Polar C-scan

Ultrasonic Polar Scan Imaging

An ultrasonic polar scan is a non-destructive evaluation technique that inspects a specific point on a sample. During the scan the transducer remains a fixed distance from the sample but its position is varied along two angular coordinates to include as many angles of incidence as possible

Ultrasonic polar scans can be used to estimate composite material properties such as stiffness, fiber orientation and/or the extent of damage. Amplitude or time-of-flight (TOF) information can be extracted from the waveforms of the double-through transmitted or reflected sound, and this information can be used to form a polar scan image. Polar scan images contain characteristic patterns, and an image can be considered as a fingerprint of the spot of the material being inspected. In particular, polar scan images of anisotropic materials produce characteristic shapes which can be used to estimate material properties like directional stiffness or the orientation of fibers. For damaged materials, the extent and direction of damage can also be analyzed, for example as fiber composites become less stiff with fatigue damage. Although amplitude information is most often used to form a polar scan image, experiments performed at the UMI have shown that the TOF information can also be used to complement the amplitude information.current work on polar scans at the UMI is divided into three parts. The first part involves the development of a model for the numerical simulation of polar scan images for a carbon fiber reinforced composite (CFRC) material. The second part of the study involves the validation of the simulation results by comparing them with experimental polar scan images of the CFRC. In order to estimate the progress of damage along the sample length, polar scans are carried out on CFRC samples which had been tested in bending and tension until fracture. Time of flight and amplitude information is used to construct images of the directional growth of damage at different distances from the localized region of fracture. The novelty of this study is the use of time-of-flight information to complement the results obtained using amplitude based measurements

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