Graduate Thesis Or Dissertation
 

A study of load-induced microdeformations within wood-based structural members using optical scanning techniques

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/p2676z35b

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  • Efficient use of wood in structural applications depends upon the accuracy with which we can predict the mechanical behavior of members under load. Most methods of lumber grading and laminated beam design depend upon statistical and/or empirical techniques in which averaged properties for complete members are derived. A knowledge of stresses and strains that develop locally within members as they are loaded would provide a more complete picture of the interactions that combine to affect the behavior of complete members. Wood's anisotropic, porous, and hygroscopic nature has limited the use of many conventional methods to experimentally obtain this information. This paper describes a technique for studying microdeformations within woodbased specimens under flexural loading in which computerised optical scanning (machine vision) is used. Specially prepared beams containing laminae of varying elastic moduli and defects were loaded nondestructively in thirdpoint flexure while being supported laterally to prevent buckling. Beam width was reduced to 0.25" to avoid significant gradients of strain perpendicular to the measured surface gradients of strain perpendicular to the measured surface. Displacements between horizontally arranged pairs of dots fixed to the beam's vertical surface were measured with a microcomputer-controlled video monitor. Digitized images of the dot positions prior to and after beam deflection were compared, and the distribution horizontal strains across the beam's vertical cross-section were calculated. Strain mappings in the vicinity of knot defects and of laminae of comparatively law elastic modulus were of substantially greater magnitude than predicted by simple elastic beam theory.
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