Influence of hygrothermal effects in the fracture process in wood under creep loading

The knowledge of crack driving forces such as energy release rate is very important in the assessment of the reliability of timber structures. This work deals with both static and creep fracture tests in opening mode crack growth under hygro-thermal and mechanical loadings. The experimental tests combining creep and hygro-thermal loadings are performed in a climatic chamber. The Double Cantilever Beam specimen with variable inertia machined in Douglas Fir and White Fir species is used to investigate the effects of these loadings on fracture processes. Two experimental protocols are presented. First, instantaneous tests are carried out in order to identify the moisture content effects on fracture properties. R-curves are studied using a finite element approach. Secondly, creep tests are performed by imposing high speed humidity variations in a climatic chamber. During these tests, the evolutions of the crack length are recorded.