Cervical spine as a complicated part in the human body, the form of its movement is diverse. The movements of the segments of vertebrae are three-dimensional, and it is reflected in the changes of the angle between two joint and the displacement in different directions. Under normal conditions, cervical can flex, extend, lateral flex and rotate. For there is no relative motion between measuring marks fixed on one segment of cervical vertebra, the cervical vertebrae with three marked points can be seen as a body. Body’s motion in space can be decomposed into translational movement and rotational movement around a base point .This study concerns the calculation of dimensional coordinate of the marked points pasted to the human body’s cervical spine by an optical method. Afterward, these measures will allow the calculation of motion parameters for every spine segment. For this study, we choose a three-dimensional measurement method based on binocular stereo vision. The object with marked points is placed in front of the CCD camera. Through each shot, we will get there two parallax images taken from different cameras. According to the principle of binocular vision we can be realized three-dimensional measurements. Cameras are erected parallelly. This paper describes the layout of experimental system and a mathematical model to get the coordinates.
The inflation of an initially stressed cylindrical shell provides a good illustration of the phenomenon of the initiation and propagation of an instability, which shares the same mathematical and mechanical features with a variety of other strain localization phenomena in engineering structures and materials. The high speed CCD camera and digital image processing system were used to measure the 3D shape of the inflated cylindrical tube. The localized bulge of a cylindrical tube with closed ends forms when the internal pressure reaches a critical value Pcr. As more air is filled into the tube, the pressure drops but the radius at the centre of the bulge will increase until it reaches a maximum value rmax. With continued inflation, the pressure stays at a constant value Pp. The purpose of this study is to investigate the critical and propagation pressures in the tubes and the profile outside when the shells under axial tension and internal pressure were inflating. We focus on the influence of the axial tension on the critical pressure. In this paper the problem is explored through experimental efforts. A series of experiments were conducted on commercially available natural rubber latex tubes involving different geometries and initial axial tensions, which were regarded as isotropic, homogeneous, incompressible and hyper-elastic materials.
This paper concentrates on the effect of out-of-plane translation on the 2D-DIC and its elimination. The strain errors caused by out-of-plane translation are presented in the form of equations. In this paper, a novel experimental technique is suggested to eliminate the effect of out-of-plane translation in 2D-DIC. A planar laser beam is projected on the surface of the specimen to form a light strip on its surface. The position of the light strip will be shifted if the specimen is translated along the optical axis of the camera. The distance of translation can be calculated by comparing the location of the laser strip before and after translation. Verification experiments were performed to validate the effectiveness of the proposed method. Then the method is combined with the theoretical model to predict and eliminate the pseudo strains caused by out-of-plane translation. Results confirm that this method can predict the strain errors caused by out-of-plane translation to a precision of within 100με.
In this paper, an experiment is executed to analyze the displacement distribution of 56-ply composite laminates under three-point bending. In the experiment, the displacement fields on the two free edges of the laminated composite are measured by using the moire interferometry method and natural micro-image processing technique based on wavelet transform at the same time. In the first part of this study, a two-beam traditional moire interferometry experiment has been carried out. And in the second part, we present a new image processing method, which combines the theory of correlation and wavelet transform technique.
A technique for measuring in-place displacement under impact loading using digital speckle pattern interferometry (DSPI) with combining the digital subtraction and add mode is presented. A new technique of the add mode filtering is used. To grab the digital speckle of field produced by a pulse laser, an instantaneous digital image grabbing system is proposed. Thus the dynamic digital speckle image can be recorded and stored in a digital frame store. As an example, the displacement field of a semi-infinite model udner impact loading is measured.
Poly(3-hydroxybutyrate) exhibits remarkable embrittlement upon storage at room temperature, and this problem limits its widely use in technical purpose. In this paper, morphology and micro-structure of PHB spherulite are investigated by using the twelve variables gradient method and polarization microscope. The results indicate that the PHB spherulites could continuously crystallize, namely: secondary crystallization, the morphology and micro-structure of PHB spherulite are changed, the embrittlement at room temperature was resulted from PHB secondary crystallization. Competition phenomenon in the process of PHB secondary crystallization was found.
