PRACTICAL APPLICATION OF PVDF SENSORS FOR DAMAGE DETECTION IN METALLIC AND COMPOSITE STRUCTURES

초록

The practical applicability of polyvinylidene di-fluoride (PVDF) sensors was investigated by employing them to the detection of fatigue damage in aluminum panels with simulated fastener holes and in composite specimens with adhesively bonded joints. The PVDF sensor has several advantages over the lead-zirconate-titanates (PZT) sensor including the cost-effectiveness, the flexibility as plastic films, and the low profile as a few tens of microns. A commercially available PVDF sensor was employed to detect acoustic emission (AE) due to fatigue cracks in the single-lap joints of carbon/epoxy (CFRP) specimens and in the smooth notch root of Al2024-T3 panels. With the acceptable level of the signal-to-noise ratio (SNR), the result appeared useful to determine the crack front during fatigue loading by AE linear location. Composites produce very energetic AE signals as expected so that the very inexpensive and disposable PVDF sensors can be utilized for structural health monitoring of composite structures. Since the SNR of the signals from the aluminum panel was not as high as that from the composites, a special treatment of wavelet transform de-noising was necessary to precisely determine the initiation time and the location of fatigue cracks by two-dimensional AE source location.