Rail Steel

An experimental study was carried out on the strain cyclic characteristics and ratcheting of U71Mn rail steel subjected to non-proportional multiaxial cyclic loading. The strain cyclic characteristics were researched under the strain-controlled circular load path. The ratcheting was investigated for the stress-controlled multiaxial circular, elliptical and rhombic load paths with different mean stresses, stress amplitudes and their histories. The experiment shows that U71Mn rail steel features the cyclic non-hardening/softening, and its strain cyclic characteristics depend greatly on the strain amplitude but slightly on its history. However, the ratcheting of U71Mn rail steel depends greatly not only on the values of mean stress and stress amplitude, but also on their histories. In the meantime, the shape of load path and its history also apparently influence the ratcheting. The ratcheting changes with the different loading paths.

Mechanical properties and charge signal characteristics in coal material failure under different loading paths

Rock burst is a catastrophic dynamic disaster caused by sudden failure and instability of coal, loading paths play an important role in the failure of coal, the coal failure process is associated with charge exception infonnation. Hence, violent coal failure mechanics and time-frequency domain distribution of charge signal such as rock burst under different loading paths should be studied in-depth. In this paper, grade and cyclic loading test were carried out for coal with impact tendency samples produced by blocks cored from 800 depth in Xiaoqing coal mine of the Tiefa coal group in northeast China. Theory discussion was carried out for the result of stress and strain, frequency-spectra analysis was conducted for the wavelet charge data, figures showing the evolution mechanism of mechanical properties and the relationship of timefrequency domain amplitude of charge signals in coal with different loading paths and stage were obtained. The failure process and characteristics of coal under different loading paths were summarized. It found that the loading path changed the manner of energy accelerate-release, there were more plastic strain generation in coal under cyclic loading than that under grade loading, the former was more likely to cause greater damage and failure, then the strength of coal under cyclic loading is generally lower than that under grade loading, an energy conversion mechanical model of stress, damage and deformation was developed and explained the effect of the loading path. Charge signal was primarily distributed in the strengthening and peak stages, where there was a high amplitude pulse at each stress drop. The charge pulse was a type of low frequency signal with a primary frequency distribution range of 1 -100Hz. Discussion on the charge generating mechanism from the perspective of friction slip, it demonstrated that the charge obtained during the coal failure process directly to stress loaded on and damage, the result verified it better. We propose that the research results in this study could be efficiently applied to daily mining activities, to provide an early warning and effectively avoid rock burst disaster.

Effective Virtual Reality Based Building Navigation Using Dynamic Loading and Path Optimization

Although computer capabilities have been improved significantly, a large-scale virtual reality （VR） system demands much more in terms of memory and computation than the current computer systems can offer. This paper discusses two important issues related to VR performance and applications in building navigation. These are dynamic loading of models based on cell segmentation for the optimal VR operation, and the route optimization based on path planning for easy navigation. The VR model of engineering and information technology complex （EITC） building at the University of Manitoba is built as an example to show the feasibility of the proposed methods. The reality, enhanced by three-dimensional （3D） real-time interactivity and visualization, leads navigators into a state of the virtual building immersion.

A STUDY OF THE POSTBUCKLING PATH OF CYLINDRICALLY CURVED PANELS OF LAMINATED COMPOSITE MATERIALS DURING LOADING AND UNLOADING

In this paper, Dynamic Relaxation Method is applied to study the postbuckling path of cylindrically curved panels of laminated composite materials during loading and unloading. The phenomenon that loading paths do not coincide with unloading paths has been found. Numerical results are given for cylindrically curved cross-ply panels subjected to uniform uniaxial compression under two types of boundary conditions. The influence of the number of layers, the panels curvature and the initial imperfection on the postbuckling paths is discussed.

