Experimental results of fracture energy and fracture toughness of Radiata Pine laminated veneer lumber (LVL) in mode I (opening)

Abstract

The load-carrying capacity of notched timber beams can be predicted using linear elastic fracture mechanics (LEFM). Material properties such as fracture toughness and energy are needed for the analysis. The micro and macroscopic complexity of wood and its anisotropic nature give different fracture properties in the longitudinal, radial and tangential grain directions. This complexity and the infrequent use of LEFM mean there is little data available. While wood is highly anisotropic, fracture analysis can use a subset of the possible material properties because wood normally cracks parallel to its grain due to its low tensile strength perpendicular to grain. This allows a significant reduction in the number of tests required to measure fracture properties, with considerable saving of resources. This paper presents the results of an experimental study investigating the fracture energy and fracture toughness of Radiata Pine laminated veneer lumber in mode I (opening). A more efficient test apparatus is proposed and shown to produce identical results to the test apparatus used by others. Results are presented for the fracture toughness properties in the grain direction, and include fifth percentiles and coefficients of variation. The influence that the specimen size has on the fracture toughness is also presented. Numerical analyses using the ABAQUS software package show good agreement with the experimental test results. The experimental results are within the range of experimental values reported in the literature for solid wood.