不同晶型纳米氧化锆增韧氧化铝基陶瓷刀具材料研究

利用不同晶型纳米氧化锆的相变增韧和纳米颗粒的增韧作用来提高氧化铝基体的综合力学性能。研制成功了纳米ZrO2增韧氧化铝基陶瓷刀具材料A15Zc和A20Z(c+m),在其最佳烧结工艺条件下,A15Zc和A20Z(c+m)材料的抗弯强度、断裂韧度和维氏硬度分别为812.83MPa、5.5MPa.m1/2、16.68GPa和869.48MPa、5.85MPa.m1/2、16.09GPa。刀具的主要增韧机理是相变增韧、裂纹偏转、裂纹弯曲和纳米颗粒的桥连等。     

SiO2颗粒增强酚醛树脂基摩擦材料力学性能研究

为探讨陶瓷颗粒对树脂基摩擦材料力学性能的影响,以SiO_2颗粒增强酚醛树脂基摩擦材料为例,利用三点弯曲实验研究颗粒特征对弯曲强度的影响,建立材料内部弹性应力场分布模型,并从细观力学角度进行分析。实验结果表明:添加二氧化硅陶瓷颗粒后,复合材料的弯曲强度降低、弹性模量升高;复合材料弯曲断裂截面显示脆性断裂特征,断裂过程中裂纹遇到颗粒贯穿通过;复合材料弯曲强度随颗粒含量增加而降低,随颗粒弹性模量增加先减小后增大。理论分析表明:陶瓷复合树脂基摩擦材料内部最大应力值位于颗粒边缘处;最大应力值随颗粒与基体弹性模量比值增大而增大;复合材料的平均应力与颗粒的含量成正相关。实验和理论研究表明,陶瓷颗粒添加引起材料内部应力集中,且与颗粒弹性模量和颗粒含量成正相关。     

沥青基碳/碳复合材料的弯曲性能

采用三点弯曲法测试了单向和三维四向碳纤维增强的两种沥青基碳/碳(C/C)复合材料(1D-C/C和3D-C/C)在室温及1 800℃高温时的弯曲性能,分析了增强体结构、温度对C/C复合材料弯曲性能的影响,并探讨了其弯曲断裂时的界面机制。结果表明:3D-C/C的弯曲模量高于1D-C/C的,但其抗弯强度却明显低于1D-C/C的;1D-C/C的弯曲断裂呈脆性断裂,而3D-C/C的弯曲断裂则表现出明显的假塑性特征;对同一种增强体结构的沥青基C/C复合材料,在1 800℃时的弯曲性能高于其在室温时的。     

不同缺口取向X70管线钢三点弯曲断裂试验研究

通过对X70管线钢不同厚度含不同V型缺口取向试样在不同温度下三点弯曲断裂试验，研究高韧性管线钢缺口取向、试验湿度和分层裂纹对材料韧性的耦合效应。发现X70管线钢具有严重的各向异性现象，其在平行钢板表面方向和沿钢板厚度方向力学性能差异较大；试样缺口取向不同，试样破坏形式不同，但均产生垂直于板厚方向的分层裂纹；分层裂纹的产生可以提高试样的单位厚度裂纹起始功和单位厚度破坏总功；分层裂纹以及由分层裂纹所产生的效应主要是试样中的应力状态和材料固有的片状缺陷或夹杂所致，有确定的方向性，同时与试验温度又有密切的关系。     

40Cr钢的三点弯曲疲劳损伤在线跟踪测量

用系统分析的方法，在线跟踪观察40Cr钢的三点弯曲疲劳损伤过程。实验结果表明，用系统分析的方法提取损伤参数，能够反映材料的三点弯曲疲劳损伤整个过程；实验结果也从一个方面验证了双线性损伤规律的合理性。此外在相同的实验条件下，损伤参数直观、敏感地反应出试样表面状态等因素对疲劳寿命的影响。     

掌指关节压缩与弯曲实验研究

研究掌指关节压缩与弯曲力学性能，为临床提供生物力学参数。在电子万能试验机上，对正常国人新鲜尸体掌骨进行压缩与弯曲实验。获得了掌骨压缩最大载荷、最大应力、最大应变数据以及掌骨弯曲最大载荷、最大弯矩、最大应力、最大应变数据，并对实验结果进行分析讨论。     

