Photothermal Porosity Estimation in CFRP by the Time-of-Flight of Virtual Waves
Sprache des Titels:
Englisch
Original Kurzfassung:
Porosity is an unavoidable defect in carbon fiber reinforced polymers and has noticeable effects on mechanical properties
since gas filled voids weaken the epoxy matrix. Pulsed thermography is advantageous because it is a non-contacting, nondestructive
and fast photothermal testing method that allows the estimation of material parameters. Using the Virtual Wave
Concept for thermography data, ultrasonic evaluation methods are applicable. In this work, the pulse-echo method for Timeof-
Flight measurements is used, whereby the determined Time-of-Flight is directly related to the thermal diffusion time
of the examined material. We introduce a signal-to-noise dependent approach, the optimum evaluation time, for evaluating
only relevant time ranges which contain information of heat diffusion. After the validation of the method for heterogeneous
materials, effective medium theories can be used for quantitative porosity estimation from the estimated diffusion time. This
model-based approach for porosity estimation delivers more accurate results for transmission and reflection configuration
measurements compared to thermographic state-of-the-artmethods. The results are validated by X-ray computed tomography
reference measurements on a wide range of different porous carbon fiber reinforced plastic specimens with different number
of plies and varying porosity contents.