The most frequent flaws of ferromagnetic components are surface or open flaws. This flaw type appears either during fabrication due to flaws in the component production process, or during their lifecycle. Indeed, when a structure is influenced by external efforts, it endures microstructural modifications which can lead to deformations and cracks. This evolution, often called fatigue, leads to a degradation of the mechanical properties of the components which can lead to the breaking down of the structure.
In this section, the detection mechanism of open flaws in ferromagnetic materials will be detailed.
Figure 4.19(a) shows a typical installation proposed for the control of components with a circular or rectangular cross-section using the thermo-inductive technique. It consists of the following elements:
– an induction generator with a variable working frequency;
– an inductor consisting of two main coils with four turns, each designed to create an axial magnetic field.
The mean coil diameter is 200 mm, the height of each turn is 10 mm, and the distance between the two main coils is 110 cm.
– an infrared camera to record the inspected component’s surface temperatures;
– a cylindrical XC38 stainless steel component with dimensions indicated in Figure 4.19(b). A surface flaw of depth 2.5 mm, length 20 mm, and width 0.1 mm was inserted by a chemical attack.
The XC38 stainless ...