模具参数对纯钛等通道转角挤压工艺变形规律影响的有限元分析

等通道转角挤压（Equal Channel Angular Pressing,ECAP）工艺能够通过材料的剧烈塑性变形,获得块状超细晶材料．等通道转角挤压（ECAP）工艺通过改变应变量大小及其均匀性对晶粒细化有着显著的效果．通过DEFORM-3D软件模拟纯钛等通道转角挤压过程,研究了不同模具参数对试样变形的影响规律,给出了不同模具转角、模具外转角和模具内转角半径对ECAP试样变形区等效应变的影响,为获得纯钛试样变形分布提供了有效的规律．     

残余应力及其表征参数对材料滚动接触性能的影响

为了深入研究残余应力对滚动接触的影响规律,建立了圆柱滚子轴承二维有限元简化模型,在施加不同残余应力的基础上进行弹塑性分析,并对残余应力的表征参数如梯度、大小和深度等进行了影响研究。结果表明：残余压应力能使弹性变形阶段的接触应力和塑性变形阶段的塑性应变下降;等大的残余拉应力则使二者增大更大的比率。通过参数研究发现：残余压应力梯度越小,塑性应变越小,残余拉应力梯度越接近0,塑性应变越小;残余压应力越大,塑性应变越小,残余拉应力越大,塑性应变越大;残余压应力加深一定值能够降低滚动接触塑性应变,从而提高疲劳寿命,残余拉应力的加深则会引起塑性应变和疲劳损伤的增大。     

Deformation division of metal flow behavior during extrusion process of 7075 aluminum alloy

To reduce defects caused by non-homogeneous metal flow in conventional extrusion, a die with guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of the deviator stress J ₂ and Lode’s coefficient μ were employed for the division of deformation area. The results show that when the metal is extruded with the guiding angle, no metal flow interface forms at the container’s bottom, the dead zone completely disappears, the deformation types of the metal in the plastic deformation area change from three types to one type of tension, and the homogeneity of the deformation as well as metal flow are greatly improved. The non-homogeneous metal flow at the final stage of extrusion is improved, reducing the shrinkage hole at the axis end. The radial stress of the furthest point from the axis is transformed from tensile stress to compressive stress and the axial stress, and decreased from 70.8 to 34.8 MPa. Therefore, the surface cracks caused by additional stress are greatly reduced.     

压痕诱导Zr65Al7.5Ni10Cu12.5Ag5非晶合金晶化动力学研究

利用X射线衍射仪(XRD),高分辨透射电镜(HRTEM)对Zr65Al7.5Ni10Cu12.5Ag5非晶合金Vickers压痕的微观结构变化进行了研究.在压头棱下方和压头尖端下方区域分别观察到了微米和纳米尺寸的晶粒析出.结合有限元模拟,分析了压应力对晶化过程中形核及晶核长大的影响.在压应力最大的尖端区域形核激活能最小,形核速率最大,需要的晶核长大激活能也最大.压应力越小形核速率越小,需要的晶核长大激活能越小.应力是影响非晶合金在塑性变形过程中发生晶化的动力学因素之一.     

不同大变形等级下层理角度对层状软岩隧道的影响

为探究不同大变形等级下层理角度对层状软岩隧道的影响,依托九绵高速全线软岩大变形隧道,通过岩石力学试验确定遍布节理模型参数,基于数值模拟,探究不同软岩大变形等级（轻微、中等、强烈）下层理角度对层状软岩大变形隧道围岩及支护体系受力变形的影响,并通过现场统计的层理角度与大变形情况对数值模拟结果进行验证。结果表明：1）层理小角度（0°、15°）与大角度（90°）围岩变形、支护结构受力变形较大,随着大变形等级的增大,层理角度引起的围岩支护变化效果越明显。2）随着层理角度的增大,围岩变形从拱底逐渐转移到右拱腰。围岩变形主要发生在隧道轮廓与层理面相切位置,其中拱底及左拱脚对层理角度变化较敏感。3）初支应力偏向及节理塑性区大致与层理弱面法向一致,随着层理角度的增大,节理的剪切塑性区由拱顶、拱底转移到左拱脚、右拱肩,最终偏移到左右拱腰上下位置;相比初支压应力,初支拉应力对层理角度更敏感,垂直节理增大了张拉剪切破坏塑性区贯通的风险,但剪切破坏塑性区半径反而有可能减小。4）现场的统计规律表现为小角度与大角度大变形等级较高,层理角度为60°以下时,岩层破坏发生在拱腰及拱肩处,随着层理角度的增大,有向拱肩发展的...     

