Lubos Pazdera

Application of acoustic emission method in contact damage identification

The contribution summarises the experimental experience of authors with acoustic emission method application in the area of improved bearing materials contact damage stages identification on testing stations Axmat and R-mat types. The paper is focused also on the first experimental results received from measurements on real axial bearings. These results proved the acoustic emission (AE) technique enables reliable recognition of running-in period, stabilised run and exact definition of origin stage of material surface damaging, leading to the pitting. It is proposed that the direction of AE analysers utilisation not only in research area, but the AE technique may be successfully used even in industrial practice. Method of acoustic emission may offer another possibility of deepening of diagnostics of real actual state of bearing; it is, without doubt, one of new perspective areas of automated diagnostics.

Application acoustic emission method during concrete frost resistance

Frost resistance is one of the most frequent characteristics of concrete. It is a very complex subject and the test methods themselves are still in development and the international consensus on methodology is still sought, too. The determination concrete frost resistance takes several weeks, months or even more than a year. However micro-structural changes as micro-cracks have not been described sufficiently. Acoustic Emission Method as unusual Non-Destructive Methods can help to monitor structural changes during common frost resistance measuring. Note the Acoustic Emission Method detects only active “defects” into monitored structure. Thus when e.g. crack grows some acoustic waves spread from crack place, i. e. from acoustic emission source. The method does not detect geometric discontinuities and “passive” defects. Selected Non-Destructive Methods as Ultrasound, Non-Linear Ultrasonic Spectroscopy, Impact Echo etc. are used to confirm micro-structural changes. The article describes the first experiment with its imperfections, difficulties and possibilities.

1/f noise in metallic thin films

Studies of 1/fa noise in vast ensembles of thin film resistors are described. The distribution of the exponent a in the spectral density power law is found to be normal, the mean value being near unity and depending on the sample preparation technology. The scattering range of the values of a is typical of the resistor manufacturers. The noise voltage spectral density distribution is shown to depend on the frequency, being close to normal. The number of fluctuators is shown to be much less than the number of free electrons in the specimen.

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 in Protected and Non-Protected Concrete During the First 24 Hours

Concrete is a composite construction material frequently used in civil engineering. We know that concrete is as a man – when concrete is made it is as a baby, then it ages and its properties change in accordance to its baby life. That means it is better to monitor and change its properties when it is young as soon as possible. However, using the methods immediately after concrete birth (making the mixture) is difficult. Article describes monitoring concrete structure during the first 24 hours from their making. Acoustic Emission Method and the measurement temperature were used for monitoring both samples.

Acoustic Emission Monitoring during Static Modulus Elasticity Test of Concrete Specimen

Acoustic emission method is often used to detect a failure at a very early stage of damage long before a structure completely fails. The paper presents experiment focused on analysing acoustic emission signals captured during commonly used static modulus elasticity test of specimens of concrete. Quantitative acoustic emission techniques were used to measure micro fracture properties. For three different concrete mixtures typical acoustic emission patterns were identified in the acoustic emission records to further describe the under-the-stress behaviour and failure development. Although we are able to predict failure loads and damage patterns to some extent, we still do not have a good understanding of the relationships between micro structural phenomena and the corresponding effects on macroscopic behaviour. It logically follows that if we have a better understanding of the relationships between micro structural events and macroscopic behaviour, we will be in a better position to formulate predictive models for large-scale structural performance and reliability. An understanding of microstructureperformance relationships is the key to true understanding of material behaviours. Since we know that material microstructure influences its properties, and that cement-based materials of different microstructure have different failure properties and then the variations in micro fracture phenomena must be manifested in the acoustic emission response of the different specimens.

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.

Nondestructive Testing of Advanced Concrete Structure during Lifetime

The paper reports on measurements and analysis of the measurements during hardening and drying of specimens using selected acoustic nondestructive testing techniques. An integrated approach was created for better understanding of the relations between the lifetime cycle and the development of the mechanical properties of concrete. Acoustic emission, impact echo, and ultrasonic techniques were applied simultaneously to the same mixtures. These techniques and results are presented on alkali-activated slag mortars. The acoustic emission method detects transient elastic waves within the material, caused by the release of cumulated stress energy, which can be mechanical, thermal, or chemical. Hence, the cause is a phenomenon which releases elastic energy into the material, which then spreads in the form of an elastic wave. The impact echo method is based on physical laws of elastic stress wave propagation in solids generated by mechanical impulse. Ultrasonic testing is commonly used to find flaws in materials or to assess wave velocity spreading.

Determine Parameters for Double-K Model at Three-Point Bending by Application of Acoustic Emission Method

As concrete is one of the most popular building materials, it is important to know its basic properties and behaviour especially at loading. When cracks occur in concrete, released fracture energy will be proportionally transformed into the energy contained in acoustic emission. According to this physical phenomenon, acoustic emission technique provides an effective monitoring method for fracture process of concrete through generated acoustic emission. However, such monitoring is limited in qualitative evaluation of fracture process in most occasions. Quantitative interpretation of fracture process is difficult to accomplish by simply acquiring the amount of acoustic emission generated or by conducting parameter-based acoustic emission analysis. This paper investigates the use of the double-K fracture model and acoustic emission for prediction of load at the beginning of stable crack propagation in three-point bending tests of concrete specimens. Double-K model combines the concept of cohesive forces acting on the effective crack increment with a criterion based on the stress intensity factor.