Influence of layer orientation and interlayer bonding force on the mechanical behavior of shale under Brazilian test conditions

The mechanical behavior of inherently anisotropic shale rocks under Brazilian test conditions are investigated in this study based on experimental studies and numerical simulations. The effects of the weak lamination planes and interlayer bonding force of these layers on the failure strength and fracture patterns are studied systematically. Numerical simulations using particle flow code in two dimensions based on the discrete element method showed a good agreement with the experimental results in the failure strength and fracture patterns. The shale revealed strong anisotropic behavior with the failure strength perpendicular to the lamination plane greater than failure strength parallel to lamination plane. The failure strength of the different interlayer bonding force against the layer orientations changed significantly. Four types of fracture patterns were observed: curved fracture, broken-linear fracture, layeractivated fracture, and central-linear fracture. The observed fracture patterns are either or a combination of tensile and/or shear fractures. Increase in interlayer bonding strength decreased the quantity of micro cracks and this directly led to reduction in the anisotropic behavior. Overall the layer orientation and interlayer bonding force of the shale thus play a very important role in the anisotropic behavior of the shale.

THE APPLICATION OF ARTIFICIAL NEURAL NETWORKS TO INVESTIGATION ON THE THICKNESS OF INTERMETALLIC LAYER UNDER SOLID-LIQUID PRESSURE BONDING OF STEEL AND ALUMINIUM

Artificial neural networks (ANN), being a sophisticated type of information processing system by imitating the neural system of human brain, can be used to investigate the effects of concentration of flux solution, temperature of liquid aluminium, temperture of tools and pressure on thickness of the intermetallic layer at the interface between steel and aluminium under solid-liquid pressure bonding of steel and aluminium perfectly. The optimum thickness has been determined according to the value of the optimum shearing strength.

Influence of holding time on microstructure and shear strength of Mg alloy/steel joint diffusion bonded with Zn-5Al interlayer

The diffusion bonding of AZ31B Mg alloy and Q235 steel was investigated with a Zn-5Al alloy as interlayer and under different holding time ranging from 3 to 1 200 s. The microstructure and phase compositions of bonded joints were characterized by scanning electron microscopy( SEM),energy dispersive spectrometer( EDS) and X-ray diffraction( XRD)methods. The shear strength of Mg alloy/steel joints was measured by tensile tester. It was found that the microstructure of bonded joints evolved dramatically along with the prolongation of holding time. Under the holding time of 3 s,the main part of joint was composed of MgZn_2 phase and dispersed Al-rich solid solution particles. When increased the holding time more than 60 s,the excessive solution of AZ31B into the interfacial reaction area led to the formation of coarse phase and eutectic microstructure,and also the complex Fe-Al and Mg-Al-Zn IMCs at transition layer closed to Q235 steel side. According to the tensile testing characterizations,the joints obtained under holding time of 3 s exhibited the best shear strength of 84 MPa,and the fracture occurred at the intermediary part of joint where the flexible Al-rich solid solution particles could help to impede the microcrack propagations. With prolonging the holding time to 600 s,the shear strength of joints was deteriorated enormously and the fracture position was shifted to the transition layer part closed to Q235 steel.

A Novel Method for Evaluating Fatigue Properties of Bonding Layers Used in Bridge Deck Pavement

A new method was used to evaluate the fatigue properties of the bonding layer used in the bridge deck pavement. The shear fatigue test of three bonding layers was conducted on a dynamic shear rheometer（DSR）. The fatigue formulas were gained for these layers. The experimental results indicate that, at the same torque level or at the same frequency, neoprene latex asphalt bonding layer exhibits excellent fatigue performance when compared to other two bonding layers.

TEM STUDY OF BONDING LAYERS IN DISSIMILAR ALLOY EXPLOSIVE BONDING JOINTS

The bonding layers in dissimilar alloy explosive bonding joints,γ/α stainless steels, copper/carbon steel and brass/γ-stainless steel have been studied by means of TEM tech- nique.The results show that the bonding is obtained by diffusion and local melting at the con- tact surface.The structure of bonding layer not only responds to the compositions of the bond- ing alloys,but also the difference between their thermal conductivities,melting points and recrystallization temperatures,Because of the small molten region and fast cooling rate,the structure of molten region could be amorphous or microcrystals,and both stable and metastable phases exsist.

