Pavel Mazal

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.

Cycle induced microstructural changes

The aim of this research was to look for systematic structural changes in a metal subjected to repetitive or fluctuating stress which may be used for monitoring structural degradation and estimating residual life of fatigued components. A special X-ray technique was used to this end, which consists in the examination of the number and size of individual diffraction spots. As each diffraction spot represents the diffraction image of a coherent scattering region, such an examination provides information on the architecture of dislocation network forming the interface between the coherent X-ray diffraction scattering regions. Analysis of the structure of an aluminium alloy EN-AW-6082 subjected to cyclic stress proved that the effect of cycling was first to transform an irregular dislocation distribution into cellular one. The cells of the dislocation network formed in this way coagulated and grew in size under repeated stress up to a certain number of cycles when the effect of cycling reversed and the cells gradually disintegrated.

Fatigue properties of materials surface hardened by plasma nitriding and laser beam

Abstract Carbon steel, standard bearing steel, grey cast iron, and structural steel, respectively, were used to determine the effect of laser transformation hardening and low temperature plasma nitriding on S-N (Wohlers) curves. For all materials and treatment conditions examined, the homogeneity of the case hardened layers seems to be the most important factor that influences the fatigue crack nucleation, much more important than the case hardened layer thickness and total level of hardening. Contradictory results obtained with the grey cast iron show that a microstructural constituent (graphite) can weaker the influence of the relatively high but inhomogeneous surface layer hardening and can be without these negative effects in the case of very thin but homogeneous hardened surface layer. Application of discontinuous surface hardening as well as the two overlapping beads yield to the almost negative influence on fatigue life.

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 +).

Basic Acoustic Emission signal treatment in the area of mechanical cyclic loading

One of promising possibilities of watching of damage course of material exposed to cyclic mechanical loading is using acoustic emission technique (AE). Various types of AE signals processing that are often used in practice are dealt with. In this paper, the basic comments of results of experimental measuring are shown that were aimed to possibilities of identification of various stages of fatigue process, realised on electro-resonance loading equipment with the help of AE technique. Results gained to date show wide possibilities of application of the AE method for the identification of fatigue processes.

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.

Diagnostics of damage development of bearings and gears by acoustic emission method

The paper presents an overview of the contemporary applications of acoustic emission method for diagnosis and condition monitoring of anomalous situations that occur during the operation of machines with rotating parts (formation of contact damage, insufficient lubrication, etc.). The main attention is focussed on operational diagnostics of axial and radial bearings. The second part of the text also mentions the possibilities of utilisation of AE method for complementary diagnosis of real state of gears and gearboxes. This summary of selected published experimental works and used evaluation procedures is confronted with the outputs of the experiments carried out in the framework of several projects in the Laboratory of Acoustic Emission of the Institute of Machine and Industrial Design in Brno University of Technology. Based on this review, the significant potential of AE method for more accurate diagnosis of malfunction of machines with rotating parts is done.

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.