Response of Wood Bars to Non-Destructive Impact

The wood bars with rectangular cross section (25 x 25 mm, 300 mm in length) were impacted by an aluminum cylindrical bar in R and T directions. The wood response to this loading was characterized by the displacement of the surface of the bar. The time history of this response has been measured by a double channel laser vibrometer. The analysis of response functions was performed both in the time and frequency domain. The bar response to the impact is described using the transfer function. The knowledge of this function enables to predict the surface displacement at the given point for various forces. It is shown that the history of the surface displacement in direction of its propagation exhibits the same qualitative features independently of the kind of wood in the direction of impact and of the position of wave detection. Experiments were performed on bars made from five tree species: Pinus sylvestris L., Picea abies (L.) Karst., Fagus sylvatica, Quercus robur and Populus nigra.