Fracture behaviors of columnar jointed rock mass using interface mechanics theorem

For a special geological structure of columnar jointed rock mass(CJRM),its mechanical properties are strongly affected by the columnar joints.To describe the fracture behaviors of CJRM using the basic theories of interface mechanics for composite materials,the interface stresses of the vertical and horizontal joints,which are the two primary joints in the CJRM under triaxial compression,are studied,and their mathematical expressions are derived based on the superposition principle.Based on the obtained interface stresses of the vertical and horizontal joints in the CJRM,the crack initiation of the joint interface in the CJRM is studied using the maximum circumferential stress theory in fracture mechanics.Moreover,based on this investigation,the fracture behaviors of CJRM are analyzed.According to the results of similar material physical model tests for the CJRM,the theoretical study is verified.Finally,the influence of the mechanical parameters of the CJRM on the joint interface stress is discussed comprehensively.

Interface characteristic of friction stir welding lap joints of Ti/Al dissimilar alloys

Lap joints of TC1 Ti alloy and LF6 A1 alloy dissimilar materials were fabricated by friction stir welding and corresponding interface characteristics were investigated. Using the selected welding parameters, excellent surface appearance forms, but the interface macrograph for each lap joint cross-section is different. With the increase of welding speed or the decrease of tool rotation rate, the amount of Ti alloy particles stirred into the stir zone by the force of tool pin decreases continuously. Moreover, the failure loads of the lap joints also decrease with increasing welding speed and the largest value is achieved at welding speed of 60 mm/min and tool rotation rate of 1500 r/min, where the interracial zone can be divided into 3 kinds of layers. The microhardness of the lap joint shows an uneven distribution and the maximum hardness of HV 502 is found in the middle of the stir zone.

Influence of tool pin profile on the interface migration of friction stir lap joints＊

Friction stir lap joints of LY12 aluminum alloy plates with a thickness of 3 mm were fabricated using several tools with different pin profiles. The effects of tool pin profile on the interface migration of friction stir lap joints were investigated with the comparison of weld morphologies. The results show that the screw thread of the pin plays an important role in the migration of weld interface in the thickness direction. The interface between the sheets will move upwards to the top of the plate when the pin with left hand thread was used. Conversely, the interface will move downwards to the tip of the pin when the pin with right hand thread was used： As for a stir pin with smooth surface was used, the upward or downward migration of the weld interface was largely reduced, but the extension of weld interface to the weld center line from the retreating side becomes more serious. By analyzing the force on the pin according to the sucking-extruding theory for the weld formation, the obtained results have been well explained.

Effects of interface slip and semi-rigid joint on elastic seismic response of steel-concrete composite frames

The stiffness matrix of semi-rigidly connected composite beams considering interface slip was established and the calculation method for elastic seismic response of composite frame was derived.The corresponding calculation programs were developed.Introducing the dimensionless quantities that were related to the connector shearing stiffness and the joint rotation stiffness,the influences of interface slip and semi-rigid joint on composite frame were transferred to quantitative parameter analysis,taking account of cross sectional properties,materials and linear stiffness of composite beam synthetically.Based on the calculation programs,free vibration frequencies and seismic responses of semi-rigid joint steel-concrete composite frame considering interface slip were calculated.The influences of interface slip and semi rigid joint on dynamic characteristics and seismic response were analyzed and the seismic design advices were presented.The results show that the interface slip decreases the free vibration frequencies and increase the seismic responses of composite frame.The semi-rigid joint reduces the free vibration frequencies and increases seismic responses of composite frame compared with rigid joint.With the increase of joint rotational stiffness,the elastic seismic responses of composite frame increase firstly and then decrease.The effects are related to the ratio of joint rotation stiffness to linear stiffness of composite beam.

Numerical Investigation on Fracture Initiation Properties of Interface Crack in Dissimilar Steel Welded Joints

Fracture toughness property is of significant importance when evaluating structural safety.The current research of fracture toughness mainly focused on crack in homogeneous material and experimental results.When the crack is located in a welded joint with high-gradient microstructure and mechanical property distribution,it becomes difficult to evaluate the fracture toughness behavior since the stress distribution may be affected by various factors.In recent years,numerical method has become an ideal approach to reveal the essence and mechanism of fracture toughness behavior.This study focuses on the crack initiation behavior and driving force at different interfaces in dissimilar steel welded joints.The stress and strain fields around the crack tip lying at the interfaces of ductile-ductile,ductile-brittle and brittle-brittle materials are analyzed by the numerical simulation.For the interface of ductile-ductile materials,the strain concentration on the softer material side is responsible for ductile fracture initiation.For the ductile-brittle interface,the shielding effect of the ductile material plays an important role in decreasing the fracture driving force on the brittle material side.In the case of brittle-brittle interface,a careful matching is required,because the strength mismatch decreases the fracture driving force in one side,whereas the driving force in another side is increased.The results are deemed to offer support for the safety assessment of welded structures.

