, Volume 47, Issue 3, pp 537-555
Date: 16 Oct 2012

An original impact device for biomass characterisation: results obtained for spruce and poplar at different moisture contents

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Abstract

This paper describes an experimental device designed to determine the mechanical behaviour of lignocellulosic products subjected to high strain rates. This impact system consists of a moving trolley equipped with an accelerometer, which is thrown against a fixed trolley. The sample is attached to the fixed trolley, and the accelerations of both trolleys during the impact are analysed to obtain stress/strain curves. A high-speed camera synchronised with a high-powered xenon flash records up to 4,000 frames/s. A set of tests on wood samples is described to illustrate the potential of this new device. In particular, the cross-effects of compression rate and moisture content were demonstrated by performing both quasi-static (1 mm min−1 using a conventional testing machine) and dynamic tests (1.7 m s−1 using the impact device). Poplar and spruce samples, equilibrated at three different moisture contents (air-dried, fibre saturation point (FSP) and fully saturated), were tested. Two findings are particularly worthy of mentioning: (1) despite the plasticising role of water, the sample at FSP exhibited a fragile behaviour at the high compression rate, (2) the resistance due to the expulsion of water out of saturated samples can be assessed only by performing an impact test.