Lockin thermography as well as flash thermography are very well suited for non-destructive testing and characterisation of inhomogeneities and damage in CFRP structures. Both methods are applied more and more in research and industry, but until know it is not clear which are the advantages of one method against the other. In
this paper, results of two research projects concerning the validation and standardisation of both methods are presented. Three different types of CFRP test specimens consisting of well-defined flat bottom holes, of artificial delaminations made of PTFE plates embedded in CFRP and of real impact damage have been investigated systematically with flash and lockin excitation. Here, the phase images of both methods are compared qualitatively as well as quantitatively.
Standards for the application of flash thermography as well as of lock-in thermography are urgently required.
Both methods are applied more and more often in research and industry, but still extensive validation procedures are required for each individual application. In this paper, the results of two research projects concerning the validation and standardisation of both methods are presented. This includes results of a detailed study of the influence of measurements parameters on flash thermography, of the comparison of the lateral resolution obtained with flash and lock-in thermography and the description of a draft standard for flash thermography.
Active thermography with lock-in excitation is a non-destructive testing method that is also feasible for testing of carbon fiber reinforced polymers (CFRP). For validating the method extensive investigations were done during a research project in order to advance a standardization process.
The most important parameters of optical and ultrasonic excitation thermography were investigated. For example, the appropriate selection of spectral sensitivity of the used infrared camera systems is important for recording undisturbed thermal signals. Regarding excitation,
influences of excitation power and ultrasonic frequency were studied. Furthermore, material parameters such as CFRP layup are known for strongly affecting the results of
measurement.