COMPLEX VARIABLE-VARIATIONALMETHOD OF SOLUTION FOR BI-METALLAMINATES WITH INTERFACE CRACKSAND ITS APPLICATION IN GLUED JOINTS

In this paper, the eigen function expansions of displacements and stresses of bi-metal laminates with interface cracks are obtained. Furthermore, the stress intensity factors are determined by the variational method to satisfy the boundary conditions and there are only line integrals in the variational equations due to the previous satisfaction of all basic equations. The computations show that this method of solution has the advantages of rapid convergency and time-saving. The results obtained by this method for homogeneous material agree with the known ones very well.

Changes in the Structure and Properties of the Cu-Pb Composites Interface Jointed in the Solid Phase

Research of structure and properties of Cu-Pb-Cu composite interface, obtained by technology of pack rolling of the pair of mutually insoluble metals, was performed using the methods of metallography, micro- and nano-hardness, mechanical tests, energy-dispersion elementary analyses. The work was aimed at the analyses of possible mechanical mechanisms of mass-transfer, determining the hardness of metal joint in conditions of absence of inter-diffusion. It was shown that different intensity of mass transfer of copper and lead takes place through the composite interface, which corresponds to the results obtained on the other system of dissimilar materials—copper-niobium. Qualitative explanation of these patterns was offered on the basis of more intensive plastic flow of fusible compound of the composite in conditions of roll-bond joining.

Effect of Metallurgical Behaviour at the Interface between Ceramic and Interlayer on the Si_3N_4/1.25Cr-0.5Mo Steel Joint Strength

By using newly developed CuNi5~25Ti16~28 B rapldly solidifled brazing filler the joining of Si3 N4/1.25Cr-0.5Mo steel has been carried out with interlayer method. If employing the interlayer structure of steel (0.2 mm)/W (2.0 mm)/Ni(0.2 mm), the joint strength can be increased greatly compared with employing that of Ni/W/Ni, and the three point bend strength of the Joint shows the value of 261 MPa. The metallurgical behaviour at the interface between Si3N4 and the interlayer has been studied. It is found that Fe participated in the interfacial reactions between Si3N4 and the brazing filler at the Si3N4/steel (0.2 mm) interface and the compound Fe5Si3 was produced. However, since the reactions of Fe with the active Ti are weaker than those of Ni with Ti, the normal inter facial reactions were still assured at the interface of Si3N4/steel (0.2 mm) instead of Si3N4/Ni (0.2 mm), resulting in the improvement of the joint strength. The mechanism of the formation of Fe5Si3 is also discussed. Finally, some ideas to further ameliorate and simplify the interlayer structure are put forward.

The Numerical Analysis of Strain Behavior at Solder Joint and Interface of Flip Chip Package

