Modeling Differently Oriented Loblolly Pine Strands Incorporating Variation of Intraring Properties Using a Stochastic Finite Element Method
Keywords:Stochastic finite element method (SFEM), Strands, modulus of elasticity (MOE), earlywood, latewood
AbstractWood strands are a biological material with variations in material properties because of the presence of earlywood and latewood, juvenile wood and mature wood as well as the sectional cut used to generate strands. This variation should be accounted for to produce reliable modeling results. This study used both a deterministic finite element method (FEM) and a stochastic finite element method (SFEM) to model the stiffness of wood strands from three different orientations (radial, tangential, and angled) incorporating intraring property variation from two growth ring positions. In addition, a homogeneous model was used as a control to compare the results from both deterministic FEM and SFEM. The homogeneous model predicted the stiffness well for radial and tangential orientation strands but provided unrealistic physical strain distributions. Assumptions of strand homogeneity oversimplified the strain distribution present in the strand, eliminating local maximum and minimum values. Cumulative probability curves comparing previous experimental results and SFEM results showed general agreement. Average differences in the effective tensile modulus of elasticity ranged 0.96-22.31%. Based on the modeling results, the earlywood tensile modulus of elasticity was the input parameter that had the greatest influence on the strand stiffness. The order of correlation of the earlywood and latewood Poisson ratios changed based on strand orientation. SFEM techniques provided accurate results and material property distributions as compared with the experimental results.
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