Optimizing loading path and die linetype of large length-to-diameter ratio metal stator screw lining hydroforming

In order to meet the high temperature environment requirement of deep and superdeep well exploitation, a technology of large length-to-diameter ratio metal stator screw lining meshing with rotor is presented. Based on the elastic-plasticity theory, and under the consideration of the effect of tube size, material mechanical parameters, friction coefficient and loading paths, the external pressure plastic forming mechanical model of metal stator screw lining is established, to study the optimal loading path of metal stator lining tube hydroforming process. The results show that wall thickness reduction of the external pressure tube hydroforming(THF) is about 4%, and three evaluation criteria of metal stator screw lining forming quality are presented: fillet stick mold coefficient, thickness relative error and forming quality coefficient. The smaller the three criteria are, the better the forming quality is.Each indicator has a trend of increase with the loading rate reducing, and the adjustment laws of die arc transition zone equidistance profile curve are acquired for improving tube forming quality. Hence, the research results prove the feasibility of external pressure THF used for processing high-accuracy large length-to-diameter ratio metal stator screw lining, and provide theoretical basis for designing new kind of stator structure which has better performance and longer service life.

Modeling of the loading path dependent magnetomechanical behavior of Galfenol alloy

The magnetomechanical behavior of single-crystal Galfenol alloy was found to be strongly dependent on the loading paths. An energy-based anisotropic domain rotation model, assuming that the interaction between domains can be ignored and the probability of the magnetic moment pointing along a particular direction is related to the free energy along this direction, is used to simulate the magnetostriction versus magnetic field and stress curve and to track the magnetic domain motion trail. The main reason for loading path dependent effect is the rotation/flipping of the magnetic domains under different loading paths. The effect of loading and unloading paths on 90° magnetic domain motion was studied by choosing different loading and unloading state and paths. The results show that prior loading magnetic field can make the 90° magnetic domains flip to the directions of 45°domains because the magnetic field is the driving force to make the domains rotate, and the final loading state and the loading path both have great influence on the motion of 90° magnetic domains.

Effect of Loading Paths on Hydroforming Tubular Square Components

The influence of loading path on tube hydroforming process is discussed in this paper with finiteelement simulation. Four different loading paths are utilized in simulating the forming process of square tubular component with hydroforming and the result of different loading path is presented. Among the result. the thickness distribution of bilinear loading path is the most uniform one. It shows that the increase of punch displacement in the stage of high pressure is beneficial to the forming of component for optimized Stress condition.

一种基于曲率和B样条的矿区装载车辆连续路径规划方法

矿区装载车辆的任务是从进入点到装载点进行装载,然后离开矿区。在进入装载点前,车辆要在回转点改变行进方向,以便倒车进入装载点。针对装载车辆的任务特点,本文提出了一种基于曲率和B样条的路径规划方法。首先,基于车辆运动模型设计了A*算法的成本函数,获得了与车辆转弯半径相关的离散路径。为了进一步获得装载车辆的连续路径,又提出了改进的B样条插值法,使得连续路径两端切线符合车辆起始点和终点的位姿。随后,基于模拟退火算法,获得了车辆的回转点,使得车辆可以在进入装载点前改变前进方向。仿真结果表明,所提出的连续路径规划方法能够保证生成曲率连续的装载车辆路径,并保证路径两端符合车辆在起始点和终点的位姿,为矿区装载车辆的自动驾驶技术提供了基础。

动态上下料路径下柔性产品族生产调度研究

针对汽车零部件柔性产品族制造单元考虑工序间动态上下料路径与时间的生产调度求解问题,文中提出一种用于动态上下料路径柔性作业调度问题优化的自适应离散差分进化算法。通过自适应缩放参数实现收敛速度提升,构建基于矩阵映射的离散编码规则实现变异操作离散化及基于机器人实际运动路径的动态调度解码。通过对某平台化车型架构的转向器壳体加工单元实例分析并验证了算法有效性及优越性。

列车荷载作用下压实花岗岩残积土累积变形特性试验研究

为研究列车荷载作用下应力及湿化条件对压实花岗岩残积土累积变形特性的影响,以围压、动应力幅值、含水率为变量,对压实花岗岩残积土进行循环空心扭剪和循环定向加载试验。结果表明:循环扭剪应力路径下主应力轴旋转效应增加了试样的累积变形量,甚至改变了累积变形的发展模式,该影响程度随试样含水率的增大而增大;试样的累积应变发展速率在加载初期(N<100)时完成大幅度衰减,围压增大可加快累积应变发展速率的衰减,动应力幅值的增加会延长累积应变发展速率的衰减时间,循环扭剪加载时试样的累积应变发展速率衰减程度小于循环定向加载试验,含水率越高该效应越显著。通过预测模型能够对两种动力加载应力路径下的稳定型和发展型累积应变发展曲线能够进行拟合,对压实花岗岩残积土的累积变形作出较好预测。

