Papers by Keyword: Speckle Interferometry

Abstract: Residual welding stresses affect significantly the strength, durability, and performance of structures. Therefore, there is an urgent need for developing and implementing techniques and equipment that allow reliably estimating stresses in experiments. This paper considers some aspects of the joint implementation of electronic speckle pattern interferometry and the spot drilling technique to determine these characteristics under the field conditions. The results of determining the distribution of residual stresses in the weld joint areas of DN 850 pipes are given for various welding modes. The study results are of independent significance and herewith, demonstrate the efficiency of the equipment developed to solve similar problems.

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 results on a numerical and experimental study of graphite/epoxy composite plates [03/903]S are presented. Each specimen was firstly impacted by the low velocity with different energy level. Compression experiment based on carrier electronic speckle pattern interferometry (carrier-ESPI) is made for the post-impact composite plate. The finite element method (FEM) is used to gain further understanding of the deformation behavior of impacted specimens. The compressive deformation of various delaminated composite plates are analyzed with software ANSYS to see that the impact parameters and delamination damage data, such as impact energy, maximum impact force and delamination area, affect the deformation fields. In addition, the comparisons between the finite element results and experimental measurements are considered under different compression loads.

Abstract: The study on deformation in impact-damaged graphite-fibre/epoxy stitched composite plates subjected to compressive load is presented. A delaminated cross-ply laminate [03/903]S obtained in low-velocity impact test has been examined using a self-designed anti-buckling device in compressive experiment. The out-of-plane displacement field of the specimen has been measured with an optical whole-filed measurement technique, which is carrier electronic speckle pattern interferometry (carrier-ESPI). Finite element (FE) simulation is also carried out to predict the deformation. The effect of the stitching line on compressive deformation is discussed for various stitched laminates. Finally, the numerical results are compared with experimental measurement deformations under different compressive loads.

Abstract: The original and significant achievement of this work is to analyse strain rate field in aluminium alloy sheets during micro tensile test. In-plane Electronic Speckle Pattern Interferometry is used to follow the evolution of the local strain in real time. This paper is based on the detection of the localization on a relatively small area of the analysed specimen: less than 5mm × 4mm area. Moreover the speed of the tensile machine is very low, 0.2 to 0.1µm/s. The phase shifting technique is used to obtain the fringes representative of the material displacement. We can therefore get a very good accuracy in the material displacement. A heterogeneity in strain rate field can be noticed from a deformation stage which doesn’t coincide with the one calculated by the classic Considère’s criterion (dF=0) for the diffuse neck initiation (or plastic instability). We also show, the moment when one of the two slip bands systems becomes predominant, and even only one band continues to exist, this occurring widely before fracture. Finally, the fracture of the specimen occurs across this remaining band. The total strain is measured with a second camera, in white light, and is correlated together with the strain rate field to study the localization.

Abstract: In this paper, a speckle microinterferometric system was employed to study the thermal deformation of the Cu microbridges with different dimensions. The deflections of the microbridges caused by the thermal loading were measured with real-time by the speckle microinterferometric system and the surface temperatures of the bridges were recorded using a digital thermometer. The deformation evaluation after microbridges buckling was also recorded with our testing system. Then, the experimental results were compared with the finite element analysis (FEA).

Abstract: In Microelectromechanical System (MEMS), the capillary force plays an important role owing to the strong capillary force often makes the suspended or moving structures in MEMS adhere to contact the substrate, which lead to the failure of the devices. This paper presents experimental and theoretical results that characterize the capillary adhesion of micro-cantilevers by means of capillary actuation. Micro-cantilever beams were loaded at various locations along the freestanding portion of the beam using the capillary force and the deflections of the beams were real-time and in-situ measured with micro speckle interferometry. The mechanical stability and adhesion of micro-cantilever under capillary forces were examined and the deflecting configurations of the beams and the relationship of the magnitude of the capillary force to the size of the specimen were presented.

Abstract: Speckle interferometry with phase shifting method is used to measure in-plane displacements of a steel plate with a partly through-thickness circular hole and a steel plate with a through-thickness circular hole. The circular hole of steel plate with a partly through-thickness circular hole is cut on the rear side of the plate, so that it is not visible during experiment. The speckle noises of fringe patterns acquired by optical experiment are processed with image processing algorithm of Gaussian blur and the in-plane displacements of the two specimens are obtained by use of the processed fringe patterns. Also the in-plane displacements of the two specimens are calculated by use of ANSYS. The results of optical experiments are quite comparable to those of calculation with ANSYS.

Abstract: The knowledge of residual stresses allows a reliable prediction of structure performances evolution, such as service life [1-3]. In this paper, we develop a new method for residual stresses determination combining Electronic Speckle Pattern Interferometry (ESPI) with the machining of a groove. The internal stress field is perturbed as the depth of the groove is increased incrementally. The structure finds a new equilibrium state generating displacements which are measured using ESPI. This method was tested on an aluminium alloy AU4G plate treated locally by an ultrasonic shot-peening. The investigation of the images obtained with the phase shifting technique and fringe patterns, makes it possible to analyze, simultaneously, the stress profile along two directions: along the depth of the structure, and along the groove direction.