Tensile testing is among the most standard tests performed by universal testing machines yet depending on how the test specimen is used in its native environment, setting up the tensile test method is not always straightforward. Wide width tensile testing is a type of tensile testing procedure used with specimens that are prepared with wider width than the standard tensile specimen coupons. This blog posts covers wide width tensile testing, standards outlining wide width testing methods, and the necessary equipment.
Wide width tensile testing is a tensile test method that covers the measurement of tensile load elongation characteristics as well as the offset modulus, secant modulus, and breaking toughness. The main difference of this method and other methods for measuring strip tensile properties is the width of the specimen.
Why wide width tensile testing?
Materials that are often tested in wide width forms include fabrics and geotextiles including woven and nonwoven geotextiles, geocomposites, knitted geotextiles, and felts. The recommended specimen width for such materials is much wider than the width of the specimen used to run strip test methods such as ASTM D5035. When force is applied, certain fabrics have a tendency to neck down in the gauge length area. The greater specimen width minimizes the contraction effect and provides a closer relationship to the expected geotextile behavior in the field.
ASTM D4595 Test Method for Tensile Properties of Geotextiles by the Wide-Width Strip Method
ASTM D4595 is a method covering the wide width tensile testing of geotextile specimen. Each wide width specimen is gripped across its entire width in grip jaws and pulled in tension with a constant rate of extension type tensile testing machine.Force is applied until specimen ruptures and tensile properties such as tensile strength, elongation, initial and secant modulus, and breaking toughness are calculated.
The specimen size per ASTM D4595 is 8 by 8 inches and the recommended grip jaw size is 8 by 2 inches. Wet and dry specimens may be tested following this method. Refer to the ASTM standard for further details.
ISO 10319 Geosynthetics — Wide-width tensile test
Similar to ASTM D4595, ISO 10319 outlines a standardized procedure to pull wide width geosynthetic specimens in tension until rupture. This standard, however, specifies different dimensions based on the material type: nonwoven geotextiles, woven geotextiles, geogrids with one axis (shown below), geogrids with two and four axes, geogrids with three axes, and metallic geotextiles. Tensile properties measured include the tensile strength and strain data and secant stiffness.
Figure 1 Typical geogrid with one axis (from ISO 10319)
Other standards that can be followed include ASTM D6637 Test Method for Determining Tensile Properties of Geogrids by the Single or Multi-Rib Tensile Method and ISO 10321 Geosynthetics — Tensile test for joints/seams by wide-width strip method.
As specified in the testing standards, a constant rate of extension type tensile testing machine is recommended for testing wide width specimen. All ADMET systems are servo controlled and meet the standardized requirements.
The eXpert 7600 single column testing machines can be used for lower force applications while the eXpert 2600 series dual column electromechanical testing systems have a broader range of force capacity, from 0.22kN (50lbf) to 400kN (90,000lbf). In addition, eXpert 1600 series servo-hydraulic frames offer capacities up to 600kN (135,000lbf).
Universal testing machines must be equipped with grips that have grip jaws covering the whole width of the specimen.
Standard grip options that accommodate wide widths include pneumatic grips, wedge grips, hydraulic grips, and self-tightening grips such as scissor grips.
If specimen ruptures on the edge of the grip jaws, we recommend using capstan or roller grips. Samples must be able to fold and be placed in the roller drum without causing damage to the material structure.
For geotextiles made from glass fibers, custom grips may be required to avoid slippage or damage from jaws.
Use a universal joint to allow the grip to rotate in the plane of the fabric to ensure vertical alignment in the direction of test.
When information on strain is required, consider utilizing an axial extensometer to measure strain data.
If you’re interested in learning more about wide width tensile testing equipment, please reach out to one of our Sales Engineers. We may ask for specimens to be sent to the ADMET lab to ensure the right equipment is recommended for you to achieve your testing goals.