Evaluation of R-curves and cohesive law in mode I of European beech

• Published in: Theoretical and applied fracture mechanics 2022-04, Vol.118, p.103220, Article 103220
• Main Authors: Gómez-Royuela, J.L., Majano-Majano, A., Lara-Bocanegra, A.J., Xavier, J., de Moura, M.F.S.F.
• Format: Article
• Language: English
• Subjects: Beech; Cantilever beams; Cohesion; Cohesive law; Crack opening displacement; Crack propagation; Crack tips; Design engineering; Digital image correlation; Digital imaging; Double cantilever beam; FEM; Finite element method; Mathematical models; Mode I; Numerical models; Strain energy release rate
• ISSN: 0167-8442; 1872-7638
• DOI: 10.1016/j.tafmec.2021.103220

This work addresses the determination of the cohesive laws in Mode I and tangential–longitudinal (TL) crack propagation system of Fagus Sylvatica L. This species is one of the ever-growing and most widely used hardwood species in Europe for engineered timber products. Double Cantilever Beam (DCB) tests are performed. The strain energy release rate (GI) is derived from the R-curves by applying the Compliance-Based Beam Method (CBBM), which has the advantage of not requiring the measurement of the crack length during propagation, but only the global load–displacement curves. The cohesive law of the material is determined from the relationship between GI, and the crack tip opening displacement (CTOD) monitored for each specimen using Digital Image Correlation (DIC). Numerical finite element models are developed by implementing the average cohesive law through Cohesive Zone Models (CZM). An average GI value of 0.46 kJ/m2 is obtained for this species. The numerical load–displacement curves are consistent with the experimental results, which demonstrates the suitability of the method for the identification of the cohesive laws in beech. The fracture properties obtained are essential in the development of advanced and reliable numerical models in timber engineering design using this species. •Mode I fracture characterization of European beech using the DCB test.•Data reduction scheme based on compliance, beam theory and equivalent crack model.•3D DIC measurements for evaluating crack tip opening displacement.•Numerical models were implemented using a three linear cohesive law.•Numerical load–displacement and R-curves are representative of experimental results.