The Mechanism of Smooth and Pre-Cracking Blasting

The paper discusses some main factors of the mecha nism of smooth and pre-cracking blasting.The results of theoretical analyses show that the formation of directional cracks isrelated to the distan ce of holes.the quasi-static pressure and the strueture of rock mass. This paperalso studies the relation of len gth of crack and distance of holes.The initial cracks occur on the wallof holes instead of in the middle of two holes.     

Numerical Simulation of Microcrack Toughening in Particulate Composite

The crack tip region in an elastic composite can be divided into three different zones. The constitutive equations corresponding to these zones and the extent of the saturated damage zones are derived. The damage isotropy in the largest saturated damage zone is expressed by utilizing the Monte Carlo technique to create uniform distribution microcracks. The interaction between the main crack and microcracks can be evaluated by an alternating iteration scheme. In the assumption of a dilute concentration of microcracks, the interaction among microcracks is neglected, and the stress intensity factor produced by interaction between the main crack and each microcrack can be superposed. Two sources of loading are analyzed: one is for the main crack microcrack interaction under an applied remote load, and the other is for the main crack microcrack interaction accompanied by the relief of residual stresses on the microcrack surfaces. The results show that two sources of loading can shield the main crack tip, and microcracks behind the main crack tip can create the most shielding whereas the micro cracks ahead of the main crack tip play no role in shielding.     

Development and Failure Principle of Differential Weathering Overhanging Rock

Differential weathering overhanging rock by hard rock and soft rock interlayer is common for geological failure.To study the influence of ground stress in rock slope and cave deepness to differential weathering overhanging rock,a mechanical model was proposed.And hollow cylinder stress meter was used to test and analyze on site ground stress at Hongyadong in Chongqing.Moreover, the development range of overhanging rock was determined.And a case studywas used to analyze the relationship among tension ground stress, cave deepness and growth of controlling crack.A method for forecasting overhanging rock failure pattern was proposed.     

Near Crack Line Elastoplastic Solution for an Eccentric Cracks Loaded by the Pore Water Pressure

By using near crack line analysis method and Mohr-Coulomb strength criterion,the elastic-plastic solution for near crack line of an eccentric cracks loaded by the pore water pressure under large scale yielding condition is analyzed.The elastic stress fields,the plastic stress field,the unit normal vector of the elastic-plastic boundary near the crack line,the elastic-plastic stress fields near crack line are identified.The change pattern of the length of the plastic zone and the pore water pressure is presented.Besides,the elastic-plastic analytical solution for an eccentric cracks loaded by the pore water pressure is obtained.     

玉米裂纹及其检测

我国粮食部门经过较长时间才认识到玉米裂纹的重要性。玉米裂纹是指人眼能观察到的玉米表面和胚乳内部裂缝宽度为0.1 mm左右的缝隙。玉米籽粒内部生来就有许多微裂纹,构成胚乳内众多的微毛细管。借助电子显微镜可以观察到纳米级的微毛细管。目前检测玉米裂纹的仪器需进一步改进。     

Simulation on crack growth of drill pipe with XFEM

Crack growth of drill pipe is a typical discontinuous problem. It is difficult to simulate with conventional finite element method and extended finite element method (XFEM) is developed in recent years for the problem. With the introduction of XFEM, the XFEM model of 5 inch drill pipe was proposed with different depth initial cracks under combined action between torque and tension. Based on the simulation, It is found that the smaller cracks is not easy to grow, whilst the crack of depth more than 2mm could grow under relatively lower external load and larger growth surface, eventually leads to pipe fracture failure. Through this simulation on crack growth of drill pipe, it is showed that the XFEM is appropriate in analysis of fracture failure.     

Prediction of material fatigue life based on industrial CT images

A two dimensional gray image of the material fault can be obtained without destruction by industrial computer tomography (ICT). This process is used to distinguish the seizure and the expansion of cracks within the initiation section. A fatigue life prediction method based on industrial CT images was studied. First, the crack initiation and expansion processes were divided into three phases: micro scale thinness sight crack, CT scale crack, and macroscopic crack. Second, different crack initiation and expansion standards were adapted to calculate material fatigue life. The fatigue life of the material was the sum of the three phase's fatigue lives. Compared with other methods, such as the fatigue cumulative damage theory method and the nominal stress method, the fatigue life predicted by this method is more precise.     

