Kyushu University Academic Staff Educational and Research Activities Database
List of Presentations
QIANG CHEN Last modified date:2020.01.27

Professor / Strength of Materials / Department of Mechanical Engineering / Faculty of Engineering

1. Xiaohong Shao, Qiang Chen, Zhen-Zhen Peng, Kazuhiro Kitamura, Xiu-Liang Ma, Deformation-induced redistribution of solute atoms in an Mg-Zn-Y alloy, THERMEC’ 2018, 2018.07.
2. N. Kawagoishi, K. Kariya, Y. Maeda, E. Kinoshita, Qiang Chen, M. Goto, Fatigue strength of aluminum cast alloy in plant oil, 12th International Conference on Fracture and Damage Mechanics, FDM 2013, 2014, Effect of plant oil on the fatigue strength of a squeeze cast Al-Si-Mg alloy was investigated. Crack growth rate was higher in plant oil than in air, inducing a decrease in fatigue strength. The reason included is explained from the viewpoint of high water absorbency of plant oils, on basis of hydrogen enhanced localized plasticity..
3. Qiang Chen, Qingyuan Wang, Norio Kawagoishi, Kohji Kariya, Yuzo Nakamura, Nu Yan, Effect of aging condition on fatigue strength of maraging steel in long life region, 13th International Conference on Fracture 2013, ICF 2013, 2013, A novel aging treatment was proposed to improve the fatigue strength of maraging steel by taking the effects of aging condition and humidity into account. Rotating bending fatigue tests were carried out for a 350 grade of 18% Ni maraging steel in the long life region up to 108 cycles in the relative humidity of 25% and 85%. Aging conditions under investigation included a conventional aging or the so called single aging at 753K, and a two-step aging or double aging by ageing at lower temperature of 473K succeeded to the single aging. Through the double aging, the susceptibility of fatigue strength to humidity was significantly improved without any deleterious effects. The main reasons for the decrease in fatigue strength in high humidity are due to the promotion of crack initiation and the acceleration of small crack propagation. The improvement of fatigue property in high humidity by the double aging was explained from the roles of the additional precipitation of supersaturated Mo atoms during the second lower temperature aging..
4. Qiang Chen, Takanori Nagano, Yuzo Nakamura, Yoshikazu Maeda, Norio Kawagoishi, Initiation and propagation behavior of a fatigue crack of maraging steel in high humidity, 13th International Conference on Fracture 2013, ICF 2013, 2013, The effect of humidity on the fatigue properties of 18% Ni maraging steels with different hardness and aging structure was investigated under rotating bending fatigue by varying relatively humidity from 25% to 95%. It was found that the initiation and the early propagation of a fatigue crack were accelerated in high humidity, which caused to a large decrease in fatigue strength of the alloys. In fact, the fatigue strength at 107 cycles obtained in RH 85% was less than a half of that in RH25%. Meanwhile, successive observation on surface fatigue progress and the fractographic analysis of fractured specimens elucidated that anodic dissolution was the main reason for promoting crack initiation whilst hydrogen embrittlement due to cathode reaction was responsible for the acceleration of crack propagation. However, the acceleration of crack propagation was suppressed by the formation of reverted austenite..
5. K. Kariya, N. Kawagoishi, H. Maeda, Qiang Chen, M. Goto, Y. Nu, Fatigue fracture mechanism of extruded Al alloy 7075-T6 in high humidity, 10th International Conference on Fracture and Damage Mechanics, FDM2011, 2012, Effect of high humidity on growth mechanism of a fatigue crack was investigated for an extruded bar of an age-hardened Al alloy 7075-T6 which had the marked texture of plane (111). Fracture in high humidity occurred by the growth of a shear mode crack under high stress levels, though a crack propagated in a tensile mode under low stress ones, macroscopically. Many voids and slip planes were observed on the fracture surface yielded by the shear mode crack. Especially most of the fracture surface was occupied by voids where the crack was small. The void percentage decreased with increasing in the crack depth. Fracture surface yielded by the shear mode crack was a plane (100). The growth direction of the shear mode crack to the cross section of specimen was about 55° corresponding to the angle composed by this plane and the texture of plane (111). These results suggest that the shear mode crack was related to microstructure, stress and environment. The growth mechanism of the shear mode crack assisted by hydrogen was proposed based on the results of the acceleration of crack growth and the formation of voids in high humidity..
6. Qiang Chen, N. Kawagoishi, G. Hashiguchi, M. Oki, K. Kusukawa, Fatigue behavior and fracture mechanism of al alloy 7075-t6 under ultrasonic cycling deformation, 17th European Conference on Fracture 2008: Multilevel Approach to Fracture of Materials, Components and Structures, ECF17, 2008, To investigate the effects of loading frequency on fatigue crack growth behavior, ultrasonic fatigue tests were carried out for an extruded age-hardened Al alloy 7075-T6 in ambient air and in N2 gas. The results obtained were compared with those in rotating bending fatigue. Fatigue strength was higher in ultrasonic fatigue than in rotating bending fatigue. This may be caused by the retardation of crack initiation and early crack propagation. In ultrasonic fatigue, the growth direction of cracks changed macroscopically from tensile mode to shear mode with the direction oblique about 35 degrees to the stress axis. Fracture mechanism involved changed from striations featured to transgranular facets and microvoids predominated. Crack growth rate at growth mode transition was ~3x10-9 m/cycle. The relation between applied stress, a, and crack depth, bT, at the transition sites can be approximated as anbT = constant. The results were discussed from viewpoints of crack tip plasticity, time dependent environment effect and the texture microstructure of the alloy..
