Low Frequency GFRP Imaging with Variable Aperture TFM

Abstract

Graphite or glass fiber reinforced polymer (GFRP) inspections are usually made with a zero-degree linear scan (L-scan) (1). Total focusing may not be applicable for some anisotropic materials, but in some cases, TFM may increase the ultrasound imaging quality. The imaging potential of 1D linear probes has been broadened by TFM by many aspects so there is an opportunity to apply the total focusing concepts to exotic composite assessment. The ultrasonic limitations associated with testing thicker sections of GFRP restrict inspections to lower frequency phased array probes. When a low frequency probe uses the L-Scan technique, the performance and sensitivity is negatively affected once compared to a typical phased array probe of a higher frequency due to the element size and pitch restrictions associated with low frequency probes. Therefore, new testing techniques should be found. The alternative imaging acquisition method presented here involves variable aperture receivers that improve the usual LScan characteristics. This study explicitly covers the differences over the L-scan type, the TFM image and its variable aperture TFM feature. In addition of the theory concepts, ultrasound metrics have been recorded on a real GFRP sample and using as reference reflector side drilled holes (SDH).