1. 50X Image of southern pine demonstrating differences in earylwood (left side) and latewood (right side) structure Abstract/Background The wood products industry has increased the harvesting plantation grown and faster growing species instead of old-growth trees Plantation grown trees tend to have larger earlywood layers with smaller latewood layers and can display weaker mechanical properties Previous research has shown that the mechanical properties of earlywood and latewood vary greatly In manufacturing models of wood strands, no differences in the intra-ring properties are considered. Mechanical Evaluation Through Modeling the Intra-ring Properties of Wood Strands Daniel Hindman, Ph.D. Jong Nam Lee, Ph.D. Gi Young Jeong, M. S. Wood Engineering Laboratory Department of Wood Science and Forest Products 1650 Ramble Road Objectives Measure the mechanical properties of earlywood and latewood layers of southern pine Develop finite element models to predict the stiffness and stress distribution for three strands with different cutting patterns Use experimental strand testing to verify the finite element models Limitations Strain was measured using crosshead deflection Strands were produced using a flaker at Virginia Tech, rather than commercial strands, for uniformity Methods A MiniMat Strand tester was used for strength and stiffness evaluation in tension and bending Finite element models were created using ANSYS v. 9 Models representing solid elements as well as cellular elements to model the shape of wood tracheids were used Results Some of the finite element models are shown below, demonstrating the bending and tension stress distributions in different colors The use of the cellular finite element model provided very good prediction for all three types of strands in both tension and bending Discussion Significant differences in the stiffness and stress distribution of the strands were noted when the intra-ring properties were considered. Earlywood sections carried higher stresses with some stress concentrations forming at the boundary of earlywood and latewood These results agree with testing of wood samples, where the failures tend to follow the intra-ring joint. Future Work Use the Zeiss microscope coupled with a CCD camera to measure strain by digital image correlation (DIC). Intensive study of intra-ring variation as a function of distance from tree pith to explore juvenile wood and mature wood properties. Model the wood strands using the stochastic spectral finite element method (SSFEM) to account for variability in the intra-ring layers. This work was funded by the USDA NRICGP grant number 2005-35504-16115. Zeiss microscope with Minimat tester MiniMat Strand Tester Implications The study of intra-ring properties can lead to a better understanding of the effects of wood structure on mechanical properties These models could be applied alternative species or transgenic species to model the effect of wood intra-ring characteristics and properties These models could be extended to other biomass fiber sources, including both perennial and annual crops (a) (b) (c) Finite Element Models of Intra-ring Properties, (a) flatsawn strand loaded in tension, (b) quartersawn strand loaded in tension, (c) nonaligned strand loaded in bending