Papers by Keyword: Image Correlation

Abstract: Agoras were central to the lives of Western European people and can be called the starting point of Western European civilization. In previous study, image processing technology was used to perform the initial restoration of the architecture and city shape. And each building in the 3D model of the plaza was then constructed, centering on the formation of the agora. In this study, 3D model of the temple was focused on the temple building and stoa, extracted the facade of each building, quantitatively evaluated similarities by performing fractal dimension analysis and image analysis, and considered the relevance of the two analysis results.

Abstract: The increase of the degree of miniaturization of the mechanical systems leads to the increase of the production requirements for micro or mili parts made using the micro and milli deep drawing processes. In the case of micro or mili drawn parts, the foil thickness has an important influence on the intensity of the specific phenomena that occur during micro and milli cold forming and has also an important effect on the drawn part integrity or accuracy. The present study was focused on the investigation of the material behaviour, including mechanical properties and forming limit curve of CuZn37 when different thicknesses of foils are used. For this purpose, experimental determinations were made by using the following two values of the foils thickness: 0.1 and 0.2 mm. For each foil thickness, the mechanical properties and the forming limit curves (FLC) were determined and compared. The obtained results concerning the influence of the foil thickness on the material mechanical and formability properties shown that the level of the stress strain curve determined for the foil thickness having 0.1 mm is greater than in the case of foil thickness having 0.2 mm but the maximum strain and the anisotropy coefficients are lower. The level of the forming limit curves (FLC) in the case of foil thickness having 0.2 mm is greater than in the case when the foil thickness is equal to 0.1 mm.

Abstract: Bone is an anisotropic inhomogeneous material, and its piezoelectric behavior is more complex than mineral piezoelectric materials such as quartz crystal or ceramics. This article aimed to understand the piezoelectric properties of bone by investigating its converse piezoelectric effect. Bending deformation of bone specimens subjected to an external electric field was observed. Displacements or deflections of bone cantilever beams were measured by a high resolution digital microscope combined with digital image correlation technique. In order to demonstrate the validity of the experiment, specimens made of non piezoelectric materials were also tested in the same experimental condition as bone. The results indicate that the bending deformation of the bone cantilever may come from the non uniform piezoelectric properties of bone, compared to an analytical solution.

Abstract: In order to improve the capability of scrambling encryption and anti-aggressive, we extended the two-dimensional Arnold transformation to three-dimensional, and designed one kind of new diffusion equation of the digital image pixel gray value, then introduced a novel digital image encryption algorithm based on them. The large number of simulation results and analysis have both shown that the proposed scheme is a very effective encryption algorithm.

Abstract: Thermally grown oxide (TGO) spallation increases the degradation rate of aluminide protective coatings during thermomechanical cycling. Thermal expansion misfit between TGO, bond coat and substrate, applied mechanical load in the system, and local instabilities are known triggers for spallation. Mechanical tests have been performed on coated and oxidised AM1 superalloy. In situ and post mortem study including digital image analysis and SEM were performed in order to characterise strain fields and associated damage field. Good correlation is found between oxide strain and damage extent.

Abstract: A novel methodology based on a combination of experimental and analytical methods is used for monitoring the stress intensity factor in fatigue cracks subjected to constant amplitude loads. Full-field displacement information is fitted, following a multi-point over-deterministic approach, to an analytical model. This is developed from Muskhelishvili’s complex formulation. The methodology allowed accurate monitoring of the stress intensity factor during three fatigue cycles when small-scale yielding conditions were achieved. Moreover for larger loads where important plastic deformation occurs around the crack tip, Dugdale’s correction accounted for the differences between theoretical and calculated stress intensity factors. Accordingly the tool provides an indirect approach for measuring crack tip plasticity. Due to the fact that image correlation is relatively simple to use and is a non-contacting technique, the approach pioneered in this work seems ideal for monitoring fatigue cracks in industrial applications.

Abstract: Work has been carried out recently, which demonstrates misorientation measurements recorded by using electron backscatter diffraction (EBSD) enables one to undertake local post mortem plastic strain quantification once the degree of misorientation is calibrated against plastic strain. The present paper builds on this work and investigates the possibility of determining strain in individual grains. Due to the anisotropy of crystalline grains, polycrystalline material deform inhomogeneously on a microstructural level. In this study, the local strain induced in a pure copper specimen during tensile loading measured using EBSD was compared to in-situ strain measurements using optical microscopy imaging in conjunction with image correlation technique. By applying an averaging procedure for improving the accuracy of the measured EBSD data, the distribution of the misorientation within grains was quantified, and, as one would expect, it tended to be highest near the grain boundaries.

Abstract: Cost effective and reliable operation of a power station plant and achieving low carbon dioxide emissions can be very dependent on maintenance activities. Planning maintenance to minimise the down-time of the plant is a key cost factor. It is important to have the latest data as to the age and state of the components and parts at the time of plant shut down. Indeed, deciding on the best time to shut down the plant for maintenance can depend upon trends in these data. For steam pipes, the required ageing information is the creep strain rate. These creep strain data obtained at shut down provide key information as to the needed replacement of pipes to maintain reliable plant operation. This paper presents the E.ON UK ARCMAC creep strain measurement systems that are being further developed by Imperial College London with the use of DIC and other techniques.

Abstract: This article presents the first part of a study on the interaction between residual stresses and crack driving force. Blunt notched CT specimens were pre-strained to introduce residual stresses at the notch, where a crack is subsequently introduced. FE modelling is used to model the specimen preload and pre-cracking. Modelling predictions are validated by two different methods. The total predicted surface residual strains are compared to image correlation measurements. The predicted residual strains were measured using neutron diffraction, both before and after fatigue cracking. The residual strain profiles show good agreement with the 3D FE model in the far field but the peak strains measured near the notch are smaller those predicted. This is a result of the low spatial resolution of the technique.

Abstract: An experimental investigation of the micro and macromechanical stress-induced martensitic transformation in a Cu-Al-Be polycrystalline shape memory alloy is undertaken using a uniaxial tension test. Digital images are acquired at different stress states. The image sequences are analyzed to estimate the optical flow to get displacement vector fields. The experiments are carried out on a miniature hydraulic loading device mounted under an optical microscope. The stress-strain curves and associated images show stress-induced martensitic transformation in specific grains. Displacement vector fields for the polycrystalline shape memory alloy are obtained. They are inhomogeneous due to the martensitic transformation and inter-granular interactions.