A Method to Control the Instabilities of the Mixed-Mode Bending Test of Wood

Abstract The present study focuses on the characterization of the quasi-brittle fracture properties of wood under mixed mode I+II. Mixed-Mode Bending(MMB) tests are carried out on Maritime pine for three mixed mode ratios and completed by pure Mode I and pure Mode II fracture tests. An External Displacement Control Technique (EDCT) is set up to obtain load-displacement curves without instabilities. The control of instabilities is essential to ensure a quasi-static failure leading to the proper development of the Fracture Process Zone (FPZ) and the self-similar propagation of the main crack with its FPZ. Three criteria are used to test the reliability of the EDCT and its capacity to increase the yield of valid tests. Loading -displacement responses are analysed within the framework of the equivalent Linear Elastic Fracture Mechanics (eq LEFM). The resistance curves (R-curves) are calculated and the fracture behaviour of wood is discussed according to the specimen geometries, the wood nature and the fracture modes.