The fork device: a test for estimating the memory creep of wood under load during moisture variation

Abstract

When a loaded piece of wood is exposed to variable climatic conditions, the stress state depends on both the stress and moisture content change history due to the memory creep. To explore this complex time-dependent interaction, a new experimental device has been developed. Called the "fork" device, this simple setup allows the evolution of the memory creep of twin wood samples to be determined continuously under different loads. In this work, this device has been used at low temperature (i.e. 30 \(^{\circ }\)C) and with six different humidity cycles to focus on the mechanosorptive part of the memory creep. The test was performed with thin quartersawn and flatsawn samples of beech and oak originally at green state. periods were chosen to obtain a moisture content quickly close to the equilibrium moisture content for each plateau. With negligible moisture gradient, the dynamics of mechanosorption was measured and compared with moisture variations, species and load direction. The results highlight an increase in mechanosorptive strain with cumulative moisture content variations with an asymptotic behavior towards a limit. For oak and beech, a common compliance can be found for each grain direction.