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Characterisation of materials subject to high velocity deformation is necessary as many materials behave differently under such conditions. It is particularly important for accurate numerical simulation of high strain rate events. High velocity servo-hydraulic test machines have enabled material testing in the strain rate regime from 1-500 ε/s. The range is much lower than that experienced under ballistic, shock or impact loads, nevertheless it is a useful starting point for the application of optical techniques. The present study examines the possibility of using high speed cameras to capture images and then extracting deformation data using Digital Image Correlation (DIC) from tensile testing in the intermediate strain rate regime available with the test machines. Three different materials, aluminium alloy 1050, S235 steel and glass fibre reinforced plastic (GFRP) were tested at different nominal strain rates ranging from quasi static to 200 ε/s. In all cases DIC was able to analyse data collected up to fracture and in some cases post fracture. The use of highspeed DIC made it possible to capture phenomena such as multiple necking in the aluminium specimens and post compression failure in GFRP specimens.
Abstract. This paper describes a dual 3D Digital Image Correlation (DIC) system application for DLS strain and displacement measurements, where two 3D DIC-systems are used in parallel. The bonded specimens were tested to failure under monotonic loading in a uni-axial tensile testing machine at ambient temperature. Both surface inplane strain and full-field displacement values were recorded using two DIC systems: high speed (HS) and high resolution (HR). The HS system was used in a parallel setup with the HR system in order to detect the initial failure location and crack propagation rate during the brittle failure mechanism, where an interface crack is propagating between the straps and the inner adherent. Using two inherently different DIC systems involve a number of problems. This involves synchronization of the HS and HR systems, a common illumination level and speckle pattern. This paper therefore describes guidelines for a mutual system setup, applied in an experimental study of steel/epoxy DLS joints under pure tension. IntroductionIn the marine industry there is future potential for adhesives in various types of constructions which include super-structures for ships and offshore platforms as well as their application in connection with patch repair of cracks and corroded areas within the structure [1]. This technology is currently under consideration for repair of onboard floating production storage and off-loading units (FPSO's), where conventional repair by welding is very expensive due to safety [1]. A suitable and good representation of a patch repair of a steel structure is the DLS (Double Lap Shear) joint, which can be studied in 2D.The aim of following paper is (a) to provide a quick guide to the application of a stereo 3D Digital Image Correlation (DIC) system setup to measure full-field 3D displacement and 2D strain fields at a specimen surface while undergoing testing, where two 3D DIC-systems are applied in parallel, (b) to describe the failure of the test specimens and finally (c) to shortly present results of the DLS-tests. a
The growing applications of layered fiber reinforced composite materials lead to the potential use of such lightweight materials for blast and ballistic impact resistant panels. Under such high strain rate loading, through-thickness damage propagation is crucial for the structural integrity of the panels. Experiments performed in composite panels under blast loading exhibited little information for the understanding of the time-line of damage propagation as only post-mortem inspection can be done. Instrumentation may be installed in order to follow the blast but the task reveals itself arduous as all the instruments must be protected against the blast. The sparse information can be valuable for configuration screening purposes, but is not su ffi cient for comparison and validation of numerical models. The work focuses on performing controlled impact experiments in narrow beams filmed side-wise with high-speed cameras. The narrow geometry of the beams leaves the thickness of the specimen exposed to the cameras allowing for a real-time monitoring of the stress waves propagating and for assessing the time-line of through-thickness damage propagation onset. Results showed that polyethylene impactors, given the right diameter, are the most suitable soft impactors. Numerical models including in-plane and out-of-plane damage propagation are being built in order to replicate the experimentally observed damage. The ultimate goal being establishing design rules for such lightweight fiber reinforced panels. It is numerically observed that, the speed propagation of delamination in the longitudinal direction reaches a common constant value for all interfaces.
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