Considerations on variability in acoustic measurements in timber property assessment

Reliability of measurement with acoustic NDT applied to timber structures improves in-situ assessments. The aim of this research is to carry out simulated in-situ measurements with acoustic NDT devices in order to analyse the influence of different sensor positions, repeatability and measurement lengths. Time-of-Flight and dynamic modulus of elasticity (MOEdyn) variability were quantified on the faces and edges of Scots pine timber from a sawmill. A comparison was also made of the models obtained at different distances between the sensors and a mean model independent of the distance between the sensors. Linear regressions between the static modulus of elasticity (MOEsta) and MOEdyn or wave velocity depending on the distance between sensors yielded coefficients of determination (R2) from 0.59 to 0.86 and residual standard errors (StE) from 737 to 1232 N mm−2. It was found that measurements taken at 1 m distance did not represent the piece as a whole, and that mean statistical models provided a better relationship, increasing by up to 14% in R2 and decreasing StE by up to 11%. It is concluded that in order to obtain a reliable model (MOEsta vs. MOEdyn) at least 2 measurements are required at different positions on each piece of the batch.</p