Digitized by Kansas Correctional Industries

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Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 291-304).

The torsion test was evaluated as a method for determining the shear strength of full-size structural lumber. The evaluation involved an experimental length study, an experimental depth study, and a finite element study. The length study consisted of fifty nominal 2x4 specimens, ten specimens for each length, and ten American Society for Testing and Materials (ASTM) shear blocks. One 14 foot long board yielded one specimen for each length: (a) 21.0", (b) 28.5", (c) 32.0", (d) 35.5", (e) 39.0", and (f) an ASTM D143-94 shear block. The statistical analysis revealed no evidence that the length affected the shear strength. The depth study consisted of fifty specimens, ten specimens for each depth: (a) 2x4, (b) 2x6, (c) 2x8, (d) 2x10, and (e) 2x12. In addition, fifty ASTM shear blocks, one block for each specimen, were tested. The statistical study did not reveal convincing evidence of a depth effect on shear strength, even after accounting for specific gravity and shear span as covariates. Failure modes for the torsion samples involved a longitudinal shear crack at the mid-point of the longest side, which propagated toward the ends of the specimen and through the cross section perpendicular to the growth rings. The finite element model revealed that uniform shear stress occurs within the shear span, which begins and ends a distance of approximately two times the depth plus the grip distance away from each end of the member. In addition, torsion theory verified that the experimental shear failure plane that occurs within the shear span is parallel to the grain and the shear slippage is also parallel to the grain, similar to the known shear failure in specimens subjected to bending loads. Based on the results of this study, the torsion test is the best practical method to determine the pure shear strength of full-size structural lumber, because the test yields 100% shear failures and the specimen is in a state of pure shear stress. / Graduation date: 1998

Aluminum single crystals were cyclically deformed in single-slip at small strain amplitudes at 77 K to presaturation. The observed mechanical behavior is consistent with other recent work. The dislocation substructure was analyzed in detail. The structure can be described as consisting of dense bundles or veins of dislocation dipoles, separated by lower dislocation density regions where debris is evident. This debris was determined to be principally relatively short dipole segments. Screw dislocations with the same Burgers vector span the channels. Dislocations were essentially all of the same Burgers vector. In-situ cyclic deformation experiments were successfully performed by the X-Y technique where thin foils are stressed in alternating perpendicular directions. Screw dislocations span the channel and easily move and reverse direction with shear reversal. Our experiments indicate that loops frequently expand from the dipole bundles into the channels and the edge component is absorbed by nearby bundles leaving screw segments behind. Dipole "flipping" was not observed and these edges are relatively difficult to mobilize. There is no obvious evidence for internal backstresses that assist plastic deformation on reversal of the applied shear. / Graduation date: 1996

Graduation date: 1994

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: John E . Novotny, Dept. of Mechanical Engineering. Includes bibliographical references.

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