长条形超声塑料焊接焊头的简明设计

焊头是超声塑料焊接设备中一个很重要的部件,其设计的好坏直接关系到焊接质量。将长条形焊头通过合理开槽划分为若干相等的单元．每个单元可作为复合阶梯形变幅杆来处理,用传递矩阵法得出了焊头单元的频率方程,为长条形开槽焊头的设计提供了理论依据。实验表明,利用该方程设计的长条形焊头,其实测频率与设计频率符合很好。本设计方法物理意义明显,计算简单,非常适合工程设计。此外利用该方法可方便的求出开槽数、槽宽度以及槽长度等因素对焊头尺寸的影响,也为焊头的优化设计提供了一定的理论依据。     

超声塑料焊接工具横向振动及开槽的研究

本文利用耦合振动理论研究了大尺寸超声塑料焊接工具的三维振动，推出了决定工具谐振频率与其材料及尺寸之间关系的频率方程。还研究了工具的横向振动与开槽之间的关系，从理论上得出了决定工具开槽位置的数学表达式，在某种程度上解决了大尺寸工具的开槽问题。实验表明，大尺寸工具的设计频率与测量值基本符合，开槽大大地改善了工具辐射面上的位移分布的均匀程度。     

基于力耦合的非谐振单元组成的超声变幅器设计

传统的超声振动系统全谐振设计方法要求组成超声振动系统的各个单元有相同的谐振频率,各个组成单元的结构尺寸由谐振频率确定,而超声珩齿系统中的齿轮结构尺寸是由它的使用要求决定,是非谐振单元,不能用全谐振理论设计,本文采用力耦合方法,将齿轮简化为环盘,将它和变幅杆组合并联合建立动力学方程,实现了非谐振单元组成的超声变幅器的设计。     

大尺寸立方体开槽超声塑料焊接工具头的优化设计

谐振频率、频率间隔性、振幅均匀度是大尺寸超声塑料焊接工具头设计中的几个主要指标。基于工程实际,以工具头纵向长度、槽宽度及槽长度为设计变量,纵向谐振频率和频率间隔值为状态变量,振幅均匀度为目标函数,利用有限元软件ANSYS的参数化分析技术,对大尺寸立方体超声塑焊开槽工具头进行了优化设计。结果表明,该优化方法能很好地解决大尺寸超声塑焊工具头的设计问题,既提高了设计效率,也降低了设计成本。     

开槽填充黏弹性材料对圆锯片振动的影响分析

为了揭示开槽填充黏弹性材料对锯片振动特性的影响规律,分别对无槽及开槽填充材料两种锯片模型的阻尼以及动态响应特性进行比较研究.首先,基于模态应变能法计算锯片模态阻尼比,利用Rayleigh阻尼表征模型结构阻尼,获得2种锯片模型的模态阻尼常数;然后,建立锯片有限元瞬态动力学分析模型,得出2种锯片模型的振动响应及衰减历程曲线,分析开槽填充材料对锯片振动的影响;最后,针对2种锯片进行试验模态分析,获得振动响应曲线,对比数值分析结果与试验数据曲线,两者吻合良好,证明了有限元数值分析的可靠性.结果表明:在相同的动力学条件下,开槽填充材料会显著降低锯片上质点的振动速度,缩短锯片振动的衰减历程.研究结果为开槽低噪声锯片的结构创新设计与开发提供了有效的理论依据.     

蛋糕超声波辅助切割刀的优化设计

为了适应切割大尺寸、粘性食品的要求,设计了频率为20k Hz的食品用超声切割刀。采用有限单元法对其进行模态分析,获取各阶固有频率、刀具刃口振幅分布等参数。通过对切割刀刀身结构进行敏感性分析,得到了切割刀结构尺寸对切割刀输出端位移的均匀性、纵向振动固有频率与邻近频率的影响。对影响程度大的结构参数进行了二次优化,使所设计的切割刀在20k Hz频率附近以纵向振动模式为主,谐振频率与邻近固有频率间距足够大,刃口振幅位移分布均匀性得到较大的提高。     

基于局部共振理论的齿轮成形磨削纵弯谐振系统设计

为获取超声磨齿纵弯谐振系统的有效设计方法,基于局部共振理论,对磨削系统中的大负载成形砂轮盘振动系统进行设计与研究。根据振动单元间的连续条件和边界条件,按照一体式设计思路建立纵弯谐振系统的理论模型和频率方程。基于该理论模型,利用MATLAB、ANSYS等分析软件对系统各部分尺寸参数进行设计与优化,并进行有限元模态分析、阻抗分析试验和超声谐振试验。仿真与试验结果表明,系统谐振效果和振型曲线输出比较稳定,振幅与理论仿真预期结果相符,且系统实测谐振频率、设计频率以及仿真频率之间误差维持在5%范围内,具有较好的设计精度。从而,有效验证了基于局部共振设计理论的砂轮盘纵弯谐振系统设计方法的可行性及准确性。     

