Justification of Selecting Ultrasonic Testing Parameters for Bundle and Impact Damage Detection in Carbon-Fiber Constructions

Abstract

Features of manufacturing process and use of carbon fibre-reinforced plastics (CFRP) define specific types of only their defects. Furthermore, the CFRP structure material and its properties considerably differ from those of the metal materials. Therefore, a relevant task is to conduct research to justify the selection of the ultrasonic testing parameters of these materials.

Optimal parameters and recommendations on quality control of such materials were grounded in the course of experimental studies on samples made from the UTR1000-12-400P carbon fabric, based on the T700GC-12K yarn and the T-31 epoxy binder, filled with artificial defects to imitate the bundles of different size and the impact damage.

It is shown that with increasing frequency of the ultrasonic oscillation propagating in the samples there is an increase both in damping and in SNR for artificial defects. In other words, on the one hand, the lower is the oscillation frequency, the less is a damping effect, but, on the other one, the higher is the frequency, the higher is the sensitivity control. It was found that the optimum frequencies for the ultrasonic test of CFRP are those in the vicinity of 5 MHz.

Furthermore, to detect the small-sized defects it is advised to use an ultrasonic beam focus, which can be achieved using phased arrays.

The most optimal method of ultrasonic testing to search for impact damage is a mirrorshadow method, which is based on the measurement of the amplitude of the bottom echo signal. It is shown that the amplitude of the bottom echo signal in defect-free zone is, in average, 14 dB higher than in the area with shock damage.