An ultrasonic‐acoustic technique for nondestructive evaluation of fiber composite quality

Abstract

AbstractThis report describes an ultrasonic‐acoustic technique used to measure a “stress wave factor” in order to nondestructively assess the quality of composite structures. In a prior study this factor was found effective in evaluating the interlaminar shear strength of fiber‐reinforced composites. Details of the method used to measure the stress wave factor are described. In addition, frequency spectra of the stress waves are analyzed in order to indicate the nature of the wave phenomena involved. The stress wave factor can be measured with simple contact probes requiring only one‐side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus, in many cases, measure material properties in directions assumed by actual loads. Moreover, the technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite polyimide composite panels and results obtained are compared with through transmission immersion ultrasonic scans.