基于最小能量原理的矩形平面预应力索网结构大变形自由振动研究

以中关村文化商厦30m×70m平面索网为工程背景,考虑矩形索网结构大变形产生的几何非线性的影响,用最小势能原理推导了非线性振动的微分方程并给出了解法;研究了线性振动频率、大振幅振动频率和大变形后小振幅的振动频率计算方法;结合实例对3个振动频率进行了计算分析。给出的非线性振动方程和解法简单准确,为大跨度平面索网结构抗风抗震设计提供参考。     

基于功率流有限元方法的异形薄板能量密度求解

在机械工程中,对结构在不同频率激励下的振动响应进行分析预测具有重要的意义。功率流有限元法以其适用频率范围较广,可得到结构响应的细节信息等优点成为振动分析领域的研究热点。利用功率流有限元方法对薄板的弯曲波能量密度进行了求解,使用加权残差法导出了薄板单元节点的能量密度残差,利用线性四边形网格对薄板进行网格划分并在此基础上建立了单元的有限元方程,进一步地通过对单元有限元方程的组装和求解得到了薄板上各个节点处的能量密度响应,引入线性三角形网格以处理复杂形状薄板能量密度的求解,对使用功率流有限元方法求解任意形状薄板上的能量密度分布问题具有一定意义。     

基于混合单元建模的复合板热诱导结构振动研究

针对复合板的热诱导结构振动问题，提出一种新的混合单元计算模型，将三维和二维单元组成混合单元，利用不同类型单元体现复合结构中不同的材料特性，实现对真实复合结构物理特征的高精度模拟。在此基础上基于虚功原理建立了三维形式的复合板瞬态热弹性动力学方程，利用该方法对空间大尺度复合薄板的热诱导扰动进行研究。仿真结果表明，结构固有频率和热容是决定热诱导振动发生的主要内囚，对于一些刚度较大的空间复合薄板，由于空间约束环境弱，整体频率低易发生热诱导结构振动。本研究对于空间大尺度复合平板结构的工程设计具有一定的参考价值。     

空心变截面杆的等效网络

设计换能器时一般忽略螺杆的影响,将前、后盖板和压电陶瓷晶堆作为均匀的实心杆件,这种方法有一定的近似性.将任意空心变截面杆等效为同种形状的实心杆件,并推导出了出几种常见形状空心杆件的等效几何参数及其网络传输系数,从而可以利用等效网络的方法方便准确地设计超声振动系统.     

Effect of units in different sizes on thermal fatigue behavior of 3Cr2W8V die steel with biomimetic non-smooth surface

Aiming to deeply research the thermal fatigue behavior of 3Cr2W8V die steel with biomimetic surface, the specimens with different sizes of concave-shape and striation-shape units were processed by laser technique. By establishing cross-section model of the units and by calculating their volume, the size of the units was quantitatively expressed, and its effect on thermal fatigue behavior of 3Cr2W8V die steel was investigated and compared. The results showed that the units in different sizes have different degrees of effects on resisting the thermal fatigue cracks; especially those in the larger size can play a greater role in preventing the crack initiation and blocking the crack propagation; and further the influence of the size of the units on thermal fatigue behavior is more sensitive to resist the crack propagation.Based on the self-strengthening of the units, the increased resistance of the units in the larger size to crack initiation can be attributed to the crack prevention mechanism owing to the reduced probability of crack nucleation and the enhanced resistance to plastic deformation on the biomimetic surface, while the enhanced resistance to crack propagation is due to the crack blocking mechanism that results in the slow crack growth rate.     

抛物线型超声变幅杆的探讨

提出了一种新型的变幅杆-抛物线型变幅杆。根据变截面杆纵向振动的波动方程,推导出抛物线型变幅杆的频率方程、节点位置方程、放大系数、形状因数等参数,并用有限元软件ANSYS分析了几个半波长抛物线型变幅杆,得出共振频率。结果表明:抛物线型变幅杆在保持圆锥变幅杆形状因数较大的优点上,放大系数有所提高;有限元分析结果与理论值符合的较好。     

Microstructure and mechanical properties of horns derived from three domestic bovines

The microstructure and mechanical properties of horns derived from three domestic bovines (buffalo, cattle and sheep) were examined. The effects of water content, sampling position and orientation of three bovid horns on mechanical properties were systematically investigated by uniaxial tension and micron indentation tests. Meanwhile, the material composition and metal element contents were determined by Raman spectroscopy and elemental analysis respectively, and the microstructures of the horns were measured by scanning electron microscopy (SEM). Results show that the mechanical properties of horns have negative correlation with water contents and depend on sampling position and orientation. The spatial variations of the mechanical properties in horns are attributed to the different keratinization degrees in the proximal, middle and distal parts. And the mechanical properties of horns in the longitudinal direction are better than those in transverse. Among the three kinds of horns, the mechanical properties of buffalo horn are the best, followed by cattle horn, and those in sheep horn are the worst. This is due to the differences in material composition, metal element, and the microstructures of the horns. But the mechanical properties of buffalo horns are not dependent on the source of the buffalo. Therefore, regular engineered buffalo keratinous materials with standard mechanical properties can be obtained from different buffalo horns by using proper preparation methods.     

