[17], but with a different gripping mechanism. The US Standards
recommend a clamping method with Clevis-type grips and one of
the two grips shall allow for rotation in two perpendicular planes
to avoid the negative effects of possible eccentricity and misalignments
[19]. In this project an alternative system was studied and
adopted after a comprehensive comparison of the two methods.
In the adopted clamping system the two extremes of the specimens
were fixed into the grips of a standard testing machine but
the lower grip allowed for torsional rotation. In this case the
clamps can produce high compressive stresses at the end of the
specimens. For this reason fiber reinforced tabs (dimensions
60 40 2 mm) were applied using epoxy resins after sand blasting
of the extremes. After several tests for comparison it was concluded
that this clamping method was satisfactory and preferable.
Furthermore it gives the possibility to reach the ultimate stress of
the textile reinforcement and explore the third phase of the stress–
strain plot (see Fig. 1) limiting the slipping of the fibers. On the
contrary the US standard foresee a bilinear behavior of the composite
limiting the analysis to the first two phases. An example
of the results obtained using the two methods of clamping is
reported in Fig. 5. The longer extension of the curve obtained with
the present clamping system is evident.