Carbon fiber testing is a material science test involving the testing of all carbon fiber containing materials. The results for the testing are used to select and design material composites, manufacturing processes and to ensured safety and integrity. Particularly safety-critical carbon fiber parts, such as structural parts in machines, vehicles, aircraft or architectural elements are subject to testing.
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Concepts
Testing sciences classify three main disciplines for material testing that especially apply to carbon fiber materials. Most common are destructive tests, such as stress, fatigue and micro sectioning tests. There are also methods that allow non-destructive testing (NDT), so the material can be still be used after testing. Common methods are ultrasonic, X-ray, HF Eddy Current, Radio Wave testing or thermography. Additionally, Structural Health Monitoring (SHM) methods allow the testing during application.
Testing methods
Carbon (carbon fiber reinforced plastic and reinforced polymers) are gaining importance as light-weight material. Particularly safety-critical carbon fiber parts, such as aircraft frames, need to be tested destructively (e.g. stress, fatigue) and non-destructively (e.g. fiber orientation, delamination, bonding). Typically, destructive tests are carried out to validate the mechanical properties, whereas NDT are used to monitor and control the manufacturing process of the CFRP parts. As carbon fiber composites are highly individual in shape and material composition novel NDT are emerging and sought for application. Applicable technologies are radio wave testing and high frequency eddy current testing, thermography, shearography, air coupled laser ultrasonics, terahertz scanning
Typical effects and defects
The specifications for integrity of structurally relevant parts depend on the individual manufacturer. However, typically relevant quality criteria of the texture are fiber orientation, gaps, wrinkles, overlaps, distortion, undulation, uniformity as well as defects in the matrix delamination, inclusion, cracks, curing, void, debonding. Furthermore, basis weight or carbon fiber volume content are important properties. Generally, defects and effects in carbon fiber materials are classified according to their location as structural defects (carbon fiber related) and matrix defects (resin related). Carbon fiber related effects are tested with X-ray and high frequency testing methods whereas matrix effects are commonly tested with ultrasonic and thermographic methods.