CFRP薄壁管件耐撞性能的实验研究

利用万能试验机开展三点弯曲和准静态轴向压溃实验研究了CFRP薄壁管腔结构件的耐撞性能，结果表明准静态轴向压溃的比性能率为60~80kJ/kg，破坏形式为花瓣型；而三点弯曲实验说明管件的侧向吸能比较差。管件的轴向与侧向初始载荷峰值与厚度成等比例的增长，轴向和侧向的比吸能率略有提高；偏薄管件在轴向压溃过程中易发生局部屈曲，偏厚管件则趋向于稳定压溃吸能。     

基于Matlab偏曲轴少齿差行星减速器最大承载能力的研究

为了解决少齿差内啮合弹性啮合效应系数是个变量问题,提出了偏曲轴少齿差行星减速器最大承载能力的概念,以单齿的齿根应力达到疲劳弯曲强度为出发点,建立各齿对的法向间隙与虚拟啮合点、最大承载能力之间数学关系,并基于Matlab对该减速器最大承载能力进行估算,且通过实例及其实验加以验证,同时研究了中心距对计算结果影响。结果表明,该方法提高了设计效率,并充分考虑弹性变形对提高承载能力影响,降低了成本。     

Hopkinson杆三点弯曲试验中试样与支座接触状态分析

分析Hopkinson杆动态断裂试验中试样与支座的接触状态.研究表明,试样与支座的接触状态取决于试样几何和材料性能参数.在按现行三点弯曲试验方法进行的试验中,确实存在试样与支座脱离接触的现象,并且试样在支座开始受力前起裂.因此,所谓Hopkinson杆三点弯曲试验实际上是单点弯曲试验.并给出标准Charpy试样在Hopkinson杆动态断裂试验中试样与支座之间保持接触的条件.     

层间短纤维增韧复合材料层板横向裂纹扩展的试验研究

对于Zylon短纤维层间增韧层板和普通碳纤维树脂复合材料层板,利用自制小型弯曲试验器和90o铺层缺口试件进行四点弯曲和三点弯曲试验,研究和比较两种层板中基体横向裂纹的发生与扩展规律。结果表明,两种层板基体横向开裂应力基本相同,而裂纹扩展有明显差别。普通层板基体裂纹贯穿90o铺层、不稳定扩展,平均速度约为17.7m/s;而层间增韧层板发生短纤维桥联,使基体横向裂纹的不稳定扩展停止,因而层间短纤维可显著提高基体横向裂纹扩展阻力。试验应用表明,小型弯曲试验器是有效的,尤其便于在光学显微镜下进行实时细观观测。     

Anisotropic characterization of particleboard by ultrasonic and static techniques

The anisotropic properties of particleboard (PB) are studied by ultrasonic and static techniques. Ultrasonic wave velocity and modulus of elasticity in bending (MOE) are determined at parallel and perpendicular to manufacturing direction and at the interval angles of 15° in clockwise and counter-clockwise directions. The experimental results are compared with the predicted values using empirical formulas such as the Hankinson and Jacoby equations. The results show that the ultrasonic wave velocity and MOE are the highest in the parallel direction in PB and the lowest values occurred in the perpendicular direction. The predicted ultrasonic wave velocity using the Hankinson and Jacoby equations are in close agreement with the measured value. The relationship among particles angle, ultrasonic wave velocities, and MOE could be successfully presented by cubic and quadratic regression equations as well.Translated from Defektoskopiya, Vol. 40, No. 9, 2004, pp. 42–50. Original Russian Text Copyright © 2004 by Kazemi Najafi, Abbasi Marasht, Ebrahimi.This article was submitted by the authors in English.     

Geometrically nonlinear analysis of functionally graded shells

The nonlinear response of functionally graded ceramic-metal shell panels under mechanical and thermal loading is studied. The nonlinear formulation is based on a modified version of Sander's nonlinear shell theory, in which the geometric nonlinearity takes the form of von Kármán strains. It is assumed that the material properties vary through the thickness according to a power-law distribution of the volume fraction of the constituents. The displacement field is expressed in terms of a set of mesh-free kernel particle functions. The bending stiffness is evaluated using a stabilized conforming nodal integration technique, and the shear and membrane terms are computed using a direct nodal integration to eliminate shear and membrane locking. The arc-length method, combined with the modified Newton-Raphson approach, is employed to trace the full load-displacement path. The characteristic of the displacement and the axial stress in panels under thermal and mechanical loading is investigated, and the effects of the volume fraction exponent, boundary conditions, and material properties on the nonlinear response of shell panels are also examined.     

