Very high cycle fatigue behavior （107 --109 cycles） of 304L austenitic stainless steel was studied with ultra- sonic fatigue testing system （20 kHz）. The characteristics of fatigue crack initiation and propagation...Very high cycle fatigue behavior （107 --109 cycles） of 304L austenitic stainless steel was studied with ultra- sonic fatigue testing system （20 kHz）. The characteristics of fatigue crack initiation and propagation were discussed based on the observation of surface plastic deformation and heat dissipation. It was found that micro-plasticity （slip markings） could be observed on the specimen surface even at very low stress amplitudes. The persistent slip mark- ings increased clearly along with a remarkable process of heat dissipation just before the fatigue failure. By detailed investigation using a scanning electron microscope and an infrared camera, slip markings appeared at the large grains where the fatigue crack initiation site was located. The surface temperature around the fatigue crack tip and the slip markings close to the fracture surface increased prominently with the propagation of fatigue crack. Finally, the cou- pling relationship among the fatigue crack propagation, appearance of surface slip markings and heat dissipation was analyzed for a better understanding of ultrasonic fatigue damage behavior.展开更多
The large plastic produced by human production and life is degraded into micro-plastics in the environment. Micro-plastics are harmful to organisms and the environment. In order to determine the hazards of micro-plast...The large plastic produced by human production and life is degraded into micro-plastics in the environment. Micro-plastics are harmful to organisms and the environment. In order to determine the hazards of micro-plastic pollution, zebrafish embryos were used as the tested organism, and 0.6-1.0 μm polystyrene micro-plastic was used to carry out embryo exposure experiment. The toxic effects of polystyrene plastic particles on zebrafish embryos were investigated comprehensively, and the toxicity was evaluated. The results of this study showed that 0.6-1.0 μm polystyrene micro-plastic had certain toxicity on zebrafish embryos, and it had a lethal effect when the concentration reached 250 mg/L; 25 mg/L 0.6-1.0 μm polystyrene particles can cause cyrtosis and pericardial edema of zebrafish embryos and other non-lethal toxic effects; and 250 and 1 000 mg/L exposure concentration can slow down heart rate. A hazard evaluation index system of polystyrene particles to zebrafish embryos was established, and it is determined that the exposure to 250 mg/L or lower concentration of polystyrene particles has slight hazard.展开更多
A two-dimensional discrete dislocation dynamics （DDD） technology by Giessen and Needleman （1995）, which has been extended by integrating a dislocation-grain boundary interaction model, is used to computationally a...A two-dimensional discrete dislocation dynamics （DDD） technology by Giessen and Needleman （1995）, which has been extended by integrating a dislocation-grain boundary interaction model, is used to computationally analyze the micro-cyclic plastic response of polycrystals containing micron-sized grains, with special attentions to significant influence of dislocationpenetrable grain boundaries （GBs） on the micro-plastic cyclic responses of polycrystals and underlying dislocation mechanism. Toward this end, a typical polycrystalline rectangular specimen under simple tension-compression loading is considered. Results show that, with the increase of cycle accumulative strain, continual dislocation accumulation and enhanced dislocation-dislocation interactions induce the cyclic hardening behavior; however, when a dynamic balance among dislocation nucleation, penetration through GB and dislocation annihilation is approximately established, cyclic stress gradually tends to saturate. In addition, other factors, including the grain size, cyclic strain amplitude and its history, also have considerable influences on the cyclic hardening and saturation.展开更多
Micro(nano)plastics(MNPs)are a growing problem as persistent environmental pollutants.Here,we investigated the impact of MNPs on microorganisms in aquatic microbial floc exposed to NPs(80 nm)and MPs(8μm)for 35 days.W...Micro(nano)plastics(MNPs)are a growing problem as persistent environmental pollutants.Here,we investigated the impact of MNPs on microorganisms in aquatic microbial floc exposed to NPs(80 nm)and MPs(8μm)for 35 days.Water quality indicators were tested weekly and microbiological analyses were conducted on Day 7 and 28 after exposure.The results showed that there were significant differences in the levels of total ammonia nitrogen or nitrite between the MNPs groups and the control group,spanning from Day 7 to Day 28.For the microbial response,microbial community richness in the NPs and MPs groups were significantly increased at Day 7.Functional prediction showed that the relative abundances of bacteria associated with the“Forms Biofilms”,“Potentially Pathogenic”,“Plastic Degradation”and nitrogen cycle processes were significantly different after MNPs exposure.The results suggest that MNPs had no significant effect on the microbial diversity of mature microbial flocs.Findings suggest MPs could cause an increase in the relative abundance of potentially pathogenic bacteria,while NPs do not.In addition,stress associated with MNPs affected the nitrogen cycle of microorganisms,and NPs exerted greater impacts than MPs.Findings from this study further our understanding of the impact of MNPs at environmentally relevant concentrations on microorganisms in aquatic ecosystems.展开更多
基金Item Sponsored by National Natural Science Foundation of China(10925211,11172188)Fundamental Research Funds from the Central Universities of China(2012SCU04A05)
文摘Very high cycle fatigue behavior （107 --109 cycles） of 304L austenitic stainless steel was studied with ultra- sonic fatigue testing system （20 kHz）. The characteristics of fatigue crack initiation and propagation were discussed based on the observation of surface plastic deformation and heat dissipation. It was found that micro-plasticity （slip markings） could be observed on the specimen surface even at very low stress amplitudes. The persistent slip mark- ings increased clearly along with a remarkable process of heat dissipation just before the fatigue failure. By detailed investigation using a scanning electron microscope and an infrared camera, slip markings appeared at the large grains where the fatigue crack initiation site was located. The surface temperature around the fatigue crack tip and the slip markings close to the fracture surface increased prominently with the propagation of fatigue crack. Finally, the cou- pling relationship among the fatigue crack propagation, appearance of surface slip markings and heat dissipation was analyzed for a better understanding of ultrasonic fatigue damage behavior.
