Uniaxial tests on composite laminates require the highest level of precision and stiffness - so that alignment can be established and maintained. Without a precision testing system (load frame), results can be compromised because composite materials are so sensitive to alignment.
Instron offers three precision platforms for testing composites and a wide range of load string accessories for tension/compression testing:
- Electromechanical:twin-screw systems for quasi-static mechanical testing from "0" to 600 kN (130,000 lbs)
- Servohydraulic:2- or 4-column systems for static and dynamic testing from "0" to 5 MN (1,000,000 lbs)
- Electrodynamic: oil-free systems for static and dynamic testing in 1 kN, 3 kN, and 10 kN capacities (200, 600, and 2,000 lbs)
Accessory Items for Tensile Testing
A variety of grips are available for tensile testing flat composites coupons. The most popular are mechanical wedge grips and hydraulic wedge grips. For the most part, it is a matter of selecting a grip with the correct capacity, and making sure that the grip faces and associated dimensions are suitable for the length and thickness of the specimen tabs.
If it is necessary to meet the alignment requirements of NADCAP, for example, hydraulic grips are necessary. This is mainly due to the precision of the grip, and the highly repeatable nature of its operation.(Manual grips are subject to higher variability simply due to differences in operator techniques).
For non-ambient testing, extended hydraulic grips are available that keep the hydraulic "driver" portion of the grip outside the chamber, yet provide the convenience of hydraulic operation to the grip faces.
Adapters are available to attach fixtures directly to the hydraulic grips such that they can be left in place while performing other types of tests - such as compression, etc.