D. D. Dann

Development prospects for nondestructive testing of heterogeneous nonmetallic materials by the parameters of electrical response to a shock action

Theoretical and experimental research has been conducted into the mechanisms of generation of electric fields under elastic shock excitation of heterogeneous nonmetallic materials that contain two types of mechanoelectric transductions, viz., double electrical layers at interphase boundaries and piezoelectric inclusions. Using the example of electrical responses from samples of heavy- and light-weight concretes and based on numerical modeling results, prospects are shown for using this phenomenon in nondestructive testing of heterogeneous nonmetallic materials that do not contain piezoelectric inclusions, e.g., layered and reinforced ones.

Effect of cyclic freezing–thawing on the parameters of electric response to elastic shock excitation of reinforced concrete

General and distinctive features have been established for the effect that cyclic freezing–thawing has on the parameters of electric response to elastic shock excitation in steel and glass-fiber reinforced concretes. Based on frequency-time and autocorrelation analyses, criteria are suggested for assessing the deterioration degree of reinforced concrete under alternating-sign temperature action.

Developing an integrated technique to evaluate crack formation in reinforced concrete under uniaxial compression

Regularities of changes in the parameters of acoustic and electromagnetic emission and of forced electric response from reinforced concrete under uniaxial compression have been studied. It has been established that the main diagnostic criteria of the onset of crack formation are the emergence of high-amplitude signals of acoustic and electromagnetic emission; considerable changes in the spectral composition of the electric signal; a decrease in the maximum coefficient of correlation between the spectra of signals registered at different stages of loading as compared with the spectrum of the signal prior to loading; and hopping shift of the frequency at which the maximum correlation coefficient is observed. On-line monitoring and periodic inspection can be used to assess the onset of crack-formation processes.

Effect of humidity on the parameters of mechanoelectrical transformations in concretes

An increase in the humidity of a cement solution from 0 to 8% is found to result in an exponential decrease in the principal spectral maximum of its electric response to an impact excitation according to the change in the electrical resistivity. A physical model is proposed for the mechanoelectrical transformations occurring in a wet heterogeneous material, and this model agrees well with the experimental data.

A Method for Evaluating Failure in Reinforced Concrete under Bending Based on the Response of Electrical Parameters to an Impact Action

The regularities of changes in the properties of the electrical response of reinforced concrete to an impact action in a four-point bending flexural test and the influence of the rebar cage configuration on the processes of failure in reinforced beams and on electrical response parameters have been studied. Criteria have been proposed for determining the stages of failure in reinforced concrete beams, based on electrical response parameters. The nucleation and growth of macrocracks in the tensile zones of reinforced beams is accompanied by a drop in the maximum cross-correlation coefficient of signal spectra at the current and previous loading levels to 0.45–0.6. An increase in the energy attenuation coefficient of electrical responses in a reinforced beam by 1.5–2.5 times can serve as a precursor to its impending catastrophic breakdown.

Detecting degradation in reinforced concrete subjected to uniaxial compression, using the parameters of electric response to mechanical impact

ABSTRACT The effect of uniaxial compression on the development of damage in reinforced concrete has been studied, using the parameters of the electric response to elastic impact. During the quasistatic loading of the samples at a constant speed, a weak impact is produced on the lateral surface of the sample during a specified period of time, and an electrical response to this impact is measured. Consistent patterns in the changes of the parameters of the electric response with various loads have been identified. Computer simulation of the parameters of elastic waves in reinforced concrete subjected to mechanical impact has also been used. Based on the simulation, the parameters of the electric response have been calculated using the mechanoelectrical transduction model. Good consistency of theoretical and experimental signals confirms the relationship between the electric response and the interaction of elastic waves and fractures in reinforced concrete caused by uniaxial compression. Based on the electric response data corroborated with the computational results, diagnostic criteria have been obtained which make it possible to predict failure of reinforced concrete structure long before it occurs.

The Relationship Between the Parameters of the Electric and the Acoustic Signal with the Destruction of Concrete Under Cyclic Freeze-Thaw

The paper presents the research results of the effect of formation crack process on the parameters of the electric and acoustic response to impact excitation. The physical basis of mechanoelectric transformations is described. It was found that with increasing number of freeze-thaw cycles observed increase of the attenuation coefficient of energy of the electric and acoustic response by a linear relationship. Differences in the dynamics of change of attenuation coefficient of energy of the electric and acoustic response associated with differences in formation and registration of electric and acoustic response.

Relationship between the parameters of an electrical response to elastic impact in concrete with a coarse filler

The influence of the filler grain size on the parameters of an electrical response in elastic-impact-excited concrete filled with a coarse filler is investigated. It is shown that as the grain size grows further, the total spectral energy of electrical signals and its dispersion over many measurements increase, whereas the decay ratio of the electrical response energy drops.

Development of a method for testing the concentration of air voids in concrete based on the parameters of the electrical response to impact

The correlation between the concentration of defects such as artificial air voids in concrete and the parameters of the electrical response to impact was examined. It was shown that the frequency shift that corresponds to the maximum cross-correlation coefficient between the spectra of electrical responses of defective and non-defective samples may be used as a diagnostic criterion for determining the concentration of air voids in concrete.

A scanner for the detection of defective areas in large concrete products

A device for the impact excitation of concrete products and the recording of electrical responses is described. The device consists of a remote probe, a portable power supply, input/output board, and a laptop computer. A differential electrical sensor that consists of receiving measuring and compensating electrodes is used for the measurements. This makes it possible to significantly improve the signal/noise ratio. The probe is equipped with long wires that make it possible to examine different parts of extended concrete products. An example of the scanning of the surface of a concrete product and defect detection is given.