Mechanical grading of Guianese structural timber using three non-destructive techniques

Abstract

This study compares three non-destructive, simple and inexpensive methods of grading lumber in structural size. The three methods are: visual grading, measuring the propagation speed of ultrasonic waves (SYLVATEST system) and transverse vibration analysis (CIRAD-Foret BING system). The edged timber (55 x 138 x 3 000 mm³) originates from two Guianese forest species that are the most widely used, locally, for building: Bosralocus/Angelique (Dicorynia guianensis Amsh., 77 lengths tested) and Mandioqueira/Gonfolo (Qualea spp., 86 lengths tested). Based on the visual grading method traditionally used in French Guiana, every quality was represented The reference factors are modulus of elasticity and bending strength obtained by a destructive static four-point bending test for this kind of species.
Comparison of the values and/or grades obtained shows that visual grading is not an effective method, that the ultrasonic technique is a practical field method, and that transverse vibration analysis alone meets all the criteria making it an effective grading method.
It is also noted that the species has an effect on reliable forecasting with regard to non-destructive techniques and that, for structural lengths ,the «gust of wind» (transversal fracture giving rise to a very low resistance to compression failure) is all the more serious a defect in so far as it is not at all easy to detect, be it visually or using the other methods adopted at the present stage of developments.