Non-destructive testing methods designed to detect material defects and evidence of deterioration of parts, particularly discontinuities of the material, its structure, its structure, deviations of physico-chemical properties.
Depending on the physical processes, the methods are divided into:
acoustic;
capillary;
magnetic;
optical;
radiation;
radio wave;
heat;
electric;
electromagnetic.
The most widespread in the production and repair of aviation engines found the following methods:
of acoustic – ultrasonic (pulse echo method);
from the capillary - color, fluorescent and luminescent color;
from magnetic - magnetic particle using magnetic suspension or air-suspension of the magnetic powder;
optical - optical-vizualni with the use of loupes and endoscope;
radiation - x-ray and radiographic;
electromagnetic method of the main harmonic of eddy currents (eddy current), and in recent years the method of pulsed magnetic fields.
Universal control methods exists, each of them has its advantages and disadvantages and, therefore, characteristic of the area of effective application. Therefore, in the manufacturing process parts can be monitored repeatedly at various stages of the process and using different methods. For example, in the manufacture of the discs of the compressor rotor titanium alloy billet is tested more than ten times at a metallurgical plant control ingot, the washer and the stamped workpiece (output control), the engine company - the original billet (input control), pre-machined workpiece and the finished disk. In this case, using ultrasonic, radiographic, eddy current and fluorescent methods.
The technological capabilities of the control methods are mainly defined by their ability to identify surface, subsurface and internal defects.
Subsurface defects are detected in virtually all methods except the optical and the capillary. The internal defects detected by ultrasonic and radiation methods, and only for ultrasonic inspection ample access to the workpiece on the one hand, radiation requires bilateral access for placement of radiation source and cassette.
In addition methods are characterized by sensitivity, that is, the size of detectable defect.