Evaluation on the Damage Evolution of the CRCP+AC Composite Pavement by the Concrete Dameged Plasticity Material Model

In the study on the CRCP+AC composite pavement, the form and distribution pattern of cracks are two important factors influencing the performance and the lifetime of the pavement. The concrete damaged plasticity material model incorporated in the general purpose finite element software named ABAUQS was adopted to describe the mechanical characteristics of the CRC slab. Combining with the temperature field database drawn from the three-dimensional transient heat transfer analysis, the structural damage under the condition of temperature changing is analyzed. The structural damage evolution and the crack behavior of the CRC slab subjected to the thermal-mechanical coupling condition are further analyzed, which suggests that the role of the asphalt concrete surface is not confined only to the scope of improving the performance of the road, its capacity for improving the stress state of CRCP slab is worthwhile to be affirmed. And the reasonable thickness of AC layer should be designed in consideration of the thermal contraction and damage properties of the CRC slab comprehensively.     

CFRP筋钢筋混凝土剪力墙自复位性能试验研究

通过对1片钢筋混凝土剪力墙和4片配有碳纤维增强聚合物(CFRP)筋的剪力墙的低周反复荷载试验,在分析试验中测得的裂缝宽度、裂缝的发展和分布形态、侧向变形的基础上,研究了在钢筋混凝土剪力墙的适当位置部分或全部配置CFRP筋对剪力墙的残余裂缝和残余变形等自复位性能的影响规律。研究结果表明:与普通钢筋混凝土剪力墙相比,配有CFRP筋的剪力墙的开裂荷载较低,裂缝较多,裂缝分布分布范围较广,墙体的最大裂缝宽度、残余裂缝宽度和侧向残余变形分别降低了60%、70%和90%,说明在剪力墙中合理配置CFRP筋能使剪力墙具有优异的自复位性能。     

Analysis of Solid Fluid Coupling for Tunnel Excavation in Complicated Fractured Rock Masses

When tunnels are through water bearing section of fractured rock mass, a complex interaction process between rock mass deformation and fluid transportation is one of the most important reasons for water gushing, water bursting and mud bursting.To study the rock mass deformation and fluid transportation in tunnel excavation under complex geological conditions, a hydraulic model of complex crack rock mass was established from the relationship between the crack growth degree of surrounding rock in deep buried tunnel and the engineering scale, with which fracture network of different levels in rock mass could be considered simultaneously.Furthermore,a computer Fortran program was put forward to simulate the solid fluid coupling of excavation process of a deep buried tunnel.And it was found that the principal fractures had strong flowing action and network fractures had storage function and lag effect in seepage area.And the yield area of surrounding rock was increased under the coupling of seepage field and stress field.     

钢筋非均匀锈蚀引起混凝土保护层内裂分析

根据自然环境下保护层锈胀开裂前的钢筋锈蚀形态,将锈蚀层简化为半椭圆状的非均匀分布,从而建立了钢筋非均匀锈蚀理论模型。经过求解得到了混凝土中锈胀应力理论解,并与有限元计算结果对比,验证了理论解的精确性。根据理论解可知最大周向应力在水平轴上,因此锈蚀层的发展会首先引起保护层内部水平裂纹的产生。增加钢筋直径可有效减低锈胀应力,提高结构抗锈裂的能力。与均匀锈蚀理论模型对比结果表明：均匀锈蚀要远小于非均匀锈蚀条件下的临界锈蚀层厚度,均匀锈蚀的计算结果偏于保守。因此,对锈胀问题进行理论分析时,应采用更接近真实锈蚀形态的非均匀锈蚀模型。     

A STUDY OF PHOTO-ELASTIC EXPERIMENT TO FRACTURE PROCESS OF LIMESTONE SPECIMEN WITH PRE-CRACKS

In this paper, the fracture process of specimen with pre-cracks is studied by using photo-elastic expe' merit.The analysis results of cracks stress field show that because the inter-effection appears between the the two cracks and the tensile fracture occured when the tensile stress concentration reaches to a certain degree, and cracks link up with each other, macroscopic failure will gradually result. Positions of cracks will have different effections to speciment's fracture.     

Nalytical study on crack magnetic flux leakage for ferromagnetic component and detection system based on geomagnetic field

Based on technical aspects of ferromagnetic components crack damage detection methods and instruments applications, this paper establishes a the magnetic flux leakage analysis model for V-Cracks to get the theoretical expressions for any probe point of flat ferromagnetic component surface. We use MATLAB software programming to do a comprehensive simulation, and obtain the relation curve between magnetic flux leakage normal component Hy and crack opening width, the relation curve between magnetic flux leakage normal component Hy and crack depth, the relation curve between magnetic flux leakage normal component Hy and crack length are obtained, crack magnetic flux leakage distribution characters: normal component of Hy with zero-crossing, maximum value of tangential component Hx, and tangential component Hz with tip zero-crossing. According to the leakage magnetic characteristics obtained underby the theoretical analysis, the array type detection device and test platform are designed and fabricated, and then the plate-type ferromagnetic component with V-Cracks is detected. The experimental results show that: there is a good agreement between the three-dimensional magnetic flux leakage obtained from thesis theoretical analysis and the test results, to a certain degree the magnetic flux leakage model has directive significance for the prediction and analysis of crack parameters, and the test device be developed according to the magnetic flux leakage model is able to detect cracks in ferromagnetic components.     

