大变位时物体变形测量的相关性恢复方法

本文提出根据白光散斑图像数据模拟刚体位移复位的相关性恢复方法，以解决物体大变位情况下的变形测量问题     

Thermoelastoplastic deformation of noncircular cylindrical shells

A method to determine the nonstationary temperature fields and the thermoelastoplastic stress-strain state of noncircular cylindrical shells is developed. It is assumed that the physical and mechanical properties are dependent on temperature. The heat-conduction problem is solved using an explicit difference scheme. The temperature variation throughout the thickness is described by a power polynomial. For the other two coordinates, finite differences are used. The thermoplastic problem is solved using the geometrically nonlinear theory of shells based on the Kirchhoff-Love hypotheses. The theory of simple processes with deformation history taken into account is used. Its equations are linearized by a modified method of elastic solutions. The governing system of partial differential equations is derived. Variables are separated in the case where the curvilinear edges are hinged. The partial case where the stress-strain state does not change along the generatrix is examined. The systems of ordinary differential equations obtained in all these cases are solved using Godunov's discrete orthogonalization. The temperature field in a shell with elliptical cross-section is studied. The stress-strain state found by numerical integration along the generatrix is compared with that obtained using trigonometric Fourier series. The effect of a Winkler foundation on the stress-strain state is analyzed Translated from Prikladnaya Mekhanika, Vol. 44, No. 8, pp. 79–90, August 2008.     

High-temperature deformation measurements using digital-image correlation

The ability of the computer-vision technique of digital-image correlation to measure full-field in-plane surface deformations at elevated temperatures was evaluated by a series of experiments. Samples were subjected to pure translation, free thermal expansion and uniform tensile loads. Results are presented which show that the digital-image-correlation technique remains fully capable of accurate measurement of the displacements and strains on the surface of a planar object at temperatures up to 650°C.     

Deformation measurements by digital image correlation: Implementation of a second-order displacement gradient

This paper outlines the procedure for refining the digital image correlation (DIC) method by implementing a second-order approximation of the displacement gradients. The second-order approximation allows the DIC method to directly measure both the first- and second-order displacement gradients resulting from nonlinear deformation. Thirteen unknown parameters, consisting of the components of displacement, the first- and second-order displacement gradients and the gray-scale value offset, are determined through optimization of a correlation coefficient. The previous DIC method assumes that the local deformation in a subset of pixels is represented by a first-order Taylor series approximation for the displacement gradient terms, so actual deformations consisting of higher order displacement gradients tend to distort the infinitesimal strain measurements. By refining the method to measure both the first- and second-order displacement gradients, more accurate strain measurements can be achieved in large-deformation situations where second-order deformations are also present. In most cases, the new refinements allow the DIC method to maintain an accuracy of ±0.0002 for the first-order displacement gradients and to reach ±0.0002 per pixel for the second-order displacement gradients.     

形状测量的光学方法应用于组合薄壳的屈曲模态测量

本文应用影像云纹法、频率编码法对短圆柱组合薄壳的屈曲现象进行了研究,给出数字化的初始曲面和屈曲模态图像,将现代光力学法用于快堆主容器结构稳定性模拟体分析实验研究,取得较好的实验结果。本项目的研究成果,为我国制定快堆主结构的安全性评估提供科学依据。     

Fringe-pattern recognition by using the polar-coordinate transform

A new method is proposed for robust evaluation of the local displacement orientation in double-exposed speckle photography by using the polar-coordinate transform. This method is intended for LSV (laser-speckle velocimetry), PIV (particle-image velocimetry), and DIV (digital-image velocimetry) applications. An apriori knowledge about fringe-pattern symmetry as well as its centering within a frame are used. All the available image data are used in fringe recognition, which makes the method robust and reliable. the polar transform domain, where the recognition is accomplished, is also a suitable tool for the pedestal (halo) elimination and for the coefficient of visibility estimation. Being realized digitally, the method provides remarkable computational speed comparable to the methods known from the literature. The method allows designing a dedicated opto-electronic processor. The fring-slope measurement accuracy for ten real and ten artificially simulated images is around 1.24 deg under the angle resolution of 1 deg. It is shown how to reduce this measurement error to keep the accuracy/performance ratio at a very satisfactory level. Vladimir Shapiro, formerly associated with Institute of Informatics, Bulgarian Academy of Sciences, is currently associated with BarGold Electronics, Ltd., P.O. Box 25045, Check-Post, Haifa-Bay 31250, Israel.     