基于决策树的电网重要用户供电路径决策方法

广州等超大城市电网中110kV网架接线主要为3T接线,其运行方式多变,对电网的规划和运行有很大影响。超大城市电网中存在着大量的重要用户,其供电可靠性是安排电网运行方式的一个重要考虑因素。若安排的运行方式使得某些重要用户的供电路径汇集在同一元件,就会大大降低重要用户的供电可靠性。基于此,建立超大城市电网重要用户供电路径优化决策模型,以最小化电网中220kV线路的平均负载率为目标,要求系统的每个重要用户都要满足多个供电路径来自最少2个不同的220kV变电站。为了快速求解此混合整数非线性规划模型,引入多变量决策树将模型转化成一个整数非线性规划问题,再通过变量代换将其转化为一个整数线性规划问题,实现快速准确求解。最后,以广州电网实际数据为例,验证所提优化决策模型和求解方法的可行性与有效性。

非线性加载路径下金属薄板成形极限研究进展

成形极限图是评判金属薄板局部成形能力的重要工具,研究非线性加载路径下的成形极限图对提高实际生产过程中工艺设计的合理性和板料的成形性具有重要意义。总结分析了国内外学者对非线性加载路径下金属薄板成形极限的研究进展,主要包括试验方法、理论预测模型及路径无关成形极限图3个方面。重点研究了不同试验方法的适用范围及优缺点,阐述了多种预测非线性加载路径下成形极限图的理论模型及应用实例,并归纳了当前在应变路径无关的成形极限图方面取得的研究成果。最后,从上述3个方面总结了当前更具潜力的研究方向,并对未来的发展趋势以及面临的困难和挑战进行了展望。

不同加卸载路径下灵敏性粉土的变形特性

山西汾河中游一级阶地的施工中发现,饱和粉土地基受扰动后会产生很大的附加沉降,且迟迟不能稳定,表现出灵敏性。基于一维固结蠕变试验研究不同的加卸载路径对灵敏性粉土变形特性的影响,结果表明:加卸载路径和加卸荷比是影响压缩曲线的重要因素;压缩曲线在出现转折时对应的应力为结构屈服应力;加荷比越大,同级荷载下沉降值、固结系数、次固结系数和主固结比都会增大,同时其压缩曲线越趋近于线性,特征转折点消失,但加荷比越大,可大大减少工期;预压荷载的大小和卸荷比都会影响灵敏性粉土的回弹量,预压荷载大于结构屈服应力时,卸荷比越大,回弹量越大,因此需要采取分级卸载方法减小回弹量,保证预压效果;目标荷载小于结构屈服应力时,超载预压法降低工后沉降效果显著。

折线应力路径条件下粉质黏土力学特性试验研究

为了探究先基坑开挖后坑边大吨位吊装的特殊应力路径条件下粉质黏土的变形规律、孔压变化以及强度指标,以济南市某隧道附近的粉质黏土原状土样为研究对象,采用K0固结先侧向卸荷后轴向加荷不排水剪切试验,并在卸荷阶段选取3个不同的卸荷比,模拟先基坑开挖后坑边大吨位吊装特殊工况下的应力路径,然后进行等压固结不排水常规三轴剪切试验和K0固结侧向卸荷不排水剪切试验,并对比3种试验结果。结果表明:先基坑开挖后坑边大吨位吊装的特殊应力路径条件下的偏应力-轴向应变试验曲线为非线性曲线,粉质黏土的破坏强度与卸荷量有关,卸荷量越大,则破坏强度越小;减围压阶段产生负孔压,轴向加压阶段孔压随着轴向应变的增加呈先增大后减小的趋势,在同一初始固结围压下,粉质黏土的卸荷比越小,则剪切时产生的最大孔压越大;先基坑开挖后坑边大吨位吊装的特殊应力路径条件下粉质黏土的卸荷比越大,则有效黏聚力越大,有效内摩擦角越小,与等压固结不排水常规三轴剪切试验相比,有效内摩擦角偏小,有效黏聚力随卸荷比的不同而偏大或偏小。

