Non-destructive testing

Like all non-destructive testing techniques, ultrasonic testing can be used to characterize defects in a structure, without damaging its integrity, and to assess the acceptability of the parts produced. This method can be used at various stages in the development of the structure in question (manufacturing, commissioning, repair). It does not quantify a defect, but requires comparison with a standard. In addition, detection limits and probabilities vary according to the device, material, surface to be inspected and operator.

Non-destructive testing methods are implemented within a quality system that guarantees process reliability in a production environment.

An efficient quality system, meeting the requirements of ISO 9001, is nowadays considered a prerequisite.

Control systems must also meet the requirements of "flexibility", "just-in-time", and rapid tool change SMED (Single Minute Exchange of Die), in line with the "just-in-time" policy.

The purpose of this article is to describe two ultrasonic techniques widely used, particularly in aeronautics, for composite materials:

• the transmission method, which is used to detect internal anomalies whose size, shape or location do not allow inspection by reflection. It is used for highly absorbent materials, especially sandwich materials and large-area, single-block parts (monoliths);

• the reflection method, which applies to the detection and dimensioning of defects specific to the material of carbon, glass and aramid fiber composites (Kevlar, Twaron), and enables manual verification of defects detected by the transmission method.