脉冲激光冲击LD31薄板变形的实验和数值模拟

激光冲击板料变形是利用高能脉冲激光和材料相互作用诱导的高幅冲击波的力效应使板料产生塑性变形的新技术 ,本文利用Nd :Glass脉冲激光对厚度为 0 .8mm的LD31薄板进行激光冲击变形实验。所用激光参数为 :脉冲能量 15～ 30J,脉冲宽度 2 5ns ,光斑直径Φ8mm。利用ABAQUS软件对激光冲击下板料的变形过程进行了数值模拟 ,建立了激光冲击波加载的数学模型 ,探索激光冲击的主要参数和板料变形之间的相互关系 ,为激光冲击变形工艺参数的优化、板料变形的理论分析 ,实现大面积金属板料的柔性激光冲压成形提供依据。     

铝合金板激光冲击变形实验及有限元模拟

为了研究金属板料在脉冲激光辐照下的响应、激光冲击下板料的变形特性、激光脉冲能量对金属板料变形量的影响以及脉冲激光光斑内冲击波压力的分布情况,采用高功率钕玻璃激光系统对LD31板进行了单次冲击变形实验,同时利用有限元软件ABAQUS对板料变形过程进行了模拟。结果表明,激光冲击条件下板料变形时呈现粘塑性性质;激光脉冲能量是影响板料变形量的主要因素,且板料变形大小随脉冲能量的增加呈非线性增大;激光冲击时激光光斑作用区域内冲击波压力并不是均匀分布,而是沿径向减小。     

金属复合板激光弯曲过程中翘曲变形数值模拟

翘曲变形是影响复合板激光弯曲成形精度的重要因素。基于ANSYS软件和电子探针面扫描实验,建立了含结合面的不锈钢-碳钢复合板激光弯曲有限元模型,对一次扫描过程中产生的翘曲变形进行数值模拟。通过模拟激光作用下复合板的温度场、应力场及残余应力分布,结合自由端的变形,分析了翘曲变形产生的过程及原因。模拟结果表明:激光扫描过程中,受初始温度及边界效应的影响,扫描线上各点最高温度分布的不均匀百分比为18.33%。经0.2 s热传导及热量散失的共同作用后,扫描线中间区域出现热累积现象,热应力增大,产生了翘曲变形。对扫描线到自由端整体区域进行残余应力模拟分析可知,板材在其区域内部产生了翘曲作用力与区域周边约束反作用力,其大小和方向与翘曲的变形吻合。对比实验数据和模拟结果,翘曲线最大误差为3.90%,其中,弦高误差为3.33%,为复合板激光弯曲成形的角度控制提供了计算依据。     

激光点热源作用下动态微变形的数值模拟与校验

采用MSC．Marc非线性有限元软件，对试件在激光点热源作用下动态微变形过程进行了数值模拟。通过激光反射放大系统测量了试件在激光点热源作用下的动态微变形过程。模拟值与实测值的结果表明：热应力和相变应力的共同作用使得试件产生微变形，最终试件的变形方向取决于热应变和相变共同作用的结果，朝向激光束或背向激光束。比较实验值和模拟值，发现变形的最大值相近，变形过程却略有不同。考虑到激光点热源作用下有限厚度的试件内，温度场分布出现的反常效应，即内部的温度大于边界温度，提出采用波动理论修正经典的热传导计算模型，可望有效地提高模拟过程的计算精度。结论为进一步研究薄板激光弯曲的变形机理及变形过程奠定了基础。     

Al-Mg-Sc合金板料激光冲击成形的有限元分析

激光冲击板料变形是利用高能脉冲激光和材料相互作用诱导的高幅冲击波的力效应使板料产生塑性变形的新型激光加工技术。基于激光冲击成形原理,建立了有限元模型,利用有限元分析软件MSC.Marc,对激光冲击载荷下Al-Mg-Sc板料成形过程进行模拟。结果表明:仿真结果与实验结果取得了良好的一致性,随着激光能量的增大,变形量增大;当激光能量大于30J时,板料最大变形量随着约束孔径的增大而增大,当激光能量小于30J时,板料最大变形量随着约束孔径的减小而增大,在距冲击中心9mm附近和冲击中心处,属于易破裂区域,距冲击中心3mm附近,应力值也比较大。     

