In-plane mechanical properties of acetylated birch plywood and its response to humidity elevation
Time: Wed 2023-05-24 10.00
Location: M108, Brinellvägen 23, Stockholm
Video link: https://kth-se.zoom.us/j/66672066712
Language: English
Subject area: Civil and Architectural Engineering, Building Materials
Doctoral student: Yue Wang , Byggnadsmaterial
Opponent: Professor Marie Johansson, RISE Research Institutes of Sweden; Linnaeus University
Supervisor: Professor Magnus Wålinder, Byggnadsmaterial; Adjunct professor Roberto Crocetti, Byggnadsmaterial
QC 20230503
Abstract
Due to the recent flourish of modern timber structures, there is an increasing demand for engineered wood products (EWPs). However, outdoor exposure of EWPs often poses a risk of durability-related issues. For load-bearing timber structures, especially those in the outdoor environment, the combination of wood modification by acetylation and concept of EWPs allows manufacturing more durable and stable timber elements. This thesis concerns the angle-dependent in-plane mechanical properties of plywood manufactured from acetylated birch veneers (ABP). Specifically, tensile, compressive, shear and bending tests were conducted at three different load-to-face grain angles, namely from 0° (parallel), 22.5°, to 45°. The test results were compared with ordinary unmodified birch plywood (UBP) concerning stress-strain relationships, failure modes, strength, and elastic properties. Besides, for better understanding the moisture effect on the mechanical properties of both acetylated and unmodified birch plywood, specimens of both type were conditioned in climate chambers under three different environments, with the temperature of 20°C and elevating relative humidity (RH) from 35% to 65% to 95%. In this case, specimens with the load-to-face grain angles of 0°, 45°, and 90° were tested. The influence of both RH and measured moisture contents (MC) on bending strength and stiffness was evaluated. Variations of utilized brittleness terms under different RH conditions and load-face grain angles were also studied. Prediction formulas of mechanical properties with MC were derived by performing linear regressions among test results. The test results reveal that ABP possesses equivalent mechanical properties to UBP specimens. Under relative humidity elevation, acetylated plywood depicts more stable mechanical properties but higher brittleness than untreated specimens.