Frantisek Vlasic

Application of Acoustic Emission for Identification of Differences in Fatigue Damage of Selected Materials for Power Plants

An acoustic emission is remarkable source of information about the fatigue process and its intensity under cyclic loading. Specimens made of reactor steel and INCONEL 713LC were subjected to bending fatigue loading in the high-cycle range. This study presents results of acoustic emission signal analysis. The main aim of this study is to propose a methodology for evaluation of the early manifestations of fatigue damage and to identify material changes in both materials by AE parameters. Signal comparison material indicates differences of damage mechanism in observed. An examination of crack initiation sites and microstructure has been also performed.Experiments were realized in cooperation between laboratories of Brno University of Technology and University of West Bohemia in Pilsen and its related to solving of project of the Czech Ministry of Industry and Commerce: “A diagnostic complex for the detection of pressure media and material defects in pressure components of nuclear and classic power plants“ and project New Technologies for Mechanical Engineering (NETME +).

Acoustic Emission Diagnostics of Roller Bearings Damage

This paper shows potential applications of the AE method for identification of damage at early stages in rolling bearings. The experimental part is concerned with the results of AE application during durability testing of axial and radial bearings. The recent group of experiments was carried out on durability test stations for radial bearings. Sensing of AE signal on these devices was complicated by the position of the tested bearing inside the station, making it to place the AE sensors in its direct vicinity. As a solution, waveguides were used, with one end touching the outer ring of the bearing and the other end connected to the sensor. Other sensors were placed on the surface of the testing station. Despite these complications with AE signal sensing, an optimal setting was found for the measuring chain resulting in collection of high-quality data from damaged radial bearings. Examples of basic AE signal records from rolling bearing and potentials of the new generation AE analysers are mentioned. These devices allow for continuous AE signal sensing. The results prove the AE technique enables reliable determination of running-in period, stabilised run and the prediction of the stage where surface damage forms. It is shown that the AE method can be used to predict bearing defects or can be used to complement traditional vibration bearing monitoring.

Study of Initial Stages of Fatigue Process in Selective Laser Melting Material Using Acoustic Emission Method

This paper deals with the evaluation of the fatigue tests and subsequent analyses of damage processes in selective laser melting (SLM) materials under bending loading. Compared to conventional production technologies (casting, forming and machining), SLM offers a wide range of benefits, e.g. production with no need for expensive molds, very low material waste and the possibility to create complex geometric shapes. The acoustic emission method was used to fully understand the processes which appear in the stages preceding the crack initiation. The fatigue tests at room temperature were conducted on standard wrought 2618A aluminium alloy as a representative testing material and the same material created by SLM. The main aim of the study was to compare the acoustic emission signal during fatigue loading at different manufacturing parameters of SLM material and to analyze in detail the signal changes in initial stages of fatigue process. The results show the high sensitivity of the acoustic emission technique to the fracture behaviour of SLM material and transition from the stage of surface relief evolution to the stage of crack nucleation and propagation. After completion of dynamic mechanical tests, a detailed fractographic analysis was conducted to assess material response to mechanical loading. Attention was focused on determining the predominant failure mechanisms and the influence of defects or inhomogeneities such as pores, cavities, etc. resulting from the production of materials using SLM method.

Use of Acoustic Emission Signal and X-ray Diffraction Analysis for Detection of Microstructural Changes in Cyclically Loaded AlMg Alloys

This paper summarizes basic experimental results of microstructural changes during high cycle fatigue loading of AlMg alloys (EN AW-6082 and EN AW-2017). These changes are detected by using of acoustic emission (AE) method. The authors targeted the main attention on more exact identification of causes of changes of AE signal activity in the stage of fatigue damage cumulation. The method of X-ray diffraction analysis of the structure is used for explanation of this phenomenon. The results of presented experimental works indicate the connections between changes of acoustic emission signal and cyclical changes of so called “mosaic blocks” of the crystal structure identified by means of X-rays diffraction during fatigue loading of material.

Study of Initial Stages of Fatigue Process Using Non-Destructive Testing Methods

This paper deals with the basic research of cyclic damage during the initial stages of fatigue process using the non-destructive testing methods. The acoustic emission method was used for monitoring of the microstructure changes during fatigue loading. The electrical potential measurements of specimen and microscopic observation were used mainly to detect the first short cracks and their propagation. The fatigue tests at room temperature were conducted on titanium alloy and creep-resistant steel specimens under bending and tension loading. The aim of the study was to compare the acoustic emission signal at different types of loading until fracture and to analyze in detail the signal changes in initial stages of fatigue process. This analysis was primarily based on the waveform similarity and division into classes. The results show the high sensitivity of the acoustic emission technology in the transition from the stage of surface relief evolution to the stage of crack nucleation and propagation.