Non Destructive Testing Laboratory

Responsible person: Dr Dariusz Płoch

 

Non Destructive Testing Laboratory

Due to the growing demand for technical design evaluation without the need to destroy them, the field of non-destructive testing is developing extensively.

 Traditionally applied research methods: penetration, ultrasonic and radiographic are developed in specialized techniques such as ultrasonic imaging with mosaic heads or new methods of defect detection such as thermographic method.

Nondestructive controls are used for safety reasons

Aerial and economic consequences of discontinuing construction from use. Checks are carried out at both the manufacturing and the operation stages. The wide range of materials used in aviation construction is also important for the selection of methods used.

The equipment of the laboratory is equipped with modern research equipment such as:

    Thermal imaging camera for thermographic testing
    
Ultrasonic flaw detector

FLIR SC 7000 high resolution thermal imaging camera

 

 

Characteristics of basic non-destructive testing methods

 

1.1 penetration method

Penetration method is one of the oldest non-destructive testing methods. Uses the capillarity phenomenon of penetrating some liquids into narrow vessels called capillaries, into which penetrates a special liquid called "penetrant". Penetration tests are most often used for testing of metallic materials such as steel, cast iron, copper, brass, bronze, aluminum. It is also possible to use them for other materials (eg glass, ceramics), provided that they are neutral to the test substances and are not porous. [1]

Penetrating reagents generally contain penetrant, cleanser and developer.

Penetrant is the main material in penetration studies, characterized by very low surface tension and high penetration into slits and other surface defects. It is a mixture of organic solvents and pigments

color.

Penetration may be given by spraying, dipping, pouring, brushing. The penetration time usually takes about 5 minutes.

In exceptional cases up to 30 minutes. It is important that the surface is completely dewy and that the penetrating agent does not dry during penetration. Depending on the research task, color or fluorescent penetrating agents are used.

The remover is a liquid used to remove excess penetrant from the surface to be tested, the remover may be, for example, water.

Rys. 1. Diagram of the Penetration Testing [11]

The developer is a highly absorbent penetrant substance, is applied after washing off excess penetrant, usually giving a strong contrast (red penetrant - white developer):

    Developers have the form of dry powders, aqueous suspensions, solvent solutions.
    
Purified surface of the test material
    
Saturation penetration
    
A fragment of the examined material after removal from the excess penetrant
    
Detected discontinuities created after application of the developer

Advantages and disadvantages of the penetration method

The advantages of penetration testing include quick and easy testing, not very qualified test takers, the ability to test different materials and products of any shape and size, the ability to detect minor defects, ease of use in workshop and field conditions as well as low test costs, The ability to automate the testing process and the significant effectiveness of fault detection.

The disadvantages of penetration methods include, but are not limited to, the need for preliminary cleaning and degreasing of the test surface and cleaning of the surface after the test. In addition, using the above methods, only open defects can be detected. The disadvantage of penetration methods is also the impact of the treatment on the effectiveness of the control, the effect of the object's temperature on the properties of the formulation, the aging of the formulation and the high toxicity of the test preparations.

 

1.2 radiographic method

Radiological tests consist of:

     Illuminate the subjects with ionizing radiation, most often X-rays (X), obtained from X-ray tubes or γ radiation, obtained from artificial isotopic sources
     
Record shadow images of discontinuities

The radiograms show two-dimensional shadows of three-dimensional discontinuities that represent the shape of the discontinuity and their dimension (length, width) in a plane perpendicular to the direction of propagation. The difference in darkness of the radiographs at the discontinuity and non-discontinuous space contains discontinuity information in a plane parallel to the direction of propagation.

 

Rys. 2. Pęcherze gazowe znajdujące się w małej objętości spoiny. [6]

 

Image registration is achieved by radiation attenuation, for places in discontinuous objects, as well as discontinuous locations. Material discontinuities are usually filled with air or material with a lower density than the material of the object. During X-rays, there are places where radiation is weakened, which in the photos gives a characteristic darker or brighter coloration in X-rays. Images of tungsten inclusions (which have a higher density than steel or aluminum) and places with objects larger than the remaining thickness, such as leaks in welded joints, are lighter than background or of lesser thickness. This makes it possible to distinguish the non-conformities of welded joints based on their radiological images.

By radiographic method, we detect internal defects in the joints of: gas blister, inclusions, glue, no melting, cracks, surface defects and shape.

 

1.3 Thermographic method

Thermography and thermography terms include remote sensing methods
And non-contact assessment of the temperature distribution on the surface of the examined body. These methods are based on the observation and recording of the distribution of infrared radiation sent by each body whose temperature is higher than absolute zero and converts this radiation to visible light.

Thermography is therefore the recording by a special camera of the infrared portion of the spectrum of radiation emitted by the body and then processing it into a color temperature map.

The thermovision system makes it possible to measure the temperature at a distance and across the entire surface.

Due to the temperature of the tested object and the need to provide heat from the outside (thermal stimulation), the thermography is distinguished:

     Passive - where we observe the radiation emitted by the examined object, not occupied by the external source of heat radiation. It is possible to use this method only to observe objects with a temperature that differs from the environment to a large extent, allowing for the execution of tests and subsequent analysis of the radiation from the examined object,
     
Active - the essence of which is to study the thermal response of the material as a function of time to stimulate the external heat pulse and this response is recorded using a thermograph.

 

IR                                

Shoulders cooled after time t = 4 min. With cooling by blow to the shoulders.

Depending on the mode of stimulation, several types of active thermography are distinguished,
Namely, thermography:

 Pulsed thermography considered to be a relatively simple type of active thermography. It consists in determining and analyzing the temperature distribution on the test surface at the time of its cooling after a uniform heating of the heat impulse.
     
Lock-in thermography with modulated heating using the theory of thermal waves. Thermal waves are generated by heating the examined area with a heat source whose intensity changes sine. Using an infrared thermograph

The oscillating temperature field is determined on the surface of the object under steady state. The time sequence of the temperature fields allows to reproduce the form of the thermal wave on the surface to be examined, which makes it possible to determine the phase shift of the wave relative to the oscillation of the heat source. A phase shifting map is obtained. The phase shift, at the set frequency, is a function of the diffusivity of the defect in the surface layer of the material.

       - pulsed phase thermography combines the advantages of pulse and modulating thermography. As in the method of impulse thermography, the surface of the examined object is stimulated by a heat pulse and by means of an infrared thermograph registers

There is a temperature distribution on the test surface when it cools down.

 

1.4 Ultrasonic Method

Polski