Nondestructive Evaluation of Composite Material Using Ultrasound
Fiber-reinforced composites are finding an increasing use in the aerospace industry. Initially the FRP components constituted only the noncritical components of the structure. Now the composites are being used in the primary load bearing members. After undergoing a certain amount of usage, the mechanical, thermal and environmental loading produces a complex damage state which includes transverse cracks, longitudinal splits, delaminations, debonding, etc. Almost all the NDT techniques are geared towards the estimation of the extent of damage to the structure. From these results it is expected that the damage modelers will be able to estimate the residual stiffness and residual strength and life of the structure. We have used ultrasonic waves to study the changes in stiffness of the structure as the damage progresses. This work will help the damage modelers in furthering their analysis.
The ultrasonic waves passing through a composite specimen interact with the various defects, and in turn, these defects affect the basic ultrasonic parameters; wavespeed and attenuation. It is well known that wavespeed is directly related to the stiffness, and attenuation is a measure of the damping characteristics of the material. A very important stiffness component is the in-plane stiffness of the plate. Hence, we propagate the waves in the plane of the plate to measure the in-plane stiffness. The mode of propagation is called the Lamb wave or Plate wave mode. The plate is immersed in a fluid and the Lamb waves leaking into the fluid are called the leaky Lamb waves. These leaky waves have been used to determine the wavespeed and attenuation of the Lamb waves traveling in the plate.
Damage is gradually introduced in the composite plate. In the work presented here, we have limited the mode of damage to transverse cracks only. The changes in the wavespeed and attenuation are measured as a function of damage. We present here some results from the tests of cross-ply and angleply graphite/ epoxy laminates. The reduction in the in-plane stiffness and an increase in the attenuation is observed as the number of transverse cracks increase.
KeywordsDispersion Curve Ultrasonic Wave Damage Modeler Lamb Wave Acoustic Parameter
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- 1.K. L. Reifsnider, E. G. Henneke, W. W. Stinchcomb, and J. C. Duke, Damage Mechanics and NDE of Composite Laminates, in: “Mechanics of Composite Materials,” Z. Hashin and C. T. Herakovich, eds. Pergamon Press. New York (1983).Google Scholar
- 2.V. Dayal and V. K. Kinra, Ultrasonic NDE of Composite Transverse Cracking, in: “Proceedings of SEM Fall Conference,” Society for Experimental Mechanics (1986).Google Scholar
- 4.V. Dayal and V. K. Kinra, “Lamb Waves in Anisotropic Plates Immersed in a Fluid--An Exact Numerical Solution,” (unpublished results).Google Scholar