Papers by Keyword: Fatigue Damage

Abstract: The three dimensional grain mapping technique for polycrystalline material, which is called X-ray diffraction contrast tomography (DCT) has proposed. In the present study, the measurement of DCT was conducted in SPring-8, which is the brightest synchrotron radiation facility in Japan, and the condition of measurement and data procedure are discussed. Developed technique was applied to aluminium alloy and stainless steel. The shape and location of grain could be determined by the developed three-dimensional mapping technique using the apparatus in a bending beam line of SPring-8. To evaluate plastic deformation, the grain orientation spreads of individual grains were measured. The grain orientation spread is caused by the mosaicity, which relates to the dislocation structure in a grain. The grain orientation spread was found to increase with increasing plastic strain. Fatigue damage also could be evaluated by the grain orientation spread in the DCT measurement.

Abstract: In recent years, fatigue limit estimation based on dissipated energy has been introduced in various industries because of its time and cost effectiveness. However, the mechanism of energy dissipation and the relationship between energy dissipation and fatigue damage have not been investigated well. In this study, mechanism of energy dissipation is investigated in relation with formulation of slip bands for JIS type 316L stainless steel through observation of slip bands by optical microscope and atomic force microscope.

Abstract: The three dimensional grain mapping technique for polycrystalline material, which is called X-ray diffraction contrast tomography (DCT) has proposed. In the present study, the measurement of DCT was conducted in SPring-8, which is the brightest synchrotron radiation facility in Japan, and the condition of measurement and data procedure are discussed. Developed technique was applied to aluminium alloy and stainless steel. The shape and location of grain could be determined by the developed three-dimensional mapping technique using the apparatus in a bending beam line of SPring-8. To evaluate plastic deformation, the grain orientation spreads of individual grains were measured. The grain orientation spread is caused by the mosaicity, which relates to the dislocation structure in a grain. The grain orientation spread was found to increase with increasing plastic strain. Fatigue damage also could be evaluated by the grain orientation spread in the DCT measurement.

Abstract: In-situ Low Cycle Fatigue test (LCF) at temperature 635 °C have been performed in SEM on flat specimen ofcast Inconel 713LC superalloy. The aim of the investigation was to studymechanisms of the fatigue damage during elastic-plastic cycling by theobservations of the characteristic surface relief evolution and theaccompanying internal dislocation structures. The selected locations on thesurface were systematically studied in-situ and documented by SEM and usingAFM. The surface relief in the first tensile half-cycle was formed by numerousslip steps on the primary slip planes (111). In the following compressionhalf-cycle additional opposite slip were formed. The relief was modified in thenext cycles but without forming additionally new slip traces in the primarysystem. The reorientation of two grains in the gauge area was measured usingEBSD. At the end of cyclic loading the relation between surface persistent slipmarkings and persistent slip bands in the interior of the material wasdocumented by TEM on lamella prepared by FIB. The early stages of extrusion andintrusion formation were documented. The damage mechanism evolution is closelyconnected with the cyclic strain localization to the persistent slip bands thatare also places of fatigue crack initiation.

Abstract: In order to analyze the fatigue of the airborne product structure, the modal analysis and random vibration analysis are conducted for the product by using the finite element analysis software ANSYS. The modal analyzing results are compared with the modal test results and the finite element model is corrected. The stress response power spectral density is obtained from random vibration analyzing. A frequency domain method for calculating the fatigue damage of the structure is presented. The simulation results are in agreement with the reliability enhancement testing results. An optimization scheme for the product structure design is given.

Abstract: Based on theory of ultrasonic nondestructive testing on surface fatigue damage of metal components, the wave law of ultrasonic nonlinearity caused by fatigue is studied. When there are lattice defects in metal material, second-order nonlinear coefficient β changes during ultrasonic propagation. According to the point, the system of nonlinear ultrasonic testing is build. The change trends of harmonic amplitudes and ultrasonic coefficients are measured during fatigue bending testing of materials such as 45 steel, 2024 aluminum alloy and 304 stainless steel. The results shows: in elastic phase, the ratios of harmonic and fundamental waves monotonically increase with fatigue life, and in plastic phase, deformations appear and micro-cracks expand into macro-cracks in materials, the ratios firstly decrease and then increase with fatigue life. However the quadratic sums of nonlinear coefficient are approximately linear with the fatigue life. Therefore, when the relationship between the quadratic sums and fatigue life is known, it can be used to characterize fatigue state of metal materials.

Abstract: This paper analyzes the problems existing in the design and operation of ring die fuel pellet machine, and proposed to optimize the key parts. Determine the reasonable number of roller on the theory of fatigue damage after drawing up the related design parameters of ring die and the roller, a three-dimensional model of the link mold pellet machine is established using Pro/E soft-ware, and transferred the model into ADAMS software through Mech/Pro which dedicated interface software, then used ADAMS to make a dynamics simulation. Through calculation, the stress amplitude impact on the ring die and the Energy consumption per unit output are smallest when roller number is four. So, ring die service life and equipment production efficiency can be improved effectively through setting up reasonable roller number. Keywords-fuel pellet machine; roller; ring die; fatigue damage; three-dimensional model; dynamics simulation

Abstract: This paper describes the correlation between fatigue life with the I-kaz coefficients. Fatigue tests were performed according to the ASTM E466-96 standard with a strain gauge attached to the specimen being tested. AISI 1045 carbon steel was used as the material for this test due to its wide applications in the automotive and machinery industry. Fatigue tests were carried out at several constant loading stresses of 610 MPa, 650 MPa and 690 MPa at the sampling frequency of 8 Hz. A set of data acquisition system was used to collect the fatigue strain signals. The integrated Kurtosis-based algorithm for Z-filter (I-kaz) technique had been used to find the I-kaz coefficient. The I-kaz coefficient is found to have a good correlation with fatigue life, other than can represent fatigue damage.

Abstract: In this work, a Ti-48Al-2Cr-2Nb alloy obtained with a additive manufacturing technique by electron beam melting (EBM) has been examined by conducting high cycle fatigue tests both with plain specimens and with specimens with artificially introduced defects with the objective of studying the growth behavior of small cracks. A consistent model for predicting the fatigue endurance strength of specimens with artificial defects is proposed, based on the Kitagawa diagram and taking into account of the presence of inherent microstructural features of the studied intermetallic alloy. Thus, the origin of fatigue failures due to intermetallic phases and orientation of lamellar colonies was investigated by means of micromechanical analysis through the use of high-resolution Digital Image Correlation (DIC). The local strain heterogeneities were measured out of the load frame by means of an optical microscope at high magnifications. The strain maps were then overlaid with the images of the microstructure and detailed analyses were performed to investigate the features of the microstructure where high local strain heterogeneities arise. High local residual plastic strains were measured inside lamellar colonies, which are detected as the precursor to fatigue crack initiation. The measure of the residual strains also provides further information on the role of the intermetallic phases on the fatigue behaviour of γ-TiAl alloys.

Abstract: Based on the probability distributions of wind direction and wave direction, the fatigue load is applied to the offshore wind turbine structure according to the actual environmental loading direction. The deterministic fatigue damage due to the wind load and the spectrum fatigue damage due to the wave load are calculated, respectively. Then, the total fatigue damage of the offshore wind turbine structure is obtained by the linear superposition. Compared with the results that the fatigue damage of the offshore wind turbine structure is computed under fatigue loads exerted in single direction, the results of omnidirectional fatigue analysis are more reasonable.