激光原位辅助单点金刚石刀具系统热变形仿真与实验分析

激光原位辅助单点金刚石刀具加工过程中,金刚石刀具吸收激光能量会产生相应的热变形,对加工精度产生影响。通过有限元软件COMSOL Multiphysics建立了激光透过金刚石刀具的热变形数值模拟,得到了金刚石刀具在激光辐照下的温升与热变形规律,并采用高精度的热像仪和电感测微仪记录刀具的温度变化和变形量。研究表明刀具模拟的温度和热变形与实验结果吻合较好,在激光辐照初期,刀具受热伸长趋势较为明显,当激光辐照超过550 s后,刀具热变形趋于稳定。刀具在激光功率为10 W、30 W辐照下,刀具稳态温度为29.96℃与49.85℃,刀具热变形测量值分别为0.78μm, 2.23μm。     

金属板料激光冲击成形数值模拟及工艺分析

激光冲击成形是指利用激光诱导产生的冲击波压力使板料变形的一种新的板料塑性成形技术。本文在激光单点冲击金属板料变形实验的基础上 ,对大面积金属板料的激光多点冲击成形进行了探讨 ,并以金属板料方盒形件为例 ,采用数值模拟技术 ,对无间隔连续冲击和间隔冲击两种方法进行了分析比较。结果表明 ,采用粗冲成形和精冲成形的工艺过程 ,可有效提高板料激光冲击成形的精度。     

激光喷丸成形中的残余应力

通过对激光喷丸成形(LPF)中残余应力场分布的研究,找出单点喷丸残余应力分布形式,以及单点多次、多点不同路径喷丸中后续冲击对前次冲击残余应力分布的影响规律。对准确控制残余应力分布,获得激光喷丸后所需的板料形状具有指导意义。利用钕玻璃高功率脉冲激光对厚度为1.2 mm的LY12CZ硬铝合金进行了单点激光喷丸,用X衍射应力测定仪考察了单点冲击后材料表面及深度方向的残余应力,用厚度为2 mm 的6061-T6铝合金板料进行三列窄条激光喷丸变形实验。以ANSYS/LS-DYNA有限元分析软件为平台,建立了具有一定精度的激光喷丸过程中冲击波压力的加载模型,对板料的变形过程进行了数值模拟, 分别考察了不同激光能量,板料尺寸,冲击路径等工艺参数对残余应力场分布的影响。实验结合数值模拟探索激光喷丸的主要参数和残余应力场之间的相互关系。     

基于温度场评估的激光熔覆顺序决策方法研究

为了在激光熔覆再制造过程中得到更优的激光熔覆顺序选择决策方法,采用有限元法对平面基材多道激光熔覆传热学模型的温度场瞬态解进行了理论分析,并利用基于热电偶的测温系统验证了整个数值模拟过程的可靠性。提出了一种评估选择法,即利用数值模拟来分析和评估基体瞬态温度场,根据评估准则选择熔覆过程激光扫描顺序的轨迹优化方法。结果表明,取得单向逐次和评估选择样件的实验硬度数据分别为625.38HV,620.58HV,623.34HV,680.09HV,673.58HV和683.01HV,变形均值为0.9722mm和0.6458mm;评估选择法有最均匀的温度场,熔池周围有最大的温度梯度,其能产生较大的熔覆层硬度及较小的组织尺度,同时测量变形较小。该方法为激光熔覆的顺序选择提供了重要的参考价值。     

激光喷丸后板料表面微观形貌的可视化数值研究

对不锈钢SUS304板料进行了激光喷丸成形的可视化数值模拟分析和实验研究。以有限元分析软件ABAQUS/CAE为平台,通过建立的激光喷丸过程冲击波加载的转换模型,把脉冲激光能量转换成冲击波压力,利用用户子程序解决了脉冲激光束连续逐点喷丸板料变形的轨迹控制,实现激光喷丸板料动态变形过程的可视化。通过所建立的模型,对脉冲激光喷丸后材料表面的微观塑性流动过程进行了分析,研究了表面微观形貌的变化。     

In Vivo IVUS-Based 3-D Fluid–Structure Interaction Models With Cyclic Bending and Anisotropic Vessel Properties for Human Atherosclerotic Coronary Plaque Mechanical Analysis

