A preliminary assessment of the Metriguard 239A stress wave timer

Considerable effort has gone into developing non-destructive testing (NDT) techniques for assessing the performance properties of wood. This research has established a relationship between certain NDT parameters and the strength characteristics of individual wood members. To date, NDT techniques have shown the most promise for this type of in-place assessment of wood structures. This report assesses the validity of non-destructive testing using the Metriguard Model 239A Stress Wave Timer recently purchased by the School of Forestry. Three pieces of Douglas fir and four pieces of radiata (each 2.0 m x 100 mm x 50 mm) have been used in various experiments to determine the accuracy of the stress wave timer. The modulus of elasticity of the pieces of timber was calculated and the results were compared to a separate 3-point mechanical bending test carried out on the same timber. These results showed that on average the stress wave timer (compared to the mechanical test) over-estimated the modulus of elasticity by 17.5%. This difference is considered to be systematic and therefore the stress wave timer appears to be accurate. Although the stress wave timer accurately indicates the strength properties of wood it remains to be seen if, in its present stage of development, it is of use on a practical basis in the industry