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

Abstract

This 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.

Characterization of adhesively bonded joints using acousto-ultrasonics

“…As the name implies, the ultrasonic techniques utilize high frequency (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) …”

“…Acousto-ultrasonics (AU) is a relatively new NDE method developed by Vary [4] which combines the beneficial aspects of conventional ultrasonic and acoustic emission techniques. Recent studies by various researchers [4][5][6][7][8][9][10][11][12][13] reveal that there is a strong correlation between the stress wave propagation characteristics determined by acousto-ultrasonics and various mechanical properties of materials. Based on these previous results, it was considered probable that the acousto-ultrasonic technique might provide information on the overall performance of adhesively bonded joints.…”

“…There are numerous examples of successful applications that show the feasibility of the acousto-ultrasonic technique as a means of estimating mechanical strength variations in structural composites [4][5][6][7][8][9] as well as estimating residual strength and degradation from cyclic fatigue and impact damage [10,11,71,72]. The technique has also been used to evaluate wire rope strength [13], nylon rope tension [73], filler content in wood and paper product [74], strength of ceramic materials [75,76], the effect of hydrothermal aging on composites [77,78] and porous metal diffusion bond quality [79].…”

Development of a High Performance Acousto-Ultrasonic Scan System

“…A "model" waveform is shown in figure 2. Described in terms of energy density (|ϕ(f,t)| 2 ) (rather than amplitude ϕ(f,t)), the exponential decaying portion of the waveform can be described by [2]:…”

“…• AU as a field of ultrasonic plate wave empirical study originated in the 1970s at NASA Glenn Research Center [1][2][3] and is most commonly applied with transducers placed in contact with the sample under test. However, the use of lasers for ultrasonic generation, and laser interferometry detection or air-coupled ultrasonic transducers for receiving the lamb waves (in this case leaky) has also been successfully employed [4,5].…”