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Tensile Testing of Fibers using Keysight T150 UTM
Quasi-static Tensile Test
Application Note
Introduction the electrospinning setup to collect
aligned nano/micro-ibers those can be
Fibers for advanced applications, such easily transferred to templates for tensile
as bulletproof vests, biomedical scaf- testing using the Keysight Technologies,
folds, microelectronics, etc. require a Inc. T150 UTM.
good combination of strength, stiffness
and toughness. However, characterizing Tensile Test of Thin
these properties for micro/nano-ibers is
challenging because of their low stiff- Fibers: Challenges and
ness. Moreover, because of the iber The T150 Advantage
drawing process, most of the chemical
bonds in a iber are oriented along the The most effective method for mechani-
iber axis. This gives rise to a big differ- cal characterization of ibers is uniaxial
ence in mechanical properties along the tensile test. During a tensile test, a iber
iber axis compared to the perpendicular specimen is pulled at a speciied rate and
direction and, hence, it is not reasonable the resulting reaction force is measured.
to interpret iber properties from their As we know the initial sample dimensions
bulk counterparts. Such differences are (iber length and iber diameter), sev-
especially evident in ibers with smaller eral key engineering parameters can be
diameters (few hundred nanometers to a calculated using the measured force and
few 10's of microns). displacement. Some of these parameters
are: ultimate tensile strength, Young's
For example, one of the popular methods modulus, yield stress, yield strain and
to fabricate ultra-thin failure strain. As more and more ibers,
nano/micro-ibers is electrospinning. De- especially micro and nano-ibers are be-
spite the importance, most of the studies ing proposed for structural applications,
on mechanical properties have been the tensile parameters are important for
limited to characterizing the ibermats better simulation and design of struc-
instead of individual ibers. However, in tures using these ibers.
a recent study, Chen et al. clearly shows
that the mechanical behavior of colla- As the iber diameter decreases, the
gen-chitosan ibermats is signiicantly absolute stiffness of a iber drops sig-
different from that of the correspond- niicantly, and it becomes challenging
ing individual ibers 1. In recent years, to measure the tensile parameters using
multiple studies, including the above conventional test equipment. The mass
reference, have shown ways to design and inertia of the grips and the driveshaft
02 | Keysight | Tensile Testing of Fibers using Keysight T150 UTM, Quasi-static Tensile Test - Application Note
for a conventional tensile test system are for thin polymeric ibers, which requires
P
much greater than the small-diameter small forces for deformation but can ex-
Grip
iber samples. Hence, although one may Spring tend to large strains. A stress-strain curve
accommodate a iber sample in a conven- Capacitive for a polymer iber, such as PET (Figure 2),
tional tensile testing system, the accu- Sensor is extremely important for understanding
racy of the results is doubtful. One way its mechanical deformation 2-4. A polymer
researchers try to avoid the challenges is iber consists of many polymer chains,
by interpreting the properties of thin ibers and their physical properties govern the
from a larger sample of same material, or properties of the iber. During a tensile
a yarn (bundle of multiple ibers) or woven/ test, extension in a polymer iber is a result
nonwoven ibermat. However, this is not of elastic extension of the polymer chains,
a convincing characterization method and elastic and non-elastic rotation of the
because of the differences in molecular chain axis towards the iber axis. Hence,
alignment, and various elastic and non- a polymer iber with small orientation
elastic interactions between ibers. The Coil (Magnet) distribution of the polymer chains exhibits
force range and the gripping arrangement high modulus. However, the strength of a
of the Keysight T150 UTM are more suit- Figure 1. Schematic of nanomechanical actuating polymer iber also depends on the nature
able for measuring these small-diameter transducer (NMAT). of overlap between the chains, since the
iber samples. There are several critical strength of the physical hydrogen or van
components behind the accurate mea- nano/micro-iber materials. The technical der Waals bonds between the chains are
surements using a nanomechanical tensile speciications for the T150 UTM can be much weaker compared to the covalent
tester like the T150 UTM. These compo- found in Table 1. bonds within the chains.
nents include a patented nano-mechanical
actuating transducer (NMAT) -- shown
Applications Spider Silk
in Figure 1 -- that can measure small
changes in force to provide a uniquely Spider silk is known to be a wonderful ma-
large dynamic force range (0.0005 to Polymer Fibers terial for many structural and biomedical
500mN) for tensile measurements. A pre- applications. Different protein glands in a
cise extension axis (35nm resolution) also Figure 2 shows an engineering stress vs. spider produce a variety of silk with diver-
enables characterization of small diameter engineering strain curve for a PET iber, siied arrangement of protein molecules.
ibers at a wide range of strain rates. In obtained by extending the iber at a speci- Hence, it provides researchers a complete
addition, the Keysight NanoSuite control ied strain rate. In this case, the large ex- toolkit to study the protein molecules
software for the T150 not only facilitates tension range (up to 200mm) of the T150 and their arrangements that gives rise to
precise test control and analysis of data, UTM makes it possible to characterize the the unique combination of high strength
but also adds the capability to add new ibers over the complete range of strain, and high ductility 5. However, mechani-
test protocols for novel characterization of through breaking. This is especially useful cal testing of the individual silk strands
Maximum load 500 mN (50.8 gm)
Load resolution 50 nN (5.1