To understand the high strain rate deformation mechanism and determine the grain size,strain rate and porosity dependent yield strength of nanocrystalline materials,a new mechanical model based on the deformation mech...To understand the high strain rate deformation mechanism and determine the grain size,strain rate and porosity dependent yield strength of nanocrystalline materials,a new mechanical model based on the deformation mechanism of nanocrystalline materials under high strain rate loading was developed.As a first step of the research,the yield behavior of the nanocrystalline materials under high strain rate loading was mainly concerned in the model and uniform deformation was assumed for simplification.Nanocrystalline materials were treated as composites consisting of grain interior phase and grain boundary phase,and grain interior and grain boundary deformation mechanisms under high strain rate loading were analyzed,then Voigt model was applied to coupling grain boundary constitutive relation with mechanical model for grain interior phase to describe the overall yield mechanical behavior of nanocrystalline materials.The predictions by the developed model on the yield strength of nanocrysatlline materials at high strain rates show good agreements with various experimental data.Further discussion was presented for calculation results and relative experimental observations.展开更多
Precipitation behavior of Ti in high strength steels was investigated by means of the equilibrium solid solubility theory. The contributions of Ti content to yield strength were calculated. The calculated results were...Precipitation behavior of Ti in high strength steels was investigated by means of the equilibrium solid solubility theory. The contributions of Ti content to yield strength were calculated. The calculated results were verified by the hot rolling experiment for C–Mn steel and C–Mn–Ti micro alloyed steel, respectively. The research results show that the precipitates are mainly Ti N at the higher temperature. With the decreasing temperature, the proportion of Ti C in precipitates increases gradually. When the temperature drops to 800 °C, Ti C will become predominant for the precipitation of Ti. When Ti content is less than 0.014%(mass fraction), Ti has little influence on the yield strength. When Ti content is in the range of 0.014%–0.03%(mass fraction), the yield strength of Ti micro alloyed steel is greatly increased, which leads to instability of the mechanical properties of the steel. Therefore, the design of Ti content in high strength steels should avoid this Ti content range. When Ti content is higher than 0.03%, the yield strength increases stably. In this experiment, when added Ti content was controlled in the range of 0.03%–0.05%, the contribution to the yield strength of Ti micro alloyed steel can reach about 92.44 MPa.展开更多
Cold-rolling was conducted on AZ31 magnesium alloy with fine and coarse grains to produce plates with high density of shear bands and{101^(-)1}twins,respectively.Then,these two kinds of plates are subjected to isother...Cold-rolling was conducted on AZ31 magnesium alloy with fine and coarse grains to produce plates with high density of shear bands and{101^(-)1}twins,respectively.Then,these two kinds of plates are subjected to isothermal annealing to reveal the effect of shear bands and{101^(-)1}twins on recrystallization behavior.During annealing,static recrystallization occurs firstly in shear band zones and{101^(-)1}twin zones,which has different effect on texture and mechanical properties.With the increase of annealing temperature,strong basal texture remains in annealed SG-17%while the basal texture is weakened gradually in annealed LG-15%.Recrystallized grains from twin zones have a random orientation which is responsible for the weakened basal texture in annealed LG-15%.In addition,microhardness decreases gradually with the prolonged annealing time due to static recrystallization.LG-15%has a lower recrystallization activation energy because{101^(-)1}twins are in favor of the nucleation and growth of recrystallized grains.After 500℃annealing,the yield strength decreases significantly with a significant improvement in failure strain.The annealed LG-15%has a much higher compressive strain than the annealed SG-17%due to texture weakening effect.展开更多
地震动持时会显著影响结构累积损伤和破坏水平,但目前抗震设计中,对地震动持时对结构响应的影响考虑不足。为研究地震动持时对结构损伤的影响,文中采用谱匹配并结合小波变换方法,从日本强震动数据库(K-NET)中匹配得到115条不同持时的地...地震动持时会显著影响结构累积损伤和破坏水平,但目前抗震设计中,对地震动持时对结构响应的影响考虑不足。为研究地震动持时对结构损伤的影响,文中采用谱匹配并结合小波变换方法,从日本强震动数据库(K-NET)中匹配得到115条不同持时的地震动记录,计算了2种恢复力模型下的地震动损伤谱,并综合分析了地震动持时、屈服强度折减系数和结构自振周期等因素对结构损伤谱的影响。然后,该文从美国太平洋地震工程研究中心(Pacific Earthquake Engineering Research Center,PEER)选取了585条不同场地条件、具有不同持时的天然地震动记录,综合考虑地震动持时、屈服强度折减系数、结构恢复力模型以及场地条件影响,采用差分进化算法建立了损伤谱预测模型计算公式。与已有预测模型的对比研究表明,文中模型相对误差降低了40%以上,能够更好地预测考虑持时的地震动损伤谱,且具有更高精度。研究结果可为考虑地震动持时效应的结构抗震设计和损伤评估等提供参考。展开更多