7. Tatsuo Sakai, Qiang Chen, Ayako Uchiyatna, Akiyoshi Nakagawa, Toshiki Ohnaka, A study on ultra-long life fatigue characteristics of maraging steels with/without aging treatment in rotating bending, 4th International Conference on Very High Cycle Fatigue, VHCF-4, 2007, Maraging steel is one of typical high strength steels used for light-weight mechanical structures due to its significantly high strength over 2000 MPa. It was melted in vacuum furnace in order to reduce the contents of unexpected inclusions so that higher mechanical properties can be achieved. After solution treatment, appropriate aging treatments were applied to some specimens to provide the desired strength levels. Ultra-long life fatigue properties were investigated by using both solution treated and aging hardened specimens under rotating bending fatigue. The effects of aging conditions were examined from the viewpoints of fatigue life, strength distribution, fatigue mechanism, and fracture morphology..
8. K. Morino, N. Kawagoishi, Qiang Chen, K. Fukada, E. Kondo, Internal fracture process in fatigue of radical nitrided bearing steel, Sixth International Conference on Computer Methods and Experimental Measurements for Surface Treatment Effects, Surface Treatment VI, 2003.12, Rotating bending fatigue tests were carried out for a radical nitrided bearing steel in order to investigate the initiation and propagation behavior of an internal crack. Surface fracture occurred under high stress levels and fish-eye fracture happened under low stress levels so that the S-N curve appeared in the shape of two-step lines. The depth of the origin of internal fracture was confined in a relatively narrow region near the boundary between the hardened and non-hardened matrix. By two-step loading fatigue tests in the internal fracture region, a circular trace corresponding to the stress change was observed within the fish-eye. In the internal fracture region, a crack was initiated at the early stage of the fatigue process, that is, most of the fatigue life of internal fracture was occupied by the growth life of an internal crack..
9. Q. Y. Wang, N. Kawagoishi, Qiang Chen, R. M. Pidaparti, Probabilistic Modeling of Pitting Corrosion Fatigue Life, Proceedings of the Twelfth (2002) International Offshore and Polar Engineering Conference, 2002, Corrosion and fatigue are two types of damages found in aircraft and offshore structures. Corrosion fatigue processes are characterized by randomness due to the random nature of materials, initial defects, loading, and environmental condition. In this study, a mechanistically based probabilistic model for prediction of pitting corrosion fatigue life in aluminum alloys has been developed which captures the effect of the interaction of cyclic load and corrosive environment and all the stages of the corrosion fatigue process. Monte Carlo simulations were performed to define the failure probability distribution. Predicted cumulative distribution functions of fatigue life agreed reasonably well the experimental data..
10. N. Kawagoishi, K. Morino, K. Fukada, Qiang Chen, E. Kondo, On fish-eye fracture of radical nitrided die steel, Fifth International Conference on Computer Methods and Experimental Measurements for Surface Treatment Effects, Surface Treatment V, 2001.12, In order to investigate the effect of radical nitriding on fatigue strength of die steel, rotating bending fatigue tests were carried out at room temperature and 450°C. Fatigue strength was increased by nitriding at both temperatures due to surface hardening and compressive residual stress generated in the surface region. Comparing with the non-nitrided steel in which the fracture origin was at surface slip bands or surface defects, the nitrided steel fractured with the origin at inner inclusions at both temperatures. In the nitrided steel, cracks initiated from inclusions in the non-hardened layer or near the boundary between hardened and non-hardened layers. The difference in fatigue strength between the two temperatures was discussed based on the feature of fish-eye..
11. Qiang Chen, N. Kawagoishi, K. Othubo, E. Kondo, M. Sakai, T. Kizaki, Ultrasonic fatigue strength in Inconel 718, SUPERALLOYS 718, 625, 706 and Various Derivatives, 2001.01, The fatigue strength of a nickel-base superalloy, Inconel 718, was investigated at room temperature under an ultrasonic frequency (19.5 kHz) loading in ambient air environment. The endurance (S-N) data show that fatigue strength was enhanced at ultrasonic frequency as compared to those at conventional frequencies. Small crack initiation and propagation behavior was observed during the fatigue progress at both ultrasonic fatigue and conventional rotary bending fatigue. The effect of frequency on the fatigue fracture mechanism was examined from a microscopic viewpoint..
12. 陳 強, 何超, 王清遠, Very high cycle fatigue strength and failure mechanisms of welded joint(溶接継手の超高サイクル疲労強度と破壊機構), 日本機械学会九州支部年次大会, 2017.03, Fatigue strength and failure mechanisms of welded joints in high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime. The effects of welding defect, micro-plasticity and second phase particle on fatigue crack initiation process are discussed based on our recent experimental studies. The results indicate that VHCF behaviors of welded joints showed strong sensitivities to microstructural and mechanical heterogeneities. In addition, we compare the fatigue strength between arc welding, laser-hybrid welding and friction stir welding so as to propose optimizations of welding parameters for fatigue life improvement..