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

Highlights ▪ Structures
Properties of microfibre
reinforced cement
Uniaxial tensile tests on microfibre rein-
forced cement with aligned fibres were
performed.
At the Institute for Building Materials steel microfibers
were produced by cutting a stainless steel fine wire
(d=50µm) in 3mm fibres. These fibres were embedded in
cement paste. The micro fibres were mixed with cement
pastes with different water/cement ratios.With these mixtures
dog bone shaped samples were produced for uniaxial
tensile tests. With a special filling method the fibres
were aligned in the loading direction in order to enhance
the performance of the material. Uniaxial tensile tests
were performed with freely rotating supports in closedloop
displacement control. During testing the surface of
the specimen was scanned with two high resolution cameras.
With digital image correlation displacements and
strains can be calculated and with this strain concentrations
and cracks can be identified (Fig. 1).
After testing the specimens were cut close to the crack.The
cross section can be used to verify the fibre alignment. It
could be shown that the filling method worked well for fibre
alignment. As a consequence of the fibre alignment
the results of the direct tensile tests showed a low scatter
in the results.
References:
Proceedings „Advances in cement-based materials“, van
Zijl & Boshoff eds. CRC press p. 67–73. Scaling of Fracture
Properties of Fibre Reinforced Cement in FraMCoS-7, in
press.
Annual Report D-BAUG, 2008, p. 42.
52 ▪ D-BAUG Annual Report 2009
The impact fragmentation of plastic mate-
rials of high industrial relevance is investi-
gated.
New universality class of
fragmentation phenomena
by C. Rieger, J. G.M. van Mier / IfB by G. Timar, F. Kun, H.J. Herrmann / IfB
Fragmentation phenomena are ubiquitous in nature and
play a crucial role in a wide variety of industrial processes
related to mining and ore processing. Experiments have revealed
a striking universality of fragmentation phenomena,
i.e. the mass distribution of pieces of heterogeneous brittle
materials has a power law form with an exponent depending
solely on the dimensionality of the system. It is an
important question of high industrial relevance whether
such universality prevails for polymeric materials which exhibit
ductile breaking.
In cooperation with the Frauenhofer Institute and Thyssen,
we carried out an experimental and theoretical study of
the fragmentation of polymeric materials by impacting
polyoxymethylen particles of spherical shape against a
hard wall. Experiments revealed a power law mass distribution
of fragments with an exponent of approx. 1.25,
which is significantly different from the known exponents
of three-dimensional bulk materials. Based on computer
simulations of a three-dimensional discrete element
model, we show that the dominance of shear in the crack
formation and the healing of compressed crack surfaces
are the key features which give rise to the emergence of
the novel universality class of fragmentation phenomena
(Fig. 2, 3).