A new full-field optical technique is developed to study surface deformation of solids. This method combines the measurement by grid method and the digital image processing. An optical information processing system and a digital image processing system of computer are used in this method. At the output plane we receive the pattern of grating lines taht can be used for the analysis of deformation of the specimen on which we have produced the phase grating. At last we show the application of this technique in the investigation of elastic-plastic fracture.
AS4/PEEK [0/+/- 45/90]7s composite laminates were subjected to a bending moment. We have obtained the displacement fields by moire interferometry with the aid of Long Distance Microscope. Based on wavelet analysis, the digital moire images were processed and analyzed. The special algorithms of unconstrained nonlinear minimization and the scale parameter were used to eliminate the influence of the noise in the digital image processing. Tension tests were carried out on AS4/PEEK [ 0/+/- 45/90 ]2s composites. When AS4/PEEK composite laminates were deformed, the images of natural surface of the AS4/PEEK specimen were recorded to study the damage initiation and growth. The experimental results show that the considerable interlaminal stresses between different plies, and these places were more prone to delaminate. The paper presents the microscopic damages and matrix crack growth observed by an optical microscope and the CCD camera.
The fully 3D orthotropic elastic-plastic analysis of interlaminar stresses and deformation for AS4/PEEK thermoplastic laminates is developed in this paper, and used to simulate the tensile stress- strain curves for (+/- 25)s4 laminates. Under uniaxial tensile loading, the 3D orthotropic elastic-plastic FE analysis and microscopic moire interferometry of interlaminar stresses and deformation are carried out for the (+/- 25)s4 laminates. It is found that the numerical tensile stress-strain curves of (+/- 25)s4 laminates agree with experimental. The numerical interlaminar displacement u and shear strain (gamma) xz are also consistent with the experimental results obtained by moire interferometry.
In this paper, a new digital-image correlation method-twelve variables gradient method is presented. The influence of second derivative terms of displacement is considered, the directional derivatives of correlation coefficient are obtained and variational step-length search is used in this method. Consequently, the truncation error caused by increasing of subset size and vast computation time are avoided. The measurement precision of displacement and strain are less than 0.011 pixels and 100 (mu) (epsilon) , respectively. Two test experiments and the application show that this is an efficient and accurate method.
IN this paper, a system of micromechanical experiments is established combining microscopic moire interferometry of high spatial resolution with optical microscope. Under uniaxial tensile loading, the quantitative local-field of interlaminar displacements of the AS4/PEEK laminates has been measured. The pictures of in-situ interlaminar damage initiation and growth process have been simultaneously collected by the experimental system continuously. The major characteristic of interlaminar damage of the laminate under tensile loading is the group of matrix cracks in 90/90 plies, which are formed due to fiber- matrix interface debondings, and the number of cracks increases when the load increases. The u fields of interlaminar displacement of a matrix crack under certain loads are gained using the microscopic moire interferometry.
A non-contact and non-destructive method for full-field in-plane strain measurements has been developed. Digital image processing is employed for monitoring the deformations of gird liens marked ona planar surface of a component or a specimen. Full-field in- plane strain distributions are obtained by processing the geometrical characteristics of the grid with computer graphics algorithms. The applications and the future evolution of this method are discussed.
Based on image and graphic technologies and synthesized preceding research achievements in the digital processing of photoelastic image, a vectorization system for interactive photoelastic image processing has been set up. The system consists of seven modules, and a toolbox. This paper describes the system structure, new techniques used in the system, and its features. By use of this system, the vectorized image files of the skeleton for stress analysis can be obtained. The application area of the system is wide, and it has quite strong interactive processing capability and user-friendly interface.
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