Passive impulse thermography during quasi-static tensile tests of fiber reinforced composites

Popow, Vitalij; Institut fur Verbundwerkstoffe GmbH; Germany

Popow, V.; Institut für Verbundwerkstoffe GmbH; Germany
Kelkel, B.; Institut für Verbundwerkstoffe GmbH; Germany
Gurka, M.; Institut für Verbundwerkstoffe GmbH; Germany

ID: ECNDT-0051-2018
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Session: Thermography and Thermosonics 1
Room: H1
Date: 2018-06-14
Time: 09:40 - 10:00

High performance composite materials and structures are of increasing importance in many industrial applications. The main advantage of this material is its exceptional lightweight capability due to individual tailoring of anisotropic fiber lay-up. Usually the materials properties like stiffness and strength are measured in quasi-static tensile tests, where the test-specimen is exposed to a controlled load until its failure. In contrast to ductile metals, the precise determination of the location of the failure or the observation of the progress of an initial damage is not possible for the more brittle behaving unidirectional fiber reinforced composites. Often the sample disintegrates in lots of small fragments. In order to get a more profound understanding of the failure behavior or to perform a more advanced tailoring of the material or design of the components made of, an in line characterization of the structural integrity of the test specimen under load would be very helpful. Active thermography, like lock-in or impulse thermography with an external heat source is well-known for its capability to detect flaws in composite structures during dedicated inspection routines.
As a promising method for contactless in-line inspection during a tensile test we used passive thermography utilizing the heat generated by the failure events (fiber breakage, delaminations etc.) itself. Combined with advanced data analysis methods from classical impulse thermography, like Principle Component Thermography, Pulse Phase Thermography, High Order Statistics etc., a significant increase of sensitivity and spatial resolution was possible, revealing different failure events like matrix failure, fiber-matrix debonding and fiber breakage. Therefore we could follow the propagation of the failure of the specimen during the test and predict the location of the final breakdown of the sample.
The measurements were done with different continuous fiber reinforced materials (thermoplastic and thermoset) and are validated by comparison with a simple theo-retical model.