Marta Korenska

Nonlinear Ultrasonic Spectroscopy Used to Detection of Ceramic Structure Damage

The paper deals with nonlinear interaction between elastic wave and structural defects in ceramic samples. The nonlinear elastic properties of the structure were probed by using the analysis of response frequency spectrum generated from a continuous wave transmission through the ceramic sample. In the first stage of the experiment, we have examined whether or not the inhomogeneous ceramic material gives rise to parasitic components being able to generate non‐linear phenomena in the signal transmission. In the second stage were measured the specimens with structure damaged integrity and a correlation between the response frequency spectrum and the specimen structure deterioration was looked for.

STUDY OF METAL TIMBER JOIN BY ACOUSTIC EMISSION METHOD

Actual behaviour and general load carrying capacity of timber structures depends primarily on the load bearing capacity of joints. The present paper deals with slotted-plate steel-to-timber joints. In addition, innovative measuring methods were used to determine the strength of the metal-wood-metal structure. One of them was the acoustic emission method, which belongs to the group of non-destructive testing methods. It is to be noted that the acoustic emission method responds to the defect generation much sooner than the visual or any other method. The time-frequency analysis can play a central role in the signal analysis.

Acoustic emission method as a tool of partial discharges indication

The present paper deals with a method of tracking the partial discharges using the acoustic emission method. The quantity under study was the overshoot counting rate in acoustic emission signals. The subject of the experiment was a high-voltage generator rod, which had been provided with Relanex insulation. Acoustic signals, which were generated in the Relanex insulation layer, were picked up by wide-band sensors. Measurement results proved that electric discharges in a cavity are accompanied by the generation of mechanical oscillations, which in turn act as a source of standing waves in the cavity and standing waves in the rod and the insulator. The frequency spectrum therefore extends from the rod fundamental oscillation mode (i.e., 3 kHz) up to the cavity natural frequencies (in the order of several MHz).

Detection of the reinforcement corrosion in pre-stressed concrete girders

Pre-stressed reinforcement is a basic element of the structural stability in a great amount of concrete structures. The corrosion of reinforcement is a major cause of a failure of such structures. The paper deals with the usage of the acoustic emission method for testing pre-stressed concrete girders from corrosive damage point of view. The experimental test investigated acoustic emission method to evaluate deterioration of pre-stressed reinforced concrete girders during flexural tests under loadings. The result provide that acoustic emission was very sensitive to detect the initiation of microcracks generated near the interface between the pre-stressed reinforcement and concrete.

Structural Integrity of Stone Blocks From Charles Bridge in Prague

ABSTRACT The Charles Bridge is the oldest, still-standing gothic bridge that crosses the Vltava River in Prague and up to now has belonged among the most sought-after historical monuments in the Czech Republic. The bridge has been repeatedly damaged due to floods and has been repaired several times. In the reconstructions, damaged sandstone blocks were substituted in facing. This experimental study focused on nonlinear ultrasonic spectroscopy for testing stone blocks that were extracted from the historical bridge structure. The objective of these experiments was verifying whether the methods can be applied to evaluating the internal structure of blocks, which are built-in in the structure in situ. Intact-structure blocks, blocks that had been repaired in the past, and damaged-structure blocks were measured. Two methods of nonlinear ultrasonic spectroscopy were applied—the method with single harmonic ultrasonic signal and with two harmonic ultrasonic signals. Measurement results of both applied methods proved resulting parameters correlation with block structure integrity quality.

Experimental study of the nonlinear effects generated in a concrete structure with damaged integrity

The paper deals with nonlinear interaction between elastic waves and structural defects in concrete specimens. Three groups of concrete specimens which differed from each other in the structure quality as a consequence of different ripening conditions were performed. Nonstandard concrete ripening conditions resulted in the development of microcracks in the specimen structure. The nonlinear elastic properties of the structure were tested by using the analysis of response frequency spectrum generated from a continuous wave transmission through the concrete specimens. It was tested whether or not the microcracks in the structure gave rise to parasitic components which were able to generate nonlinear phenomena in the signal transmission. A single harmonic ultrasonic signal method was applied to the specimens and evaluation, especially of the second and third harmonic components as indicators of nonlinearity was carried out. Verification measurements which have been carried out in parallel with the ultrasonic ones, give evidence of the specimen structure integrity deteriorations and confirm the correlation between the nonlinear effects on the transfer characteristics with the existence of defects in the specimen internal structure.