Papers by Keyword: Optical Strain Measurement

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Authors: Mazen Ayoubi, Martin Trautz
Abstract: The use of self-tapping screws with continuous threads to reinforce and join timbers in addition to glulam elements represents an effective, simple and economic method. The high withdrawal resistance of the screws as well as its continuous bond with the wood enables an effect similar to steel reinforcement in concrete structures. Within the framework of a research project, funded by the German Research Foundation (DFG) at the Chair of Structures and Structural Design in cooperation with the Institute for Building Material Research of the RWTH Aachen University, several tests have realized to investigate the bond behaviour, the force transfer and the anchorage length of the screws. Herewith the stress distribution will be determined with an optical 3D field measuring system, based on the digital image correlation (DIC) method, which measures the strain by observing the surface of the test specimens. To ensure the accuracy of the measurements for a wide measuring field of wood surface, a comparison study was conducted involving traditional electrical sensors (i.e. strain gauges and LVDTs). The results of this study, which confirm the accuracy regarding the determination of stress distribution for small deformations on the wood surface with optical 3D field measuring system, will be presented in this article.
Authors: Eduard Schenuit, Rainer Bolkart, Thomas Becker, Oliver Spinka
Abstract: Progresses in developments of high resolution digital cameras and processors power as well enable the use of optical systems for axial and biaxial strain measurements. The main benefit of these systems is a contact free measurement on the sample surface without any influence to the sample. The commonly used optical systems based on following markings attached to sample surface which have to be applied before testing. This paper presents an alternative optical measuring system using the speckle-correlation-technique. The laser based method does not need any special sample markings before testing. The speckle correlation in the presented extensometer measures up to two-dimensional surface strains in tensile as well as in compression tests; original gauge lengths down to 1.5 mm are supported.
Authors: Harald Friebe, Markus Klein, Ingo Heinle, Arnulf Lipp
Abstract: Axisymmetric die and binder are typically used in the bulge test, where the test specimen is formed by increasing the level of oil pressure (Fig. 1). With this experimental setup a biaxial stress state is induced at the specimen dome, assuming that it is not influenced by friction. The increasing oil pressure in the region of the top of the dome is recorded and the deformation field measured during the forming process. The optical measurement system determines the coordinates, the deformations and the curvature on the outer surface. Based on the forthcoming ISO 16808 these results are directly used for the calculation of the flow curve. In order to determine the flow curve based on the bulge test, an analytical approach is needed for the computation of the stress state at the top of the dome.
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