Nondestructive testing of damage in aerospace composites

Nondestructive testing (NDT), nondestructive inspection (NDI), and nondestructive evaluation (NDE) (collectively, NDT/I/E) are concerned with the techniques and measurements that provide data on the condition of the materials and stmcmres at the time of manufacturing and in-service. The NDT/I/E methods are, generally speaking, discrete inspections performed during manufacmre and at specified intervals or events during the service of a stmcture. 

This chapter starts with a brief overview of composite damage situations. This is followed by a description of the major NDT methods applied to composite structures during manufacturing and in-service inspection. 

Polymer Composites in the Aerospace Industry. http //dx.doi.oi l0.1016/B978-0-85709-523-7.00015-3 Copyright 2015 Elsevier Ltd. All rights reserved. 

Tension, compression, and shear are the three fundamental modes in which a composite lamina may fail. As the composite material is made up of multiple laminae (layers and plies) of various orientations, the stresses in the lamina s principal directions vary from lamina to lamina. As the load is increased, so do the various stresses in the laminae, and failure values may be attained in a certain lamina in a certain principal direction without the overall laminate experiencing actual failure in other words, the failure of the composite laminate is a progressive phenomenon. This progressive damage evolution is subcritical for a while, but eventually leads to ultimate failure of the composite laminate. 

Worst-case impact damage is defined as the damage caused by an impact event (e.g., a 1-in hemispherical impactor) at the lesser of the following two energy levels (1) 100 ft-lb, or (2) enough energy to cause a visible dent (0.1-in deep). A schematic of the various damage mechanics that take place in a laminated 

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