Relation of Composite Part Strength to Ultrasonic Inspection

Although standard conventional ultrasonic testing is capable of indicating defects in composite parts, the lack of quantitative indication of the mechanical strength of the parts and the need to use liquid coupling limits its use in the non-destructive testing of automotive composites.

By utilizing soft-tip dry transducers, the efficiency of ultrasonic scanning is greatly improved and ultrasonic measurement can be conducted on composite parts where the use of a liquid coupling medium is objectionable. The through-transmission ultrasonic signal amplitude measured in several automotive FRP samples (SMC) was found to correlate well with the tensile and short-beam shear strength of the samples at the location of failure. Another use of ultrasonic inspection is to determine the critical flaw size for a particular application. The assessment of critical flaw size in composites and the merit of using this novel technique for the strength evaluation of FRP composites is discussed.