In this paper, a modeling approach combining in vivo intravascular ultrasound (IVUS) imaging, computational modeling, angiography, and mechanical testing is proposed to perform mechanical analysis for human coronary atherosclerotic plaques for potential more accurate plaque vulnerability assessment. A 44-slice in vivo IVUS dataset of a coronary plaque was acquired from one patient, and four 3-D models with fluid-structure interactions (FSIs) based on the data were constructed to quantify effects of anisotropic vessel properties and cyclic bending of the coronary plaque on flow and plaque stress/strain conditions. Compared to the isotropic model (model 1, no bending, no axial stretch), maximum stress-P₁ (maximum principal stress) values on the cut surface with maximum bending (where applicable) from model 2 (anisotropic, no bending, no stretch), model 3 (anisotropic, with bending, no stretch), and model 4 (anisotropic with bending and stretch) were, respectively, 63%, 126%, and 345% higher than that from model 1. Effects of cyclic bending on flow behaviors were modest (5%-15%). Our preliminary results indicated that in vivo IVUS-based FSI models with cyclic bending and anisotropic material properties could improve the accuracies of plaque stress/strain predictions and plaque vulnerability assessment. Large-scale patient studies are needed to further validate our findings.     

Bending characteristics of dual-hole PM-PCF based on LP01 and LP11 modal interference

The bending characteristics of dual-hole polarization maintaining photonic crystal fiber (PM-PCF) are demonstrated in this paper. The modal interference is induced by the LP01 mode and LP11 mode propagating in a single PM-PCF with the same polarization direction. Simulation results demonstrate that the bending radius induces the phase difference between LP01 mode and LP11 mode, which leads to the change of light interference intensity on the fiber output facet. The relationship between bending radius and normalized interference intensity with three different bending angles is discussed, where the bending angle is defined as the angle between hole axis and the x axis. The bending sensitivity is obtained to be about -188.78/m around the bending radius of 1.5 cm with the bending angle of 90°. The bending characteristics can contribute for online bending detection in widespread areas.     

硬质合金的激光增韧研究

报道了经激光处理后硬质合金表面抗弯性能的提高及其与钴相结构的关系。讨论了能量密度与抗弯强度的关系。通过YG2 0硬质合金经激光处理后表面结构的变化 ,分析了显微硬度、耐磨性、韧性等提高的原因 ,给出了相关的实验结果。     

掺镱多模双包层光纤激光器弯曲选模研究

为了使大芯径多模双包层光纤激光器实现基模输出以抑制高功率双层光纤激光器中的非线性效应,采用将大芯径的多模双包层光纤适当弯曲进行选模使双包层光纤激光器获得单模激光输出的方法,进行了理论分析和实验验证,取得了大芯径多模双包层光纤内包层折射率、纤芯半径、光纤内传输信号光波长、光纤弯曲半径等因素对弯曲损耗及激光器输出光场模式影响的数据,并采用国产掺镱多模双包层光纤进行了弯曲选模实验,实现了多模光纤激光器的单模输出.结果表明,激光器最大输出功率达9W,斜率效率达17.3%,输出为基模.这一结果对大芯径多模双包层光纤激光器的选模是有帮助的.     

Fiber Bragg Gratings in Small-Core Ge-Doped Photonic Crystal Fibers

This paper reports fiber Bragg gratings （FBGs） inscribed in a small-core Ge-doped photonic crystal fibers with a UV laser and a Talbot interferometer. The responses of such FBGs to temper- ature, strain, bending, and transverse-loading were systematically investigated. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. The bending and transverse- loading properties of the FBGs are sensitive to the fiber orientations.     

光纤弯曲损耗的研究与测试

本文从光纤弯曲损耗的理论入手,重点介绍了光纤弯曲损耗的计算以及弯曲损耗与截止波长、高功率激光注入、光纤寿命等因素的关系,针对弯曲不敏感光纤(G.657)和其他普通单模光纤(G.65x)进行了弯曲损耗的对比测试,以期为光纤接入网的设计和工程技术人员提供参考.     

