Evaluation of interlaminar shear moduli of structural wood composites via five-point bending test
Abstract
This study investigated the use of five-point flexure, in combination with simple span quarter-point flexure of the same specimen, to simultaneously determine shear modulus (G) and shear-free Young's modulus (E) of structural wood composites. In addition, interlaminar shear strength was also examined by testing specimens to failure while subjected to five-point loading. Direct solution of E and G based on superposition of shear and bending deflection formulas gave nearly identical results when compared to an iterative solution based on Timoshenko beam theory. The five-point method was evaluated experimentally through testing of two types of oriented strandboard--a 23/32-inch commodity product and a 1-1/8-inch specialty product. Experimental testing indicated that E and G results were not overly sensitive to the broad range of span-to-depth ratios (L/D) evaluated. It is, however, recommended that testing be conducted within an L/D range that results in a minimum of 40 percent of the five-point midspan deflection being attributed to shear. This will ensure that adverse effects due to errors in measurements of depth and span and those associated with determination of E will have a tolerable influence on the outcome of G. Specimen width effects were studied at intervals of 2, 6, and 10 inches; in which increases in width resulted in significant increases in E at the 0.01 probability level. G results between widths, however, were generally not significant at the 0.05 level. Comparing interlaminar G by the five-point method to ASTM D 2718 revealed that five-point results were an average of 50 to 60 percent less than those of D 2718. This disparity highlights the need for shear tests, such as the five-point method, which mimic the performance of materials in their end-use application.
Degree
Ph.D.
Advisors
Hunt, Purdue University.
Subject Area
Wood|Technology|Civil engineering
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