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1.
When the silicon material is irradiated by laser, it absorbs the laser energy leading to the temperature rise and the thermal stress. The damage effect includes melting, vaporation and thermal stress damage. Once the thermal stress exceeds the stress strength the crack will initiate. The silicon surface cracks induced by a millisecond laser are investigated. The experimental results show that three types of cracks are generated including cleavage crack, radial crack and circumferential crack. The cleavage crack is located within the laser spot. The radial crack and circumferential crack are located outside the laser spot. A two-dimensional spatial axisymmetric model of silicon irradiated by a 1064 nm millisecond laser is established. To assess what stresses generate and explain the generation mechanism of the different cracks, the thermal stress fields during laser irradiation and the cooling process are obtained using finite element method. The radial stress and hoop stress within the laser spot are tensile stress after the laser irradiation. The temperature in the center is the highest but the thermal stress in the center is not always highest during the laser irradiation. The cleavage cracks are induced by the tensile stress after the laser irradiation. The radial crack and the circumferential crack are generated during the laser irradiation. 相似文献
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A finite element model was constructed using a commercial software Fidap to analyze the Cu-base filler metal droplet spreading process in laser brazing, in which the temperature distribution, droplet geometry,and fluid flow velocity were calculated. Marangoni and buoyancy convection and gravity force were considered, and the effects of laser power and spot size on the spreading process were evaluated. Special attention was focused on the free surface of the droplet, which determines the profile of the brazing spot.The simulated results indicate that surface tension is the dominant flow driving force and laser spot size determines the droplet spreading domain. 相似文献
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激光激发声表面波在缺陷板材中散射过程的有限元分析 总被引:8,自引:5,他引:3
利用有限元法模拟了金属板材中激光激发的声表面波经过缺陷位置时发生散射的瞬态过程,采用线状激光源作为超声导波的激发源.针对三种不同深度的表面缺陷以及三种亚表面缺陷的模型进行了对比计算,结果显示缺陷的深度及位置对声表面波的时域特征存在显著的影响.表面缺陷深度越深将产生较大幅度的表面反射回波,亚表面缺陷的影响将取决于缺陷上顶面距离板材上表面的距离.因此,数值模拟结果表明通过分析激光产生的表面波形可以判定近表面缺陷的尺寸和所处的位置. 相似文献
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为了探索纳秒脉冲强激光与材料的相互作用机理,建立了二维数值模型,利用有限差分法对纳秒激光脉冲烧蚀金属铝的温度场进行了数值模拟.通过对比不同脉宽、光斑和能量下激光引起的温度场随时间的演化,发现脉冲的前期温度升高比后期快.等温图显示中心温度升高最快,烧蚀轮廓与激光束形状相似,烧蚀深度达1—5 μm.脉宽越长,烧蚀越窄和越深,光斑越大,烧蚀越宽和越浅.数值研究表明,1)激光的脉冲形状、脉宽和功率密度直接影响烧蚀的形状和深度,2)激光功率密度在109 W/cm2量级烧蚀 相似文献
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This study presents a new model for analyzing the temperature distribution and weld pool shape in Nd:YAG pulsed laser welding. In the proposed approach, a surface flux heat transfer model is applied in the low laser energy intensity region of the weld, while a keyhole heat transfer model based on a volumetric heat source is applied in the high laser energy intensity region of the weld. The correlation between the intensity of the laser input energy and the geometric parameters of the volumetric heat source is derived experimentally. A series of MARC finite element simulations based on the proposed single pulse model are performed to investigate the shape and size of the weld pool given different laser energy intensities. A good agreement is observed between the simulation results and the experimental results obtained under equivalent single pulse welding conditions. Thus, the basic validity of the proposed model is confirmed. 相似文献
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针对激光对红外成像系统的干扰效果是光电对抗领域的一个研究热点,采用波长10.6 μm的CO2调谐脉冲激光器,通过漫反射板反射激光能量到像元数为320×240的多晶硅非制冷焦平面红外热像仪上进行激光干扰红外成像系统的实验。在实验中研究了干扰激光能量、重复频率、波长、光斑大小等激光参数对干扰效果的影响,并从图像质量的角度分析了激光参数对干扰效果的影响。结果表明,随着干扰激光能量密度、重复频率、波长和光斑的增大,干扰效果提高。此外,漫反射干扰的效果证明这种干扰方式是可行的,该方式可避免干扰源成为未来将出现的反辐射光电制导武器的诱饵,为CO2激光干扰装备提供一种新的战术配置方法。 相似文献
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This paper is to investigate the mechanisms of micro-scale particle removal by surface wave, which was induced by a short pulse laser in a cleaning process. The authors analyzed the adhesive forces of particles on substrate surface and the clearance force produced by surface wave in laser cleaning. The physical model of particle removal by laser-induced surface wave was established to predict the removal area and the processing conditions of laser cleaning. In this research, a KrF excimer laser was applied to irradiate 304 stainless steel specimen distributed with copper particles to generate surface wave for copper particle removal. Considering that a time-varying and uniformly distributed heat source irradiates on material surface with thermao-elastic behavior, the displacement and acceleration of substrate induced by a pulsed laser were solved by an uncoupled thermal–mechanical analysis based on the finite element method. The processing parameters such as laser energy, laser spot size are discussed, respectively. A series of laser cleaning experiments were designed to compare with computation results. The results show that the removal area by surface wave beyond the laser spot increases with the laser energy and that, the surface acceleration decreases with the increase of the laser spot size. 相似文献
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D.J. Gibbons 《Optics & Laser Technology》1983,15(2):95-99
