Tensile testing is the most commonly applied test method for analyzing the mechanical properties of fabric materials. Although the direction of applied force is always in tension, there are a variety of tensile test methods available for capturing the most relevant data for final product usage.
The strip test is a tensile test in which the full width of the test specimen is gripped in the tensile grip jaws of a universal testing machine. During this test, tensile force is applied on the fabric specimen until it ruptures. Mechanical properties to analyze include the force at rupture and the elongation (expressed as percentage) at maximum force and/or at rupture.
The tongue tear method is often used to measure the tear force and the tear strength of a fabric specimen.
Trapezoidal tear is another tear strength test that uses a specimen prepared as an isosceles trapezoid with a small cut on one side. When testing starts and force is applied, the trapezoid tear produces tension along a reasonably defined course such that the tear propagates across the width of the specimen. This test method applies to most fabrics such as woven fabrics, air bag fabrics, blankets, napped, knitted, layered, and pile fabrics.
Seam strength is the strength of the connecting seams constituting the fabric. The grab test method and the strip test method can be used to measure the seam strength of fabric specimen.
Adhesion Coating Testing
Adhesion coating testing is applicable to fabrics with an adhesive coating compound applied, forming a chemical bond between the adhesive and the fabric material. The bond strength that is created between the coating compound and the fabric material can be measured running adhesion coating tests. If the adhesion is not strong enough, seam strength will decrease. If adhesion is too strong, problems may arise as tear strength will be affected. Standards outlining the minimum required criteria for specific fabric constructions can be used to ensure both the seam and tear strength are acceptable.
Puncture testing of fabric specimens determines the strength of a material by measuring the force required to penetrate the specimen. Contact with sharp edged objects in a real-world scenario is simulated by the use of puncture fixtures. Puncture fixtures are often used in the tensile direction but may also be used in the compressive direction. In order to calculate the specimen puncture resistance, the specimen is first stretched and placed on the ring clamp mechanism of the puncture fixture. Load is then applied by the puncture probe until specimen rupture.
Shear testing ensures accurate data is collected to analyze the draping, flexibility and handling of textiles which show a wide range of complex deformations, such as woven fabrics. Depending on the fabric material, textile fabrics may show anisotropic behaviors and have different strength values in different directions, affecting the bending and tensile properties in various directions.
The ±45 degree off-axis tension test is recommended for shear characterization of woven fabric composites. Prior to applying load, the test specimen is prepared with strain gauges, one perpendicular and one parallel to the specimen length, and another 45ﹾ off-axis to determine the off-axis modulus of Elasticity, the off-axis Poisson’s ratio, and the shear coupling ratio.
Recommended Equipment for Fabric Strength Testing
A universal testing machine with constant-rate-of-extension equipped with a stationary bottom grip and with a top grip mounted on the moving crosshead is recommended for fabric tensile testing. The machine should be able to move at a constant speed throughout the test.
Pneumatic vise and manual vise grips are recommended for tensile testing of fabrics. Testing standards often recommend grips with specific jaw material and dimensions.
Specimen cutting dies may be required in the preparation stage of the specimens. Cutting dies are made following the specific sample dimensions delineated in testing standards.