A Calculating Method for the Crack Tensor of theOrthotropic Rockmass by the Elastic Wave Velocity

A method was proposed for calculating the crack tensor by the elastic wave velocities in the orthotropic rock masses,based on the theoretical relations of crack tensor and compliance tensor and elastic wave velocities,The numerical results show that there is a good correlation with the measured data.     

高速铁路隧道基底软岩动力累积损伤特性

利用相似材料模拟高速铁路隧道基底软岩,采用荷载控制和非对称正弦波循环加载方式对软岩试件进行动三轴疲劳与损伤检测综合试验。通过试验结果分析,建立了软岩3参数多项式疲劳寿命计算模型和4参数多项式累积损伤参量计算模型,获得了软岩疲劳损伤特性,即：软岩疲劳破坏表现为端部拉-剪复合破坏和中部压-剪复合破坏两种模式;疲劳破坏全过程表现为初始微孔隙压密、裂纹发生与稳定扩展以及损伤裂纹加速发展3个发展阶段;软岩疲劳寿命主要取决于本身强度和动应力水平,强度愈高、动力应力水平愈低,其疲劳寿命就越长;当动应力水平相同时,软岩疲劳寿命与其弹性模量呈线性增长关系。     

Studies on the Relationship between TotalAcoustic Emission Count and Stress IntensityFactor for Rock Crack Yielded within Small Scope

Based on the crack tip microcrack density theory,a supposition that total AE count is directly proportional to the total microcrack length is proposed,a relationship between total AE count and stress intensity factor for stable crack growth is derived.With a series of experimental results,the relationship between theoretical derivation and the experimental results is compared,it shows that the theoretical derivation coincides better with the experimental results.     

Numerical simulation for the residual stress of U-rib welding onto the flat steel box girder

The flat steel box girder is commonly used for long-span cable-stayed bridges. the structural complexity, construction details and manufactures cause damage to the bridge and the damages seriously grow overtime. The main reason for these damages is that welding technology of flat steel box girder with thin plates and rib elements produces residual stress and strain fields during the welding process, and further more welding cracks commonly appear. In this study, thermal-structural couple methods was adopted to numerically simulate the welding high temperature fields and the stress fields at the joint of U rid and decks of a flat steel box. The welding residual stress distribution was studied as well for further analyzing on the structural damage and strengthening design strategies.     

复合岩体的TBM破岩机理数值模拟

为了指导TBM刀盘刀具的研制和不同地质条件下刀盘刀具的选型,TBM破岩机理的研究成为核心。在TBM滚刀的作用下,岩体中裂纹的生成、扩展和连接规律是深刻理解TBM破岩机理的前提,因此,TBM滚刀破岩机理的研究具有重要的工程应用价值。目前,TBM滚刀破岩机理的研究主要集中在单一岩体中,但在TBM施工过程中会遇到各种复杂的地质条件。笔者采用离散元方法,研究了复合岩体的破岩机理,复合岩体中岩片的形成不同于单一岩体,其裂纹的最终连接是由起裂于复合岩体交界面上的微裂纹的扩展,将两滚刀之间的赫兹裂纹连接,最终形成岩片。因此,在一定情况下复合岩体更有利于TBM隧道施工。     

Application of Fracture Mechanics in Explosion of Large Iron and Steel Wastes

The ex plosio n process a n d paramete rs in the blast of large iron a nd steel wastesare analysed by using the theory of fracture mechanice.A three-dimensional model is established us-ing pressurised cylinder with multiple semi-elliptical surface cracks.Reasons are given for the expla-nation that the dynamic fracture toughness for iron and steel is generally lower than the correspond-ing static value during the blast.The importance is emphasized of the critical duration time of the dy-namic stress intensity factor for crack extension.     

Study Of Three-Point Bending Marble Beam Elastoplastic Damage

An elastoplastic damage constitutive model based on incremental theory is deduced in strain space.A mesoscopic numerical model to study the progressive failure process and the nonlinear mechanical behavior of heterogeneous rock is established in combination with an elastoplastic damage constitutive for rock mesoscopic element.The failure elements deleting method is used to simulate crack propagation in program.The calculation results achieved by numerical simulation and practical projects application agree well with those of in-situ tests,which illuminates that elastoplastic damage mesoscopic model could reflect local plastic characteristics of fractured rock masses.Three-dimension marble model is more reflect mesoscopic failure than two-dimension model.The failure element deleting method is good at showing explicitly crack propagation.It is proven that the numerical model is right and feasible.The failure elements deleting method solves the difficult problem of FEM to simulate the propagation.The model and method might be valid in practical projects.