NDE methods for polymer composite structures

Nondestructive methods of testing, inspecting, or evaluating a product utilize physical measurements that do not alter the condition or life of the product for its continued use. NDT and NDI are generally considered synonymous, with both being related to the use of measurement tools per specification and assessment against specified criteria. NDE and nondestructive characterization are terms intended to convey the use of nondestructive measurements for material condition, property, or state assessment, especially in a quantitative manner. For the purposes of the remainder of this chapter, the acronym NDT will be used to represent all these issues. 

Polymer composite structures used in aerospace applications require NDT at various levels depending on their designation as a primary or secondary structure. A primary structure is a structure where the failure could result in loss of the air vehicle or life and therefore usually requires 100% instrumented NDT. A secondary structure 

The two major categories of polymer composite used in aerospace are laminates and sandwich stmctures, which require some differences in NDT inspection methods. The inspection of choice at the time of manufacture may be different from the inspection of choice for in-service assessments. The form of the stmcture determines the types of features of concern and the NDT techniques that may be apphed to detect and measure them. Table 15.1 summarizes some general thoughts and considerations on NDT of polymer composite stmctures. American Society for Testing and Materials (ASTM) also provides guidance on NDT for polymer composites [12]. The primary concerns in laminates are voids and porosity, inclusions, delamination, the fiber-to-resin ratio, and wrinkles (wavy or out-of-plane ply). Ultrasound is the predominate method for composite laminate inspection. In sandwich structures, the core material-to-facesheet bond, core condition, and fluid ingress are the usual concerns. 

Laminate Hand la)oip Tape layup Fiber placement Resin transfer molding 

Fiber-to-resin ratio Inclusions Microcracks Delamination Wrinkles In service  

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