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1.
冲击相边界传播过程中梯度材料的形成   总被引:1,自引:0,他引:1       下载免费PDF全文
 采用一种基于简单混合物模型的本构,研究了不可逆相变材料中一维的冲击相边界的传播规律,发现在突加载荷并连续卸载的应力边界条件下,样品内部有梯度材料形成。分析了边界条件对材料梯度变化的影响,并且用基于特征线的数值方法计算了不同的边界条件下材料的梯度分布,从而提出利用冲击相边界的传播制备梯度材料的可能性。最后对这种方法的利弊做了探讨。  相似文献   

2.
冲击载荷作用下,相变波的传播及相互作用是一热力耦合过程。采用理论和实验相结合的方法研究了固定温度界面对相变波传播特性的影响。首先基于形状记忆本构模型和一维特征线理论分析了各类间断面和温度界面的基本相互作用规律,发现温度界面对相变波的作用与相变波强度及界面两侧温度的相对高低有关;然后进行了相变波在具有固定温度界面的形状记忆TiNi杆中的传播实验,并实时测量了相变波传播过程中的温度变化。实验结果与理论分析基本一致,冲击载荷作用下相变波不仅是物质间断面,还是移动的温度界面。  相似文献   

3.
本文发展了二维非定常热导热并带有多重相变运动边界问题的双倒易边界元方法.对热储能系统中相变材料的多重相变运动边界问题进行了模拟,得出了温度分布及相变界面随时间的变化,结果表明,双倒易边界元方法能够很好地处理这类问题.  相似文献   

4.
本文以相变微胶囊复合板隔热组件为研究对象,基于焓法方程建立了蓄热/隔热型耦合相变传热数值模型,预测了板内的温度分布、相界面移动等响应特征,系统地分析了Stefan数及相变温度区间对传热的影响。结果表明:相变微胶囊板内固相界面的移动速度大于液相界面,固相界面消失后,液相界面移动明显加速;固、液相界面移动速度随Stefan数的增大而增快,同时板内整体温度水平升高;固相界面移动速度随着相变温度区间的增大而增快,但相变温度区间对相变材料完全熔化所需时间影响不大。  相似文献   

5.
利用离散元方法结合基于无扩散相变的两相模型、热力学相容的自由能函数与有限速率相变动力学方程,模拟α铁的冲击相变过程.得到铁的相边界、冲击Hugoniot关系及自由面速度剖面,并对不同冲击压力下加卸载过程的波系传播和相互作用过程进行分析,获得了加卸载波速特征.  相似文献   

6.
张妮  刘丁  冯雪亮 《物理学报》2018,67(21):218701-218701
为改善晶体相变界面形态,提高晶体品质,提出了一种融合浸入边界法(immersed boundary method,IBM)和格子Boltzmann法(lattice Boltzmann method,LBM)的二维轴对称浸入边界热格子Boltzmann模型来研究直拉法硅单晶生长中的相变问题.将相变界面视为浸没边界,用拉格朗日节点显式追踪相变界面;用LBM求解熔体中的流场和温度分布;用有限差分法求解晶体中的温度分布.实现了基于IB-LBM的动边界晶体生长过程研究.得到了不同晶体生长工艺参数作用下的相变界面,并用相变界面位置偏差绝对值的均值和偏差的标准差来衡量界面的平坦度,得到平坦相变界面对应工艺参数的调整方法.研究表明,相变过程与晶体提拉速度、晶体旋转参数和坩埚旋转参数的相互作用有关,合理地配置晶体旋转参数和坩埚旋转参数的比值,能够得到平坦的相变界面.  相似文献   

7.
水嘉鹏  陈秀梅 《物理学报》1997,46(9):1782-1787
在连续升温条件下,测量了共析Zn-Al合金的应变速率和黏度随温度的变化曲线,在共析转变温区观测到伴随相变过程的黏度极小值,研究了应力对应变速率和升温速率对黏度极小值的影响,发现在相变温区材料的力学行为遵从Newton黏滞流变定律,用相界面的数量和性质解释了相变温区Zn-Al合金的黏滞流变行为.将相变激活能和相界面的流变激活能进行比较,说明界面的流动性是影响相变的主要因素.结合过去在非晶Pd-Cu-Si合金的结构转变过程中观测到的伴随玻璃转变和晶化过程的黏度极小值,说明伴随着结构转变或相变过程,黏度出现极小 关键词:  相似文献   