The flip chip package is a kind of advanced electri ca l packages. Due to the requirement of miniaturization, lower weight, higher dens ity and higher performance in the advanced electric package, it is expected that flip chip package will soon be a mainstream technology. The silicon chip is dir ectly connected to printing circuit substrate by SnPb solder joints. Also, the u nderfill, a composite of polymer and silica particles, is filled in the gap betw een the chip and substrate around the solder joints to improve the reliabili ty of solder joints. When flip chip package specimen is tested with thermal cycl ing, the cyclic stress/strain response that exists at the underfill interfaces and solder joints may result in interfacial crack initiation and propagation. Therefore, the chip cracking and the interfacial delamination between underfill and chip corner have been investigated in many studies. Also, most researches h ave focused on the effect of fatigue and creep properties of solder joint induce d by the plastic strain alternation and accumulation. The nuderfill must have lo w viscosity in the liquid state and good adhesion to the interface after solidif ying. Also, the mechanical behavior of such epoxy material has much dependen ce on temperature in its glass transition temperature range that is usually cove red by the temperature range of thermal cycling test. Therefore, the materia l behavior of underfill exists a significant non-linearity and the assumption o f linear elastic can lack for accuracy in numerical analysis. Through numerical analysis, this study had some comparisons about the effect of linear and non -linear properties of underfill on strain behaviors around the interface of fli p chip assembly. Especially, the deformation tendency inside solder bumps could be predicted. Also, it is worthily mentioned that we have pointed out which comp onent of plastic strain, thus, either normal or shear, has dominant influence to the fatigue and creep of solder bump, which have not brought up before. About the numerical analysis to the thermal plastic strain occurs in flip chip i nterconnection during thermal cycling test, a commercial finite element software , namely, ANSYS, was employed to simulate the thermal cycling test obeyed by MIL-STD-883C. The temperatures of thermal cycling ranged from -55 ℃ to 125 ℃ with ramp rate of 36 ℃/min and a dwell time of 25 min at peak temperature. T he schematic drawing of diagonal cross-section of flip chip package composed of FR-4 substrate, silicon chip, underfill and solder bump was shown as Fig.1. Th e numerical model was two-dimensional (2-D) with plane strain assumption and o nly one half of the cross-section was modeled due to geometry symmetry. The dim ensions and boundary conditions of numerical model were shown in Fig.2. The symm etric boundary conditions were applied along the left edge of the model, and the left bottom corner was additional constrained in vertical direction to prevent body motion. The finite element meshes of overall and local numerical model was shown as Fig.3. In this study, two cases of material model were used to describe the material behavior of the underfill: the case1 was linear elastic model that assumed Young’s Modulus (E) and thermal expansion coefficient (CTE) were consta nt during thermal cycling; the case2 was MKIN model (in ANSYS) that had nonlinea r temperature-dependent stress-strain relationship and temperature-dependent CTE. The material model applied to the solder bump was ANAND model (in ANSYS) th at described time-dependent plasticity phenomenon of viscoplastic material. Bot h the FR-4 substrate and silicon chip were assumed as temperature-independent elastic material; moreover, FR-4 substrate is orthotropic while silicon chip is isotropic. From the comparison between numerical results of linear and nonlinear material a ssumption of underfill, (i.e. case1 and case2), the quantities of plastic strain around the interconnection from case1 are higher than that in case2. Thus, the linear

断续节理作用的Interface模型及工程应用

断续节理是影响地下洞室围岩稳定的重要因素,要有效反映其影响提出 Interface 界面模型模拟断续节理的力学效应。以二滩水电工程大型地下洞室群为背景,对主厂房开挖考虑与不考虑断续节理作用进行了多种地应力工况的数值计算与分析,获得了主厂房洞周在断续节理影响下的位移场和塑性区分布规律,为大型地下工程围岩稳定分析提供了有益的参考。

Interface模型模拟断续节理洞群渗流效应的数值分析

采用三维有限差分FLAC3D程序,以二滩工程地下洞群的结构形式为背景,提出interface界面模型模拟断续节理的力学效应,考虑与不考虑节理岩体静水渗流对围岩稳定性进行了大量计算工况的准三维数值模拟。通过系统分析得出相应的结论,为大型地下工程围岩稳定分析提供了有益的参考。

Study on the Microstructure of Human Articular Cartilage/Bone Interface

For improving the theory of gradient microstructure of cartilage/bone interface, human distal femurs were studied. Scanning Electron Microscope （SEM）, histological sections and MicroCT were used to observe, measure and model the micro- structure of cartilage/bone interface. The results showed that the cartilage/bone interface is in a hierarchical structure which is composed of four different tissue layers. The interlocking of hyaline cartilage and calcified cartilage and that of calcified car- tilage and subchondral bone are in the manner of＂protrusion-pore＂ with average diameter of 17.0 gm and 34.1 lam respectively. In addition, the cancellous bone under the cartilage is also formed by four layer hierarchical structure, and the adjacent layers are connected by bone trabecula in the shape of H, I and Y, forming a complex interwoven network structure. Finally, the simplified structure model of the cartilage/bone interface was proposed according to the natural articular cartilage/bone interface. The simplified model is a 4-layer gradient biomimetic structure, which corresponds to four different tissues of natural cartilage/bone interface. The results of this work would be beneficial to the design of bionic scaffold for the tissue engineering of articular cartilage/bone.

