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激光重熔对Al-Si合金快速凝固共晶生长的数值模拟 总被引:3,自引:0,他引:3
本文通过数值模拟,计算出Al-Si合金共晶共生区,达到对实际加工中激光处理参数的优化。数学模型从计算物体表面温度场三维分布入手,考虑到激光空间Gaus分布特性,得到物体表面温度梯度分布;同时结合枝晶分布KGT模型以及共晶分布经修正的TMK模型,计算了微观结构的共晶生长的范围,得到一个完整的从激光重熔到共晶生长的计算模型。 相似文献
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脉宽调制技术目前已广泛应用于高频电磁加热系统、开关电源等领域1,本文首次将脉宽调制技术用于激光扫描测量系统,解决了激光扫描测量中国不同材料对激光的散射光强不同、不同曲面对激光光强反射各异以及物体表面镜面反射等问题给测量精度带来的严重影响2,利用激光扫描系统中的摄象机直接作为光强反馈系统,实现了测量过程中的光强自动控制,有效地降低了光强饱和等问题给测量带来的误差. 相似文献
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利用激光全息干涉测量梁的微小位移 总被引:4,自引:3,他引:1
全息干涉测量利用二次曝光记录物体在不同载荷状态下的相对位移场.通过在干板上记录和比较不同状态产生的光波的干涉,可以得到在不同载荷时干涉条纹随物体位移的变化情况,实现对物体微小变形、微小位移量的测量.本文利用激光全息干涉技术测量了金属梁的微小位移量,计算得到金属梁的弹性模量和挠度. 相似文献
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为了分析飞秒激光烧蚀过程,在双相延迟模型的基础上建立了双曲型热传导模型.模型中考虑了靶材的加热、蒸发和相爆炸,还考虑了等离子体羽流的形成和膨胀及其与入射激光的相互作用,以及光学和热物性参数随温度的变化.研究结果表明:等离子体屏蔽对飞秒激光烧蚀过程有重要的影响,特别是在激光能量密度较高时;两个延迟时间的比值对飞秒激光烧蚀过程中靶材的温度特性和烧蚀深度有较大的影响;飞秒激光烧蚀机制主要以相爆炸为主.飞秒激光烧蚀的热影响区域较小,而且热影响区域的大小受激光能量密度的影响较小.计算结果与文献中实验结果的对比表明基于双相延迟模型的飞秒激光烧蚀模型能有效对飞秒激光烧蚀过程进行模拟. 相似文献
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This paper presents a heat transfer model to calculate the temperature field in moving glass rods heated by a CO2 laser. Conduction and radiation heat transfer in radial and axial directions are taken into account in the current model. The Rosseland diffusion approximation is incorporated to analyze the radiation heat transfer in the glass rod. A two-band model is used to simulate the spectral property of the glass. Results of the simulation show that glass rods of sufficiently large optical thickness should be treated as a semitransparent medium for radiative transfer, and it is reasonably accurate to assume it to be opaque to CO2 laser irradiation. It has been shown that the resulting temperature profile is strongly dependent on the laser parameters, i.e., the size of laser beam and the power of the laser. The diameter and speed of the moving glass rod are also important in determining the temperature field although the convective heat transfer coefficient between the glass rod and the environment has little effect. 相似文献
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S. P. Aktershev 《Journal of Engineering Thermophysics》2009,18(2):138-150
Heat transfer in a viscous liquid film moving under the action of gravity and a gas flow on a substrate with a locally heated
rectangular area is investigated. The heat exchange coefficient is given on the liquid-gas surface; the heat flux to the liquid
is given on the heated area; the substrate surface outside the heated area is heat-insulated. An analytical solution in a
form of a convergent series is obtained for the liquid temperature distribution in the film. The influence of the dimensionless
criteria on the obtained solution is analyzed. The effect of heat flux inhomogeneity on the temperature distribution is considered. 相似文献
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Patel PK Mackinnon AJ Key MH Cowan TE Foord ME Allen M Price DF Ruhl H Springer PT Stephens R 《Physical review letters》2003,91(12):125004
A new technique is described for the isochoric heating (i.e., heating at constant volume) of matter to high energy-density plasma states (>10(5) J/g) on a picosecond time scale (10(-12)sec). An intense, collimated, ultrashort-pulse beam of protons--generated by a high-intensity laser pulse--is used to isochorically heat a solid density material to a temperature of several eV. The duration of heating is shorter than the time scale for significant hydrodynamic expansion to occur; hence the material is heated to a solid density warm dense plasma state. Using spherically shaped laser targets, a focused proton beam is produced and used to heat a smaller volume to over 20 eV. The technique described of ultrafast proton heating provides a unique method for creating isochorically heated high-energy density plasma states. 相似文献
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Discussion forthe Semiinfinite Medium Approximation and the Thermal Diffusion Velocity in Laser Heat Treatment 总被引:2,自引:0,他引:2
