D-BAUG - Departement Bau, Umwelt und Geomatik - ETH Zürich

Highlights ▪ Structures
Air-Coupled Ultrasound Inspection of
Glued Timber Components
Non destructive bonding quality assessment
of glued timber products is necessary in order
to prevent security hazards.
by S. J. Sanabria, J. Neuenschwander, U. Sennhauser /
EMPA Dübendorf; P. Niemz / IfB
Air coupled ultrasound investigations allowed successful imaging
of glued and non-glued regions with high reproducibility
and spatial accuracy. Glued laminated timber, solid wood panels
and prefabricated wood components currently experience
a strong increase of use in timber constructions; bonding quality
assessment is necessary in order to prevent security hazards.
Air-coupled ultrasound (ACU) is a novel non-destructive
method with important improvements in reproducibility and
fine scanning capability with respect to other traditional ultrasonic
technologies used for wood.
As part of an ongoing PhD project,ACU measurements in normal
transmission mode with 120 kHz transducers were performed
on samples consisting of two 5 mm Norway spruce
solid wood lamellas glued together with a polyurethane adhesive,
with artificially introduced delaminated areas. Ultrasonic
scanning with high resolution was performed to image
the presence or absence of glue.The samples were broken up
after measurement and the glued and non-glued regions were
photographed and compared with the ultrasonic amplitude
images.
(Fig. 1) demonstrates successful ACU imaging of glued and
non-glued timber down to a spatial resolution of 20 mm. Ultrasound
amplitude variations up to 55 dB are observed between
glued and non-glued material,which ensures a reliable
glue line assessment,despite amplitude variations below 8 dB
in bonded regions due to the heterogeneity of wood structure.
The reproducibility of the measurement is below 1.5% after one
year. Future research work is planned to inspect thicker multiple
laminated glued timber structures.The main challenge is
to resolve ultrasonic signal changes between bonded and disbonded
areas from those introduced by wood heterogeneity.
50 ▪ D-BAUG Annual Report 2009
Modeling the Growth and Impact of
Wood Decay Fungi
The wood decay fungus P. Vitreus increa-
ses the permeability of wood and thereby
the uptake of wood preservatives.
by M. Fuhr, H.J. Herrmann / IfB
The selective degradation of pit membranes in refractory
wood species e.g. Norway spruce (Picea abies [L.] Kast.) by
the basidiomycete Physisporinus vitreus increases the
permeability of the wood. This process which has been
termed bioincising can be used to improve the uptake of
wood preservatives and environmentally-benign wood
modification substances.The bioincised wood can be used
for a range different industrial purposes.
The objective of this project is to develop a mathematical
model of hyphal growth and expansion of P. vitreus by
means of stochastic processes both in space and time
(Fig. 2). Irreversible growth has been investigated for a long
time in the context of cancer growth, dendritic growth
and gelation and penetration in porous media. In addition,
the project allows to examine degradation patterns of
the fungus and its enzyme activity. By focusing on these
fundamental processes, we hope to improve our knowledge
on how the complex system (fungus - wood) interacts
under defined conditions.This information is crucial for the
scaling up of the bioincising process. This work is a joint
project of the two research groups Wood Protection and
Biotechnology, EMPA St. Gallen (Prof. Dr. F.W.M.R. Schwarze)
and Computational Physics for Engineering Materials (Prof.
Dr. H.J. Herrmann).