Abstract
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 e/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 e/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.
Highlights
High speed tensile tests at intermediate strain rates up to 500 ε/s are accessible with high speed servo-hydraulic test machines [1]
Some initial work on the application of Digital Image Correlation (DIC) to the derivation of strains from metallic and composite specimens subjected to high speed deformation has been presented
Noteworthy findings that will provide guidance for other practitioners, It should be noted that the DIC system used to control the acquiring and the processing of the data was the ARAMIS system by GOM and some of the features discussed in the paper are only applicable to this system
Summary
High speed tensile tests at intermediate strain rates up to 500 ε/s are accessible with high speed servo-hydraulic test machines [1]. 10 ε/s the load is measured with local force transducers to suppress the effect of load cell ringing [2, 3] For heterogeneous materials, such as fibre reinforced polymer composites, it is generally necessary to use straight sided strip specimens. For strain rates higher than 1 ε/s strain gauges or high speed non-contact measurement methods such as laser Doppler The present paper provides some guidelines for application of DIC to data captured from high speed imaging of specimens of different materials loaded in a high-velocity servo-hydraulic test machine. Stress-strain curves are produced based on simultaneous measurement of load with image capture at different test velocities that demonstrate the feasibility of using the DIC approach for material characterisation
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