The deteriorated degradation resistance of Mg alloy microtubes for vascular stent under the coupling effect of radial compressive stress and dynamic medium

The degradation of Mg alloys relates to the service performance of Mg alloy biodegradable implants.In order to investigate the degradation behavior of Mg alloys as vascular stent materials in the near service environment,the hot-extruded fine-grained Mg-Zn-Y-Nd alloy microtubes,which are employed to manufacture vascular stents,were tested under radial compressive stress in the dynamic Hanks'Balanced Salt Solution(HBSS).The results revealed that the high flow rate accelerates the degradation of Mg alloy microtubes and its degradation is sensitive to radial compressive stress.These results contribute to understanding the service performance of Mg alloys as vascular stent materials.

Displacements, Strains, and Stresses Investigations in an Inhomogeneous Rotating Hollow Cylinder Made of Functionally Graded Materials under an Axisymmetric Radial Loading

In this paper, an analytical and numerical study of strain fields, stress fields and displacements in a rotating hollow cylinder, whose walls were completely made in Functionally Graded Materials (FGM), was conducted. We have considered the rotating hollow cylinder submitted to an asymmetric radial loading. It is assumed that, because of the functional graduation of the material, the mechanical properties such as Young elastic modulus and the density varies in the radial direction, in accordance with a the power law function. The inhomogeneity parameter was selected between -1 and 1. On the basis of the second law of Newton, Hooke’s law and the strain-stress relationship, we established the differential equation which governs the equilibrium for a rotating hollow cylinder. We found the analytical solution and compared to the numerical solution obtained by using the shooting method and the fourth order Runge-Kutta algorithm. The analytical and numerical results lead to the conclusion that the magnitude of the tangential stresses is greater than that of the radial stresses. The changes due to the graduation of FGM does not produce consistent variations in the distribution of radial stresses, but strongly affects the distribution of tangential stresses. The tangential stresses, tangential strains and displacements are much higher at the inner surface of the cylinder wall. The internal radial pressure intensely affects the radial stresses and the radial strain.

An Analysis to the Driving Forces for Water and Salt Absorption in Roots of Maize Seedlings Under Salt Stress

When maize seedlings were subjected to salt stress,a decline in root xylem pressure was observed within seconds,followed by a gradual increase in Na＋ deposition in the seedlings.The magnitude of xylem pressure response was positively correlated with,but not proportional to the intensity of the stress.A continuous recording of the xylem pressure profile showed that self-regulation of the xylem pressure existed before and after the imposition of salt stress when the environmental conditions were relatively stable.The salt induced increase in xylem tension dominated the total water potential of the plant when the salt stress was mild,but the osmotic potential became more prominent when the NaCl concentration in the root bathing solution was raised to over 100 mol m-3.The average transpiration rate of the seedlings dropped by 40% when the NaCl concentration in the root ambient was increased to 150 mol m-3.Although salt stress resulted in the decline of both the xylem pressure potential and the osmotic potential in the root xylem,the changes in the total water potential of the root xylem solution were always smaller than the changes in the water （osmotic） potentials of the solution bathing the root.An analysis to the water relations of maize seedlings showed that not only the water potential components,but the radial reflection coefficient of the roots was also dependent on the level of salinity.When the NaCl level in the root bathing solution was raised from 25 to 150 mol m-3,the radial reflection coefficient of the root declined from 0.43 to 0.31.This small change resulted in a remarkable increase in the normalised relative NaCl absorption by 2.4 times,indicating that the radial reflection coefficient of root played a very important role in regulating the absorption of NaCl in maize seedlings under salt stress.

EDGE REYNOLDS STRESS STRUCTURE OF LOWER HYBRID WAVE INJECTION IN THE HL-1M PLASMA

The radial profiles of electrostatic Reynolds stress,plasma poloidal rotations,radial and poloidal electric fields have been measured in the plasma boundary region on the HL 1M tokamak using a multi array of Mach/Langmuir probes.During experiments of lower hybrid wave current drive,the variations in LHW drive power will cause changes in the edge electric field,poloidal rotation velocity and Reynolds stress.The results indicate that sheared poloidal flow can be generated in the edge plasma due to radially varied Reynolds stress.

