PREDICTION OF MECHANICAL PROPERTIES - MODULUS OF RUPTURE AND MODULUS OF ELASTICITY - OF FIVE TROPICAL SPECIES BY NONDESTRUCTIVE METHODS

This paper analyzes the usability of different dynamic moduli of elasticity and wood density for the prediction of mechanical properties - static modulus of elasticity and modulus of rupture - in samples with grain deflection from the longitudinal direction. Five tropical hardwoods (Afzelia bipindensis, Intsia bijuga, Millettia laurentii, Astronium graveolens and Microberlinia brazzavillensis) with different grain characteristics were used for this purpose. The fiber deflection was caused by the presence of interlocked grain or the working process. The three nondestructive techniques used in this study - longitudinal and flexural resonance method and ultrasound method - provided higher values of modulus of elasticity than the static bending test, but close correlation was observed between these variables. The weakest correlation was found for the ultrasound method which is probably caused by its measuring mechanism. The prediction of the modulus of rupture is less accurate when the dynamic modulus of elasticity is compared with the static modulus of elasticity; on the other hand, it was still good in comparison with the density model, which is inapplicable when grain deflection occurs in wood. In the wood of Zebrano where the interlocked grain was strongly developed, almost all of the correlation coefficients showed the lowest values and the prediction of modulus of rupture by nondestructive techniques was unsatisfactory.