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Properties of Textiles
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Testing for textile properties is widely used to measure breaking tenacity
and elongation, tensile strength, initial modulus, and many other
parameters. Many test specifications for textiles relate to the
end use including testing of tire cord for strength and adhesion,
grab tests, fabric seam slippage and tear tests.
Since finished product performance relates to the testing of
yarn, fiber and fabric samples, the textile industry acknowledges
the importance of testing to achieve high quality products.
Calculating Strain at Failure Using the “Effective Gauge Length” Method
With most highly twisted yarns and tightly woven textiles, the stress-strain
curve is reasonably linear from 90% of the failure load up to failure.
This characteristic can be used to extrapolate a known true strain at 90% to
obtain the true strain at failure. The strain calculated using the initial grip
separation at gauge length is in error due to grip penetration.
The “effective gauge length” is a value by which the increase in grip
separation must be divided to obtain the true strain of the specimen. The
effective gauge length, EGL, can be determined by conducting a “calibration”
test where two marks have been placed on the specimen at a known separation, L.
The initial grip separation, S, is noted. The test is now performed but stopped
at 90% or the failure load. At this point, the changes in separation dL and dS
are noted. Then:
So subsequent tests, with an initial separation,S:
This technique can only be used for calculating strain at failure, because
of the varying degrees of grip penetration as the specimen properties change
during a test.
How to Perform Textiles Tests / Testing to Standards
Many of these tests are detailed by industry standard testing
methods. For example, when testing man-made staple fibers, ASTM
method D540 is applicable. Typically, ten tests are conducted on one
millimeter lengths of fibers to determine the average breaking tenacity
which is measured in grams per denier (denier being defined as the
weight in grams of 9,000 meters of yarn). This is a measure of the
maximum load which can be carried. Extremely low forces are
encountered in evaluating fiber properties, requiring a precise
measuring instrument capable of accurately reading gram range loads.
Measurement of Breaking Force
In evaluating monofilaments,
multi-filaments and spun yarns, the
ASTM method D2256 describes the technique of evaluating breaking load,
elongation, single strand strength, knot breaking strength, loop
breaking strength, tenacity and breaking tenacity. Since utilizing
knotted and looped specimens reduces overall strength, this test is
considered to be a measure of the brittleness of the yarn. In
addition, load at specified elongation, initial elastic modulus,
and compliance may also be measured, since yarns are sensitive to
the rate of testing, a test instrument having an accurately controlled
drive system is required. These tests are conducted at a constant rate
of travel to achieve consistent results.
Elongation
Seat Belt Testing
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Webbing Grips
Elastomeric materials made from either rubber or other synthetics
for elastomeric yarns are typically evaluated for quality using method
D2653. Tests include stretching elastomeric yarn to at least twice the
original length and observing it returning to its starting length.
Other parameters such as elongation at specified load
(EASL), load at specified elongation
(LASE),
and area under the curve (i.e., work done
on the specimen) may be calculated from the load/elongation curve).
Tests are typically conducted at 20 inches per minute (500 millimeters
per minute) with a two-inch gauge length (50 millimeters). Results
include breaking load
and breaking tenacity as well as elongation.
Method D885 describes the appropriate technique for evaluating tire
cord, tire cord fabric and industrial filaments and yarns made from
man-made organic-based fibers. Typical results include load at
specified elongation (LASE), or elongation at specified load (EASL)
as well as load and extension at break.
Tear Strength
Testing of textile fabrics for tear strength is often required as
described in method D2261. By definition, tear strength is the force
required to start or continue a tear in a fabric under specified
conditions. After starting a cut in the center, the opposing tail or
“tongue” is gripped in the instrument and pulled apart. The tear test
parameters include tearing strength,
peak load and median load. An
integrator is helpful in averaging the random load curve produced.
Seam Breaking Strength
Seam Breaking Strength of Fabrics
w/
Pneumatic Side Action Grips
Seam breaking strength of fabrics may be evaluated using the
grab test method for breaking load determinations (D1683). This
test evaluates the seam quality. Other techniques for evaluating textile
fabrics including geotextiles and pond liners for breaking load and
elongation include grab, ravel strip and cut strip methods
(described in D1682).
Other textile test methods cover testing of bonded and laminated
apparel fabrics (D2724) and backing fabrics such as used in carpeting
or tufted floor coverings (D2646). The breadth of test results, and
precision at very low forces, require accurate testing instruments
and a variety of grips. Often, automated data collection is needed
for statistical quality control.
More Standards
- EN12332-1 Coated Fabrics - Ball Burst
- EN29073-3 Non-wovens - Tensile Strength and Elongation
- EN29073-4 Non-wovens - Tear Resistance
- EN1875-3 Trapezoidal Tear Strength of Coated Fabrics
- EN ISO 1421 Coated Fabrics Tensile
Textiles Applications
The textile industry manufactures fabrics, cords, yarns, and the individual fibers
all of which may be either natural or synthetic materials.
The textile industry is varied in its applications and manufacturing methods.
- Carpets are created from fiber, natural, synthetic and mixed fibers. They can be
produced by the process of knitting and plaiting (woven), weaving, or produced without
the process of plaiting (non-woven).
- Fabrics can be constructed by knitting, crocheting or lacework and in a variety
of natural and synthetic materials. They can then be used to create apparel, home
goods, or industrial textiles.
- Laminated textiles offer the benefits of combining fabrics, polymers and films to
improve and modify the physical properties and appearance of fabrics. Some applications
include sailcloth, filters, automobile convertible tops, sports apparel, tire cord,
and belting.
- Filaments can be twisted, twined or spun into yarns, threads, cords, ropes, wire
ropes, cables, etc.
- In the medical field, the use of textile materials for medical and healthcare products
ranges from simple gauze or bandage materials to a large variety of prostheses for
permanent body implants and bioresorbable textile supports for growing human organic
tissue.
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