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What does this type of testing measure?
—Many different material parameters can be obtained from this test including rupture or yield force, stress (commonly referred to as tensile strength), strain and energy, and extensional stiffness/elastic modulus. For laminated sheets with components of sufficiently different yield strains, a strip tensile can also yield information about the various component layers. Adding a cyclic strain to a simple strip tensile test, allows the measurement of hysteresis and visco-elastic/plastic properties. While most users only are looking for the ultimate tensile strength or strain, there is much additional information available from this relatively simple test and much of that information comes for the low price of adding a few calculations to the raw data curve.
What type of test method standard(s) do you follow when performing this test?
—There are literally scores of standardized methods for different strip tensile tests. Some of the most common include TAPPI T494, TAPPI T220, and ASTM D882. However, it is very common to modify gage lengths, specimen widths and test speeds for the standard tests, usually because limited sample size limits specimen dimensions or counts.
How do you perform this test?
—In general, the strip tensile is quite easy to perform. A rectangular specimen is cut from a piece of sample material. Typically, because sheet materials are anisotropic, the cut dimensions are aligned either parallel to or perpendicular to the sheet machine direction. The length to width ratio of the specimen should be greater than five to one. The specimen is clamped in a tensile frame using appropriate grips. The machine is started and typically pulls the specimen at a constant speed to rupture. During the test, a computer records load and elongation points. All calculations are performed on these data pairs.The underlying details can be quite important. Proper selection of test machine grips, speeds, data filter rates and data correction (e.g. slack and machine compliance corrections) are imperative.
How has this test method most commonly been used for a specific industry?
—For both paper and non-woven materials, tensile strength is often an end use measurement. For example, a dinner napkin or surgical wrap must have sufficient strength to not tear in use. But tensile strength also relates back to the manufacturing process. It can be an indicator for process efficiency or raw material utilization. Other strip tensile parameters have different uses. For example, elastic modulus is often related to sheet ‘feel’. The ratio between modulus and strength can be a proxy for sheet formation. There are several watchouts for proper interpretation of strip tensile data. Users seldom care about fundamental material properties but producers do. The same data from a tensile test might need to be expressed differently depending on the use. As a simple example, that dinner napkin user cares only that the napkin is strong enough. She doesn’t necessarily care if the fiber utilization is efficient. An appropriate strip tensile strength parameter for this end user might be rupture force per unit width. However, the napkin producer wants to minimize fiber cost. For the producer, the appropriate strength parameter might be rupture force per unit width per unit basis weight. So the identical piece of data might be used in two different calculations, one by the QA Department and one by the Pulp Development Team.