Home About Browse Search
Svenska


Crack formation, strain distribution and fracture surfaces around knots in thermally modified timber loaded in static bending

van Blokland, Joran and Olsson, Anders and Oscarsson, Jan and Daniel, Geoffrey and Adamopoulos, Stergios (2020). Crack formation, strain distribution and fracture surfaces around knots in thermally modified timber loaded in static bending. Wood Science and Technology. 54 , 1001-1028
[Journal article]

[img] PDF
4MB

Abstract

The effect of thermal modification (TM) on the chemistry, anatomy and mechanical properties of wood is often investigated using small clear samples. Little is known on the effect of growth-related and processing defects, such as knots and checks, on the bending strength and stiffness of thermally modified timber (TMT). Nine boards of Norway spruce with different combinations of knot types were used to study the combined effects of checks and knots on the bending behaviour of TMT. Digital image correlation (DIC) measurements on board surfaces at sites of knots subjected to bending allowed to study strain distribution and localise cracks prior to and after TM, and to monitor development of fracture (around knots) in TMT to failure. DIC confirmed that checking in knots was increased after TM compared to kiln-dried timber, specifically for intergrown knots and intergrown parts of encased knots. Effects appear local and do not affect board bending stiffness at these sites. Bending failure in TMT initiated mainly at knot interfaces or besides knots and fractures often propagated from checks. Scanning electron microscopy analyses of fracture surfaces confirmed this, and fractures were typically initiated around knots and at knot interfaces due to crack propagation along the grain in the longitudinal-radial plane (TL fracture) under mixed mode I and II loading, such that boards failed in simple tension like unmodified timber. Images of fracture surfaces at the ultrastructural level revealed details of the brittle behaviour of TM wood. This was especially apparent from the smooth appearance of transwall failure under mode I loading across the grain.

Authors/Creators:van Blokland, Joran and Olsson, Anders and Oscarsson, Jan and Daniel, Geoffrey and Adamopoulos, Stergios
Title:Crack formation, strain distribution and fracture surfaces around knots in thermally modified timber loaded in static bending
Year of publishing :2020
Volume:54
Page range:1001-1028
Number of Pages:28
Publisher:Springer
ISSN:0043-7719
Language:English
Publication Type:Journal article
Article category:Scientific peer reviewed
Version:Published version
Copyright:Creative Commons: Attribution 4.0
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Wood Science
URN:NBN:urn:nbn:se:slu:epsilon-p-105915
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-105915
Additional ID:
Type of IDID
DOI10.1007/s00226-020-01190-5
Web of Science (WoS)000537418400001
ID Code:17402
Faculty:S - Faculty of Forest Sciences
Department:(S) > Department of Forest Biomaterials and Technology
Deposited By: SLUpub Connector
Deposited On:04 Sep 2020 07:11
Metadata Last Modified:04 Sep 2020 07:11

Repository Staff Only: item control page

Downloads

Downloads per year (since September 2012)

View more statistics

Downloads
Hits