AERolling element bearings are widely-used machine components and their failure can result in damage to the whole machine. A bearing failure can be caused by many factors, such as improper lubrication, the presence of abrasive particles, overloading, moisture, a corrosive environment, improper mounting, electrical discharges and material defects. These causes can be eliminated by observing the correct operating conditions, except for rolling contact fatigue (RCF). In this case, full-scale bearing life tests, or material tests for RCF resistance, are performed. Various methods of condition monitoring are used to detect damage to these components or specimens in industry or during testing in laboratories. An analysis of vibrations from the tested bearings/specimens is the most widely used method for damage detection and is based on vibration acceleration measurement and its analysis in the time or frequency domain. A more sensitive method for surface damage or subsurface crack detection is the acoustic emission (AE) method. Over the past three decades, AE-based monitoring has developed as a potential tool for rolling bearing diagnostics. This paper is aimed at the detection and monitoring of the onset and propagation of natural defects of steel specimens using AE technology. The experiments were carried out under various loading conditions on specimens of case-hardened 16MnCr5 steel. The AE signal parameters, such as count rate, cumulative count rate and RMS, were compared with vibration levels and temperature. In conclusion, the results of this study suggest that the AE monitoring method can be employed as an evaluation tool for rolling contact fatigue testing of material specimens.
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.
The work deals with measurement techniques of water conducting system in the trees. Water conducting system (including xylem and phloem) indicates its importance for related physiological processes. There are still problems how to measure its functioning (which variables and how), especially in the open field (e.g., forests and orchards) in order to get maximum information about it. Simple band dendrometers measuring seasonal dynamics of stem growth have been already applied for many years, being gradually replaced by their more sophisticated electronic versions most recently. The sap flow is a suitable variable, because it links roots and crowns and provide information about transporting the largest amount of mass in plants, which can be decisive for their behavior. Following pioneering work in the last century (Huber, 1932), many types of sap flow measurement methods based on a variety of principles (e.g., thermodynamic, electric, magneto-hydrodynamic, nuclear magnetic resonance, etc.) have been described. Only a few of these, particularly those based on thermodynamics, have been widely used in field-grown trees. E.g., heat pulse velocity system developed by Green (1998) and Cohen et al. (1981). Heat ratio method also works with pulses, but interpreted the data in more sophisticated way (Burgess, 2001). Widely used is a simple heat-dissipation method (Granier, 1985). Direct electric heating and internal sensing of temperature was applied in the trunk heat balance method (Čermák et al., 1973, 1976, 1982, 2004; Kučera et al., 1977; Tatarinov et al., 2005). The heat field deformation method is based on measurement of the deformation of the heat field around a needle-like linear heater (Nadezhdina et al., 1998, 2002, 2006; Čermák et al., 2004).Another important variable is water potential, which could be measured in the past only periodically on selected pieces of plant material using pressure (Scholander) bomb, but most recently also continuous measurements became possible due to application of psychrometric method (Dixon and Tyree, 1985). There exist also other physical variables carrying important information, which can be measured using different principles. This includes e.g., acoustic methods, which can detect quantitative variation of pulses occurring during cavitation events, associated with interruptions of water columns in vessels. This must not necessarily be a single source of acoustic emissions. In this study we are focused on a general description of acoustic events measurable in a wide range of their spectrum. The first aim was to detect such signals and the second to learn them and gradually analyze in order to better understand the associated processes causing their occurrence and their relations to plant life.
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