Papers by Keyword: ESPI

Abstract: In order to study crack evolution in concrete, Electronic Speckle Pattern Interferometry (ESPI) technique was applied to measure full-field displacement of concrete beam subjected to three-point bending. Basic principles of ESPI technique were introduced. Mid-span deflection and crack mouth opening displacement were measured by linear variable differential transformers (LVDTs) and clip gauge, respectively. Typical load-displacement curves measured by different methods were compared and analyzed. Analysis results indicated that ESPI results were in good agreement with that measured by LVDT (clip gauge), verifying the validity and accuracy of ESPI measurement. From displacement contours, crack evolution including its initiation and propagation was observed. Furthermore, strain profiles near the crack at different loading levels were determined. Strain profile was nearly linear before crack initiation and became nonlinear with crack growth.

Abstract: With high resolution, electronic speckle pattern interferometry (ESPI) technique can be useful in measuring full-filed deformation of laboratory specimens. In this study, ESPI was applied to measure the full-field displacements of mortar beam subjected to three-point bend. Load-displacement curves measured by ESPI were compared to that measured by clip gauge and LVDTs. Satisfactory agreement was observed in all the comparisons, demonstrating the effectiveness and accuracy of ESPI measurement. Furthermore, load versus crack tip opening displacement curve was obtained from ESPI results. Finally, extent of the fracture process zone and neutral axis of the mortar beam were analyzed based on full-filed displacement contour measured by ESPI.

Abstract: An essential part of cell cultivation via cell culture technology is the determination and monitoring of culture parameters. Such parameters refer to the vitality or mutual mutations of the cell culture, while the actual number of living cells in each batch indicates the correct growth rate rather than stagnation or an overgrowth of the cell culture. Today such parameters are determined by applying light microscopy methods or by staining specific constituents of the cells. Commonly such methods are a stressful procedure for the studied cells. Most applied dyes are toxic over a certain period of time and thus they are used in low concentrations only when necessary. Within this work a new kind of measurement device prototype was designed to address these problems. This device is based on the Electronic Speckle Pattern Interferometry (ESPI). ESPI is an optical high-resolution method combined with a photonic analysis system capable of analyzing cellular deformations and oscillations. In this approach the combination of a greatly modified microscope together with ESPI method is presented. The apparatus allows the determination of cellular deformation (i) at very high magnifications, (ii) with high lateral resolution. Furthermore the system studies (iii) contact free, (iv) in vitro cells, in a non-invasive and non-destructive way. A co-developed cultivation system allows monitoring the culture parameters in real time minimizing the stress for the cell culture. Since no additional substances are needed, the presented prototype is automated to a large extent and can be operated by a special control-and regulation system (CRS) based on a microcontroller development board (Arduino Mega).

Abstract: The determination of mechanical properties can provide insight into complex biochemical processes such as the cell cycle and even the progression of diseases. However, this field of biomechanical research strongly depends on a high-resolution measurement technology and a gentle stimulation method in order to examine these mostly biological samples in their original condition. In terms of this work, a different approach utilizing a modified ESPI setup and two types of ferro-fluids is presented. By exposing the prepared specimen to an electro-magnetic field it has been possible to induce a local displacement and to monitor the deformation with the adapted ESPI setup.

Abstract: Strain localization in low carbon steel DC04 undergoing uniaxial tension is investigated by Electronic Speckle Pattern Interferometry (ESPI). The necking in the sheet specimens occurs by forming two narrow crossing bands. A model of strain rate distribution is used to extract quantitative information about the localization bands, such as bandwidths, bands orientations and their maximum strain rates. Thus, their evolutions are followed from the diffuse necking up to the rupture. The influence of specimen geometry on localization phenomenon is studied.

Abstract: The purposes of this paper are to weld dissimilar aluminum alloys joints, AA1050 and AA6061, and to find Young’s modulus on the welded zone along the thickness. Dissimilar aluminum alloys plates are friction stir welded in the butt configuration by using an adapted milling machine. Young’s modulus of components is found out by applied a reverse method and the out-of-plane displacement is measured by Electronic Speckle Pattern Interferometry. The out-of-plane displacement of the welded cantilever beam is subjected to a concentrated load. The results reveal that Young’s modulus in the welded zone is the deeper the smaller.

Abstract: Modern speckle optical methods use the properties of coherent light for identification of displacement fields. One of these methods is method ESPI. Using of this method strain and stress fields on surface of flat test samples with symmetric notches by tensile and shear loading were identified. A special fixture for shear loading of test samples was designed. The shape and dimensions of the fixture were modified on the basic results of experimental measurements. A modification allowed us to obtain a better analyse of strain and stress fields of test samples with symmetric V notches.

Abstract: An electrode system for inducing a high density pulsed electric current (PEC) into the material for residual stresses (RS) relaxation has been proposed. A new non-destructive technology for determination of RS using electron speckle interferometry in combination with a local PEC treatment has been developed. Application of PEC at increased power parameters was investigated for control of stressed state of welded structures used in aircraft engineering. Results of practical application of the developed technologies and equipment are presented.

Abstract: Shot-Peening is used to generate surface-near compressive residual stresses in final shape parts, usually to improve their fatigue properties. The success of the process can be checked in different ways. XRD and Hole-Drilling determine quantitative stress depth profiles in specific locations. Barkhausen noise measurements evaluate a near-surface zone in real-time and can cover large areas quickly. It is a fully nondestructive method. This study compares ESPI Hole-Drilling, which is a very fast technique, and XRD, which is very precise but slower, to Barkhausen Noise results for the case of three steel rings shot-peened with different intensities.

Abstract: A micro-displacement, strain and stress measurement method based on electronic speckle pattern interferometry (ESPI) technique is proposed, and the measuring device is designed. Two symmetric laser beams are illuminated on the optical rough surface of a steel cantilever beam, and then speckle images are photographed by CCD. A series of filtering processing is carried out for subtracted images and FEM analysis is performed. Using the speckle fringe patterns finally achieved, displacement, strain and stress can be calculated. By comparing displacement, strain and stress measured by this method with simulation results, feasibility and engineering application value of this method have been proved.