三区段振动钻削动态轴向力和扭矩的计算机仿真

根据斜角切削理论,假设将钻头主切削刃和横刃上的变形过程分别处理为一系列微小的具有动态特性的振动切削单元,从而构造出三区段振动钻削动态轴向力和扭矩的预报模型,并根据该模型对三区段动态轴向力和扭矩进行了计算机仿真。     

轴向振动钻削过程的有限元动态仿真

针对钻削工艺特点,分析了轴向振动钻削的有限元动态特性。利用有限元分析软件DEFORM建立了轴向振动钻削的有限元数学模型,进行了动态仿真分析,同时,建立了相应的普通钻削系统的有限元模型,对两种加工过程中的切屑、轴向力与钻削扭矩等进行了比较。结果表明,与普通钻削相比,轴向振动钻削过程具有较好的断屑效果,轴向力小,钻削扭矩小。研究结果可对轴向振动钻削机理与特点的研究提供参考。     

应用简易法建立钻削轴向力和扭矩公式

切削力的计算一般可用正交法及简易法。两者都是应用正交回归原理的试验和计算,所不同的是后者在试验数据的处理上采用角正围法,其试验范围点的分布是空间角正交图形,使试验次数减少,计算简化。作者借助于正交法中部分试验数据,应用简易法建立钻削轴向力和扭矩公式。     

轴向超声振动钻削的钻削力和切屑形态研究

建立了钻削加工仿真模型,并采用麻花钻对钛合金进行振动钻削试验。利用ABAQUS软件进行轴向超声振动钻削仿真,试验验证和对比分析了轴向超声振动钻削在不同加工参数下的切屑形态和钻削力。仿真与试验结果表明:随着进给量和振幅增加,钻削力增大,但进给量对钻削力的影响大于振幅;无论是进给量还是振幅的改变,对切屑形态均有影响。     

轴向低频振动辅助皮质骨钻削的钻削力和温升

为了研究轴向低频振动钻削方式在皮质骨钻削中对钻削力和温升的影响,基于一种自主研发的低频振动钻削设备,对常规和轴向低频振动辅助皮质骨钻削的钻削力和温升进行了实验,建立了钻削力和产热速率模型.实验结果表明:轴向低频振动钻削方式的进给力和转矩明显减小,温升降低了3～5℃;通过统计方法确定主轴转速是影响钻削力和温升的最显著因素...     

超声振动微孔钻削轴向力研究

超声振动微孔钻削技术可在硬脆材料上加工出大长径比的微孔,因而越来越受到工业重视。根据动态切削厚度建立轴向力计算模型,使用MATLAB软件模拟得到微细钻头切削轨迹和动态切削厚度,结合已建立的三维钻削模型计算钻削过程中刀具受到的轴向力和转矩,并使用有限元软件Advant Edge来进行切削模拟,得出微细钻头受轴向力情况。可以得出,计算结果和模拟结果中轴向力变化趋势相同。     

阶跃式多元变参数振动钻削的动态轴向力、扭矩及加工精度分析

针对叠层复合材料的微小孔加工,提出阶跃式多元变参数振动钻模型。按照双刃针斜角切削理论和单刃正交切削理论,分别把钻头主切削刃和副刃分解成一系列微小双刃动态斜角切削单元,把横刃分解成一系列微小单刃动态正交切削单元,从而建立了振动钻削叠层复合材料7个区段的动态轴向力和扭矩的理论公式,并以入钻定位误差,孔扩量,出口毛刺高度作为钻削过程质量评价指标进行了试验优化分析,结果表明,阶跃式多元变参数振动钻削显著提高了叠层复合材料的微小孔加工精度。     

碳纤维复合材料钻削仿真及轴向力预测

为了研究钻削加工中切削用量和刀具几何参数对钻削质量的影响,利用ABAQUS软件模拟研究了碳纤维复合材料的钻削过程。以主轴转速、进给量、钻头顶角为设计变量,基于响应曲面法构建了钻削轴向力预测模型,并分析了各变量对轴向力的影响。结果表明:轴向力随主轴转速的增加而降低,随进给量和顶角的增加而增加;对轴向力大小的影响顺序依次为:进给量、转速、顶角。预测模型具有较高的置信度,在实际加工中宜采用较高的主轴转速、较小的进给量和钻头顶角,以降低碳纤维复合材料钻削轴向力,改善钻孔质量。     