Irregular Characteristics of Bond Interface Formation in Ultrasonic Wire Wedge Bonding

The mechanism of ultrasonic wire wedge bonding, one of the die/chip interconnection methods, was investigated based on the characteristics of the ultrasonic wire bonding joints. The Al-1%Si wire of 25 μm in diameter was bonded on Au/Ni/Cu pad and the joint cross-section was analyzed by scanning electron microscopy （SEM） and energy-dispersive X-ray spectroscopy （EDX）. The results indicated that it is irregular for the ultrasonic bond formation, non-welded at the centre but joining well at the periphery, especially at the heel and toe of the joint. Furthermore, the diffusion and/or reaction at the cross-section interface are not clear at C-zone, while there exists a strip layer microstructure at P-zone, and the composition is 78.96 at. pct Al and 14.88 at. pct Ni, close to the Al3Ni intermetallic compound. All these observations are tentatively ascribed to the plastic flow enhanced by ultrasonic vibration and repeated cold deformation driving interdiffusion between AI and Ni at bond interface.

Interfacial microstructure and properties of YG11C/42CrMo joint brazed with BCu64MnNi filler metal

Brazing hard alloy to high strength steel, incomplete atomic diffusion and excessive brittle reaction product precipitation at the faying interface are usually suffered because of incomplete understanding the process of the initial interface disappearing and diffusion layer forming and evolving. In this paper , hard alloy YG11C （ WC-11wt. %Co） and high strength steel 42CrMo were picked up as base metals and BCu64MnNi as filler metal to clarify the interfacial microstrncture evolution. The process parameters of dwell time were set as 30 s, 60 s, 120 s, and 300 s and braze temperature were set as 950 ℃, 970 ℃, 990 ℃, 1 010 ℃, the effect of which on the evolution of interfacial microstructure, tensile strength, integrated with fracture morphology analysis, were conducted. The results showed that increasing brazing temperature from 950 ℃ to 970 ℃, no signifwant difference existed in the joint interface, whereas brazed at 990 ℃, the binder phase erosion occurred, i. e. the liquid filler metal etched into Co binder phase of WC-Co base metal, which caused WC particles debonding from the base metal surface and formed an micro-anisotropic zone.. Increase temperature to 1 010 ℃, severe binder erosion happened so as to micropores appear. Through the parameters optimization, the tensile strength can reach to the maximum 589 MPa at temperature of 970 ℃. The dwell time showed similar effect on tensile strength because longer dwell time also caused erosion and porosity owing to long-time diffusion and reaction.

连接界面黏滑摩擦行为的非线性载荷重构方法

提出一种连接界面黏滑摩擦行为的非线性载荷重构方法。基于非线性动力学子结构建模方法,将复杂连接结构视作线性子结构和非线性连接两部分,通过虚拟非线性激励载荷进行关联。以线性子结构为研究对象,采用两次动刚度矩阵求逆的反转技术消除传递函数的病态奇异性,建立观测点自由度和非线性连接自由度之间的传递关系。考虑连接界面黏滑摩擦行为的影响,将观测的非线性动力响应进行谐波级数展开,直接辨识连接界面的局部非线性接触载荷。利用螺栓连接梁结构的数值仿真和实验结果进行验证。结果表明:重构的虚拟非线性激励载荷能够直接反映连接界面黏滑摩擦行为的影响,并且能够有效地识别螺栓连接界面预紧性能的变化。

CFRP层合板单搭胶接接头胶板界面剥离强度仿真分析

基于异材界面奇异应力场理论,以CFRP层合板单搭胶接结构为对象,通过有限元和实验的方法分析了结构承载时板胶结合界面上出现的应力分布,锁定界面剥离强度关键区域,通过网格无关的有限元应力比值法提升仿真求解精度,最大限度还原板胶界面应力分布,着重探讨了多层各向异性CFRP板与传统均质材料在仿真过程和结果的差异,及搭接长度、胶层厚度、结构胶参数等对板胶界面应力分布及起裂点位置的影响,为板胶界面剥离应力的优化、胶接工艺的改进和单搭胶接接头强度的提升提供理论支撑。结果表明:各层参数不同的CFRP板胶界面承载时,剥离应力的最大处需由三个维度共同约束,其中两个维度的约束结果与均质材料相同,极值位于板胶界面垂直于拉伸方向的边缘,实际结构中失效的起始亦常见于此处,第三维度受层合板多层异性影响,该边缘上应力最大的点既不位于该边缘的中点也不位于界面角部,具体位置由材料参数和胶接结构共同影响。