Evolution mechanism of the interfacial reaction layers in the joints of diffusion bonded Mo and Al foils

Mo foil （10 -20 μm in thickness） and Al foil （20 -60 μLm in thickness） were vacuum diffusion bonded at 600 - 640 ~C under 20 MPa for 54 min - 6 h. The joints were examined by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） to study the evolution mechanism of the reaction layers. The results show that Al atoms diffuse into Mo grain boundaries and form reaction products as Mo3Al8, MoAl4 , MoAl5 and MoAl12. The surface oxide film is eroded by the growths of the reaction products that plow into the lamellar texture of Mo grain boundaries. Mo3Al8 layer grows by ＂taking root＂ downwards and transforms into MoAl4 and MoAl5 phases upwards by absorbing Al atoms. MoAl12 layer grows up from MoAl5 layer in the same way. When the supplement of Al atoms ceases, MoAl12 transforms reversely into MoAl5 and MoAl5 into MoAl4 via the loss of Al atoms. However, MoAl4 continues to precipitate from Mo3Als layer. At last, there are MoAl4 and Mo3Al8 remained on the joint interface.

Reactive diffusion bonding of SiCp/Al composites by insert layers of mixed Al-Si and Al-Si-SiC powders

Mixed Al-Si and Al-Si-SiC powders were employed as insert layers to reactive diffusion bond SiCp/6063 MMC （metal matrix composites）. The results show that SiCp/6063 MMC joints bonded by the insert layer of the mixed Al-Si powder have a dense joining layer with a typical hypoeutectic microstructtn＇e. Using the mixed Al-Si-SiC powder as the insert layer, SiCp/6063 MMC can be reactive diffusion bonded by a composite joint. Because of the SiC segregation, however, there are a number of porous zones in the joining layer, which results in the bad shear strength of the joints reactive diffusion bonded by the insert layer of the mixed A1-Si- SiC powder, even lower than that of the joints reactive diffusion bonded by the insert layer of the mixed Al-Si powder. Ti and Mg added in the insert layers obviously improve the strength of the joints reactive diffusion bonded by the insert layer of the mixed Al- Si-SiC powder, especially, Mg has a more obvious effect.

Characteristic of Bond Zone between Powder Surfacing Layer and Base Metal

The characteristic of the bond zone between Ni-based alloy light beam surfacing layer(SL)and base metal(BM)was investigated by scanning electron microscope,energy dispersive spectrometer and X-ray diffraction.The results show that the bond zone,which consists ofγ-Ni orγ-(Fe,Ni)planar crystal band close to SL andα-Fe bright band close to heat affected zone(HAZ),is actually the transition zone of composition and microstructure between SL and HAZ,and the metallurgical bond interface lies between theα-Fe bright band and HAZ.With the increase of light beam heat input from 2kJ/mm to 4kJ/mm,the width of the bond zone increases from 4μm to 15μm,and the morphology of bond interface changes from zigzag to straight.The formation of bond interface indicates the formation of reliable metallurgical bond between SL and BM.

Diffusion bonding of copper alloy to stainless steel with Ni and Cu interlayer

CuAlBe alloy is an attractive shape memory alloy with many important usages in industrial field, in order to spread its range of application it is desirable to be able to join CuAlBe soundly with other metallic materials, for example stainless steel; however the weldability between CuAlBe alloy and stainless steel has never been studied, therefore an experimental investigation of different transition metals was carried out in the diffusion bonding joints of Cu alloys (CuAlBe) to stainless steel (1Cr18Ni9Ti). The microstructure and phase composition of the joint were analyzed by SEM, EPMA and X ray diffraction. The following conclusions have been drawn: 1) The joint strength with Ni interlayer is higher than that with Cu interlayer when the welding parameters are the same; 2) When Ni interlayer is thinner, Al will interact with Ni and Fe, and the intermetallic compounds such as Fe 3Al are formed in the interface, which decreases the strength of the joints; 3) When the bonding temperature is higher, because the diffusion of Cu in Ni is faster than Ni in Cu, a Kirkendall effect occurs, which also decreases the strength of the joints.

Reactive Diffusion Bonding of SiCp/Al Composites by Insert Powder Layers with Eutectic Composition

Mixed Al-Si and Al-Cu powders were investigated as insert layers to reactive diffusion bond SiCp/6063 metal matrix composite （MMC）. The results show that SiCp/6063 MMC joints bonded by the insert layers of the mixed Al-Si and Al-Cu powders have a dense joining layer of high quality. The mass transfer between the bonded materials and insert layers during bonding leads to the hypoeutectic microstructure of the joining layers bonded by both the mixed Al-Si and Al-Cu powders with eutectic composition. At fixed bonding time （temperature）, the shear strength of the joints by both insert layers of the mixed Al-Si and Al-Cu powders increases with increasing the bonding temperature （time）, but get maxima at bonding temperature 600℃ （time 90 min）.

