Composite materials are most commonly tested to determine their in-plane properties. However, there is also an increasing demand for measurement of their through-thickness properties, which is only likely to become more common with the development of reinforcements.
Instron recently participated in a Round Robin test program lead by the National Physical Laboratory to support the development of a new ISO standard for the through-thickness testing of polymer composite materials. The new standard, ISO NP 20975-1 “Fiber-Reinforced Plastic Composites – Determination of Laminate Through-Thickness Properties, Part 1: Specimen Designs for Direct Tension and Compression Tests,” covers both tension and compression testing in the through-thickness direction.
This testing was performed on an Instron 5985 electromechanical testing system with a 250 kN capacity. The tensile test specimens were supplied with bonded metal studs, which were gripped between a pair of Instron hydraulic grips which had been precisely aligned using an AlignPRO fixture and checked using a strain gauged alignment specimen.
The compression test specimens were tested between a pair of compression platens mounted on the hydraulic grips. The upper compression platen incorporated a lockable spherical seat which allowed the alignment of the platens to be adjusted.
For strain measurement we used four axial and four transverse strain gauges (for determining Poissons ratio). The gauges were connected using Instron strain gauge adapters and along with an expansion channel module. Test control, data collection, and analysis were performed using Bluehill Universal software.
Successful tests were carried out on both carbon and glass fiber specimens, and the data will help to validate and establish the precision of the new test method.