MARC 主機 00000nam  2200313   4500 
001    AAINR26820 
005    20121102113759.5 
008    121102s2007    ||||||||||||||||| ||eng d 
020    9780494268209 
035    (UMI)AAINR26820 
040    UMI|cUMI 
100 1  Wang, Brad Jianhe 
245 10 Experimentation and modeling of hot pressing behaviour of 
       veneer-based composites 
300    230 p 
500    Source: Dissertation Abstracts International, Volume: 68-
       04, Section: B, page: 2007 
502    Thesis (Ph.D.)--The University of British Columbia 
       (Canada), 2007 
520    To understand the unique hot pressing behaviour of veneer-
       based composites, the key objectives of this research were
       to: (1) characterize air permeabilities of veneers and 
       gluelines; (2) examine fundamentals of veneer contacts for
       bonding; (3) explore mechanics of veneer compression; and 
       (4) develop the first hot pressing simulation model to 
       predict heat and mass transfer and panel densification in 
       veneer-based composites 
520    To determine the mechanism of heat transfer, transverse 
       air permeabilities of aspen (Populus tremuloides) veneers,
       phenol formaldehyde (PF) gluelines and aspen plywood/
       strandboard were first investigated. The laminate 
       permeability theory was adopted to determine the relative 
       contribution of the veneers and gluelines to panel 
       permeability. A concept of effective porosity was also 
       proposed based on the classic Carman-Kozeny theory to 
       explain the difference in panel permeability and resulting
       hot pressing behaviour. It was concluded that veneer 
       compression rather than glueline curing serves as the main
       barrier to gas and moisture movement, resulting in a 
       negligible rate of transverse heat convection during hot 
       pressing 
520    By examining veneer compression behaviour under various 
       temperature and moisture content (MC) conditions, a 
       revised wood transverse compression theory was proposed to
       include the first stage of "progressive contact" and 
       define true yield displacement, and a novel method was 
       developed for assessing veneer surface roughness/quality 
       on an area basis. Through analyses of veneer contact area 
       (glue coverage) under changing loads, the minimum 
       compression required for achieving adequate veneer-to-
       veneer contacts was determined. Furthermore, the Greenwood
       and Tripp's contact theory was modified to explain how 
       veneer surface roughness and compression affect panel 
       bonding contacts. This led to the establishment of an 
       optimum panel densification target for performance plywood
       /LVL products and shed a light on how to help prevent 
       panel delamination 
520    Finally, the revised compression theory was applied to 
       characterize veneer compressive stress-strain relationship,
       creep and springback behaviour during hot pressing. By 
       introducing a concept of wood-glue mix layers and applying
       theories of heat and mass transfer and solid mechanics, a 
       one-dimensional hot pressing model was successfully 
       developed and validated. The model can predict the changes
       of temperature, MC, gas pressure and vertical density 
       profile during hot pressing. The outcome of this research 
       provides insight into the plywood/LVL hot pressing 
       processes 
590    School code: 2500 
650  4 Agriculture, Wood Technology 
690    0746 
710 2  The University of British Columbia (Canada) 
773 0  |tDissertation Abstracts International|g68-04B 
856 40 |uhttp://pqdd.sinica.edu.tw/twdaoapp/servlet/
       advanced?query=NR26820