光纤马赫曾德尔干涉曲率传感器的膝关节曲率检测系统研究

在人体运动监测的过程中,膝关节运动信息在中老年慢性疾病的诊断和康复评估方面具有重要意义。研制了一种基于光纤马赫曾德尔干涉曲率传感器（Mach-Zehnder interferometer-based directional bending,MZI-BDB）的膝关节弯曲检测系统。该系统由MZI-BDB传感器、扫频激光光源、光纤耦合器、光纤隔离器、光电探测器及信号处理系统构成。MZI-BDB传感器由偏心光纤和单模光纤错位熔接而成,封装于软硅树脂片内,通过绑带固定于膝关节处。当膝关节屈曲和伸展时,诱导MZI-BDB传感器发生弯曲,传感器内透射光信号干涉场的模场状态发生变化,谐振波长发生漂移,从而对膝关节的弯曲方向和曲率进行监测。MZI-BDB传感器在正向和负向弯曲的测量角度范围为0°~90°;在正向弯曲方向上灵敏度和分辨率分别为5.29 nm/m?1和0.11 m?1;在负向弯曲方向上的灵敏度和分辨率分别为?3.11 nm/m?1和0.12 m?1。实验测试MZI-BDB传感器温度敏感度为0.043 nm/℃,该结果显示传感器对温度的不敏感特性。光电编码器与MZI-BDB传感器同时进行数据的传感采集。实验结果表明:该检测系统和光电编码器验证平台在准确度和响应度上具有一致性。     

Dynamic characteristics of planar bending actuator embedded with shape memory alloy

Planar bending actuators embedded with a shape memory alloy (SMA) are a novel type of actuator capable of outputting high bending angle and bending moment. This actuator has a simple structure and high power–weight ratio, which enable it to have wide-ranging applications in the field of biomimetic robots, including biomimetic fish fins and soft robots. However, the existing mechanical model of planar bending actuators embedded with SMA is still quasi-static. Thus, the dynamic characteristics of this kind of actuator cannot be effectively described. Therefore, actuators are difficult to control during the deflection process. To effectively describe this process, a dynamic model of the actuator must be built. This paper aims to identify the dynamic characteristics of the actuator. First, a dynamic model for planar bending actuators embedded with a single SMA wire is established. Second, before SMA wire application, the constitutive characteristics are identified to obtain the necessary parameters for simulation. Third, stable planar bending actuators are fabricated for experiments on characteristics, and then the process flow chart of the planar bending actuator is developed to ensure consistency of the properties of all actuators. Finally, the actuator characteristics obtained experimentally are presented in comparison with those obtained by theoretical simulation. Analysis of the experimental data and simulation results indicates that the planar bending actuator performs better in pulse current heating mode, and that bending angle can be accurately predicted.     

材料性能参数与板料激光弯曲成形角度的相关性研究

板料激光弯曲成形是一种柔性、无模成形新工艺，它通过激光扫描金属板料所导致的非均匀热应力使板料产生塑性变形。材料的性能参数(包括力学性能与热物理性能)对激光弯曲成形的影响很大，通过三维热机耦合有限元仿真研究了材料性能参数与板料激光弯曲角度之间的相关性，研究表明，小弹性模量、低屈服强度的材料容易产生大的弯曲变形。热膨胀系数与弯曲角度之间成正比关系，当热膨胀系数趋于零时，弯曲角度也趋于零。小的热传导系数有利于形成大的温度梯度，从而使板料产生大的弯曲变形；比热越小，加热区内材料的温升越大，使板料容易弯曲变形。     

A Small Polymeric Ridge Waveguide With a High Index Contrast

In this paper, an optimal design of a small polymeric ridge waveguide with a high index contrast is presented. In order to reduce the leakage to the substrate and pure bending losses, the buffer layer of the present waveguide is etched partially. The single-mode condition, the bending characteristics, and the birefringence of the present small polymeric ridge waveguide are also studied. By adjusting the core width and the core height, it is possible to obtain a polarization-insensitive small polymer ridge waveguide. For the bending loss, the numerical results show that the dominant part is the transition loss between the straight and bending sections (other than the pure bending loss) and the transition loss could be reduced greatly by introducing a lateral offset. However, the transition loss is still too large to obtain a very small bending radius (e.g., 10 $mu $m). When only the pure bending loss is necessary to consider in some special case (e.g., microrings without any transitions), one can have a bending radius less than 10 $mu$m due to the possibility of low pure bending loss.