Effects of shear rates on radial distribution of different types of heavy particles in light media

In order to study distribution properties of different types of heavy particles in light media and to link macro-properties of a system with its micro-structures,radial distribution functions(RDF)of partly charged metallic particles in uni-and bi-polar systems at various shear rates were investigated by Brownian dynamics simulation.The results are good in agreement qualitatively or quantitatively compared with ones in non-polar systems and other works.The investigation indicates that dispersibility of the particles in the uni-polar system of high ionic concentrations is the largest.Therefore,it is the most unfavored to grow into clusters for precipitation.The dispersibility in the bi-polar systems is less than that in uni-polar systems,but larger than that in non-polar systems.Furthermore,all the RDFs at the same shear rates in three systems approach a limit,which implies that a threshold value exists.

Rolling Deformations and Residual Stresses of Large Circular Saw Body

Rolling path squeezes and rolling residual stresses of large diameter circular saw body for wood, generated by rolling pressure from 10 up to 120 bar were examined. X-ray diffraction, Barkhausen noise (BN) and Full Width of the peak at a Half Maximum (FWHM) (o) methods for evaluation of residual stresses were used. Dependencies of a tangential rolling residual stresses inside rolling paths upon rolling pressure p (bar) and rolling area A (mm2) were evaluated. The rolling pressure, as large as 60 bar, resulting in the rolling squeeze as high as 0.04 mm2, and, tangential residual compression stresses inside a rolling path, as large as ?TI = ?822 MPa, was considered to be the largest for the practical application.

单双向循环荷载作用下砂砾料动模量和阻尼比试验研究

通过大型振动三轴试验,研究了单双向循环荷载作用下砂砾料动弹性模量和阻尼比的变化规律,分析围压和径向循环动应力对砂砾料动力参数的影响。研究结果表明:在双向振动三轴试验中,砂砾料的轴向动应变受径向动应力的影响较小,动应变主要与施加的轴向动应力大小有关;单双向振动下砂砾料的动弹性模量均随着动应变的增大而逐渐降低,双向振动时砂砾料动弹性模量随动应变的衰减速率基本不变,在相同动应变下双向振动的动模量均低于单向振动;砂砾料在双向振动时的阻尼比大于单向振动,双向振动时消耗的动应变能更大。通过对两种试验条件下的最大动弹性模量、动模量比进行分析,建立了表述单双向试验条件下最大动弹性模量的换算关系式和双向振动试验中动模量比和动应变的修正模型。

Numerical Analysis of Stresses on Layer-by-Layer Basis in FML Composite Cylinder Subjected to External Hydrostatic Loading

The aim of the research work was to numerically investigate the residual stresses induced between the layers of fiber metal laminate (FML) cylinder (glass/epoxy reinforced aluminum laminates) under buckling hydrostatic loading. For the analysis of buckling behavior of FML cylinders, various fiber orientations such as 0/90&deg, 60/30&deg, ±45&deg and ±55&deg and different FRP thickness of 1, 2, and 3 mm were considered. The aluminum cylinder of inner diameter 80 mm, length 800 mm and wall thickness 1 mm was modeled with SHELL281 element type and a total of 1033 elements were used for computing the induced residual stresses between the layers. The results show that magnitude of residual stresses between the layers decreased along the thickness from outer layer towards the inner layer in sine wave form. The maximum residual Von-Mises stress was at inner aluminum layer while the maximum residual radial stress was at the outermost layer of FML cylinder due to the inward pressure. Among all types of FML cylinder 0/90&deg fiber oriented FML cylinder exhibited the least radial stress and a maximum Von-Mises stress along the FRP thickness.

