Abstract
The use of Acoustic Emission (AE) to detect impacts is of interest within industries where vital components are prone to impact damage, in particular where Carbon Fibre Reinforced Polymers (CFRP) are used, as damage can often go un-noticed within them. For AE monitoring of impacts piezoelectric sensors are used to detect the ultrasonic wave produced by an impact. Classification is also possible of these waves enabling a distinction between damaging and non-damaging impacts. These sensors do however have resonance, so do not give an accurate picture of how the waves propagate, better knowledge would enable better selection of sensors. Laser Doppler Vibrometry is a non-contact and non-resonant method of analysing the surface displacement on a structure. In this study, a vibrometer was used to monitor CFRP plates during impact to assess its applicability for distinguishing between damaging and non-damaging impacts, compared with a surface mounted AE sensor. The vibrometer was able to detect both low frequency flexural modes due to the impact process and the higher frequency extensional modes, initiated by damage. When compared to the AE sensor the vibrometer was comparable in its results, and unlike the sensor, not susceptible to resonance or decoupling. For the tested material the vibrometer identified frequencies greater than 20 kHz to be associated with damaging impacts.
Highlights
The use of Carbon Fibre Reinforced Polymer (CFRP) composites is increasing significantly in the aerospace, automotive, and marine industries due to their high strength-to-weight and stiffness-to-weight ratios compared with metallic structures
This paper presents the results from low velocity impact testing on CFRP monitored with both a physical Acoustic Emission (AE) sensor and Laser Doppler Vibrometry (LDV)
This work presents the first reported use of a LDV to monitor the response of composite panels during low velocity impacts, both damaging and non-damaging
Summary
The use of Carbon Fibre Reinforced Polymer (CFRP) composites is increasing significantly in the aerospace, automotive, and marine industries due to their high strength-to-weight and stiffness-to-weight ratios compared with metallic structures. They benefit from excellent fatigue and corrosion resistance properties [1]. Their inherent reaction to external dynamic excitations, such as structural impacts, is still a significant concern in real life application where threatening internal damage, such as delamination and interfacial debonding, can exist and not be visually detectable [2, 3]. Structural Health Monitoring (SHM) is promising due to its ability to possess self-sensing capability to continually monitor structures during service [8, 9]
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