8.
本文以管肋式熔盐相变蓄热结构为对象,将相变材料填充入高孔隙率泡沫金属中以弥补熔盐导热系数低的缺陷。考虑周期性边界和重力方向相邻结构的影响,以三层管肋式结构代替整个系统建立多孔介质固-液相变输运三维物理数学模型。利用数值模拟方法,探讨在重力环境中,管式加热条件下相变材料蓄热过程的传热性能。揭示出相变界面随时间的演化,以及自然对流对蓄热过程的作用机制;讨论了泡沫金属、肋片参数及加热温度对蓄热能力的影响。  相似文献   

9.
为深入探讨固-液相变材料在相界面内(糊状区)的流动和传热对固-液相变过程的影响,本文基于"焓-多孔介质"模型,提出研究糊状区的"多相流-多孔介质"两区域复合模型,将糊状区的高含液率视为多相流区域,而低含液率区域视为多孔介质,采用格子Boltzmann方法对固-液相变糊状区的流动和传热过程进行研究.重点讨论了相变温度半径,不同高、低含液率区的分界点γ_(tr)对糊状区的发展、迁移以及对相变过程的影响.研究结果表明糊状区厚度随相变半径的增大而增加,进而影响相变过程中流动和换热;对比复合模型的不同高、低含液率分界点γ_(tr)时和单纯多孔介质模型时的糊状区的边界、流动和换热情况,表明将糊状区高液相率区采用多相流模型进行分析,可以正确反映出高含液率区域内固相微粒随液相流动的特性及其对相变过程的影响。  相似文献   

10.
采用平均场近似方法对两组元面心立方合金薄膜的有序无序相转变过程进行模拟计算,结果表明,合金薄膜的有序无序相变受薄膜层数奇偶性的影响.薄膜层数奇偶性不同,会导致薄膜具有不同的相结构和热力学性质.在弱表面偏析作用下,对于偶数层薄膜,由于薄膜边界对称性破缺,对应体组分x=0.5的化学势区间,偶数层薄膜有序无序相变过程中出现了中间温度相和浸润现象.而奇数层薄膜的有序无序相变类似体材料的相变.在强表面偏析作用下,由于受表面偏析作用和有限尺寸效应影响,对应体组分x=0.5的化学势区间,奇数层薄膜中出现AB(AB)nA相,它不存在严格热力学意义上的有序无序相变.  相似文献   

11.
Dynamic behavior of a weightless rod with a point mass sliding along the rod axis according to periodic law is studied. This is the pendulum with periodically varying length which is also treated as a simple model of a child’s swing. Asymptotic expressions for boundaries of instability domains near resonance frequencies are derived. Domains for oscillation, rotation, and oscillation-rotation motions in parameter space are found analytically and compared with a numerical study. Chaotic motions of the pendulum depending on problem parameters are investigated numerically.  相似文献   

12.
In this paper, two novel types of semi-slow light photonic crystal waveguide with large transmission bandwidth obtained by shifting the boundaries of a W1 waveguide in the direction of light propagation are presented. One includes air rings localized at only one side of the line defect and the other replaces the holes at each side of the waveguide by the uniform air rings which are constructed by the homocentric square dielectric rod inserted into the air holes. The structure produces unusual “n-type” transmission spectrum depending on the different parameters such as inner radius of air ring, dielectric constant of square dielectric rod, etc. It is shown that the transmission spectra of the two structures are completely different from each other. A versatile control of light propagation with large normalized bandwidth and slow light phenomena can be obtained using a unique geometrical parameter. Numerical simulation by the finite-difference time-domain (FDTD) method demonstrates the propagation of the broadband pulse.  相似文献   

13.
The excitation and propagation of acoustic waves along curvilinear boundaries between two media are investigated. Formal high-frequency asymptotic expressions practicable for approximate calculations in the case of media with slightly different velocities are derived. Dispersion equations and wave excitation coefficients at weak-contrast boundaries are investigated numerically.  相似文献   

