No 7 (2023)

With samples made of carbon fiber, static tests were carried out to failure. Defects were controlled using acoustic emission and tensometry. Four wire strain gauges were glued to each sample in the area of the hole, and four piezoelectric gauges were installed along its edges, forming the working zone of control. Registration of signals associated with the destruction of the composite material of the samples, and their location was carried out by the acoustic emission system. In the process of testing, the tensometric system recorded loads and deformations, at which the process of destruction of carbon plastics began. The types of destruction were determined during the analysis of micro-glyphs, which were made from location zones. The main informative parameters (amplitude, dominant frequency, MARSE, structural coefficient) of acoustic emission signals were associated with the type of failure of carbon fiber reinforced plastics.

Six types of infrared imagers characterized by different technical performance (arrays from 160×120 to 640×512 and temperature sensitivity from 25 до 110 mK) and cost were used in active thermal nondestructive testing of delaminations with size from от 5×5 to 45×45 mm located at the depth of 3,1 mm in a reference sample made of polymethylmetacrilat. The efficiency of TNDT was evaluated by 9 thermographers to demonstrate that reasonable inspection results can be achieved by using IR imagers and modules of an economic cost segment.

Laser shearing interferometry is one of the new methods of non-destructive testing, which is based on the interference of monochromatic waves reflected from the surface of the sample. This method can evaluate the entire surface of the sample with high accuracy and speed, by directly measuring the out-of-plane displacement gradient. In this paper, the possibility of detecting subsurface cracks with various lengths and angles in composite samples has been investigated using the shearing method and thermal stimulation system. To this aim, artificial and controlled cracks of different lengths and angles were created in the manufactured composites. After validating the performance of the shearing arrangement, two radiation heat sources were used to apply the load on the samples. The effect of loading size variables, shearing size and direction, crack length, and their angle on the quality of the results was investigated. The results show that the change in loading size plays a more important role than the change in shearing size in correct crack detection. To achieve the best results in crack detection on the selected samples, optimal loading in thermal mode equal to 12 and 15 seconds from the front of the sample was obtained. Moreover, the optimal size of the shearing in the examined composite samples was estimated to be about 10% of the width of the image recorded by the camera. Using the optimized values, all subsurface cracks were identified.

The paper considers the factor of temperature influence on the sensitivity of ultrasonic testing and the detection of cracks in rails. Research have shown that the sensitivity of control and the detectability of defects significantly depend on the temperature of the test object and the transducer. The results of the experiments should be taken into account in order to increase the reliability of detection of real fatigue cracks.

The analysis of the influence of the surface roughness of the electrically conductive base and partial discharges on the process of testing dielectric coatings by the electrospark method is given. The simulation results and the obtained dependencies made it possible to formulate proposals regarding the operating modes of the equipment and the principles of fixing the discharge current, which reduce their influence on the reliability of the control.