Page 65 - Handbook of Properties of Textile and Technical Fibres

46 Handbook of Properties of Textile and Technical Fibres

human hair came the developments to a wider range of applications of other fibers/
filaments. In 1992, Dia-Stron Ltd introduced an automated tensile tester, a cassette-
based system that allowed up to 100 single fibers to be measured in a single automated
sequence. Compared to the traditional manual mounting and testing of each fiber, the
user benefits were clearly identified in terms of productivity and quality of the data.
Focusing on the tensile properties, fiber extension, creep, relaxation, and fatigue
properties can be automatically obtained from a series of fibers. Depending on the
nature of the fiber, testing and mounting protocols are proposed. Most of the fibers
are manually affixed on ferrules or polymeric tabs at the desirable gauge length and
then placed in cassettes of several dozens of fibers. An automatic dimensional analysis
can be carried out through the use of a laser Mitutoyo micrometer or a laser diffraction
instrument described previously and the fibers are then automatically transferred to the
high-resolution tensile tester. Results can be directly analyzed on the Dia-Stron Ltd
application software or easily exported to formatted text files.
TexTechno is a German company that proposes a single fiber tester called
Favimatþ able to automatically determine several fiber properties such as the static
tensile properties, the linear density, and several crimp test methods in a single testing
instrument. All the tests are carried out on the same fiber section and no fiber transfer is
thus required. The effective cross section of the fiber is obtained from the linear density
using vibrational experiments (see Section 2.2.2), and failure stress values can thus be
obtained with a high-resolution force-measuring system. The clamping system allows
testing very short fibers down to a minimum of 3 mm. A feed unit, Robot 2, can be
added to the Favimatþ to automatically transfer fibers from a storage unit with a total
capacity of 500 fibers. A variant of the Robot 2, called Airobot 2, uses a suction device
to pretension and stores the fibers in a further substantial increase in test preparation
efficiencies (Madara et al., 2015).

2.4.1.4 Mechanical localization on single fiber tensile testing

Because of the small diameters of most fibers, the mechanisms of crack propagation in
polymer fibers have been very rarely investigated experimentally (Michielsen, 1992).
Often, postmortem observations by SEM remained the unique tool to infer the fracture
mechanisms. Quite recently, as illustrated in Fig. 2.17, observations of the fracture
mechanisms for PA66 fibers were made using an SEM equipped in-situ with a micro-
tensile machine.
FIB has also been used by Stockdale et al. in 2016 to mill opposing notches on high-
performance fibers to “facilitate direct failure along a longitudinal shear plane, and
expose the internal surface of the fiber.”

2.4.2 Single fiber transverse compression test

One aspect makes synthetic or natural polymer fibers quite remarkable materials. By
inducing a highly oriented structure, a great enhancement of the specific modulus
along the fiber axis can be achieved compared to the nonoriented or bulk material.
Identifying the mechanical responses at the single fiber scale along the fiber axis