Vibration method for grading of large cross-section coniferous timber species

Abstract

Abstract The non-destructive testing (NDT) of timber using the longitudinal vibration method is based on the natural frequency of wood which is in relation to its quality. In the present paper, the suitability of this tool is investigated and the results of grading 395 pieces are presented. Structural timber of Radiata pine (Pinus radiata D. Don.), Scots pine (Pinus sylvestris L.), and Laricio pine [Pinus nigra ssp. salzmannii (Dunal) Franco] from Spanish sources were investigated. The specimens were tested for bending according to the European standard EN 408 (2003) and the values of strength and stiffness were compared with the results estimated by means of NDT. The vibration equipment applied permits the measurement of the longitudinal natural frequency and mass of the specimen, and then the density and the dynamic modulus of elasticity can be calculated. There is a strong relationship between the static modulus of elasticity obtained from the bending test and the dynamic modulus of elasticity obtained by the NDT technique. There is an acceptable relationship between modulus of rupture and dynamic modulus of elasticity if the visual defects (knot sizes) are taken into account. Acoustic measurements have become widely acceptable, and they have great potential for stress grading of coniferous timber.