LI Junchang LI Xingyi CHEN Jingbo FAN Zebin CHEN Qinghua 《Chinese Journal of Lasers》1999,8(4):377-383
ntroduction Inapplicationsandstudiesoflaserheattreatmentonmaterialsurface,thethermalinteractionbetweenlaserandmaterialsisanessentialproblem.Theactingtimeoflaserheattreatmentisshortanditsheatedzoneisonlylocalizedwithinasmallspacenearthelaserirradiat… 相似文献
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We examine the temperature fields of human enamel [Yu D, Fox JL, Hsu J, Lynn Powell G, Higuchi WI. Computer simulation of surface temperature profiles during CO2 laser irradiation of human enamel. Opt Eng 1993; 32(2)] during multi-modes CO2 laser irradiation. For this we use the integral transform method as well as direct and inverse Laplace transform [Oane M, Sporea D. Temperature profiles modeling in IR optical components during high power laser irradiation. Infrared Phys Technol 2001; 42(1): 31–40; Oane M, Sporea D. Study of heat transfer in IR optical components during CO2 laser irradiation. Proc SPIE 2001; 4430: 898–904; Oane M. Mathematical modeling of the thermal field distributions in solids under multiple laser irradiations. Proc SPIE 2003; 5227: 329–34; Oane M, Apostol I, Timcu A. Temperature field modeling in laser heated metals for laser cleaning of surfaces. Proc SPIE 2003; 5227: 323–8]. The enamel block is modeled as homogeneous cylinder in three dimensions. Results indicate that (i) the thermal field depends on multi-modes structure; (ii) heat transfer coefficient plays an important role in temperature distribution. 相似文献
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It is a conventional method to regard laser-iradiated object as a semi-infinite medium with invariable thermal physical property parameters for approximate analyses of thermal acting of laser heat treatment. So far, 2 and have been taken as the thermal diffusion distance and the thermal diffusion velocity respectively, at the time t after heat fluctuation in materials with a thermal diffusion coefficient α, and as a result, the feasibility of the approximately estimating method about semi-infinite medium is judged. This paper indicates that, due to quantitative investigation of heat energy diffusion, the thermal diffusion distance of 3 and the thermal diffusion velocity of 1.5 can more accurately describe the physical process of heat conduction. Finally, an applied example of approximately estimating the temperature field of laser heat treatment is presented. 相似文献
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提出了一种利用电加热丝作为校准源的高能激光能量计校准方法,将水流从吸收腔前端导入至加热容器,在加热后流入吸收腔。通过精确计量水流吸收的热能并与能量计测量结果进行比较,达到对高能激光能量计校准的目的。研究表明校准系统的热交换模型与吸收腔内的热交换模型一致,均经历了储能和功率平衡两个阶段。水流及相变气体的散射效应对测量结果的影响较小,经过修正后可以忽略其影响。通过深入分析各个环节的测量不确定度表明,残留能量和流量变化对测量不确定度的影响最显著,增加水箱的容积可以有效降低残留能量对测量不确定度的影响。在对各个环节的影响修正后估算出系统的测量不确定度约为4.8%(k=2),被校高能激光能量计校准后的测量结果与其他类型的参考高能激光能量计进行比对,两者具有很好的一致性,修正因子仅为1.006,标准偏差为1.4%。 相似文献
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Summary A mathematical model able to describe the temperature profiles generated in a thin film by the steady-state illumination by
a Gaussian laser beam is presented. The film is supposed to be made by a weakly absorbing liquid sample bounded by two parallel
transparent plates, the cell walls, whose thermal exchange to the surrounding ambient may be assumed to be linear with the
temperature difference. An analytical solution of the problem is presented in form of Hankel transform and a matrix numerical
approach to the computation of the temperature profiles is reported. It is particularly well suited to a computer implementation
and allows one to get very accurate results in very short computing times. The influence of the heat exchange coefficient
to the ambient is shown in an example. A check of the method accuracy is performed by comparison with literature results in
the particular case of infinite heat exchange coefficient.
To speed up publication, the authors of this paper have agreed to not receive the proofs for correction. 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