Modelling Variability in Full-field Displacement Profiles and Poisson Ratio of Wood in Compression Using Stochastic Neural Networks

Vertical and horizontal displacement profiles in compression parallel-to-grain in a 20x20mm area (30 x 21 or 630 points) in the Tangential-Longitudinal (T-L) and Radial Longitudinal (R-L) sections of small wood columns were obtained from digital image correlation applied to simultaneously captured images of the two surfaces. These consisted of 21 displacement realisations of 30 points along the length of the specimen. They revealed considerable local variations. Stochastic neural networks were Successfully developed to simulate trends and noise across and along a specimen in both displacements as well as Poisson ratios in T-L and R-L sections for two selected load levels of 20kN and 40kN. These networks specifically embed noise characteristics extracted from data to generate realistic displacement and Poisson ratio realisations with inherent variability. Models were successfully validated using independent data extracted based on bootstrapping method with high accuracy with R-2 ranging from 0.79 to 0.91. The models were further validated successfully using a second approach involving Confidence Intervals generated from the data extracted from the models. Models and experimental results revealed that for 20kN load, both vertical and horizontal displacements in T-L section were less heterogeneous across the specimen (smaller vertical shearing and horizontal strain, respectively) than those in the R-L section. For the 40kN load, both displacement profiles in the T-L section were less noisy and more compact than those for the 20kN load indicating less heterogeneity due to compaction of structure. In the R-L section, larger vertical shearing and horizontal strains persisted at 40 kN load. Poisson ratio decreased with load and it was nonlinear in both sections but T-L section showed much less noise across the specimen than the R-L section.