轴向振动钻削仿真系统的研究与实现

提出了轴向振动钻削仿真系统的总体结构,详细论述了轴向振动钻削仿真的关键技术及实现方法。该系统采用Pro／E对钻头部件进行几何建模,然后利用OpenGL和VC＋＋将3ds文件导入仿真环境,利用布尔减运算,实时模拟工件材料的去除加工过程,从而模拟整个轴向振动钻削过程。     

Rosen-type Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal piezoelectric transformer

In this study, a Rosen-type Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) single crystal piezoelectric transformer is presented. First, we simulate the operation of this transformer using the finite element method and ANSYS. By adjusting the dimensions of the piezoelectric transformer, a maximum voltage step-up ratio of 138 can be obtained at a frequency of 33.8 kHz when the output part is open. Second, we fabricate a transformer with the size of 20 mm length, 4 mm width, and 1 mm thickness to examine the simulation results. It is found that this transformer exhibits a maximum voltage step-up ratio of 134 at 37 kHz, with the efficiency over 95% when driving a liquid crystal display backlight, which shows good consistency with the numerical simulation results. Besides, we investigate the electrical properties under different frequencies and load resistances. When the input voltage increases, a maximum output power of 1 W is obtained with the temperature rise less than 10 degrees C.     

新型3-PCRNS球面3自由度并联机构

提出一种新型3-PCRNS球面3自由度并联机构,其分支运动链由一个带环形导轨的移动副PC,一个转动副RN (下标N表示三个分支中转动副的轴线都交于一点)和一个球铰S构成。运用约束螺旋理论,对该机构的自由度、奇异位形和输入选取进行分析。在一般非奇异位形下,该机构中三个PCRNS分支运动链对动平台施加三个汇交于机构中心点的约束力,约束机构动平台的3移动自由度,机构具有3转动自由度;在奇异位形下,三个PCRNS分支对动平台施加六个线性相关的约束力,其最大线性无关数为五,机构具有一个绕z轴的瞬时转动自由度。可选用带环形导轨的移动副PC作为主动副,此外该机构动平台绕z轴的转动自由度和其他转动自由度解耦。     

3DXpert金属3D打印斯特林发动机模型

宾夕法尼亚州立大学是世界领先的从事增材制造研究和教育的高等院校之一,拥有很有特色的增材制造与设计工程硕士(MEng AMD)项目。该项目的特色之一是它不仅招收全日制学生,还招收在职工程师,这些工程师可以用宾夕法尼亚州立大学世界校区(网络虚拟校区)在线完成学习。为帮助学生成为技术专家,将其所学的增材制造知识用于实践,该项目将多学科理论知识与亲身实践相结合,学生们可在宾夕法尼亚州立大学增材制造车间获得实践经验。     

Structural properties of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 relaxor ferroelectric thin films on SrRuO3 conducting oxides

Coating of 0.65Pb(Mg(1/3)Nb(2/3))O(3)-0.35PbTiO(3) (PMN-PT) relaxor ferroelectrics by a sol-gel method is followed by growth of epitaxial SrRuO(3) (SRO) metallic oxide electrodes on SrTiO(3) (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN-PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN-PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed.     

并联双三角机构精度分析

并联双三角机构是Stewart平台的一种特殊型式。由于其结构的特点 ,直接精确测量该机构的结构误差有一定困难。文中采用一种有效的误差正解分析方法 ,分析包含球铰、驱动杆长在内的全部结构参数误差以及平台半径的变化对主轴端位姿误差的影响。应用这种误差正解方法可定量地确定结构参数设计精度 ,并能找出特定位姿下的敏感结构参数。为这类并联机器人的设计、制造及装配提供了一种有效的途径     

O.9Pb(Mg1/3Nb2/3)O3-O.1PbTiO3功能铁电薄膜的制备及其电性能研究

利用溶胶凝胶(sol-gel)技术制备Pb(Mg1/3Nb2/3)O3-PbTiO3(PMNT)铁电薄膜,研究了不同的溶剂对溶胶的配制和溶胶稳定性的影响,得到了可以长期稳定放置的溶胶;采用热重分析和差热分析的方法研究了凝胶的热解过程,确定了420℃为溶胶的热解温度,750℃为合理的结晶温度;以Pt/Ti/Si(100)为衬底,成功地制备了0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3铁电薄膜.通过X射线衍射分析了热处理温度对薄膜相的影响.通过高倍显微镜研究了薄膜的表面形态,通过ZT-Ⅱ型铁电参数测试仪对PMNT薄膜进行了铁电性能测试.测试结果表明,制备的PMNT铁电薄膜为具有完全钙钛矿相的弛豫性PMNT铁电薄膜,薄膜无裂纹,致密性好,其剩余极化和矫顽场分别可达到2.5μC/cm2和45kV/cm.     

