Conference: Publication Date: 27 October 2014Testing Method:
Uncured and continuously produced materials cannot afford exposure to a device via contact or be immersed in liquid coupling. This makes conventional contact and immersion ultrasound unsuitable for inspection. However, UT is highly desirable for inspection of uncured composite materials as amplitude and time of flight measurements often reveal vital material properties. Non-contact (air-coupled) ultrasound has improved to a level of efficiency comparable to conventional ultrasound, usable at frequencies from 30 kHz to 5 MHz. As such, it can be used to relate signal measurements directly to material properties in materials such as fiber-based composite prepreg and most cured and uncured composites. A safe and non-destructive measurement process of relatively low cost, non-contact ultrasound presents opportunities to lower cost, reduce and identify waste, and improve production efficiency. Direct relationships exist between ultrasonic amplitude in non-contact through transmission and key material properties such as porosity, delamination, homogeneity and other defects and metrics in composites. By converting amplitude and velocity measurements into material property values through characterization formulas (i.e. moisture content = ultrasonic amplitude x + y), one can apply standard methods of manufacturing process control to hold production processes within desired control limits with real-time feedback. Mapping such measurements to webline material positions allows direct identification of sections of undesirable material, reducing waste and improving manufacturing yields by avoiding unnecessary disposal of uninspected sections. Utilizing multiple points of measurement (multiple channels) in the cross-web direction allows for up to 100% inspection and high accuracy of spatial identification on finished products.
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