Monitoring Damage Initiation And Growth In Composite Structures By Acoustic Emission Method
Abstract
In this dissertation, acoustic emission technique is examined as candidate for monitoring the integrity of polymer matrix structural members. Acoustic emission technique has so far been largely limited to laboratory tests and field applications have been mostly limited to qualification tests of aerospace structures. The lack of quantitative indications of damage in composite structural members associated with the complex nature of damage in these materials has been a limiting factor. Generally, a number of failure modes operate simultaneously at a site of damage, and each of these failure modes generates a different type of acoustic emission signal. In addition, issues including anisotropic wave propagation including variation velocities and attenuation in composites leads to difficulties in damage location and assessment of damage magnitude. Further, extraneous noise that is invariably present when the structure is experiencing cyclic loading, increases the uncertainty in interpreting acoustic emission data. The goal of the present work is to address a few of these issues individually. They include (a) experimental measurement of attenuation of fundamental Lamb wave modes and frequency components of acoustic emission signal in representative composite laminates, (b) experimental characterization of friction related acoustic emission signals between two metallic surfaces, (c) monitoring and characterization of acoustic emission signal from delamination growth in coupon specimens and (d) numerical modeling of acoustic emission signals generated by different failure modes in a cross-ply laminate, including mode I and delaminations and matrix cracks. In this report, results and findings from each of the above works, both numerical and experimental are included.