橡胶球铰径向压缩刚度变化特性的研究

通过试验,系统性分析了某型橡胶球铰径向压缩刚度变化趋势。结果表明,橡胶球铰径向压缩刚度随着试验时间的延长呈现逐渐变小的趋势;随着试验次数和恒温时间的增大慢慢趋于稳定;橡胶层厚度对球铰径向压缩刚度变化趋势的影响不大。

宽转子极无轴承开关磁阻电机径向力模型全周期拓展

针对单绕组宽转子极无轴承开关磁阻电机在定转子极非完全交叠区间的径向悬浮力模型空白、已有定转子极完全交叠区间径向悬浮力模型推导过程复杂且计算量大的不足,首先通过磁场有限元分析,分别确定了该电机在定转子非完全交叠区间和完全交叠区间的电磁场几何分布,计算了气隙磁密,再根据麦克斯韦应力法分别推导了这2个区间的径向力表达式,从而建立该电机在一个完整周期范围内的径向力数学模型,并通过与三维有限元计算结果的对比验证该模型的准确性。相比于利用等效磁路图推导径向力模型而言,该建模过程更简便,计算量也更小。全周期径向力模型的建立,不仅能为电机本体和控制器设计提供理论参考,还有助于提高该电机控制策略设计的灵活性,也可以提高与传统单绕组无轴承电机控制器的通用性。

考虑纵径向热应变的竖向受荷能量桩简化分析方法

为探究温度对能量桩荷载传递机理及相关力学响应的影响,引入平面瞬态温度场方程,将温度场与应力场解耦。基于平面应力模型,将能量桩与桩周土考虑为具有协调变形的整体,计算了径向热应力。在此基础上,将其与双曲线荷载传递模型结合,对桩土界面处的极限摩阻力进行修正。将纵向热应变考虑在竖向荷载传递方程中,得到可同时衡量纵向和径向热效应的竖向受荷能量桩承载特性分析方法。利用增量法对能量桩荷载传递控制方程进行求解,得到桩身轴力、桩侧阻力、桩身位移等相关力学响应。通过与既有文献进行对比,验证了该模型的合理性。通过参数分析,研究了温度和竖向力作用下能量桩的荷载传递特性。结果表明:温度会改变能量桩的荷载传递特性,提高能量桩的运行温度可小幅增加其承载力。该文方法的计算流程清晰,可为能量桩的设计提供参考。

芳纶纤维增强复合材料转子的有限元分析

转子是机械转动部件中的一种,存在于电动机、水轮机、风力发电机、飞轮储能系统等各种机电设备中。在飞轮储能系统中,转子的材料、形状等关键因素都会对系统的性能产生影响。文中以提高飞轮储能系统转子的转速为出发点,建立了复合材料转子的数字化模型,并且对芳纶纤维复合材料转子开展了有限元分析,确定了复合材料层数变化、过盈量变化等对轮毂和轮缘的径向应力、周向应力及转速的影响。数值模拟结果为芳纶纤维增强树脂基复合材料在复合材料飞轮中的应用提供了参考。

基于多目标粒子群算法的隔膜压缩机膜腔曲线优化

膜腔曲线直接影响着隔膜压缩机排气量与膜片可靠性,原始膜腔曲线不能较好满足今后加氢站隔膜压缩机高压力、大流量工况需求。针对此问题,依据隔膜压缩机工作原理,采用多目标粒子群算法对膜腔曲线进行面积与弧长的双目标优化计算,得到了一种新曲线。同时,结合压缩机工程实际对膜腔曲线进行了改进,并对改进后的膜腔曲线与原始曲线进行容积计算与有限元应力对比。研究结果表明:在给定新曲线内参数m=0.95、n=2.5且膜腔半径与膜片厚度不变的情况下,新曲线膜腔下膜片气侧最大径向应力较原始曲线降低了13.89%,膜腔容积较原始曲线增加13.72%。