Electroless plating composite coatings of Ni-Ti-Re on the surface of diamond

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Principal shear bands in metal plastic deformation

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Experimental study on mechanical behavior of high performance concrete under multi-axial compressive stress

Experimental investigation was conducted to characterize the responses of high performance concrete(HPC) subjected to multiaxial compressive stresses. The HPC specimens were prepared with three different mix proportions, which corresponds to three different uniaxial compressive strengths. The cubic specimens with size of 100 mm for each edge were tested with servo-hydraulic actuators at different stress ratios. The principal stresses and strains of the specimens were recorded, and the failure of the cubic specimens under various stress states was examined. The experimental results indicated that the stress states and stress ratios had significant influence on the strength and deformation of HPC under biaxial and triaxial compression, especially under triaxial compression. Failure criteria were proposed for the HPC specimens under biaxial and triaxial compressive loading. The test results provided a valuable reference for obtaining multi-axial constitutive law for HPC.     

拉压性能不同材料全量型本构关系及其应用

将经典全量理论进行了推广，考察了应力状态及塑性体积变形对拉压性能不同材料塑性行为的影响。计算了环板的应力分布。结果表明。材料的拉压性能不同，对环板的环向应力影响较大，因此，不能将拉压性能不同的材料简化成体积不可压缩的理想材料。     

Finite element and experimental analysis of Vickers indentation testing on Al2O3 with diamond-like carbon coating

Numerical simulation and experimental study of the Vickers indentation testing of the Al₂O₃ ceramic coated by diamond-like carbon (DLC) layer were conducted. The numerical analysis was implemented by a two-dimensional finite element (FE) axis symmetry model. FE analysis results gave insight into the fracture mechanism of DLC films coated on brittle ceramic (Al₂O₃) substrates. The maximum principal stress field was used to locate the most expected area for crack formation and propagation during the Vickers indentation testing. The results show that the median crack initiates in the interface under indenter, before ring crack occurs as the indenter presses down. Finally, the plastic deformation appears when the indenter penetrates into the substrate. The thicker DLC coating increases the Vickers hardness and fracture toughness.     

Dimensional analysis of the impact toughness test for synthetic diamond grits

The method, in which a few carats of diamond grits are placed inside a capsule together with a steel ball, shaken for a number of times, and the unbroken ratio of the grits is then used to evaluate the quality of the diamond, has been well established for many years. However, the unbroken percentage, in an equivalent view, represents the impact toughness of the grits and cannot reflect the value of the crushing energy. Most of the previous empirical formulas obtained from experiments by scholars cannot be applied to practical tests. In this paper, a dimensional analysis was applied to investigate the impact toughness experiment, and the dimensionless relationship has been built among those variables such as the toughness index, the impact time, the impact frequency and the crushing energy per unit area. According to the results of a large number of experiments with synthetic diamond grits of mesh size 45/50, the percentage of the broken grits H is proportional to the impact time T^1.14 when the impact frequency is 2400 r/min, and the impact frequency f^2.576 when the number of impacts is 2000.     

YT01低能量多碰塑性变形研究

为研究碰撞能对金属材料多碰塑性变形的影响,在实验室用自制的凸轮机械式多碰试验机对YT01试样进行了低能量多碰试验,采用坐标网格法、SEM、金相显微镜等方法研究了不同碰撞能对试样的塑性变形率、显微组织结构的影响.实验结果表明:峰值冲击应力不变时,多冲碰撞能量越大,试样累积塑性变形量也越大;随着碰撞次数的增加,试样塑性变形率减小并趋于平缓,塑性变形终止于距冲击表面69 mm处;256 000次碰撞后,试样显微组织细化,晶粒界增多.金属材料多冲碰撞塑性变形不仅与峰值冲击碰撞应力有关,也与冲击碰撞能有关.     

Roadway deformation during riding mining in soft rock

“Riding mining” is a form of mining where the working face is located above the roadway and advances parallel to it. Riding mining in deep soft rock creates a particular set of problems in the roadway that include high stresses, large deformations, and support difficulties. Herein we describe a study of the rock deformation mechanism of a roadway as observed during riding mining in deep soft rock. Theoretical analysis, numerical simulations, and on site monitoring were used to examine this problem. The stress in the rock and the visco-elastic behavior of the rock are considered. Real time data, recorded over a period of 240 days, were taken from a 750 transportation roadway. Stress distributions in the rock surrounding the roadway were studied by comparing simulations to observations from the mine. The rock stress shows dynamic behavior as the working face advances. The pressure increases and then drops after peaking as the face advances. Both elastic and plastic deformation of the surrounding rock occurs. Plastic deformation provides a mechanism by which stress in the rock relaxes due to material flow. A way to rehabilitate the roadway is suggested that will help ensure mine safety.     

