Mode II Fracture Behavior of Bonded Viscoelastic Thermal Compressed Wood
Keywords:Densification, VTC, bond line, mode-II fracture toughness, over-notched flexure, end-notched flexure
AbstractThe influence of viscoelastic thermal compression (VTC) of wood on bonding performance was studied. Mode-II (shear mode) fracture of the bonded interphase was performed using the over-notched and end-notched flexure methods. The study examined four groups of specimens; a control and VTC specimens with three different degrees of densification (63, 98, and 132%). The specimens were bonded with phenol-formaldehyde (PF) adhesive. Prior to fracture testing, the bonded interphase was examined and the effective penetration (EP) of PF into the capillary structure of wood was measured. The results showed that EP was greatest in the control wood specimens, but in the case of the VTC specimens decreased with increasing degree of densification. The mode-II fracture performance of the VTC wood specimens with PF differed from the control wood specimens. In the control specimens, the mode-II crack propagation occurred in the interphase, while in the VTC specimens the crack diverted away from the interphase into the VTC wood. A hypothesis of relative shear resistance was used to explain the bonding performance of the control and VTC specimens.
Cantwell WJ (1997) The influence of loading rate on the mode II interlaminar fracture toughness of composite materials. J Compos Mater 31(14):1364-1380.nDavies P, Blackman BRK, Brunner AJ (1998) Standard test methods for delamination resistance of composite materials: Current status. Adv Compos Mater 5:345-364.nEbewele R, River B, Koutsky J (1979) Tapered double cantilever beam fracture tests of phenolic-wood adhesive joints, Part 1. Development of specimen geometry; effects of bondline thickness, wood anisotropy and cure time on fracture energy. Wood Fiber Sci 11(3):197-213.nFollrich J, Müller UM, Gindl W (2006) Effects of thermal modification on the adhesion between spruce wood (Picea abies Karst.) and a thermoplastic polymer. Holz Roh Werkst 64:373-376.nGagliano JM, Frazier CE (2001) Improvements in the fracture cleavage testing of adhesively-bonded wood. Wood Fiber Sci 33(3):377-385.nGérardin P, Petric M, Petrissans M, Lambert J, Ehrhrardt JJ (2007) Evolution of wood surface free energy after heat treatment. Polym Degrad Stabil 92:653-657.nHung PC, Voloshin AS (2003) In-plane strain measurement by digital image correlation. J Braz Soc Mech Sci Eng 15(3):215-221.nImage J (2007) Research Services Branch, National Institute of Mental Health, Bethesda, MD. Available on: http://rsb.info.nih.gov/ij/'>http://rsb.info.nih.gov/ij/nJennings JD, Zink-Sharp A, Kamke FA, Frazier CE (2005) Properties of compression densified wood. Part I. bond performance. J Adhes Sci Technol 19(13-14):1249-1261.nJennings JD, Zink-Sharp A, Frazier CE, Kamke FA (2006) Properties of compression densified wood. Part II. surface Energy. J Adhes Sci Technol 20(4):335-344.nKamke FA (2004) A novel structural composite from low density wood. Proc. 7th Pacific Rim Bio-Based Composites Symposium, Nanjing, China, Oct. 31-Nov. 2. Pp 176-185.nKutnar A, Kamke FA, Sernek M (2008) Density profile and morphology of viscoelastic thermal compressed (VTC). Wood Sci Technol (accepted May 2008).nNairn JA (2006) On the calculation of energy release rates for cracked laminates with residual stresses. Int J Fracture 139:267-293.nPetrissans M, Gerardin P, Elbakali I, Serraj M (2003) Wettability of heat-treated wood. Holzforschung 57:301-307.nSchmidt RG (1998) Aspects of wood adhesion: applications of wood C CP/MAS NMR and fracture testing. PhD dissertation, Virginia Tech, Blacksburg, VA.nSernek M, Kamke FA, Glasser WG (2004) Comparative analysis of inactivated wood surfaces. Holzforschung 58:22-31.nSernek M, Resnik J, Kamke FA (1999) Penetration of liquid urea-formaldehyde adhesive into beech wood. Wood Fiber Sci 31(1):41-48.nSzekrenyes A (2005) Delamination of composite specimens. PhD Dissertation. Department of Applied Mechanics, Budapest University of Technology and EconomicsnSzekrenyes A, Uj J (2005) Mode-II Fracture in E-glass-polyester composite. J. Compos Mater. 39(19):1747-1768.nWang J, Qiao P (2003) Fracture toughness of wood-wood and wood-FRP bonded interfaces under mode-II loading. J Compos Mater 37(10):875-897.nYang Z, Sun CT (2000) Interlaminar fracture toughness of a graphite/epoxy multidirectional composite. J Eng Mater-T ASME 122:428-433.nYoshihara H, Ohta M (2000) Measurement of mode II fracture toughness of wood by the end-notched flexure test. J Wood Sci 46:273-278.nYoshihara H, Ohta M (2003) Resistance curve for the mode II fracture toughness of wood obtained by the end-notched flexure test under the constant loading point displacement condition. J Wood Sci 49:210-215.nYoshihara H, Ohta M, Furushima T (2003) Shear strengths of wood measured by various short beam shear test methods. Wood Sci Technol 37:189-197.nKamke FA, Sizemore H (2005) Viscoelastic thermal compression of wood. U.S. Patent Application No. US2005/006004AI, Jan. 13, 2005nKusaka T, Hojo M, Fukuoka T, Ishibashi M (2006) Effect of strain rate on the interlaminar fracture toughness of Zanchor reinforced composites. J Phys IV France 134: 1105-1111.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.