14.
A method investigating the beam propagation in a pumped laser rod is proposed. In this method, the pumped laser rod in a resonator is evenly divided into N segments along the laser rod axis, and each segment is considered as a small thermal lens with thermal focus length of f. Accordingly, the beam radius distributions in the laser rod for the symmetric and asymmetric resonators are thus calculated, respectively. The beam radius distribution in the whole resonator is also calculated. Moreover, the calculated beam distribution in the whole resonator and in the rod is also described in detail.  相似文献   

15.
The sectors of propagation directions of dispersionless polaritons localized at the optically uniaxial crystal-optically isotropic medium interface are determined. The region of possible orientations of the crystal surface containing these sectors is revealed. The boundaries of the sector of possible propagation directions are analytically described as functions of the crystal surface orientation with respect to the optical axis of the crystal. Consideration is given to the optimum ratios of permittivities at which the width of the propagation sectors appears to be maximum. It is found that the boundaries of the sectors of polariton propagation along different surfaces change drastically in the limit of small dielectric anisotropy of the crystal.  相似文献   

16.
The connection of the natural resonances and the symmetry group of the cross-section of the diffracting-cylinders is established. As is done in spectroscopy, selection rules for the propagation directions of the diffracted field are deduced. Some remarks about the case of propagating modes along a dielectric rod are also made.  相似文献   

17.
An analysis is carried out of the spread of a flame along a horizontal solid fuel rod, for which a weak aiding natural convection flow is established in the underside of the rod by the action of the axial gradient of the pressure variation that gravity generates in the warm gas surrounding the flame. The spread rate is determined in the limit of infinitely fast kinetics, taking into account the effect of radiative losses from the solid surface. The effect of a small inclination of the rod is discussed, pointing out a continuous transition between upward and downward flame spread. Flame spread along flat-bottomed solid cylinders, for which the gradient of the hydrostatically generated pressure drives the flow both along and across the direction of flame propagation, is also analysed.  相似文献   

18.
The transverse vibrations of a beam and the propagation of tension, compression, and shear deformation waves along the axis of a rod are studied by recording the electric field that appears under these conditions near the rod. Experiments are performed on samples made of various plastic materials in order to compare the effect of the properties of a material on the electric response during dynamic deformation, all other things being equal. Dynamic Young’s moduli are determined during bending vibrations and the propagation of longitudinal waves. It is shown that the location and type of antenna should be taken into account to adequately interpret a recorded signal and a dynamic mechanical process.  相似文献   

19.
为了研究超声表面脉冲波在钢、铁等不透明曲面材料中的传播规律,我们采用和金属材料声速比较接近的光学玻璃作样品,利用研制的数字化动态光弹系统,分析了表面波和次表面波沿玻璃圆棒侧面传播时的行为,记录了不同时刻的横截面上的脉冲声场传播图像,求出了表面波和次表面波沿曲面爬行的传播速度。  相似文献   

20.
In the present paper, the coupling effect of transverse magnetic field and elastic medium on the longitudinal wave propagation along a carbon nanotube (CNT) is studied. Based on the nonlocal elasticity theory and Hamilton's principle, a unified nonlocal rod theory which takes into account the effects of small size scale, lateral inertia and radial deformation is proposed. The existing rod theories including the classic rod theory, the Rayleigh-Love theory and Rayleigh-Bishop theory for macro solids can be treated as the special cases of the present model. A two-parameter foundation model (Pasternak-type model) is used to represent the elastic medium. The influence of transverse magnetic field, Pasternak-type elastic medium and small size scale on the longitudinal wave propagation behavior of the CNT is investigated in detail. It is shown that the influences of lateral inertia and radial deformation cannot be neglected in analyzing the longitudinal wave propagation characteristics of the CNT. The results also show that the elastic medium and the transverse magnetic field will also affect the longitudinal wave dispersion behavior of the CNT significantly. The results obtained in this paper are helpful for understanding the mechanical behaviors of nanostructures embedded in an elastic medium.  相似文献   

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