Untersuchungen zur abrasiven Wirkung verschmutzter Schmieröle in engen Strömungsquerschnitten

Investigation of the Abrasive Action of Contaminated Lubricating Oils in Narrow Cross-Section Flow Channels . An apparatus is described with which abrasive wear in narrow cross-section channels in model test-pieces, structural units and products can be studied. In the study of abrasive wear, a distinction is made between wear by contacting structural parts and erosion by suspended particles. Narrow cross-section flow channels in pumps, valves, cocks and sealing slits of all kinds are particularly subject to abrasive wear by contaminated operating liquids. Hard particles (e.g. abraded metal particles or minerals such as quartz and corundum) have a particularly severe abrasive effect. Particle size and its distribution, particle quantity and operating pressure all have considerable influence on wear. A simple quantity, which in practice yields valuable information on wear in narrow cross-section channels, is the ratio of particle diameter to channel width (d/h₀). In design, a distinction has to be made between static and dynamic slits. The investigations here described were restricted to static slits of breadth between 100 and 600 μm. Particle sizes of 5, 14, 30 and 50 μm were studied at pressures of 60, 120 and 300 bar. Wear increases with increasing operating pressure and with increasing value of d/h₀. Even at d/h₀-values of 0,02 and contamination concentrations of 20 mg/l, measurable wear occurs. At d/h₀-values of 0,5, static slits begin to block. By means of a graph of wear against d/h₀, information on the susceptibility to wear of various widths of static slits over a wide range of operating conditions can be obtained. This gives important indications as to the necessary fineness of filter.     

一种适用于声化学的新型复合超声变幅杆

提出一种新型复合超声变幅杆,该变幅杆总长为一个波长,由五段组成,其中三段为等截面圆柱杆,两段为变截面圆柱杆。给出了该类复合变幅杆的设计方法,并计算了两个实例。结果表明,和普通使用的半波长复合变幅杆相比,该类复合变幅杆具有在不减少甚至增大辐射面积的情况下放大振幅的特点,这对提高整个超声系统的辐射声功率和辐射效率具有积极意义。此类复合变幅杆特别适合在声化学等超声液体处理领域使用。     

Characterization of poly(L-lactide)-block-poly(ethylene oxide)-block-poly(L-lactide) triblock copolymer by liquid chromatography at the critical condition and by MALDI-TOF mass spectrometry

Poly(L-lactide)-block-poly(ethylene oxide)-block-poly(L-lactide) triblock copolymers (PLLA-b-PEO-b-PLLA) were fractionated in terms of the number of LLA units by liquid chromatography at the critical condition (LCCC) of PEO block. The fractionated samples were identified using MALDI-TOF mass spectrometry. The dependence of the LCCC retention of the diblock and triblock copolymers on the degree of polymerization of PLLA block(s) follows Martin's rule very well. Unlike the case of PEO-b-PLLA diblock copolymer reported earlier (Lee, H.; et al. Macromolecules 1999, 32, 4143), however, a splitting of the elution peaks containing the same number of LLA units was found. The peak splitting was ascribed to the different length distributions of PLLA blocks at the two ends of the PEO block. From the relative intensities of the peaks, the split peaks were assigned to different isomeric structures of the PLLA blocks. From these results we conclude that the interaction of the triblock copolymers with the stationary phase is affected by the distribution of the interacting blocks at the two ends of the center PEO block, in addition to the total number of LLA units in the triblock copolymer.     

An analogy between radially-loaded rubber bush mountings and axially-loaded bonded rubber blocks

The validity of the widely-quoted experimental data for the reduced radial stiffness of a cylindrical rubber bush mounting of finite length is discussed by proposing an analogy between such a bush and two tandem cylindrical rubber blocks of circular cross-section which are axially loaded. Previously-derived expressions for the radial stiffness of a finite-length cylindrical bush and the apparent Young’s modulus of an axially-loaded bonded rubber block of circular cross-section are exploited. This leads to an adaptation of the data that incorporates the possible failure of the bushes due to internal rupture. The analytically-derived values of this stiffness are demonstrated to have improved agreement with these appropriately modified data. Representative numerical results are presented for a range of bushes in tabular and graphical forms.     

余弦型和类余弦型超声变幅杆的研究

本文导出余弦型纵振变幅杆和扭振类余弦型变幅杆的频率方程及参数的计算式和曲线，对简单型杆及由其与圆柱型段和双曲正割型段组成的复合杆件进行谐振频率和放大系数测试，实验结果与理论值基本吻合。     

矩形横截面耦合振动复合变幅杆的设计

本文研究由一部分变截面杆和一部分定截面杆构成的大尺寸矩形横截面复合变幅杆。文章中引进了变幅杆各轴向的等效弹性常数，并推出了具体表达式，利用表观弹性法探讨了大尺寸矩形变幅杆的耦合振动，得出了变幅杆的共振条件，即频率方程。实验表明，与一维理论的计算结果相比，利用耦合振动理论得出的变幅杆的共振频率更加接近于实测值。