Date of Award

5-2005

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Stephen M. Shaler

Second Committee Member

Lech Muszynski

Third Committee Member

Roberto Lopez-Anido

Additional Committee Members

William G. Davids

Robert W. Rice

Douglas J. Gardner

Abstract

The reliability of wood structures is strongly affected by duration of loading and environmental conditions. The goal of this study was to develop a simple method for measuring the mechano-sorptive character of the hygro-mechanical behavior of wood and to develop a model capable of predicting long term beam behavior under changing climates. The model predictions were compared with experimental results. Red spruce was the species selected for investigation. The mechano-sorptive properties were measured in tension and compression on thin specimens where moisture content variation within the material was minimal when exposed to a varying environment. The measured mechano-sorptive deformation in compression was significantly greater than that measured in tension (4 times higher at cumulative MC 60% than in tension). However, the developed compression protocol was less accurate, with a tendency to overestimate the magnitude of subsequent experimental creep behavior.

A multi-physics model of hygro-mechanical uniaxial beam behavior was developed that rigorously couples spatially varying time-dependent moisture content with the uniaxial stress-strain relations. To verify the model and accuracy of the measured uniaxial mechano-sorptive characteristic of red spruce, the behavior of beams loaded by four point bending was measured in cyclically varying climate over 2.5 months. Although the model did not properly account for the immediate effect of moisture content change on mid-span deflection, as was observed in real beams, the overall trend of the predicted deflection was in good agreement with experimental results.

An additional part of the thesis dealt with development of an analytical model to predict the hygro-mechanical behavior of multi-directional polymer matrix composite laminates which incorporate the mechano-sorptive effects of a phenol resorcinol formaldehyde resin. E-glass / phenol resorcinol formaldehyde resin composite material parameters were used in the model. Simulation of wetting showed that the contribution of resin compliance change due to moisture content change is approximately half of initial resin compliance which decreases the stiffness of multi-directional laminates accordingly, based on lay-up sequence.

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