基金Supported by Innovation and Entrepreneurship Program Project of Students in Hainan Medical University(HYCX2016040)Program of Hainan Association for Science and Technology Plans to Youth R&D Innovation(2015013)
文摘The large plastic produced by human production and life is degraded into micro-plastics in the environment. Micro-plastics are harmful to organisms and the environment. In order to determine the hazards of micro-plastic pollution, zebrafish embryos were used as the tested organism, and 0.6-1.0 μm polystyrene micro-plastic was used to carry out embryo exposure experiment. The toxic effects of polystyrene plastic particles on zebrafish embryos were investigated comprehensively, and the toxicity was evaluated. The results of this study showed that 0.6-1.0 μm polystyrene micro-plastic had certain toxicity on zebrafish embryos, and it had a lethal effect when the concentration reached 250 mg/L; 25 mg/L 0.6-1.0 μm polystyrene particles can cause cyrtosis and pericardial edema of zebrafish embryos and other non-lethal toxic effects; and 250 and 1 000 mg/L exposure concentration can slow down heart rate. A hazard evaluation index system of polystyrene particles to zebrafish embryos was established, and it is determined that the exposure to 250 mg/L or lower concentration of polystyrene particles has slight hazard.
基金supported by the National Natural Science Foundation of China(No.10672064).
文摘A two-dimensional discrete dislocation dynamics （DDD） technology by Giessen and Needleman （1995）, which has been extended by integrating a dislocation-grain boundary interaction model, is used to computationally analyze the micro-cyclic plastic response of polycrystals containing micron-sized grains, with special attentions to significant influence of dislocationpenetrable grain boundaries （GBs） on the micro-plastic cyclic responses of polycrystals and underlying dislocation mechanism. Toward this end, a typical polycrystalline rectangular specimen under simple tension-compression loading is considered. Results show that, with the increase of cycle accumulative strain, continual dislocation accumulation and enhanced dislocation-dislocation interactions induce the cyclic hardening behavior; however, when a dynamic balance among dislocation nucleation, penetration through GB and dislocation annihilation is approximately established, cyclic stress gradually tends to saturate. In addition, other factors, including the grain size, cyclic strain amplitude and its history, also have considerable influences on the cyclic hardening and saturation.
基金the Science and Technology Project of Guizhou Province,China([2020]4Y027)the National Natural Science Foundation of China(32002392)the Program Foundation for Talents of Guizhou University(No.[2021]15 and No.[2021]65).
文摘Micro(nano)plastics(MNPs)are a growing problem as persistent environmental pollutants.Here,we investigated the impact of MNPs on microorganisms in aquatic microbial floc exposed to NPs(80 nm)and MPs(8μm)for 35 days.Water quality indicators were tested weekly and microbiological analyses were conducted on Day 7 and 28 after exposure.The results showed that there were significant differences in the levels of total ammonia nitrogen or nitrite between the MNPs groups and the control group,spanning from Day 7 to Day 28.For the microbial response,microbial community richness in the NPs and MPs groups were significantly increased at Day 7.Functional prediction showed that the relative abundances of bacteria associated with the“Forms Biofilms”,“Potentially Pathogenic”,“Plastic Degradation”and nitrogen cycle processes were significantly different after MNPs exposure.The results suggest that MNPs had no significant effect on the microbial diversity of mature microbial flocs.Findings suggest MPs could cause an increase in the relative abundance of potentially pathogenic bacteria,while NPs do not.In addition,stress associated with MNPs affected the nitrogen cycle of microorganisms,and NPs exerted greater impacts than MPs.Findings from this study further our understanding of the impact of MNPs at environmentally relevant concentrations on microorganisms in aquatic ecosystems.
