Long Term Performance of Wood Based Panels. Part 1: Non-destructive System for Stress Determination for Creep Loading

Abstract

Six non-destructive test (NDT) techniques were studied for the stress determination for the long-term creep loading of wood based panels, determining the property as a whole (density and modulus of elasticity), across the thickness (maximum density and differential density) and along the transverse or longitudinal direction (flexural dynamic modulus of elasticity and ultrasonic modulus of elasticity) of board. The optimum alternatives to side matching method were derived and assessed by creep demonstration tests on particleboard (PB) and oriented strand board (OSB. The theoretical analysis and test results showed that the capability of new techniques for predicting the modulus of rupture (MOR) varies considerably, depending on the types of the density profile of the materials tested. The best correlation between actual MOR and predicted MOR by NDT techniques was achieved by combining the dynamic modulus of elasticity and density parameters for the materials with a type I density profiles (density gradually changing from the centre to surface layers), with R2 ranging from 0.41 to 0.89. That was achieved by combining the dynamic modulus of elasticity and the modulus of elasticity (MOE) parameters for the materials with a type II (similar density throughout board) and III (irregular density across the thickness of board) density profiles, with R2 ranging from 0.33 to 0.59. The NDT techniques tested were not able to accurately predict the MOR of the materials with type IV density profiles (like type III materials but not dominated by wood). Creep tests for PB and OSB confirmed that the MOR of the materials tested had been predicted more accurately by the NDT techniques selected than by the side matching method.