Use of acoustic testing to detect decay and sort western juniper for modulus of elasticity and modulus of rupture

Abstract

ABSTRACTWhile wood has numerous attributes that make it an excellent material for many uses, its properties can also vary widely according to wood species and even within the same species. Wood used in structural applications is categorized into classes. For many wood products, these classes or grades are based upon visual assessments that account for grain characteristics along with natural defects such as knots or splits. These approaches are simple, but also limit the potential for identifying products based upon actual material properties. One alternative is to use acoustic tests to estimate modulus of elasticity and then correlate these values to actual material properties. The potential for using acoustic tests to estimate wood properties was assessed with a prototype acoustic device (Metriguard Model 242) on western juniper (Juniperus occidentalis) posts that were then tested using a destructive bending test. These tests could allow the identification of decayed areas within a post if they were directly in the tested area, but predicted modulus of elasticity was poorly correlated with actual modulus of rupture (r2 = 0.23). The correlation was improved by only considering those samples where the acoustic test was made through the same area where the test load was applied, but the relationship was still weak (r2 = 0.33). Acoustic testing did appear to be able to identify unacceptably weak samples with minimal rejection of acceptable samples, suggesting that acoustic testing might be a useful sorting tool to improve the reliability of timbers.