具有开槽结构的大尺寸立方形超声塑料焊接焊头的设计

提出一种具有开槽结构的大尺寸立方形超声塑料焊接焊头的设计方法,并对其进行了实验验证.首先通过合理开槽将大尺寸立方形焊头划分为若干单元,然后将各焊头单元和立方形半波振子比较,利用等效机械阻抗的概念得出焊头单元的频率方程,其间考虑了耦合振动的影响.最后利用该方程研究了开槽数、槽宽度以及槽长度等因素对焊头振动特性的影响.按此方法设计加工了几组具有开槽结构的大尺寸立方形焊头,结果表明焊头谐振频率的实测值和理论值吻合得很好.     

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。     

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。     

基于频率和振型摄动的结构损伤识别方法研究

根据矩阵摄动理论,将结构的质量矩阵和刚度矩阵表示为单元损伤参数的函数,提出了根据频率和振型摄动进行结构损伤识别的方法。首先根据结构损伤前后振型变化建立损伤初定方程和损伤确定方程,利用振型摄动求解单元损伤参数,当两次求解得到的同一单元损伤程度基本一致时,可判定该单元损伤;再将损伤识别结果代入基于频率变化的损伤校核方程,用于检验识别结果的准确性。该方法建立的损伤识别方程为超静定方程,可以保证识别结果的唯一性,避免出现"伪损伤"现象。数值算例表明,即使结构出现损伤程度较小的多个单元损伤,只需测试其一阶振型,也可识别。此外,当结构损伤程度较小时,只需采用一阶摄动方程;当结构损伤程度较大时,可采用二阶摄动方程,以提高识别结果的精度。     

A1 超声塑焊变幅器的有限元分析

本文根据有限元原理自编了ＭＶＵＨ程序，可以在微机上运行，并对超声塑料焊接用的变幅器（焊头）进行分析计算，比较了平板变幅器开槽前后以及槽宽对固有频率及变幅器工作端面位移振幅分布的影响，表明开槽后变幅器的固有频率下降，位移分布较均匀，而槽加宽时固有频率略有下降。为检验程序的正确性，曾用ＡＤＩＮＡ程序包进行计算比较，得到较满意的结果，并对固有频率进行实验验证，理论计算和测量结果符合较好。     

余弦型扭转振动超声变幅杆的研究

从波动方程出发,对余弦型变幅杆的扭转振动进行了系统探讨。利用传统方法,推导出了"余弦型变幅杆"扭转振动的频率方程和各特性参数表达式,为余弦型扭转振动变幅杆的设计提供了一定的理论依据,对巳有阶梯型、锥型、指数型杆的结果是一个完善。     

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.     

抗性负载超声复合变幅杆振动特性研究

在抗性负载情况下,利用纵振型变幅杆等效四端网络,对频率方程和放大系数进行了研究,并推导出圆锥过渡段和指数过渡段阶梯形复合变幅杆频率方程和放大系数的一般公式;并通过MATLAB编程,分别绘制了共振频率及放大系数随负载变化的曲线图。这将对超声复合变幅杆的设计和应用提供一定的理论依据。     

功能梯度材料Timoshenko型剪切梁的自由振动分析

基于Timoshenko梁理论,研究各向异性功能梯度材料梁的自由振动。假设材料参数沿梁厚度方向按同一函数规律变化,建立了功能梯度材料梁的振动方程,求得简支条件下其自振频率表达式。通过算例,给出指数函数梯度变化Timoshenko梁的自振频率和模态图,结果表明不同梯度变化对材料结构动力响应有较大影响。该方法为发展功能梯度材料梁的设计与数值计算提供了理论依据。     

变频率条件下Galfenol驱动器参数辨识方法研究

利用线性压磁方程和欧拉-伯努利方程建立了基于Galfenol(Fe-Ga合金)驱动器的动力学模型,在变频率条件下,驱动磁场存在扩散效应,直接影响模型对于驱动器动态特性的预测。为解决普通梯度算法无法收敛的问题,提出了一种基于遗传算法的动力学模型参数辨识方法,无需满足持续激励条件,可对变频率条件下驱动器的压磁系数和阻尼系数进行辨识。计算结果表明,辨识算法收敛性好,经过7次迭代以后即可寻找到最优值。同时进行了对比实验,结果显示驱动频率低于220Hz时模型参数变化较小,更高驱动频率时模型参数发生较大的变化。利用该方法可以在变频率条件下准确掌握驱动器结构参数的变化,为Galfenol驱动器磁路的设计与控制提供理论指导。     

超声珩齿中弯曲振动变幅器的设计与研究

齿轮是超声珩齿加工中的一类特殊负载,它的振动特性和固有频率对系统的加工频率影响很大.由于齿轮的尺寸和质量大,且其尺寸不能任意更改,现有的振动系统设计理论,如全谐振设计理论、质量置换理论、局部共振理论等,都不能适用于这一情况.为解决此问题,应用Mindlin中厚板理论、变幅杆设计原理和机械阻抗理论对由变幅杆、齿轮组成的变...     

