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Adiabatic sheer measurement

23rd October 2018


Specialised Imaging has published a new application report that describes how its Kirana ultra-high-speed video camera has been used by a leading material science laboratory to measure the movement of an aluminium sample undergoing adiabatic sheer along a 2mm sheer region.

The Kirana camera was set to acquire 5 million pictures/second with a 100nS shutter and used a 50mm Titanar F2.8 lens with 10cm of extension tube to bring the camera closer to the test piece and provide a field-of-view of approximately 5mm x 4mm.

The movement in the aluminium test piece was measured using Digital Image Correlation (DiC) software. The sheer impulse was imparted onto the specimen using a Split Hopkinson Bar experimental set up. Two AD500 flash lamps were used to illuminate the sample evenly and prevent any shadows that might affect the DiC measurements.

The presented DiC data shows from the first image, a shear band of heightened strain occurs at approximately 45° to normal. As the specimen begins to ‘slide’ relative to itself, pure shear is induced, starting from the outside edges and converging in the centre. In this adiabatic shear test, the Kirana camera was able to capture high quality images showing how the strain localises along precise shear bands. This occurs due to high-strain rate loading giving rise to localised heat concentrations which do not have time to conduct in the bulk material. This high temperature ‘band’ deforms far more readily than the cooler bulk material. 

As the test proceeded, cracks appeared on the sample surface. The process of crack formation and propagation from the outside edge of the specimen moving horizontally through the centre of the shear region was also captured using the Kirana ultra-high-speed video camera.

The Kirana is a high-speed video camera that combines the flexibility of video technology with the resolution of the ultra-high-speed framing camera. In this new application report the utility of the camera for making DiC measurements in material science applications is clearly shown.

 





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