The diameter of the individual filament lies in the micrometer range. The filament is first secured to a small paper frame according to ISO 11566 and then aligned and fixed in the clamping mechanism of the testing machine. After cutting through the frame, the properties can be determined under tensile load.
Normally, the filament strands are coated in resin first and then cut into lengths. Cap strips made from cardboard or plastic are glued to the ends so that the tensile force can be applied evenly to the specimen. Tools such as the makroXtens and multiXtens extensometers are ideal for measuring elongation.
Unidirectional laminates are normally tested longitudinally for fiber strength and transversely for bond strength. The specimens are reinforced at the ends with cap strips to avoid jaw breaks. This test, which is described in ISO, ASTM, EN, AITM, BSS, DIN, SACMA and CRAG standards, places high demands on the quality of the extension measurement and on the alignment accuracy.
Depending on the size of the textile structure, multidirectional laminates are tested with large specimen widths of 25 mm or even 50 mm. According to ISO 527-4, the thickness of the specimen can equal 10 mm or less. Due to the large specimen cross-sections, very large tensile forces of over 300 kN can occur.
To measure strain, ZwickRoell uses strain gauges, mechanical extensometers (clip-on, makroXtens, multiXtens) or optical extensometers (videoXtens HP).
2D DIC: a powerful analysis tool
2D digital image correlation visualizes deformations and strain over the entire visible specimen surface. The non-contact videoXtens extensometer records image series during the test, compares image for image, and calculates the displacement in a pre-defined facet field, whereby each facet comprises a certain number of camera pixels. This data is used to create two-dimensional color strain maps, which allow you to analyze the specimen behavior at a glance.