Abstract
Carbon fibre reinforced polymers (CFRP) have been used significantly more in recent years due to their increased specific strength over aluminium structures. One major area in which their use has grown is the aerospace industry where many now use CFRP in their construction. One major problem with CFRP's is their low resistance to impacts. Structural health monitoring (SHM) aims to continually monitor a structure throughout its entire life and can allow aircraft owners to identify impact damage as it occurs. This means that it can be repaired prior to growth, saving weight with the repair and the time that aircraft is grounded. Two areas of SHM being researched are Acoustic Emission (AE) monitoring and AcoustoUltrasonics (AU) both based on an understanding of the propagation of ultrasonic waves. 3D Scanning laser vibrometry was used to monitor the propagation of AU waves with the aim of gaining a better understanding their interaction with delamination in carbon fibre reinforced polymers. Three frequencies were exited with a PZT transducer and the received signal analysed by a cross correlation method. The results from this and the vibrometer scans revealed 100 kHz as the most effective propagating frequency of the three. A high resolution scan was then conducted at this frequency where it could be seen that only the out of plane component of the wave interacted with the damage, in particular the A0 mode. A 3D Fast Fourier Transform was then plotted, which identified the most effective frequency as 160 kHz.
Highlights
Carbon Fibre reinforced polymers (CFRP) components have many additional issues over aluminium ones, a major one being their ability to withstand impact damage and the difficulties associated with spotting said damage, due to delamination between the ply’s of the material
Acousto-Ultrasonics (AU) is an active form of Structural health monitoring (SHM) which consists of exiting ultrasonic lamb waves using a transducer bonded to a surface of the structure
Experimental Procedure The tested specimen was manufactured from Carbon fibre reinforced polymers (CFRP) 2/2 twill with fibres running 00 and 900, eight ply’s were laid in a 0/0 format
Summary
Carbon Fibre reinforced polymers (CFRP) components have many additional issues over aluminium ones, a major one being their ability to withstand impact damage and the difficulties associated with spotting said damage, due to delamination between the ply’s of the material. Structural Health Monitoring (SHM) aims to continually monitor a structure throughout its entire life, both during manufacture and throughout its service life The benefits of this over the traditional method of inspections at regular intervals is the early detection and repair of damage, leading to lighter and more efficient structures. Acousto-Ultrasonics (AU) is an active form of SHM which consists of exiting ultrasonic lamb waves using a transducer bonded to a surface of the structure. This wave is received by a sensor and by comparing the change in received signal over time using a method such as cross correlation, an indication of whether damage is present can be gained.
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