层状土中静压桩连续贯入现场试验与数值模拟

为探讨层状土中静压桩连续贯入过程的沉贯特性,依托上海市某桩基工程开展静压桩贯入过程现场试验,探究沉桩阻力随贯入深度的演变规律,并结合ABAQUS数值模拟,明确静压桩贯入过程中沉桩阻力、桩周土体竖向应力、径向应力以及径向位移的变化规律。结果表明:层状土的软硬程度制约着沉桩阻力的大小;当桩端贯入浅部粉质黏土层和淤泥质黏土层时,沉桩阻力增长较慢甚至出现减小趋势,当桩端贯入到深部砂质粉土层、粉质黏土层和粉砂层时,沉桩阻力增长较快,其中在砂质粉土层中增长率最高可达174%;桩周土体中竖向应力和径向应力与土层性质密切相关,竖向应力和径向应力最大值均出现在桩端贯入至黏质粉土层时,分别为558.0、1 178.0 kPa,当桩端贯入到下部较软的淤泥质黏土层时,最大竖向应力和径向应力均出现明显退化现象,径向应力退化率达到52%;径向位移随径向距离的增加而减小,其变化规律基本反映了土层性质的变化特征。

径向脉冲力下薄壁内衬再生复合管层间应力分析

为深入研究径向脉冲力对薄壁内衬复合管层间应力的影响,基于以建立的层间相互作用本构关系,对X52N钢板和玻璃钢板通过黏结而成的复合板进行模态试验,并与有限元模拟结果进行对比,验证了胶层本构在有限元模拟中的可行性。通过建立薄壁内衬复合管有限元分析模型,研究径向脉冲力作用下,外基层管厚度与衬层厚度的比值及黏结强度对层间应力状态的影响。研究结果表明,随着层厚比的增加,层间应力的改变较为显著,而黏结强度的影响相对较小。在一定层厚比范围内,外基层管的支持效应能有效降低层间应力,但外基层管厚度也不宜过厚,过厚的外基层管会增加其质量和刚度,进而加大对内衬层的约束作用,从而导致层间应力增加。

不均匀温度场下钢管混凝土拱桥管内混凝土脱空分析

为了解不均匀温度场作用下钢管混凝土拱桥管内混凝土脱空原因,依托高原山区某跨径430 m的钢管混凝土拱桥,进行强辐射、大温差联合作用下拱肋拱顶节段足尺模型试验,分析模型温度场分布,并对该不均匀温度场作用下管内混凝土脱空机理进行研究。结果表明:钢管混凝土拱桥水化阶段和运营阶段径向温度场可简化为多段式折线变化规律。14:00时刻,水化阶段温度沿竖直径向(从向阳侧至背阳侧)先减小后升高再减小,在距向阳侧界面D/8~3D/8处(D为钢管内径)存在一个大温差面,运营阶段温度沿竖直径向(从向阳侧至背阳侧)呈先减小后不变再增加的非对称分布规律,从钢管混凝土界面至距其D/8处温度变化大。混凝土水化阶段和运营阶段管内混凝土脱空机理为:在温度场作用下钢管混凝土界面最大纵向应力差分别高达82.6 MPa和61.95 MPa,最大界面径向拉应力分别为0.8 MPa和2.06 MPa,均超过钢管和混凝土间的粘结强度。

Effect of Initial Stress on Wave Frequencies of Elastic Solid with Rotation

In this paper, the effect of initial stress on the radial vibrations of elastic hollow cylinder with rotation is discussed. The one-dimensional equation of elastodynamic is solved in terms of radial displacement. The frequency equation is obtained when the boundaries are free;fixed and mixed boundary condition is examined numerically. The determination is concerned with the eigenvalues of the natural frequency of the radial vibrations in the case of harmonic vibrations. The effect of rotation and initial stress on the natural frequencies was examined. It was shown that the dispersion curves of guided waves were significantly influenced by the rotation and initial stress of the elastic cylinder. Numerical results are given and illustrated graphically for each case considered. The results indicate that the effect of rotation and initial stress are very pronounced.