A simple and fast TEM preparation method utilizing the pre-orientation in plate-like, needle-shaped and tubular materials

In order to observe anisotropically grown crystalline materials perpendicular to a certain preferred orientation, a standard cross-sectional TEM preparation method has been modified. The material is embedded in an organic epoxy resin between two Si-wafers. Plates, needles and tubes lay flat inside the resulting sandwich, which is then cut into slices perpendicular to the wafers. The slices are thinned by mechanical abrading and, finally, by ion milling. Crystals located near the central hole are electron-transparent, and their orientation often allows for an observation along the desired direction. The usefulness of this procedure is demonstrated on the examples of high-Tc superconductors and vanadium oxide nanotubes.     

Some failure modes of four clinical bone cements

The fracture or failure behaviours of four commercial acrylic-based bone cements have been examined in tensile, bending and compression modes, and their mechanical properties are reviewed. It was found that Palacos R-40 bone cement had high radiopaque agent concentration, with high surface hardness. It exhibited a much lower bending strength and bending modulus compared with the other three bone cements (CMW1, CMW2000 and Simplex P). The textures of tensile fracture surfaces produced were similar for the four bone cements studied. The fracture surface was fragmented by crevices, which developed through the matrix and around large undissolved polymethylmethacrylate (PMMA) beads. Three bands with different features existed on the bending fracture surfaces, with an abrupt transition between them. It appears that the agglomerates of zirconium dioxide particles are implicated in Palacos R-40 bone cement fracture surface. The examination of compressive failed specimens revealed that a 'yielded crack band' existed across the transverse section. Plastic deformation resulted in the PMMA beads being squashed in the longitudinal direction and dilated in the transverse direction.     

Development of a new method to determine bending sequence in progressive dies

In progressive dies, two or more stations are used to produce sheet metal components. In each station, one or more processes are applied. The progressive dies reduce the time and cost of producing complex sheet metal components. However, the design and manufacture of these dies are difficult. CAD/CAM systems have been proved to be very useful tools for this task. The main problem of CAD/CAM systems used in progressive die design is determining the bending operations sequence. In this paper, a new method for determining the sequence of the bending operations is described. In this method, sequencing is done in two stages. First, the bending operations, which can be carried out simultaneously, are defined by a classification method. In this method, all the bends are initially divided according to their bending directions (feed direction or perpendicular to it). Then for each direction, the bends are divided into operation groups according to classification rules. Three rules are used to determine the bending operation groups in this paper. These rules are based on relations between the bends in the component. The sequence of the bending operation groups is then determined using fuzzy set theory. Four components taken from industry and previous papers are used to show the capabilities of the proposed method.     

单模态驱动的V形板结构直线超声电机

为克服双模态超声电机频率一致性的限制和进一步提高V形直线超声电机的输出性能,设计了一种板结构直线超声电机。该电机包括V形定子和直线导轨,定子由2个相互垂直的板结构振子构成,驱动足位于2个变截面梁的连接点上。利用两振子弯曲振动形成的对称和反对称模态,通过两相模态切换,实现电机的双向运动。研制了样机并对其进行了模态实验和机械输出特性测试。借助三维激光测振仪分别测试了驱动足在接触和不接触导轨情况下的运动轨迹,阐述并验证了单模态超声电机的驱动机理。实验结果表明,该电机具有良好的机械输出特性:最大空载速度为690 mm/s,最大推力达100 N,推重比达59.7。     

高强度高韧性云母微晶玻璃的热压制备和力学性能

采用热压形变工艺,成功地制备出了具有择优取向的高强度高韧性云母微晶玻璃。用三点弯曲法和单边切口梁（SENB）法在不同工艺条件下对微晶玻璃的抗弯强度和断裂韧度进行了测定。结果表明：在热压形变过程中,玻璃相发生粘性流动,云母晶体随之转动并产生择优取向,增强了对平行于热压方向的裂纹的偏转和分叉作用,材料的力学性能得到显著提高。基础玻璃在950℃晶化3h并经1000℃热压形变处理后,所得的云母微晶玻璃在热压方向上的抗弯强度和断裂韧度分别可达390Mpa和2.92MPa·m{sup}(1/2),比热压前提高了2倍多。     

