Monika Manychova

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.

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).

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.

Monitoring of the Damage in Stone Blocks by Means of Non-Destructive Methods

This paper deals with the damage assessment in stone blocks dismantled from a historic bridge construction. Nonlinear ultrasonic spectroscopy and impact echo methods were used for evaluating the stone block integrity structure. Harmonic analysis of the sample response on well defined ultrasonic excitation was used in the case of nonlinear ultrasonic method application. The amplitude dependent spectral changes of the probing signals were measured in the damaged blocks. Measurement results showed that the analysis of amplitude dependent spectral changes is a promising method for the damage assessment in structures. The Impact-Echo method is a technique for detecting defects in material structure such as stone blocks. It is based on monitoring the propagation of elastic waves from a short-duration mechanical impact. The aim of this paper is to provide an overview of the technique and to discuss the important parameters involved in this type of testing. The impact echo method is used to generate low-frequency stress waves from 500 Hz to 50 kHz that propagate into the structure and are reflected by defects and external surfaces.

An Initial Investigation on the Potential Applicability of Non-Destructive Methods to Assessing Joint Condition in Prefabricated Structures

Prefabricated structures have brought quite a new quality into the design of building construction method, which in turn required deeper theoretical knowledge, replacing empirical approaches by theory, replacing idealized and often simplified models of structure behaviour by accurate material physical models and load models. High rigidity of prefabricated concrete structures and the resulting stress states, which are mainly due to the volume change effects (temperature, humidity), effects of the foundation base shape variations etc., are among the most frequent causes of failures, particularly of joints of building elements featuring insufficient yield and bearing capacity. Investigation of all prefabricated building types shows progressing joint armature corrosion, considerable impairment of welds, which should secure the positional reliability of façade slabs.The paper presents some results of our experimental study of the application potential of the impact-echo method to the non-destructive assessment of the present joint condition in prefabricated structures.

Determination of Capillary Conductivity Coefficient by Using Electromagnetic Microwave Radiation

Moisture in building structures affects negatively construction material physical properties, particularly thermally insulation properties. The porous structure of most building materials distinguishes by the ability to absorb water in liquid and gaseous state into its internal cavities, to fill the accumulative space of pores, to transport moisture and to re-transmit to the surroundings. The moisture characteristics of building materials are the base for evaluation of building structure thermal insulation properties. The moisture spreading via capillary conduction is the most significant material parameter of a moisture appraisal. However, it is necessary to incorporate also spreading the liquid phase into the moisture appraisal for certain structure material compositions. The article deals with determination of capillary conductivity coefficient by using electromagnetic microwave radiation. The radiation passed through a wet sample is detected and then the value of capillary conductivity coefficient is determined. The coefficient of capillary conductivity is property dependent on several physical parameters, but primarily on the moisture.