Civil Engineering Reference
In-Depth Information
4.2.2 De
nitions
A testing protocol should describe the principle adopted in the experiment, how to
prepare and load the sample, and what data to record and how to measure it.
However, it is not granted that the person in charge of the test is deeply involved in
the research
field being and thus able to understand the testing protocol contents.
For this reason it is necessary that the description of the procedure is preceded by
the description of the main technical terms used, such as anisotropy, conditioning,
constant rate of extension, constant rate of stress, elongation, elongation at break,
elongation at maximum force, extension, force at break, load pro
le, maximum
force, force ratio, nominal gauge length, non-linear model, percentage of elonga-
tion, plane stress model, Poisson
s ratio, pre-stress, response surface, tensile stiff-
ness, ultimate tensile strength, weaves of fabric, etc.
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4.2.3 Principle
The testing principle describes the general approach adopted for the investigation of
the material properties. It should specify how the test is executed, how the force is
applied, the data recorded during the test and how they are used in order to
determine the material properties.
Thus, it should be indicated that the protocol is based on the plane biaxial test,
employing a slitted cross-shape specimen pulled in both warp and
fill directions at
the same time according to a stress, strain or displacement mode. Moreover, it
should be described that the applied force and material strain are recorded con-
tinuously during the test, with consequent identi
cation of parameters such as the
maximum force, the elongation at maximum force and, if required, the force at
break and the elongation at break. Finally, if included, the method proposed for the
material properties representation, such as the constants for a plane stress model or
a non-linear model or through a stress-strain response surfaces.
4.2.4 Apparatus Description
The testing rig used plays a fundamental role in the accuracy and reliability of the
results obtained. The testing protocol should describe the features required for a
correct execution of the procedure and the requirements which the apparatus must
satisfy. They generally concern the overall shape of the machine (horizontal or
vertical), the means for reading and recording both forces applied to the sample and