柔性再生碳纤维湿法取向仿真模拟及其复合材料性能研究

基于珠链模型,采用离散单元法对纤维模型进行柔性化处理;通过搭建EDEM-Fluent耦合仿真模型,对柔性再生碳纤维在渐缩流场中的流动取向过程进行仿真模拟。采用湿法取向技术对6 mm纤维进行重新取向排布制备取向毡,将仿真结果与实验结果进行对比。采用模压法制备了碳纤维/环氧树脂基复合材料,对其力学性能进行表征。结果表明：在纤维跟随流体运动的过程中,纤维会受到轴向剪切力的作用,发生不同程度的弯曲变形,并沿着流体流动方向发生旋转,从而在移动过程中完成取向。利用二维方向张量对纤维毡取向度进行表征,其取向度为98%;制备的取向复合材料弯曲强度和模量较未取向材料分别提升70.6%和88.5%。     

Two-Body Abrasive Wear of the Outside Shell Surfaces of Mollusc <Emphasis Type="Italic">Lamprotula fibrosa</Emphasis> Heude, <Emphasis Type="Italic">Rapana venosa</Emphasis> Valenciennes and <Emphasis Type="Italic">Dosinia anus</Emphasis> Philippi

Natural biological surfaces and biomaterials have some distinguishing properties for adapting themselves to natural surroundings. The outside shell surfaces of mollusc species often undergo the abrasive wear action from the sand particles in water sand slurry in natural conditions. The two-body abrasive wear behavior of the outside shell surfaces of three mollusc species Lamprotula fibrosa Heude, Rapana venosa Valenciennes and Dosinia anus Philippi was examined. Abrasive material used for tests were quartz sand (96.5 wt.%) with three different size ranges and powdered bentonite (3.5 wt.%). The two-body abrasive wear tests were run on a rotary disc type abrasive wear testing machine. The results showed that the abrasion resistance of the outside shell surfaces of the three mollusc species was higher when the corrugations on the shell surfaces were perpendicular to the sliding direction of the abrasive material than that when the corrugations on the shell surfaces were parallel to the sliding direction of the abrasive material. Basically, the shell of Lamprotula fibrosa Heude possessed the highest abrasion resistance among the three species of shell; the abrasion resistance of the shell of Rapana venosa Valenciennes was the lowest; and the abraded depth of the three species of shell increased with an increased abrasive particle size and relative sliding velocity. The abraded surfaces were observed with scanning electron microscope.     

Mechanical anisotropy of the human knee articular cartilage in compression

Articular cartilage exhibits anisotropic mechanical properties when subjected to tension. However, mechanical anisotropy of mature cartilage in compression is poorly known. In this study, both confined and unconfined compression tests of cylindrical cartilage discs, taken from the adult human patello-femoral groove and cut either perpendicular (normal disc) or parallel (tangential disc) to the articular surface, were utilized to determine possible anisotropy in Young's modulus, E, aggregate modulus, Ha, Poisson's ratio, v and hydraulic permeability, k, of articular cartilage. The results indicated that Ha was significantly higher in the direction parallel to the articular surface as compared with the direction perpendicular to the surface (Ha = 1.237 +/- 0.486 MPa versus Ha = 0.845 +/- 0.383 MPa, p = 0.017, n = 10). The values of Poisson's ratio were similar, 0.158 +/- 0.148 for normal discs compared with 0.180 +/- 0.046 for tangential discs. Analysis using the linear biphasic model revealed that the decrease of permeability during the offset compression of 0-20 per cent was higher (p = 0.015, n = 10) in normal (from 25.5 x 10(-15) to 1.8 x 10(-15) m4/N s) than in tangential (from 12.3 x 10(-15) to 1.3 x 10(-15) m4/N s) discs. Based on the results, it is concluded that the mechanical characteristics of adult femoral groove articular cartilage are anisotropic also during compression. Anisotropy during compression may be essential for normal cartilage function. This property has to be considered when developing advanced theoretical models for cartilage biomechanics.