Damping and Poisson factor behaviour in timber considered as an orthotropic material, part 1; the loss factor

Abstract

In this paper measurements are described which were used to determine damping (loss factors) in two timber species, King William pine and spruce. Tests were conducted by loading uniaxially in each of the three principal material property directions. Testing was conducted over the frequency range 0·5–70 Hz by applying axial forces well below system resonance and measuring the phase between force and response. The investigation allowed for assessment of the effect of frequency, stress level and stress history on loss factor. Stress levels investigated were between 1·3 MPa and 11·3 MPa for axially loaded specimens (i.e., strain levels between 145 με and 2020 με). In radially loaded specimens the stress range was 0·5–3·9 MPa (230–2040 με) while tangentially loaded specimens were loaded in the range 0·5–1·5 MPa (155–3330 με). Measured values have shown that loss factors can be dependent on frequency, stress level and conditioning particularly in the radial and tangential directions.