full text is available online.
|Title:||Optical Measurement of Strang Geometry and Orientation and Their Influence on Oriented Strand Composite Formation Quality|
|Committee Chair:||Stephen M. Shaler, Professor of Wood Science and Technology|
|Committee Members:||Douglas Gardner, Professor of Wood Science and Technology ; William Halteman, Professor of Mathematics ; Roberto Lopez-Anido, Professor of Civil Engineering ; Robert Rice, Professor of Wood Science and Technology|
|Subjects:||Composite materials -- Measurement; Engineered wood -- Measurement; Optical measurements; Strength of materials -- Measurement|
|Date of Defense:||2009|
The use of optical methods to quantify formation quality of oriented strand composite mat formation quality was investigated. The main objectives of this research were 1) to develop a methodology based on optical methods for measuring strand geometrical distributions; 2) to determine the influence of changes in strand geometrical distribution (SGD) on the formation quality of the mat and 3) to define a formation quality index based on optically measured parameters. In order to respond to the objectives three experiments were defined. Techniques to acquire images of strand groups with subsequent image processing were developed to measure strand width, length, area and irregularity defined as the fractal dimension by dilation. The technique was used on aspen, red maple and Balsam fir strands produced from logs submitted to -6°C, 21°C and 60°C conditioning temperatures. The species and the conditioning temperature were shown to significantly influence strand geometry. Log conditioning at 60°C resulted in wider strands. Frozen logs rendered more fines and irregular strands. The three species responded differently to the conditioning temperatures. It was found that Balsam fir strands experienced less change in their geometrical distribution than maple and aspen. In a second experiment oriented strand composite mats were formed using aspen, eastern hemlock, yellow birch and commercial strands which exhibited two nominal strand lengths and a variety of width/area characteristics. Measurements of the bulk density and strand orientation of the forming mats were determined through gravimetric measures and developed algorithms of digital images of the top surface. The strand geometrical distribution was found to significantly influence mat bulk density and strand alignment. Smaller and more irregular strands resulted in a poorer alignment and lower bulk density reducing the quality of the meso-structure. The third experiment consisted of standard mechanical tests performed on the panels produced with the formed mats. A significant effect of the mat formation quality on the flexural modulus of elasticity and modulus of rupture was detected. Poor formation quality resulted in reduced properties of the composite. The formulation of a formation quality index was introduced as a result of the studied data. The statistical analysis provides evidence to state that the proposed index describes more accurately (R2=0.82) the variation of the mechanical properties than the linear statistical model (R2=0.60) and compares with previously reported models. The formulation index may be used to evaluate and predict the mechanical properties in the longitudinal direction. The proposed optical methods to evaluate the quality of the OSC mat formation provided reliable and suitable information to define structure/property relationships expressed in terms of a single quality index.
Gaete-Martinez, Victor, University of Maine, FTY2009-004