多层次路网接轨站联锁系统功能及接口方案探讨

[目的]在多层次路网中,不同信号制式线路的接轨站面临着多种挑战,为满足多网融合运行的新需求,有必要深入研究并提出接轨站联锁功能和接口配置方案。[方法]通过对比CBTC(基于通信的列车控制)与CTCS-2(中国列车运行控制系统二级)信号制式下联锁系统的差异性,详细分析了信号控制功能需求、建设运营需求,进而明确了接轨站联锁系统的功能要求。在此基础上,进一步分析了联锁系统的接口对象和接口内容,最终构建了接轨站联锁接口配置方案。[结果及结论]接轨站联锁系统不仅需要完成基本的进路安全防护功能,还应能够适配多种信号制式对基础信息提供的要求,具备移动闭塞适应性,以及区间结合、站台门控制、保护区段防护、自动折返进路办理、运行灵活调整适配等全面功能。同时,接轨站联锁系统应支持信号安全数据网、有线环网、无线网、继电等多通道接口,以确保系统的兼容性和可靠性。

碾压混凝土分层碾压离散元模拟及施工成层细观机理研究

碾压混凝土(RCC)坝特有的大仓面分层碾压工艺带来的层间结合质量问题,是影响其安全运行的重要因素。从施工控制的角度分析RCC施工成层机理,进而合理调整碾压参数,可有效保证大坝的施工质量。首先,通过RCC分层碾压试验,分析了碾压过程中含层面RCC的沉降规律、压实度及抗剪强度,为后续离散元模拟提供了基础;然后,建立并验证了RCC双层碾压与抗剪试验离散元模型;最后,给出了表征层间结合质量的骨料嵌入值指标,进而从孔隙率、层间骨料嵌入、层面应力分布、层间抗剪强度等方面分析了RCC施工成层的细观机理。结果表明:碾压参数对RCC的嵌入值、压实特性、层面应力和层间结合质量均有一定影响;嵌入值是影响层间抗剪强度的重要因素,二者呈线性相关,嵌入值每增加1 mm,模拟抗剪强度约增加1.583 MPa;激振力的增加以及行进速度、碾压厚度的减小均有利于提高层间结合质量,且碾压厚度是影响层间结合质量的最敏感参数。研究结果可为施工中RCC层间结合质量控制标准的制定提供理论依据。

计及硅橡胶应力松弛的电缆接头界面压力演变仿真研究

高压电缆中间接头的电气性能与其硅橡胶-交联聚乙烯界面压力的大小密切相关。为探究实际电缆接头界面压力的演变规律,开展了考虑老化过程中硅橡胶应力松弛现象的220 kV电缆中间接头界面压力仿真研究。首先综合电缆接头处物理场特点建立有限元模型,确定了电缆中间接头硅橡胶-交联聚乙烯界面的初始压力分布情况;其次通过力学理论计算的解析解以及预置压力传感器的实测结果对有限元分析结果进行验证;之后结合硅橡胶的热机械老化实验结果,提出一种将老化过程中硅橡胶应力松弛转化为过盈量变化的方法,得到了考虑老化过程中应力松弛与弹性模量变化的多参量有限元分析方法,并成功应用于电缆中间接头绝缘硅橡胶-交联聚乙烯界面压力的分析。分析认为,硅橡胶的老化同时导致应力松弛和弹性模量增大。综合考虑弹性模量和应力松弛的仿真结果表明:对中间接头硅橡胶在100℃、125℃、150℃下分别经过2040 h、1680 h、1200 h热机械老化后,界面压力从0.156 MPa分别下降到0.129 MPa、0.125 MPa、0.107 MPa。这说明应力松弛对于界面压力的影响更显著,界面压力随着老化时间的增加而下降,同时温度升高会显著加快中间接头界面压力的衰减过程。该文研究结果可为提升电缆中间接头设计与运行可靠性提供理论依据。

Microstructure and properties of Cu/Al joints brazed with Zn-Al filler metals

The mechanical properties and microstructural distribution of the Cu/A1 brazing joints formed by torch-brazing with different Zn-A1 filler metals were investigated. The microstructure of the Zn-A1 alloys was studied by optical microscopy and scanning electron microscopy, and the phase constitution of the Cu/A1 joints was analyzed by energy dispersion spectrometry. The results show that the spreading area of the Zn-A1 filler metals on the Cu and A1 substrates increases as the A1 content increases. The mechanical results indicate that the shear strength reaches a peak value of 88 MPa when A1 and Cu are brazed with Zn-15AI filler metal. Microhardness levels from HV122 to HV515 were produced in the three brazing seam regions corresponding to various microstructure features. The Zn- and Al-rich phases exist in the middle brazing seam regions. However, two interface layers, CuZn3 and A12Cu are formed on the Cu side when the A1 content in the filler metals is 2% and more than 15%, respectively. The relationship between intermetallic compounds on Cu side and Zn-xA1 filler metals was investigated.