Papers by Keyword: Fatigue Loading

Abstract: 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.

Abstract: 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 +).

Abstract: This study analyzed requirements of the wind turbine blade fatigue loading, and proposed a novel design method for blade fatigue loading control system. The hardware and software of the control system were designed. Frequency scanning, frequency control and amplitude tracking flow chart have been presented. A control system of the fatigue loading facility was built based on this investigation. The loading test of wind turbine blade has been completed. The data and curve acquired from the test prove that the control system could satisfy loading requirements.

Abstract: 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.

Abstract: Through indoor simulation test of double-block ballastless track sleeper loose hydrodynamic pressure, this paper study the variation laws of hydrodynamic pressure of different position, different load and frequency variation. The results show: The location of the biggest hydrodynamic pressure is in the middle of the crack and near the not void area. The amplitude and frequency of load have obvious influence on the hydrodynamic pressure. When the load amplitude is more than 30kN or load frequency exceeds 10HZ, the effect on the hydrodynamic pressure is particularly notable.

Abstract: The aim of the paper is to analyse how different mechanical properties of bonded metals influence the cyclic behaviour of bimetallic components. The simulations also include different initial state of stress since one of the methods for manufacturing bimetals is explosive welding which introduces residual stresses into bonded materials. The analysed cyclic behaviour concerns cyclic stress-strain relation in elastic-plastic strain state. The multi-surface plasticity model of Mróz-Garud was applied. Results shows that depend on residual stresses the ratchetting phenomena could occur.

Abstract: In this paper, the ultrasonic vibration uniaxial tension experiment was carried out on the 20# steel with a set of ultra-high-frequency vibration device. It showed that the material defect was the important factors of ultrasonic “soften” mechanism and obtained the crack extension mechanism under ultrasonic fatigue loading, there were：(1)The high frequency vibration of the ultrasonic fatigue loading weakened the influence of the plastic zone of the crack tip and residual stress on crack extension; (2)When the fatigue crack extension, the ultrasonic wave spread in the specimen, and reflected in the crack surface, resulting the crack closure effect decreased, the plastic zone of the crack tip decreasing; (3)The high vibration frequency and deformation velocity resulted the increase of the thermal effect, crack extension energy spread to the continuous medium in the form of heat, promoting crack extension and releasing energy. It also study the influence of different groove depth and groove curvature on the material ultrasound fatigue limit, and obtained the relation curve of fatigue limit with groove depth and groove curvature.

Abstract: In order to verify the role of fiber bragg grating strain gauge in strain measurement of concrete bridge, and the influence of concrete and steel strain properties by fatigue loading, the relevant experimental researches were carried out. The results indicated that the Fiber Bragg grating strain gauge could reflect the strain regularity of concrete and steel well; for the fiber grating strain rosettes inside the concrete, the pasting equipments of fiber gratings had a certain impact of the measurement effect. The fatigue loading had a certain impact of the properties of concrete and steel, in conditions of the same number of fatigue, the greater the stress amplitude the more obvious the effects. The results analysis shown that, fiber grating strain measurement innovated the means and methods of strain measurement in detailed structure of the concrete bridge, for the strain measurements of concrete bridge under fatigue loading, the FBG could still play very good effect.

Abstract: Cracking is the most common damage in the secondary lining concrete because of its continuous thin-walled structure, potential surrounding rock pressure and poor curing conditions. In order to improve the fatigue and gas perimeability resistance of concrete and to reduce the responding costs, four series modern concretes including ultra-fine pozzolanic powder and organic fibers are prepared and investigated. The optimized modern secondary lining concrete is determined as the concrete including 0.08% or 0.1% volume fractions of ultra-fine organic fiber (UF), based on the test results of fatigue life and coefficient of gas-permeability under fatigue loading. The result show fiber concrete is positive for enhancing the fatigue and gas permeability resistance and can apply for the tunnel secondary lining.

Abstract: New composite metal foams are processed using powder metallurgy (PM) and gravity casting techniques. The foam is comprised of steel hollow spheres, with the interstitial spaces occupied by a solid metal matrix (Al or steel alloys). The cyclic compression loading of the products of both techniques has shown that the composite metal foams have high cyclic stability at very high maximum stress levels up to 68 MPa. Under cyclic loading, unlike other metal foams, the composite metal foams do not experience rapid strain accumulation within collapse bands and instead, a uniform distribution of deformation happen through the entire sample until the densification strain is reached. This is a result of more uniform cell structure in composite metal foams compared to other metal foams. As a result, the features controlling the fatigue life of the composite metal foams have been considered as sphere wall thickness and diameter, sphere and matrix materials, and processing techniques as well as bonding strength between the spheres and matrix.