The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
S C Chen - One of the best experts on this subject based on the ideXlab platform.
-
effect of residual stress on thermal Fatigue in a type 420 martensitic stainless steel weldment
Journal of Materials Processing Technology, 2003Co-Authors: S C ChenAbstract:Abstract This paper aimed at the investigation of the effect of residual stress on thermal Fatigue in martensitic stainless steel. In this study, a submerged arc welding was utilized. In order to obtain the different magnitude of residual stresses, the parallel heat welding, vibration stress relief, shot peening, and controlled low temperature stress relief processes were used for reduction of residual stresses due to welding. During welding, the thermal Cycle of different locations in weldment were recorded. The residual stresses were determined by using the hole-drilling strain-gage method of ASTM standard E837. The retained ferrite content was determined with a digital optical microscope and image process software. The experimental results showed that the residual stresses decrease with increase of thermal Fatigue Cycle number. This is because that the formation of crack relieves residual stresses of specimen. Because of solidification structure difference, at low thermal Fatigue Cycle, the density of cracks on near fusion line is the higher than centerline. At high thermal Fatigue Cycle, the density of crack from near fusion line is lower than centerline, but very longer crack is found easily. The retained ferrite content and thermal Fatigue crack tendency exist a critical value. The retained ferrite less than about 31.5 vol.% will increase crack propagation tendency. The retained ferrite become a harmful factor for crack propagation tendency when the retained ferrite more than this critical content. It is because that too much ferrite content in martensitic matrix may result in a lower strength structure and crack can propagate easily. In addition, the dual phase structure may introduce more harmful interior stress due to different volume shrinkage between retained phase and matrix.
G Hammersley - One of the best experts on this subject based on the ideXlab platform.
-
Fatigue crack initiation and propagation on shot peened surfaces in a316 stainless steel
International Journal of Fatigue, 1995Co-Authors: E R De Los Rios, A Walley, M T Milan, G HammersleyAbstract:Abstract Shot-peening was found to affect crack behaviour by delaying both crack initiation and crack propagation. Cracks were formed preferentially at the specimen edges, and crack propagation was found to be higher in the depth direction than along the surface, giving initial quarter-elliptical crack fronts with the major axis along the thickness direction. Shot-peeing significantly increases the ratio of initiation life to propagation life in comparison to unpeened specimens. Surface polishing was found to be detrimental to Fatigue resistance. Indeed, it was observed that polishing had a similar effect for specimens of different peening intensities and thereby different depths of residual compressing stress. For high stresses with low lifetimes, the propagation period dominates, whereas for low applied stresses with long lifetimes the initiation period dominates. At high applied stress, cracks were initiated at the lower surface rather than the upper surface of the specimen even though a stress ratio R of −0.8 was used. This suggests that relaxation of residual stresses is more readily achieved by the action of the compressive stress in the Fatigue Cycle.
Choongdo Lee - One of the best experts on this subject based on the ideXlab platform.
-
Effect of strain rate on Fatigue property of A356 aluminium casting alloys containing pre-existing micro-voids
International Journal of Fatigue, 2020Co-Authors: Choongdo LeeAbstract:Abstract This study aims to investigate the dependence of Fatigue life on strain rate variations by loading frequency, and simultaneously, to evaluate the mutual relation between the strain rate and microporosity on the Fatigue property in terms of the defect susceptibility of Fatigue life to microporosity variation. The test specimen was prepared from the rim section of an automotive wheel fabricated by low-pressure die-casting on an A356 alloy. The high-Cycle Fatigue test was carried out in a strain rate range corresponding to the frequency range of 0.3–30 Hz at a stress ratio of R = −1. The strain rate increased to a two-order interval from 10−2 to 100 s−1 as the loading frequency increased from 0.3 Hz to 30 Hz. The nominal Fatigue strength coefficient and exponent decreased from 754 MPa and 0.18 to 293 MPa and 0.09, respectively, with increasing strain rate. The Fatigue life in low-stress amplitude slightly increased with the strain rate, while it remarkably decreased with the strain rate as the stress amplitude increased. This is because the elastic/plastic strain component ratio (Δee/Δep) decreased upon increasing the plastic strain component, accompanied by increasing strain rate. The plastic strain component was remarkably increased with the strain rate and stress amplitude, and decreased by the strain-hardening effect on the lapse of Fatigue Cycle, even though the elastic strain component remained at a constant level, depending mainly upon the stress amplitude. Additionally, the contribution of microporosity to the variation of Fatigue life was underestimated as the strain rate increased, and became more sensitive with the variation of the elastic/plastic strain component in the Fatigue Cycle as the stress amplitude increased. The main propagation path of Fatigue cracks is changed from a mixed mode of the cracking failure by the damage evolution of eutectic Si particle and the matrix penetration by shear deformation of matrix region, to a cracking failure mode where the damage evolution of eutectic Si particles dominated as the strain rate increased.
Luquan Ren - One of the best experts on this subject based on the ideXlab platform.
-
Microstructure, hardness, and thermal Fatigue behavior of H21 steel processed by laser surface remelting
Applied Surface Science, 2013Co-Authors: Zhihui Zhang, Pengyu Lin, Luquan RenAbstract:Abstract We investigate the effects of laser surface remelting on the resistance to thermal Fatigue of a hot working die steel H21 in this work. Laser treatment was engineered to process samples with several treated morphologies. A dominantly martensitic microstructure, nano-sized carbide and high dislocation density in the treated area, were resulted. The average microhardness of the treated area is ~780 HV. The thermal Fatigue resistance of laser-treated samples is notably higher than their as-received counterpart. As the thermal Fatigue Cycle increases, the microhardness of treated area is reduced and then flatted. Crack initiation and propagation both are hampered by it.
P J Withers - One of the best experts on this subject based on the ideXlab platform.
-
relaxation of residual stress in shot peened udimet 720li under high temperature isothermal Fatigue
International Journal of Fatigue, 2005Co-Authors: Alex Evans, Sunoog Kim, Judith Shackleton, Giovanni Bruno, M Preuss, P J WithersAbstract:Abstract The extent of residual stress relaxation in turbine disc material Udimet 720Li was measured using laboratory X-rays with the sin2ψ technique, for Fatigue samples as a function of temperature and number of Fatigue Cycles for strain controlled loading to 1.2%. Results showed that extensive relaxation occurs upon the initial Fatigue Cycle. The maximum compressive residual stress (RS) parallel to the loading direction is found to decrease by 50% for all testing temperatures. The extent of relaxation upon further cycling increased with temperature. In the plastically deformed near surface region, the diffraction peak width decreased with increasing testing temperature and number of Fatigue Cycles (and exposure time), indicating that the relaxation of cold work is controlled by both thermal and mechanical processes.
