Identification and Development of Test Methods for More Accurately Evaluating the Bond Strength of Adhesively Laminated Wood Products

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Date

2021-09

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University of New Brunswick

Abstract

Adhesively laminated wood products (ALWPs), such as glue laminated timber and cross laminated timber, are increasingly used in construction due to the global forest resource shortage. Therefore, to accurately evaluate their bond quality is crucial. However, the commonly used existing methods have some shortcomings of producing accurate results. The overall objective of this thesis project was to understand, analyze and improve the block shear testing methods for measuring the shear strength of a bondline of ALWP. The wood and adhesive used for making specimens were sugar maple (Acer saccharum) and PVAc, respectively. Based on the configurations and deficiencies in the standard block shear test methods adopted in various countries and regions, two jigs modified with a Teflon® plate and a roller plate were designed, fabricated and used in this study. In addition, two non-standard testing methods (namely, double block shear test and Arcan test) were employed and explored as well. All the test results from modified standard and non-standard methods were analyzed and compared with the standard block shear test results. The digital image correlation (DIC) system was used to investigate the strain distribution on a specimen surface. It was found that (1) The bondline shear strength results tested via the modified jigs were more consistent than those via the standard test jig; (2) The DIC analysis showed that the modified jig with a roller plate was least affected by friction and stress concentration, producing an average shear strength of 17.40 MPa, the closest to the value provided by the adhesive manufacturer; (3) The double block shear test and Arcan test results had greater data variability, which were not recommended for testing shear strength in industry for the quality control purpose; (4) When conducting double block shear test, it required the wood had a relatively high perpendicular to grain tensile strength to avoid failure appearing in wood of the middle section; and (5) It was recommended to use a jig modified by a roller plate for testing the bond strength, in particular for quality control in industry.

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