Evidence of multimicrometric coherent γ′ precipitates in a hot‐forged γ–γ′ nickel‐based superalloy

This paper demonstrates the existence of large γ’ precipitates (several micrometres in diameter) that are coherent with their surrounding matrix grain in a commercial γ–γ’ nickel‐based superalloy. The use of combined energy dispersive X‐ray spectrometry and electron backscattered diffraction (EBSD) analyses allowed for revealing that surprising feature, which was then confirmed by transmission electron microscopy (TEM). Coherency for such large second‐phase particles is supported by a very low crystal lattice misfit between the two phases, which was confirmed thanks to X‐ray diffractograms and TEM selected area electron diffraction patterns. Dynamic recrystallization of polycrystalline γ–γ’ nickel‐based superalloys has been extensively studied in terms of mechanisms and kinetics. As in many materials with low stacking fault energy, under forging conditions, the main softening mechanism is discontinuous dynamic recrystallization. This mechanism occurs with preferential nucleation on the grain boundaries of the deformed matrix. The latter is then being consumed by the growth of the newly formed grains of low energy and by nucleation that keeps generating new grains. In the case of sub‐solvus forging, large γ’ particles usually pin the migrating boundaries and thus limit grain growth to a size which is determined by the distribution of second‐phase particles, in good agreement with the Smith–Zener model. Under particular circumstances, the driving force associated with the difference in stored energy between the growing grains and the matrix can be large enough that the pinning forces can be overcome, and some grains can then reach much larger grain sizes. In the latter exceptional case, some intragranular primary γ’ particles can be observed, although they are almost exclusively located on grain boundaries and triple junctions otherwise. In both cases, primary precipitates have no special orientation relationship with the surrounding matrix grain(s). This paper demonstrates the existence of high fractions of large γ’ precipitate (several micrometres in diameter) that are coherent with their surrounding matrix grain, in a commercial γ–γ’ nickel‐based superalloy. Such a configuration is very surprising, because there is apparently no reason for the coherency of such particles.     

3-RRR 3自由度球面并联机构静刚度分析

3自由度球面并联机构是重要的少自由度机构之一,各支链的构件为球面上的弧杆,其刚度计算十分复杂.基于此,采用计算杆件变形的方法,利用小变形叠加原理,推得机构动平台的角位移、球心点线位移与各支链两构件上力的关系.利用机构静力学分析的结果,即支链两构件上的力与动平台上的外力关系,建立机构动平台、球心点位移与外力的关系.进而得到机构的整体柔度、刚度矩阵.采用正交变换方法,得到机构的6个主刚度指标,最大、最小刚度及所在的方向.研究结果表明,机构的主刚度及主方向随着机构运动位姿的变化而变化,远离零点逐渐增大,其中3个主刚度(即扭转刚度)较大,另3个主刚度(线位移刚度)较小,两者差距巨大.研究成果为该机构的工程设计和应用提供了理论基础.     

3自由度球面并联机构3-RRR静力全解

采用传统的拆杆法建立机构的静力学平衡方程,考虑构件弹性,利用小变形叠加原理建立机构的变形协调补充方程,进而完成3自由度球面并联机构的静力学分析.求得包括机构输入与输出载荷关系的每个构件上的全部力、力矩.通过计算,得到在三种外载荷下构件上的全部(各)力、输入转矩与机构运动位姿的关系图.结果表明,当作用在机构的外力(仅)F通过球心时,机构的输入力矩恒等于零,而构件上的力在全空间内随着机构位姿的变化比较平缓,机构等价一般结构架体而与机构的特性无关.仅在外力矩M作用下,机构的输入力矩、构件上的作用力随着机构位姿的变化与机构的特性相关(与雅可比矩阵的奇异性一致),力与力矩在构件上所产生的两部分力是独立的,并可以分离.研究为该机构在工程中的结构设计与应用提供静力学理论基础和依据.