Civil Engineering Reference
In-Depth Information
Chapter 5
Recent Applications and Potentialities
Abstract This chapter presents two recent examples of biaxial tests for advanced
applications such as strain controlled tests and
flexible solar cells. The example of a
strain-controlled biaxial test aims to investigate the potential offered by new testing
equipment and the controlling software in order to reproduce strain histories
assigned to the central zone of the cruciform specimen. The example of a biaxial
procedure applied to laminated lightweight, thin-
fl
lm, organic solar cells and ETFE
foils offers a groundbreaking example of the future applications for biaxial tests due
to the increase of lightweight and
fl
flexible building products.
Keywords Strain-controlled
Compensation factor
Coated fabric
Biaxial
Konarka power plastic
Flexible
Organic
Thin
lm
PV-cells
5.1 Strain Controlled Biaxial Tests
The last decade has been characterised by a remarkable improvement in biaxial
testing equipment and procedures for architectural coated fabrics and foils. In
addition, the developments in computational mechanics offer a wide range of
approaches for the adequate structural modelling of tensioned membrane structures,
from the well-known plane stress theory (Gosling and Bridgens
2008
) to the recent
investigation on the neural networks (Bartle et al.
2013
).
The load is generally applied according to a predetermined stress rate and the
elongation of the material is constantly measured, recorded and combined with the
corresponding imposed stress histories in order to obtain the response curves in
warp and
fill direction. In some cases the procedure prescribes a predetermined
displacement rate in correspondence of the clamping system. This control is
commonly required by uniaxial procedures but it loses its meaning in the presence
of a cruciform sample where the displacements at the clamps are mainly absorbed
by the arms of the sample. The result is that the speed of the actuators is not directly
related to the strain rate at the centre of the sample which is visible in the discordant
strain between the centre and the arms shown in Fig.
4.8
.
