Abstract
In this paper, the analysis of non-contact elastic waves generation in carbon fiber reinforced-polymer (CFRP) plate was conducted. Full non-contact elastic waves generation and sensing methods were also analyzed. Elastic waves generation was based on an air-coupled transducer (ACT) while waves sensing was based on a laser Doppler vibrometer. The excitation frequency was equal to 40 kHz. An optimal ACT slope angle for the generation of elastic waves mode was determined with the aid of dispersion curves calculated by using a semi-analytical model. Due to the stack sequence in the composite plate (unidirectional composite), ACT slope angles were different for waves generation in the direction along and across reinforcing fibers direction. Moreover, experimental verification of the optimal ACT slope angles was conducted. It was possible to generate A0 wave mode in the direction along and across the reinforcing fibers. Optimal angles determined using ACT were equal to 16° (along fibers) and 34° (across fibers). In the case of optimal angles, elastic waves amplitudes are almost two times higher than for the case of ACT oriented perpendicularly to the plate surface. Moreover, experimental results based on ACT showed that it was possible to generate the SH0 mode in the direction across the fiber for optimal angles equal to 10°. Finally, based on the A0 wave mode propagation, the process for localization of discontinuities was performed. Discontinuities in the form of additional mass simulating damage were investigated. A simple signal processing algorithm based on elastic wave energy was used for creating damage maps. Authors compared discontinuity localization for ACT oriented perpendicularly to the plate and at the optimal slope angle. The utilization of non-contact waves excitation at optimal ACT slope angles helped to focus the wave energy in the desired direction. Moreover, in this case, elastic waves with the highest amplitudes were generated.
Highlights
A carbon fiber-reinforced polymer (CFRP) is one of the most popular materials used in modern industry branches
There are many non-destructive testing (NDT) methods that are devoted to an inspection of structures [1,3], with various accuracy, it should be underlined that CFRP structures are highly anisotropic, which makes the process of their monitoring difficult and challenging [4]
It should be noted that air-coupled transducer (ACT) works based on resonance principles and for the particular transducer used here it is 40 kHz
Summary
A carbon fiber-reinforced polymer (CFRP) is one of the most popular materials used in modern industry branches (including the aerospace and automotive industry). It is mainly due to its interesting material properties (good elastic properties and load resistance while keeping low mass [1,2]). There are many non-destructive testing (NDT) methods that are devoted to an inspection of structures [1,3], with various accuracy, it should be underlined that CFRP structures are highly anisotropic, which makes the process of their monitoring difficult and challenging [4]. A group of NDT methods that can be especially distinguished is ultrasonic testing (UT), due to its important advantages (possibility of fast and accurate inspection over the relatively big region while keeping the operation costs and safety of the inspection process at a low level). Researchers are recently focused on the non-contact ultrasonic methods [5,6,7], which rely on non-contact generation and sensing of elastic waves propagating in the structure
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