BASE-INDUCED RELEASE OF MOLECULES FROM HYDROGEN BONDING DIRECTED LAYER-BY-LAYER FILM

On the basis of hydrogen bonding directed layer-by-layer (LbL) assembly we have fabricated two multilayersystems, poly(acrylic acid) bearng spironaphthoxazine (PAA-SO)/poly(4-vinylpyridine) and carboxyl-terminated polyetherdendrimer (dendrimer-COOH)/poly(4-vinylpyridine). UV-Vis spectroscopy indicates that either PAA-SO or dendrimer-COOH can be released from the corresponding multilayer assemblies upon immerssion in a basic aqueous solution.Furthermore, the rate of molecule release can be controlled either by changing the pH value or by adjusting the layerstructure.

Shear Creep Properties for Bond Layer at Wood-CFRP Interface

To know more about the bond layer’s long term properties between carbon fiber reinforced polymer(CFRP) sheets and the wood member as well as its connecting point,shear creep performance was studied using a consistent load with the Burger model.And samples were placed in dry conditions (temperature 60℃,relative humidity 90%) and wet conditions(temperature 24℃,relative humidity 45%).Results showed that the Burger model precisely simulated the bond layer’s short-term shear performance(correlative coefficient R^2≥98%). Compared to dry conditions,with wet conditions, the amount of creep was larger.Also,with an increase in thickness of the bond layer,creep deformation and stress relaxation increased.For high stress levels,a high creep rate,which could lead to a fracture of the bond layer,should be contained. Under the consideration of safety,a pressure(above 0.05 MPa) should be placed on the connection process between CFRP and wood to reduce the thickness of the bond layer.Also,in application,the shear stress level of the bond layer should be maintained within 50%of the maximum stress level.

超音速火焰喷涂制备CoNiCrAlY涂层性能研究

CoNiCrAlY涂层常用作工作层和金属基体之间的过渡层。采用了SHV-50超音速火焰喷涂设备在45钢表面制备了CoNiCrAlY涂层。分析了CoNiCrAlY涂层的微观组织结构、显微硬度、孔隙率、表面粗糙度、结合强度、电化学性能。结果表明:SHV-50超音速火焰喷涂获得的CoNiCrAlY涂层的孔隙率为0.48%,涂层的平均显微硬度为497.2HV0.2,涂层结合强度均值达70 MPa,抗热震次数达26次,涂层的表面粗糙度平均值为Ra6.43,利于工作层与过渡层的结合。CoNiCrAlY涂层的抗电化学腐蚀能力强于基体。SHV-50超音速火焰喷涂设备制备的CoNiCrAlY涂层可用作工作层和金属基体之间的过渡层。

多层堆叠中晶圆级金金键合的可靠性提升

基于电学互联的贯穿硅通孔技术和高精度金金圆片键合技术,开发了一套可应用于制备三维集成射频(RF)收发系统的工艺,并利用反应离子刻蚀机(RIE)中氧气加六氟化硫的键合前处理技术解决了多层堆叠中键合强度较弱的问题。经过扫描电镜(SEM)观察和分析,键合强度弱确认为芯片贴装过程中晶圆表面沾污所致。传统的湿法前处理有一定的局限性,氧气等离子体方法去污能力较弱,均无法用于去除遗留的沾污。利用反应离子刻蚀机氧气加六氟化硫的前处理方式进行键合前处理,不仅增强了去污能力,而且将旧金表面低活性的金层去除,露出干净、活性高的新金表面,有效提升了金金键合的强度,为多层金金键合提供了一种有效的键合前处理方法。

基于机器学习的黏钢构件黏接层缺陷识别方法研究

对黏钢加固结构黏接层缺陷对超声检测信号的影响进行了深入研究,并提出了一种基于机器学习的黏接层缺陷识别的新型方法.首先,该文基于直接接触式的脉冲回波反射法对黏钢构件进行有限元模拟,并阐述了超声波在黏钢构件中的传播规律;其次,通过分析局部段超声回波信号及相关信号特征,讨论了不同缺陷变量对超声回波信号的影响规律;最后,建立了黏钢构件超声时程响应数据集,并对比了不同机器学习模型对缺陷大小、位置的分类识别性能,形成了黏钢构件黏接层缺陷识别方法.结果表明,局部段超声回波信号及其特征随着缺陷大小、位置的改变呈规律性变化,能够对缺陷信息进行初步区分.同时,该文提出的基于RF模型的黏钢构件黏接层缺陷识别方法能够有效识别黏钢构件黏接层缺陷,具有较广阔的工程应用前景.

