Acoustic Emission Signals in Thin Plates Produced by Impact Damage

Acoustic emission (AE) signals created by impact sources in thin aluminum and graphite/epoxy composite plates were analyzed. Two different impact velocity regimes were studied. Low-velocity (less than 0.21 km/s) impacts were created with an airgun firing spherical steel projectiles (4.5 mm diameter). High-velocity (1.8 to 7 km/s) impacts were generated with a two-stage light-gas gun firing small cylindrical nylon projectiles (1.5 mm diameter). Both the impact velocity and impact angle were varied. The impacts did not penetrate the aluminum plates at either low or high velocities. For high-velocity impacts in composites, there were both impacts that fully penetrated the plate as well as impacts that did not. All impacts generated very large amplitude AE signals (1-5 V at the sensor), which propagated as plate (extensional and/or flexural) modes. In the low-velocity impact studies, the signal was dominated by a large flexural mode with only a small extensional mode component detected. As the impact velocity was increased within the low velocity regime, the overall amplitudes of both the extensional and flexural modes increased. In addition, a relative increase in the amplitude of high-frequency components of the flexural mode was also observed. Signals caused by high-velocity impacts that did not penetrate the plate contained both a large extensional and flexural mode component of comparable amplitudes. The signals also contained components of much higher frequency and were easily differentiated from those caused by low-velocity impacts. An interesting phenomenon was observed in that the large flexural mode component, seen in every other case, was absent from the signal when the impact particle fully penetrated through the composite plates.

[1]  H Prosser William,et al.  AE Source Orientation by Plate Wave Analysis , 1994 .

[2]  S. Lih,et al.  Wave Field Produced in a Composite Laminate by a Concentrated Surface Force , 1992 .

[3]  A. H. Shah,et al.  Transient response of a laminated composite plate , 1992 .

[4]  M. R. Karim.  Impact response of a unidirectional composite laminate , 1991 .

[5]  M. Gorman.  Plate wave acoustic emission , 1991 .

[6]  Boeing Helicopters,et al.  Impact Detection in Composite Skin Panels Using Piezoelectric Sensors , 1991 .

[7]  H Prosser William,et al.  The Propagation Characteristics of the Plate Modes of Acoustic Emission Waves in Thin Aluminum Plates and Thin Graphite/Epoxy Composite Plates and Tubes , 1991 .

[8]  Stephen A. Schwartz,et al.  Space program: Space debris a potential threat to Space Station and shuttle , 1990 .

[9]  Martin N. Gibbins,et al.  Space station integrated wall design and penetration damage control , 1987 .

[10]  L. H. Pearson,et al.  Acoustic-Emission Monitoring of Composite Damage Occurring Under Static and Impact Loading , 1985 .

[11]  D. O. Thompson,et al.  Review of Progress in Quantitative Nondestructive Evaluation , 1985 .

[12]  Nobuo Takeda,et al.  Wave Propagation Experiments On Ballistically Impacted Composite Laminates , 1981 .

[13]  C. T. Sun,et al.  Exact and Approximate Analyses of Transient Wave Propagation in an Anisotropic Plate , 1974 .

[14]  Francis C. Moon,et al.  Wave Surfaces Due to Impact on Anisotropic Plates , 1972 .

[15]  B. P. Konstantinov,et al.  Micrometeors in Circumterrestrial Space Observed by "Kosmos-163" , 1969 .

[16]  O. E. Berg,et al.  REVIEW OF DIRECT MEASUREMENTS OF INTERPLANETARY DUST FROM SATELLITES AND PROBES , 1963 .

[17]  W. D. Crozier,et al.  High‐Velocity, Light‐Gas Gun , 1957 .