Wood: a quasibrittle material R-curve behavior and peak load evaluation

From load-unloading cycles applied on wood notched specimens subjected to three-point bending, we show that the concept of ‘equivalent LEFM’, usually used for the quasibrittle materials, can be successfully applied to the fracture behavior of wood in mode I. Within this equivalent linear elastic framework, the quasibrittle fracture behavior of wood leads to an R-curve which is evaluated and discussed. On the other hand, the estimate of the peak load (or maximum load) of a structure as a function of the corresponding R-curve is an important problem for a building material such as wood. After a review of some general results about the connection between the R-curve and the shape of the load-deflection curve, we propose a single equation, i.e., valid for a fracture test under load-control or displacement-control, allowing to estimate the crack length corresponding to every extremum of a load-deflection curve.