Significance and Use
This AE examination is useful to detect micro-damage generation, accumulation and growth of new or existing flaws. The examination is also used to detect significant existing damage from friction-based AE generated during loading or unloading of these regions. The damage mechanisms that can be detected include matrix cracking, fiber splitting, fiber breakage, fiber pull-out, debonding and delamination. During loading, unloading and load holding, damage that does not emit AE energy will not be detected.
When the detected signals from AE sources are sufficiently spaced in time so as not to be classified as continuous AE, this practice is useful to locate the region(s) of the 2-D test sample where these sources originated and the accumulation of these sources with changing load and/or time.
The probability of detection of the potential AE sources depends on the nature of the damage mechanisms, flaw characteristics and other aspects. For additional information see X1.4.
Concentrated damage in fiber/polymer composites can lead to premature failure of the composite item. Hence, the use of AE to detect and locate such damage is particularly important.
AE-detected flaws or damage concentrated in a certain region may be further characterized by other NDE techniques (for example, visual, ultrasonic, etc.) and may be repaired as appropriate. Repair procedure recommendations and the subsequent examination of the repair are outside the scope of this practice. For additional information see X1.5.
This practice does not address sandwich core, foam core or honeycomb core plate-like composites due to the fact that currently there is little in the way of published work on the subject resulting in a lack of a sufficient knowledge base.
Refer to Guide E2533 for additional information about types of defects detected by AE, general overview of AE as applied to polymer matrix composites, discussion of the Felicity ratio (FR) and Kaiser effect, advantages and limitations, AE of composite parts other than flat panels, and safety hazards.
Scope
1.1 This practice covers acoustic emission (AE) examination or monitoring of panel and plate-like composite structures made entirely of fiber/polymer composites.
1.2 The AE examination detects emission sources and locates the region(s) within the composite structure where the emission originated. When properly developed AE-based criteria for the composite item are in place, the AE data can be used for nondestructive examination (NDE), characterization of proof testing, documentation of quality control or for decisions relative to structural-test termination prior to completion of a planned test. Other NDE methods may be used to provide additional information about located damage regions. For additional information see Appendix X1.
1.3 This practice can be applied to aerospace composite panels and plate-like elements as a part of incoming inspection, during manufacturing, after assembly, continuously (during structural health monitoring) and at periodic intervals during the life of a structure.
1.4 This practice is meant for fiber orientations that include cross-plies, angle-ply laminates or two-dimensional woven fabrics. This practice also applies to 3-D reinforcement (for example, stitched, z-pinned) when the fiber content in the third direction is less than 5 % (based on the whole composite).
1.5 This practice is directed toward composite materials that typically contain continuous high modulus greater than 20 GPa [3 Msi] fibers.
1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