The theory of pulsed and scanned laser beams is developed and the results are shown to agree with similar analyses by other authors. A new expression, however, for the temperature rise caused by a very small laser spot agrees well with recent experiments. 相似文献
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Temperature distribution in the Nd- and Yb- doped YAG and KGdW laser crystals under flashlamp- and diode-pumping was characterized by means of finite element analysis. For KGdW, two laser crystal orientations were considered for light propagation along the Np and Ng optical indicatrix axes, taking into account the anisotropy of thermal conductivity coefficient. The influence of the cooling conditions, pump spot size and dopant concentration on the temperature distribution was analyzed. For flashlamp-pumping conditions, the applicability of the quasi-steady-state model is discussed. The main concerns in the thermal management of KGdW laser host is the relatively low thermal conductivity that results in poor cooling and significant absorption coefficients under diode pumping that result in highly non-uniform volumetric heat deposition. “Athermal” Ng-cut KGdW crystal was found to produce higher temperature gradients that the “standard” Np-cut one, that should results in higher internal stresses and higher probability of thermally-induced cracks. 相似文献
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Laser heating of a cemented carbide tool is considered and the temperature field as well as phase changes in the heated region is modeled. Temperature rise, liquid layer thickness, and mushy size are predicted numerically. A control volume approach is introduced to solve the governing equations of heat transfer and phase change. Consecutive pulses with the duty cycle of 60% are accommodated in the simulations in line with the experimental conditions. An experiment is carried out to treat the cemented carbide tool surfaces using the CO2 laser delivering consecutive pulses. The treated surfaces and their cross-sections are examined using the scanning electron microscope (SEM). It is found that the temperature gradient is high along the laser beam axis resulting in cracks at the irradiated surface. The rapid solidification of the surface causes compact structures with very fine grains in the surface region of the laser irradiated spot. 相似文献
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Jijun Wang Zhonghua Shen Baiqiang Xu Xiaowu Ni Jianfei Guan Jian Lu 《Optics & Laser Technology》2007,39(4):806-813
The use of a pulsed laser for the generation of the elastic waves in non-metallic materials in the thermoelastic regime is investigated by using finite element method (FEM), taking into account not only thermal diffusion and the finite spatial and temporal shape of the laser pulse, but also optical penetration and the temperature dependence of material properties. The optimum finite element model is established based on analysis of two important parameters, meshing size and time step, and the stability of solution. Temperature distributions and temperature gradient fields in non-metallic material for different time steps are obtained, this temperature field is equivalent to a bulk force source to generate ultrasonic wave. The laser-generated ultrasound waveforms at the epicenter and surface acoustic waveforms (SAWs) are obtained and the influence of optical penetration into the material on the temperature field and the ultrasound waveforms are analyzed. The numerical results indicate that the heat penetration into non-metallic material is caused mainly by the optical penetration, and the ultrasound waveforms, especially the shape of the precursor, are strongly dependent on the optical penetration depth into non-metallic material. 相似文献
17.
Propagation of an intense short laser pulse through under-dense plasma can produce huge amplitude plasma wake field. A 3D particle in cell (PIC) method was used to simulate the wakefield generation for different laser parameters such as intensity, pulse duration, spot size and temporal pulse shape. Our study shows that the amplitude of wakefield is increased with laser intensity, but it is decreased with spot size. The results for pulse shape and pulse duration depend on their optimum values. 相似文献
18.
Li Li Zhang Duan-ming Li Zhi-hua Tan Xin-yu Fang Ran-ran 《Frontiers of Physics in China》2007,2(3):322-326
In this paper, the effect of the absorptivity of metal on femtosecond pulsed laser ablation is investigated. The formulas
for the absorptivity depending on target temperature are derived from Maxwell Equations and the Lambert-Beer’s law. Based
on this, a new two-temperature model is proposed to describe the femtosecond pulsed laser ablation with metal. Then, using
Au as an example, a finite difference method is employed to simulate the space-dependent and time-dependent absorptivity and
the target temperature. The temperature evolution of our model is compared with the result obtained form the heat conduction
model taking the absorptivity as constant. It is shown that the absorptivity plays an important role in the femtosecond pulsed
laser ablation. The results of this paper are helpful in choosing the best technical parameters in femtosecond pulsed laser
ablation.
相似文献
19.
采用数值计算的方法,对脉冲激光二极管三向侧面抽运固体激光器中,激光晶体的温度场时变分布进行了计算. 分析了三向侧面抽运情况下晶体内光强分布,在此基础上,采用有限元法,以脉冲激光二极管侧面抽运Nd∶YAG激光器为例,对单脉冲过程中晶体温度分布及其影响因素进行分析. 结果表明,晶体升温过程受到抽运条件以及散热条件的影响,但是主要受到抽运条件即抽运光强度和光束半径的影响,降温过程受到晶体热物性参数和晶体半径以及散热条件的影响. 当晶体温度达到周期性分布后,由于晶体径向温度梯度的周期性变化,引起通过晶体的平面光波的中心和边缘光线相对光程差也随时间作周期性变化.
关键词:
激光二极管侧面抽运固体激光器
热效应
有限元法
时变过程 相似文献