Detection of incipient decay and assessment of residual strength of wood using nondestructive techniques

The purpose of this study was to investigate the feasibility of using ultrasonic stress-wave technique and Pilodyn techniques for the nondestructive detection of incipient decay and assessment of residual strength of decayed wood. Ultrasonic wave velocities and Pilodyn pin penetrations were determined in southern pine sapwood dimension stock which had been exposed to the brown-rot decay fungus Gloeophyllum trabeum for various time periods. The specimens were then tested to failure in edgewise static bending.; Ultrasonic techniques appeared to be ineffective in delineating incipient decay in lumber. However, interval measurements of velocity indicated the techniques might be capable of detecting localized incipient decay areas. Pilodyn pin penetration gave promise as a nondestructive evaluation (NDE) method for estimating incipient decay. The increase in pin penetration was correlated closely with the density decreases associated with decay.; Brown-rot decay had a significant effect on the modulus of rupture (MOR) in the early stages of decay. The results indicated that all load-bearing members subjected to periodic wetting should be inspected regularly, even though no visible sign of decay is found. In general, decay reduced the strength of lower grade (strength ratio {dollar}<{dollar}0.65) specimens more than that of higher grade (strength ratio {dollar}geq{dollar}0.65) material.; Linear regression analysis was performed to identify the best nondestructive parameter(s) for predicting MOR. The best single predictor of modulus of elasticity (MOE) and MOR was dynamic MOE derived from wave velocity. When multi-variable regression was used, the model having velocity and pin penetration was considered as the best for predicting strength because of the simplicity of measurements that were required for evaluation. Even though ultrasonic NDE is not suitable to accurately predict the bending strength of an individual specimen, the screening of decayed specimens based upon ultrasonic parameters might be a viable supplement to visual inspection.; In testing on small, defect-free specimens, a relatively strong correlation between weight loss caused by G. trabeum and Coriolus versicolor and decrease in transverse velocity was observed, indicating that ultrasonic techniques can be used to detect incipient decay in controlled studies.