平均应力及塑性体积变形敏感材料全量型本构关系及其应用

对拉压性能相同的全量理论加以推广，使其成为能够反映具有塑性体积变形及平均应力敏感特点的拉压性能不同材料的本构模型，并用该本构模型进行了平面应变条件下厚壁圆筒的应力分析，由分析可凶，对于拉压性能不同材料，考虑到平均应力及塑性体积变形敏感时，是不能将其简化为拉压性能相同，体积不可压缩的理想材料的。     

基于非线性的新老混凝土粘结问题的数值模拟及分析

采用ANSYS非线性模块,同时考虑工作过程中大变形、接触等多种非线性因素,对新老混凝土粘结试件和整体试件的复合受力进行数值模拟.从应力分析角度研究在复合应力下,新老混凝土粘结的应力分布规律,考察新混凝土强度、压应力对粘结强度的影响规律,探索新老混凝土粘结复合受力的强度特性.     

W丝／Zr-Ti-Cu-Ni-Be-Co非晶基复合材料的制备与塑性变形

采用渗流铸造方法制备了W丝／Zr—Ti—Cu—Ni—Be—Co非晶基复合材料，研究了复合材料的变形方式及其机理。结果表明：W丝／Zr—Ti—Cu—Ni—Be—Co非晶基复合材料在准静态压缩条件下表现出很高的塑性和断裂能，与纯非晶相比提高超过十倍。随着W丝体积分数的增加，复合材料的变形方式由剪切滑移转变为W丝的弯曲和劈裂。W丝对非晶基体单一剪切带滑移的阻碍，促进多重剪切带的产生和扩展是复合材料产生大量塑性变形的微观机理。     

金属塑性变形的不均匀性

以金属塑性变形理论为基础,分析金属压力加工过程中应力和变形不均匀分布的原因及产生的后果.提出了工艺设计和生产加工过程中可采取的防范措施.     

浸水粉土路基竖向稳定性模型试验研究

针对黄河冲积平原区低矮粉土浸水路基进行足尺模型试验研究,主要研究了不同浸水条件下,粉土路基在分级循环荷载作用下的受力、竖向变形特性。研究证明：黄泛区粉土路基具有强烈的毛细现象和水敏特性;新建及浸水粉土路基中路床区附加应力值较大,后沿深度急剧减小;浸水路基强度衰减现象明显,超载作用下,弹、塑性变形显著,且变形值随着浸水水位的上升而不断增大;路基塑性变形易在饱水区积聚发生,该区域在低应力水平下亦会产生较大的塑性变形。     

Particle Removal Mechanism of High Volume Fraction SiCp/Al Composites by Single Diamond Grit Tool

Particle removal mechanism was presented during machining particle SiC/Al composites with diamond grinding tool. The relevant removal modes and their mechanisms were discussed considering the impact and squeezing effect of diamond grit on the SiC particle. The experimental results show that the aluminum matrix has larger plastic deformation, so the aluminum mixed with the surplus SiC particles is cut from the surface. The SiC particles can be removed in multiple ways, such as broken/fractured, micro cracks, shearing and pulled out, etc. More particles removed by shearing, and less particles removed by fractured during material removal progress can produce a better machined surface.     

Effects of heating temperature on interfacial microstructure and compressive strength of brazed CBN-AlN composite abrasive grits

CBN-AlN composite abrasive grits and AISI 1045 steel were brazed using Ag-Cu-Ti active filler alloy by heating up to the temperature of 890,900 and 920 ℃,respectively,and then held at the temperature for 8 min.Optical microscope,scanning electron microscope and X-ray diffraction equipment were utilized to study the effects of heating temperature on the microstructure of the joining interface.The compressive strength of the brazed composite grits was also measured.The experimental results show that the atoms of Ti,Al,B and N have preferentially penetrated towards the joining interface of composite grits and filler alloy.The compounds of Ti-nitride,Ti-borides and Ti3AlN were formed in the reaction layer.Degradation effect was not made on the compressive strength of the CBN-AlN composite grits when the brazing process was carried out in the temperature range of 890-920 ℃.