二维柱坐标系中守恒的保球对称的中心型拉氏方法

提出了一种Godunov型中心型拉氏方法,用于求解二维柱坐标系中的可压缩多介质Euler方程组,该方法完全在体积控制体上离散,不仅保证质量、动量和总能量守恒,且该方法在二维柱坐标系中保一维球对称;并且对一维球对称问题在球对称网格划分下,精度测试表明该方法具有一阶精度,算例显示方法非常有效。     

基于未标定序列图的形貌测量方法

提出一种形貌测量方法,从未标定序列图中同时提取出特征点的三维坐标和摄像机的运动矩阵,实现对目标物体的三维测量。首先用齐次坐标表达了空间点的投影变换矩阵,并根据该矩阵推导出投影比例式,运用投影深度和投影矩阵之间的循环相关性进行迭代运算,得到比普通双目视觉更加精确的深度数据。其次对分解得到的摄像机运动矩阵和空间点坐标施加度量约束。运用基于因式分解的归一化算法,恢复出欧氏空间里的摄像机运动矩阵和空间点坐标。基于这种方法,实现了曲面标记点的坐标测量,得到了三维形貌数据,误差小于0.16mm。     

A moiré microscope for finite deformation micro-mechanical studies

A new version of a moiré microscope is presented that embodies the theory of optical moiré interferometry. To interrogate the deformed specimen grating, the device uses a transmission diffraction grating that allows for a simple and quick change of the virtual reference grating vector without disturbing the optical alignment of the other components in the optical train. To analyze deformation from the acquired moiré interference fringe patterns, the displacement light-itensity moiré optical law introduced by Sciammarella is revisited. The analysis of deformation is consistent with the continuum principles of finite deformation and can readily be used to obtain micro-mechanical quantities of interest such as the local strains, stretches and rotations.     

直角坐标下厚圆柱扁壳弯曲的一般解

基于直角坐标下考虑横向剪切变形情况下厚圆柱扁壳的几何方程、物理方程、平衡微分方程,建立了以3个中面位移和2个中面转角为独立变量的中厚圆柱扁壳弯曲的位移型基本微分方程.因该方程可退化为薄圆柱扁壳弯曲的基本微分方程,说明了其推导过程的正确性及一般性.此外,厚圆柱扁壳的位移型基本微分方程是一个10阶微分方程,对其使用双重三角...     

用于柱形爆炸容器周向大变形历程测量的应变丝技术

为了测量柱形爆炸容器的动态周向大变形历程,开发了应变丝测量技术。选用性能良好的合金丝沿爆炸容器周向固定,容器膨胀变形驱动合金丝同步伸长,配合适当的电路,检测合金丝的电阻变化,从而获得容器的变形历程。在钢筒的中心进行了120 g TNT当量球形装药下的爆炸加载实验,获得了峰值超过20%的钢筒周向变形历程。测量结果与实验后钢筒变形实测结果及数值模拟结果吻合较好。

     

约束层对金属柱壳膨胀变形影响的数值模拟

对金属铝和硬质聚氨酯泡沫组合的约束层对45钢柱壳膨胀断裂性能的影响进行了数值模拟,得到三种约束条件下45钢柱壳在膨胀过程中表面的速度和位移历史剖面,对比分析了在约束层作用下45钢柱壳膨胀变形动态行为。利用高速分幅相机及中能X光机获得了多个时刻45钢柱壳的动态图像和柱壳膨胀后的工程应变,实验结果与数值模拟结果吻合。结果可对爆轰加载下约束层对45钢柱壳膨胀变形的物理规律进行定量认识。

     

用于物体表面形貌和变形测量的三维数字图像相关方法

使用单个摄像机的二维数字图像相关方法通常仅局限于平面物体的面内变形测量,而使用两个摄像机基于双目立体视觉原理的三维数字图像相关方法克服了这一局限,可对平面和曲面物体表面的三维形貌和载荷作用下的三维变形进行测量。本文介绍了三维数字图像相关方法的基本原理及其关键技术,并用两个典型的实验验证了该方法的有效性。     

