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Shi Y.,Key Laboratory of Energy Engineering Safety and Disaster Mechanics | Li B.,Key Laboratory of Energy Engineering Safety and Disaster Mechanics | Lei T.,Key Laboratory of Energy Engineering Safety and Disaster Mechanics | Lei T.,China Coal Technology and Engineering Co. | Mo S.,University of Sichuan
Wuhan Ligong Daxue Xuebao (Jiaotong Kexue Yu Gongcheng Ban)/Journal of Wuhan University of Technology (Transportation Science and Engineering)

The static cyclic testing data of 7 reinforced concrete columns with different axial load or different stirrup ratio were chosen from the PEER database. The effects on hysteretic behavior, ductility index and secant stiffness of reinforced concrete columns due to axial forces and stirrup ratio were investigated. The relationship between damage index and energy dissipation was analyzed based on Park-Ang damage model in order to study damage developing procedure of RC columns with different axial load or stirrup ratio. It was concluded that somewhat fat hysteretic loop and increased displacement ductility to the RC column with low axial force or high stirrup ratio was observed, larger yield deformation, higher yield load and peak capacity happened on the specimens with higher axial load or higher stirrup ratio, the contribution to damage index due to maximum response deformation was larger than that due to accumulative hysteretic energy at the first several cycles, the contribution to damage index due to accumulative hysteretic energy increased with the number of cycles, and the space of stirrup was one of the crucial factor to seismic behavior of RC column. Source

Yang S.B.,Key Laboratory of Energy Engineering Safety and Disaster Mechanics | Pu X.X.,Polymer Research InstituteSichuan UniversityChengdu610065 China | Huang Z.Y.,Key Laboratory of Energy Engineering Safety and Disaster Mechanics | Wang Q.Y.,Ministry of EducationSichuan UniversityChengdu610065 China
Journal of Applied Polymer Science

In this study, we aimed to characterize the mechanical response of polytetrafluoroethylene (PTFE) laminates under a tension-tension load-control fatigue test (frequency=5 Hz, load ratio=0) and provided an analysis of the failure patterns of the PTFE material with consideration of crystalline phase transformation. In the final results, the evolution of the cyclic creep strain and stress-number of cycles to failure (S-N) curves presented duplex properties accompanying the fatigue life increasing to high cycles (cycle fatigue>105). A simple phenomenological damage index was defined in this study to describe the cyclic creep process. Additionally, the scanning electronic machine investigation suggested that local fibrosis caused by crystalline phase transformation to phase I led to the initiation of fatigue crack, and the fiber formation and orientation was found to be beneficial to a higher tensile strength and better resistance to crack propagation. The aspect of cyclic-load-induced crystallization was observed by the microfocus hard X-ray diffraction beamline from a new insight. The crystalline phase transformation led to a gradient distribution of crystallinity and lateral crystallite size along the crack propagation direction. © 2014 Wiley Periodicals, Inc. Source

Fan H.,University of Sichuan | Fan H.,Key Laboratory of Energy Engineering Safety and Disaster Mechanics | Fan H.,Johns Hopkins University | El-Awady J.A.,Johns Hopkins University | And 2 more authors.
Journal of Nuclear Materials

The mechanisms leading to stacking fault tetrahedron (SFT) absorption via interactions with dislocations, and subsequent formation of plastic flow localization in defect-free channels, which were frequently observed in irradiated materials in transmission electron microscopy experiments, are still unclear. To address this, screw dislocation interactions with SFTs in copper were investigated using molecular dynamics (MD) simulations. The interaction details reveal that a screw dislocation can fully absorb an SFT through the thermally activated transformation of Lomer-Cottrell lock into Lomer dislocations. After absorption, almost all the vacancies in the SFT are transferred into Lomer dislocations, which are able to move transversely under complex loading conditions. As a result, SFTs can be removed from the material (for SFTs near surface) or from defect-free channels (for SFTs in the bulk) with the aid of Lomer dislocations. In addition, it was shown that this absorption process is favorable only at high temperature, low applied shear stress and/or high SFT density. These results are in good agreement with in situ TEM observations. The current simulations and analyses provide useful insights into the formation mechanisms of defect-free channels in irradiated materials. © 2014 Elsevier B.V. All rights reserved. Source

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