Al掺杂CoCrNiAlY金属黏结层的高温抗氧化行为研究

采用电弧离子镀技术在GH4169高温合金表面制备CoCrNiAlY和Al掺杂CoCrNiAlY涂层,系统开展涂层的高温抗氧化行为与机理研究,利用XRD、SEM和EDS等微尺度分析表征方法,全面解析涂层的物相结构特征、氧化反应产物及表/截面微观形貌。研究结果表明,未掺杂CoCrNiAlY涂层表现较差的结构稳定性和抗氧化性能,涂层呈持续氧化增重趋势,200 h涂层质量增重达0.38 mg/cm^(2)。然而,Al掺杂显著提升CoCrNiAlY涂层的高温抗氧化性能与结构稳定性,质量增重率先迅速增大后趋于稳定,200 h涂层的质量增重约0.30 mg/cm^(2)。本研究结果充分证实Al元素掺杂可显著改善CoCrNiAlY金属黏结层抗氧化性能。

1 mm圆柱形压电微驱动器的有限元分析与设计

研究设计了一种直径为1 mm、长度为5 mm的压电微驱动器,拟用于光学相干层析成像(OCT)内窥镜样机驱动与控制。利用有限元分析(FEA)软件对定子进行有限元建模和仿真,研究了材料参数和结构尺寸对定子振动特性和模态频率的影响。研究结果表明:微型驱动器定子的一阶弯曲振动频率为21 kHz。定子谐振频率随定子长度的增加急剧降低,随陶瓷厚度的增大而增大;粘接剂的材料特性与厚度对定子的模态频率影响不大,但对定子的振动特性有较大影响。当激励电压为100 V时,频率为21 kHz,驱动器空载转速达到400 r/min,堵转力矩为2.5 mN·m,基本满足OCT内窥镜应用要求。

碲化铋基热电器件的界面研究进展

热电转换技术是一种直接将电能和热能相互转换的技术,在航空航天、新型能源、电子通信等领域具有重要的应用价值。碲化铋材料是最早被发现的半导体热电材料之一,它在室温附近所展现出的优异热电性能,使碲化铋基热电器件成为目前唯一成功商业化应用的热电器件。近年来,随着5G光通信和电子芯片行业对新型制冷技术需求的持续增长,热电制冷器件的应用备受瞩目。此外,碲化铋基发电器件在低温废热回收领域也具有巨大的应用前景。然而,碲化铋基热电器件发展仍然存在一些挑战,其中器件的界面问题严重制约了其产业化应用。尤其在发电器件制备方面,仍然缺乏有效的高温界面阻挡层材料。本文从碲化铋基热电器件应用面临的界面问题出发,重点介绍相关界面研究进展,阐述界面对器件性能的影响机制,并分析改善界面性能的有效策略。

TiC钢结硬质合金与堆焊过渡层的界面组织及性能研究

采用ERNiCrMo-3焊丝在TiC钢结硬质合金上堆焊过渡层,使用扫描电子显微镜、能谱仪、显微硬度计、万能试验机对不同热输入下TiC钢结硬质合金/ERNiCrMo-3熔敷金属界面的组织性能进行研究。结果表明:TiC钢结硬质合金和ERNiCrMo-3熔敷金属之间存在厚度为60~150μm的熔合区。随着焊接热输入的增加,熔合区的厚度逐渐增加;当热输入为3.5 kJ/cm时,界面处组织分布均匀,无气孔、裂纹以及晶粒异常长大现象。母材和堆焊金属之间存在元素扩散现象,二者实现了冶金结合;母材和堆焊焊缝之间存在一个硬度逐渐变化的缓冲区域;TiC钢结硬质合金/ERNiCrMo-3堆焊金属界面剪切强度最高可达到443 MPa,满足恶劣工况下对耐磨件与基体结合性能的要求。

退火温度对Mg/Al轧制复合层组织和性能影响

采用扫描电镜(SEM)、光学显微镜(OM)、拉伸实验机、X射线衍射仪(XRD)等研究了退火温度(220~380℃)对MgAZ31和Al(1A99)轧制复合层的微观组织结构、力学性能、拉伸断口的形貌及物相成分影响。结果表明:随着退火温度的升高,镁、铝原子逐渐进行扩散迁移,扩散层厚度增加,从220℃时的1.80μm逐渐增加到380℃时的45.10μm,且扩散层的生长速率逐渐增大;当退火温度达到300℃时,断口处出现密集的韧窝,镁基体的断裂形式向塑性断裂转变,镁基体的塑性增强,断口的物相为Mg_(2)Al_(3)相,抗拉强度达到最大,为272.35 MPa,此时试件的综合力学性能达到最佳,故300℃为最佳退火温度。