带障碍物惩罚因子的多机器人路径规划

轻载环境中,复杂障碍物区域将引起机器人之间局部冲突加剧,进而导致路径求解效率下降,针对该问题,提出轻载环境下带障碍物惩罚因子的多机器人路径规划方法。在基于冲突搜索(conflict-based search,CBS)算法框架的下层单机规划过程中,通过对即将拓展机器人位置的周围障碍物分布类型进行判断,赋予与之对应的障碍物惩罚因子;对路径规划过程中的惩罚因子进行累加,作为单机规划的启发值对路径进行选取;结合CBS算法框架的上层冲突消解策略进行多机器人的路径规划与冲突协调。测试结果表明,在10%障碍物分布的轻载环境中,所提算法的求解时间约为CBS算法的81.38%~83.67%,二叉约束树(constraint tree,CT)拓展量为CBS算法的60.14%~71.66%。在Gazebo中仿真表明,所提方法可减小通过复杂障碍物区域的次数。

公铁两用运输车连挂冲击下的纵向载荷传递规律研究

针对中国拟自助研发设计的公铁两用运输车,在编组连挂时由车钩经转向架传递至车体的载荷,其传递路径及规律尚不明确的问题,进行了试验测试与仿真研究。该车型的转向架在纵向能传递载荷的部件包括牵引板与抗蛇行减振器装置,需掌握载荷传递路径及其大小以便为后续结构部件的强度考核提供支撑。试验中,对转向架可能传递纵向载荷的部件进行了布点和载荷测试。仿真研究中,根据铁道车辆多体动力学理论与建模方法,建立了3车体4转向架的编组模型,模拟碰撞机车为含质量与速度的简化质量块。建立了抗蛇行减振器装置的力学模型,其力学结构为阻尼与刚度的串联模型;而构架到车体的纵向连接部件为牵引板⁃抗蛇行减振器装置的并联结构。运用多体动力学软件SIMPACK进行求解。结果表明:车钩与牵引板所受纵向载荷会随着碰撞体冲击速度的增大而增大,仿真结果略小于试验结果,但规律一致,且牵引板所受冲击载荷小于车钩载荷;而抗蛇行减振器装置结点几乎不受纵向载荷,与牵引板受载相比可忽略不计。由试验与仿真结果对比分析,明确了冲击载荷经车钩传递至车体时,几乎完全通过转向架上的牵引板传递,抗蛇行减振器装置作用很小,相关结果能够用于该车结构的优化设计及为部件强度校核提供载荷谱。

考虑分布式电源的配电网灾中-灾后两阶段协同韧性恢复决策

频繁的极端自然灾害极易引发配电网大规模故障,基于分布式电源的负荷恢复是提高配电网韧性水平的重要手段。然而,现有研究一般将灾中和灾后阶段进行独立决策,忽略了二者决策的连续性和耦合性,延缓了恢复进程。为此,文中提出一种基于灾中-灾后两阶段协同决策的配电网快速恢复方法,充分考虑灾中-灾后过程中的相互作用,综合分布式电源调度、网络拓扑改变、维修人员调度等在内的恢复措施,保障灾中-灾后阶段连续决策的最优性。首先,考虑灾后供能路径对灾中网络拓扑的需求关系,建立灾中阶段以分布式电源为核心的拓扑调整模型与负荷元胞恢复模型,实现部分重要负荷的供电;其次,考虑灾中决策对灾后恢复的影响,建立灾后阶段故障维修人员调度和负荷快速恢复的联合决策模型,实现所有负荷的有序恢复;然后,以灾中-灾后全阶段失负荷量最小为目标,实现灾中-灾后恢复的协同决策;最后,基于IEEE 123节点配电系统验证了所提模型的有效性。