Practical, Cost-Effective, Nondestructive Evaluation Technique for Composite Materials

The mechanical characteristics of advanced composite materials are strongly affected by physical parameters such as ply orientation, thickness of the layers, and homogeneity of the fibers. Although proper material integrity is critical for performance, many factors influencing mechanical properties cannot be detected by visual inspection Small anomalies or incipient degradations including delaminations or heat damage represent a detection problem for ultrasonics. Research with techniques such as ultrasonics, backscattered X-ray, eddy current, thermography, DRIFT and LPF spectroscopies, acousto-ultrasonics, and hardness testing have not resulted in a demonstration of the ability to correlate nondestructive testing results with loss of strength of the material. Recent research at TPL indicates that dielectric spectroscopy is able to detect physical and chemical properties that result from improper fabrication or thermal degradation, and may be able to determine the internal structure at both the macroscopic and microscopic levels. The results of Phase I are expected to establish that dielectric spectroscopy is significantly more sensitive for the detection of physical characteristics affecting mechanical properties than other techniques such as ultrasonics. It will also show that the new NDE technique can be used both during the manufacturing process and during in service inspection USI) of aircraft.