金属柱壳膨胀断裂的实验与数值模拟

基于一端起爆的柱壳外爆加载装置,采用多普勒速度测量仪(DPS)及高速分幅相机联合诊断柱壳的膨胀断裂过程。实验获得了壳体表面的速度历史和膨胀变形、裂纹萌生扩展到爆轰产物泄露的动态图像。利用光滑粒子流体动力学方法(SPH)开展了对应的数值模拟,计算结果与实验结果吻合较好。实验与数值模拟结果系统地给出了冲击波入射柱壳角、爆轰波稀疏角、内壁速度压力历史及壳体变形应变、壳体断裂等物理信息。

     

Inelastic deformation of flexible cylindrical shells with an elliptic hole

The elastoplastic state of isotropic homogeneous cylindrical shells with elliptic holes and finite deflections under internal pressure is studied. Problems are formulated and numerically solved taking into account physical and geometrical nonlinearities. The distribution of stresses (displacements, strains) along the boundary of the hole and in the zone of their concentration is analyzed. The data obtained are compared with the numerical solutions of the physically nonlinear, geometrically nonlinear, and linear problems. The stress-strain state of cylindrical shells in the neighborhood of the elliptic hole is analyzed with allowance for nonlinear factors __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 5, pp. 46–54, May 2007.     

Dynamic stability of viscoelastic circular cylindrical shells taking into account shear deformation and rotatory inertia

The present work discusses the problem of dynamic stability of a viscoelas- tic circular cylindrical shell,according to revised Timoshenko theory,with an account of shear deformation and rotatory inertia in the geometrically nonlinear statement.Pro- ceeding by Bubnov-Galerkin method in combination with a numerical method based on the quadrature formula the problem is reduced to a solution of a system of nonlinear integro-differential equations with singular kernel of relaxation.For a wide range of vari- ation of physical mechanical and geometrical parameters,the dynamic behavior of the shell is studied.The influence of viscoelastic properties of the material on the dynamical stability of the circular cylindrical shell is shown.Results obtained using different theories are compared.     

基于Haar小波变换的位移场测量方法

本文提出了一种应用小波变换对固体表面位移场进行测量的新方法，在图像分析时，用各点属于不同尺度的小波变换系数来表征该点周围的子区。将试件表面位移前后的两幅数字图像进行小波变换，通过变形前后两幅图像小波变换系数之间的相互匹配，使位移前后两幅图中的子区对应起来，从而确定图像的位移场。本文应用Haar小波变换进行了计算机模拟实验和实物位移实验。引入亚像素技术，获得了0．02的位移测量精度。     

Inelastic deformation of flexible cylindrical shells with a curvilinear hole

The elastoplastic state of thin cylindrical shells weakened by a curvilinear (circular) hole is analyzed considering finite deflections. The shells are made of an isotropic homogeneous material. The load is internal pressure of given intensity. The distributions of stresses (strains, displacements) along the hole boundary and in the zone of their concentration are studied. The results obtained are compared with solutions that account for physical (plastic strains) or geometrical (finite deflections) nonlinearity alone and with a numerical linear elastic solution. The stress-strain state around a circular hole is analyzed for different geometries in the case where both nonlinearities are taken into account __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 12, pp. 115–123, December, 2006.     

Equivalence conditions between linear Lagrangian finite element and node‐centred finite volume schemes for conservation laws in cylindrical coordinates

A complete set of equivalence conditions, relating the mass‐lumped Bubnov–Galerkin finite element (FE) scheme for Lagrangian linear elements to node‐centred finite volume (FV) schemes, is derived for the first time for conservation laws in a three‐dimensional cylindrical reference. Equivalence conditions are used to devise a class of FV schemes, in which all grid‐dependent quantities are defined in terms of FE integrals. Moreover, all relevant differential operators in the FV framework are consistent with their FE counterparts, thus opening the way to the development of consistent hybrid FV/FE schemes for conservation laws in a three‐dimensional cylindrical coordinate system. The two‐dimensional schemes for the polar and the axisymmetrical cases are also explicitly derived. Numerical experiments for compressible unsteady flows, including expanding and converging shock problems and the interaction of a converging shock waves with obstacles, are carried out using the new approach. The results agree fairly well with one‐dimensional simulations and simplified models. Copyright © 2013 John Wiley & Sons, Ltd.     

On the deformation of a ribbed cylindrical shell with initial deflection under dynamic loading

The finite-difference method with explicit time coordinate is used to study the dynamic stress-strain state of a cylindrical shell with ribs and initial deflections. A specific numerical example is considered to trace the time evolution of longitudinal and transverse displacements for different parameters of the initial deflection __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 12, pp. 61–66, December 2005.