Design of highly uniform spool and bar horns for ultrasonic bonding

Although the groove and slot have been widely utilized for horn design to achieve high uniformity, their effects on uniformity have not been analyzed thoroughly. In this work, spool and bar horns for ultrasonic bonding are designed in a systematic way using the design of experiments (DOE) to achieve high amplitude uniformity of the horn. Three-dimensional modal analysis is conducted to predict the natural frequency, amplitude, and stress of the horns, and the DOE is employed to analyze the effects of the groove and slot on the amplitude uniformity. The design equations are formulated to determine the optimum dimensions of the groove and slot, and the uniformity is found to be influenced most significantly by the groove depth and slot width. Displacements of the spool and bar horns were measured using a laser Doppler vibrometer (LDV), and the predicted results are in good agreement with the experimental data.     

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。     

超声珩齿振动系统动力学特性分析与仿真

为研究超声珩齿振动系统的非谐振设计,通过MATLAB软件对振动系统的动力学频率方程进行求解,分析了变幅杆设计长度和变幅器振动频率对频率方程解误差的影响,并得出一组变幅器的设计参数。为验证非谐振设计方法的可行性,通过ANSYS模态分析,能使变幅器的谐振频率与理论设计的结果基本一致。     

Acoustic Horn Design and Effects of Process Parameters on Properties of Dissimilar Ultrasonic Welding Aluminum to Brass

Ultrasonic welding technology is a new and emerging concept, which can be applied to many industrial applications. The vital part of this technology is the horn, which acts as a tool, upon which the pressure and high-frequency vibration is applied to create a solid-state weld. In this study, a special type of horn is designed and its length is determined analytically. Dimensions obtained by finite-element method (FEM) are employed for the horn used in the present experiments to weld brass with aluminum sheet of thickness 0.1 mm. The dynamic analysis is also performed to find out the stress and amplitude distribution in the horn under loading conditions. Welding has been carried out using various parameter combinations in order to improvise the weld strength. Maximum weld strength of 4.05 MPa is obtained under the optimum welding conditions of 0.21 s weld time, 0.26 MPa weld pressure, and 60 µm vibration amplitude. The microhardness test also has been done on the optimized results to show the plastic flow at the weld zone. It confirms that the hardness of both materials up to 20 µm distance around the weld zone is increased with respect to the parent materials.     

Numerical analysis of welded joint treated by explosion shock waves

This paper focuses on the simulation of welding residual stresses and the action of explosion shock waves on welding residual stresses. Firstly, the distributions of welding temperature field and residual stress on a butt joint were numerically simulated with the sequentially coupled method. Secondly, the effect of explosion shock waves, produced by plastic strip-like explosive, on welding residual stress distribution was predicted with coupled Lagrange-ALE algorithm. It was implicated that explosion treatment could effectively reduce welding residual stresses. The simulation work lays a foundation for the further research on the rule of explosion treatment’s effect on welding residual stresses and the factors that may influence it.     

Unsteady slot Suction from a High-Reynolds-Number Cross-Flow

The problem of unsteady suction from a high-Reynolds-number cross-flow into a slot is considered in the case where the suction is driven by a time-dependent slot pressure. The model uses linearised asymptotics based on a small parameter that defines the suction strength. An integro differential equation is derived for the mass flow into the slot and this is solved for various time-dependent slot pressures of practical interest. Closed-form expressions are also found for the shape of the shear layer dividing the external flow from the fluid in the slot. For a step function change in the slot pressure, a non-monotonic decay to the steady solution is observed, and for an oscillatory slot pressure there is a phase lag between the slot pressure and the mass flow. For rapidly changing slot pressures it is shown that slot injection can occur, even when the slot pressure remains below the free-stream pressure.     

Film cooling effectiveness for subsonic slot injection into a cross flow

Summary A model is developed that allows the prediction of the film cooling effectiveness produced by slot injection into a uniform cross flow. The model relies on the fact that when the slot pressure exceeds the cross flow pressure by a small amount only so that injection is weak, the resulting small parameter may be exploited to solve the flow problem. The energy equation for the flow may then be solved to determine how much protection cold gas injection gives to the wall downstream of a slot. Although the leading order energy equation must be solved numerically, a simple asymptotic expression may also be derived to allow predictions of heat transfer at large distances from the injection slot.