真三轴应力下水射流冲击不同层理面倾角煤的破坏机制

煤的层理面倾角(bedding plane angle,BPA)对射流破岩的效果影响显著。为探讨真三轴应力下不同BPA煤的射流破坏机制,开展了不同BPA煤在真三轴应力下的纯水射流冲蚀试验。结果表明,当煤的BPA较低或较高时,射流冲击分别容易形成锥形破碎坑和裂缝坑,破碎坑开口随着BPA的增大由圆形逐步向椭圆形过渡,煤的破坏模式由剪切破坏主导转变为拉伸-水楔效应主导。随着BPA增至60°,破岩体积增加了154.35%。当施加三轴应力时,煤层理面对射流破煤性能的影响被抑制,不同BPA煤的破坏模式仅呈现圆孔破碎坑,水锤压力引起的剪切破坏是煤在三轴应力下破坏的主要原因,60°BPA煤样的破坏体积减少了95.60%,相比其他倾角降低幅度达到最大。BPA对煤的轴向损伤演化具有驱动作用,随着倾角增大,轴向损伤发生波动。当施加三轴应力时,三轴应力抑制了射流破煤的损伤演化,煤的轴向损伤出现收缩。煤的破碎坑壁面的扫描电子显微镜(scanning electron microscope,SEM)结果表明:当施加三轴应力时,0°BPA煤样的破碎孔壁不再出现微裂隙与脆性剪切破坏的痕迹,并且孔隙的数量与尺寸大幅减小;60°BPA煤样的破碎孔壁不再出现水楔作用导致的大量锯齿状痕迹,三轴应力下不同BPA煤的破碎孔壁面均出现明显的延性剪切破坏特征。

圆柱滚子轴承滚子对数修形优化研究

为了提高轴承的疲劳寿命,采用Romax Designer工程分析软件,在充分考虑径向游隙和内外圈相对倾斜量(影响轴承寿命的主要因素)对修形效果影响的基础上,对某大兆瓦风电机组齿轮箱输出轴轴承进行了对数修形优化分析。首先,对国际标准ISO/TS 16281寿命计算方法进行了简要分析;然后,对不同径向游隙情况下对数修形的效果进行了分析;最后,对不同内外圈相对倾斜量情况下对数修形的效果进行了分析。研究结果表明:以轴承最大接触应力最小为优化目标和以国际标准ISO/TS 16281寿命最长为优化目标的轴承对数修形,其最佳修形量不同,相应的ISO/TS 16281寿命有很大不同;在该轴承的具体条件下,以ISO/TS 16281寿命最长为优化目标的最佳修形凸度量对应的ISO/TS 16281寿命比以最大接触应力最小为优化目标的最佳修形凸度量对应的ISO/TS 16281寿命长2.39%~10.63%;以ISO/TS 16281寿命最长为优化目标的最佳修形凸度量对应的ISO/TS 16281寿命比未修形的ISO/TS 16281寿命长111.47%~1054.88%,建议以ISO/TS 16281寿命最长为优化目标对轴承进行修形优化设计。该研究结果可为滚子类轴承的优化设计提供参考。

径向游隙对深沟球轴承疲劳寿命影响精细分析

采用Romax Designer工程分析软件,应用ISO/TS 16281寿命计算方法,根据经典的滚动轴承理论,对某风机用电机轴深沟球轴承,在不同径向游隙时的轴承内部载荷分布、接触应力、套圈滚道当量动载荷和ISO/TS 16281寿命进行了大量的计算,重点对轴承的疲劳寿命进行了精细分析,分析了径向游隙对轴承ISO/TS 16281寿命的影响。研究结果表明,径向游隙对寿命的影响不仅仅是通过对轴承内部载荷分布、接触应力和套圈滚道当量动载荷的影响而对寿命产生影响,还通过对寿命修正系数等因素的影响而对寿命产生影响;相同工况条件下,存在一个相对最优的径向游隙,由于所研究电机的两个轴承所受载荷不同,因而相对最优的径向游不同。研究结果可为深沟球轴承的优化设计提供参考。