Pierre, F., Almeida, G., Huber, F. et al. Wood Sci Technol (2013) 47: 537. doi:10.1007/s00226-012-0512-9
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.