Civil Engineering Reference
In-Depth Information
system consists of a removable plate which holds the sample in position by pressure
on the fabric previously folded over a cylindrical bar, which prevents any slippage.
The arms are partially divided into 12 strips by slits 16.5 mm wide.
3.4.2.2 Newcastle University
The biaxial testing apparatus developed by Alex Heslop and Newcastle University
is based on the
concept which leads to a considerable optimisation
of the equipment of the testing instrument.
The con
'
fl
'floating frame
'
guration (Fig.
3.13
) is obtained by the combination of two uniaxial
apparatuses on the fundamental assumption that, while the reaction frame in one
direction is
fixed and leans on the ground, the other is mounted on spherical
bearings and free to move in the plane of the fabric (Bridgens and Gosling
2008
).
This approach allows the spontaneous alignment of the actuator with one of the two
weaving directions, which are not necessarily orthogonal due to bow or skew of the
fill yarns. The tensile force is applied by means of two hydraulic actuators, one for
each direction, which stretches one side of both directions of the cruciform sample.
The applied force is measured by means of a 50 kN pancake load cell in each
direction designed for a maximum force equal to 50 kN. The stress on the other
extremity of the sample is obtained by means of the counterbalancing force
developed by each frame. The hydraulic cylinders are connected with an external
hydraulic pump and the maximum force developed is equal to 150 kN. However,
due to the type of materials and protocols tested, the operating range is considerably
lower. The slitted cruciform sample is held by means of a single clamping system
which consists of two grooved steel plates 300 mm wide, one
fixed to the reacting
frame (or the actuator end) and the other removable in order to easily place the
sample through a hem sleeve with a single, rigid steel bar instead of a
fl
flexible keder.
Fig. 3.13 The biaxial
machine available at
Newcastle University (UK).
Image by the Author EMPA
D
ΓΌ
bendorf
