Tensile Tests

Tensile and tensile shearing tests are performed in a variety of ways.

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Single filaments
Filament strands
Pultruded GFRP bars
Unidirectional laminates
Multidirectional laminates
Notch tensile tests
Bolted laminates

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Tensile Tests on Single Filaments

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.

Tensile Tests on Filament Strands

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 Zwick makroXtens and multiXtens extensometers are ideal for measuring elongation.

Tensile Tests on Pultruded GFRP Bars

Depending on the design and surface structure of the specimen, testing is done with cap strips on the clamping ends, or without cap strips with special jaw inserts for hydraulic or pneumatic specimen grips. This test is described in ASTM D3916.

Tensile Tests on Unidirectional Laminates

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.

Tensile Tests on Multidirectional Laminates

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, Zwick uses strain gages, mechanical extensometers (clip-on, makroXtens, multiXtens) or optical extensometers (videoXtens HP).

Notch Tensile Tests (Open Hole Tensile)

This test characterizes the influence of a hole on the tensile strength of a laminate. The result is usually presented as a notch factor, which gives the ratio of damaged to undamaged specimen.