探究聚-γ-谷氨酸(γ-PGA)对直播稻抗倒伏性、产量和品质的影响,为高产优质的水稻栽培技术提供理论依据和技术参考。于2022和2023年在湖北省武穴市花桥镇开展田间试验,采用双因素裂区设计,以直播方式水直播(W)和旱直播(D)为主区,不施加...探究聚-γ-谷氨酸(γ-PGA)对直播稻抗倒伏性、产量和品质的影响,为高产优质的水稻栽培技术提供理论依据和技术参考。于2022和2023年在湖北省武穴市花桥镇开展田间试验,采用双因素裂区设计,以直播方式水直播(W)和旱直播(D)为主区,不施加γ-PGA发酵液(P0)和施加25 kg hm–2γ-PGA发酵液(P1)为副区,共4个处理,对水稻抗倒伏能力相关指标、产量、稻米品质进行测定。结果表明,施加γ-PGA能分别使水、旱直播下水稻第一基节茎粗增加10.3%~10.6%和7.5%~13.3%,第二基节茎粗增加10.5%~11.8%和8.2%~17.5%,茎秆壁厚增加23.7%~27.9%和12.5%~22.0%,抗折能力提高37.3%~52.7%和50.8%~54.5%,弯曲力矩提高3.8%~7.6%和4.1%~5.9%,折断弯矩提高37.3%~52.7%和50.8%~54.5%,倒伏指数降低21.9%~29.1%和30.2%~32.2%。施加γ-PGA能改变水稻的茎秆强度,提高产量和稻米品质。展开更多
基金Project(10502025) supported by the National Natural Science Foundation of ChinaProject(101005) supported by Fok Ying Tong Education FoundationProject(BK2007528) supported by the Natural Science Foundation of Jiangsu Province,China
文摘To understand the high strain rate deformation mechanism and determine the grain size,strain rate and porosity dependent yield strength of nanocrystalline materials,a new mechanical model based on the deformation mechanism of nanocrystalline materials under high strain rate loading was developed.As a first step of the research,the yield behavior of the nanocrystalline materials under high strain rate loading was mainly concerned in the model and uniform deformation was assumed for simplification.Nanocrystalline materials were treated as composites consisting of grain interior phase and grain boundary phase,and grain interior and grain boundary deformation mechanisms under high strain rate loading were analyzed,then Voigt model was applied to coupling grain boundary constitutive relation with mechanical model for grain interior phase to describe the overall yield mechanical behavior of nanocrystalline materials.The predictions by the developed model on the yield strength of nanocrysatlline materials at high strain rates show good agreements with various experimental data.Further discussion was presented for calculation results and relative experimental observations.
基金Project(U1460204) supported by the Joint Funds of The Iron and Steel Key Project,ChinaProject(2015020180) supported by the Natural Science Foundation of Liaoning Province,ChinaProject(N140704002) supported by the Fundamental Research Funds for the Central Universities,China
文摘Precipitation behavior of Ti in high strength steels was investigated by means of the equilibrium solid solubility theory. The contributions of Ti content to yield strength were calculated. The calculated results were verified by the hot rolling experiment for C–Mn steel and C–Mn–Ti micro alloyed steel, respectively. The research results show that the precipitates are mainly Ti N at the higher temperature. With the decreasing temperature, the proportion of Ti C in precipitates increases gradually. When the temperature drops to 800 °C, Ti C will become predominant for the precipitation of Ti. When Ti content is less than 0.014%(mass fraction), Ti has little influence on the yield strength. When Ti content is in the range of 0.014%–0.03%(mass fraction), the yield strength of Ti micro alloyed steel is greatly increased, which leads to instability of the mechanical properties of the steel. Therefore, the design of Ti content in high strength steels should avoid this Ti content range. When Ti content is higher than 0.03%, the yield strength increases stably. In this experiment, when added Ti content was controlled in the range of 0.03%–0.05%, the contribution to the yield strength of Ti micro alloyed steel can reach about 92.44 MPa.
基金Project(52405369) supported by National Natural Science Foundation of ChinaProject(BK20210891) supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(BX2022030) supported by the Special Project of Introducing Foreign Talents of Jiangsu Province,China。
文摘Cold-rolling was conducted on AZ31 magnesium alloy with fine and coarse grains to produce plates with high density of shear bands and{101^(-)1}twins,respectively.Then,these two kinds of plates are subjected to isothermal annealing to reveal the effect of shear bands and{101^(-)1}twins on recrystallization behavior.During annealing,static recrystallization occurs firstly in shear band zones and{101^(-)1}twin zones,which has different effect on texture and mechanical properties.With the increase of annealing temperature,strong basal texture remains in annealed SG-17%while the basal texture is weakened gradually in annealed LG-15%.Recrystallized grains from twin zones have a random orientation which is responsible for the weakened basal texture in annealed LG-15%.In addition,microhardness decreases gradually with the prolonged annealing time due to static recrystallization.LG-15%has a lower recrystallization activation energy because{101^(-)1}twins are in favor of the nucleation and growth of recrystallized grains.After 500℃annealing,the yield strength decreases significantly with a significant improvement in failure strain.The annealed LG-15%has a much higher compressive strain than the annealed SG-17%due to texture weakening effect.
文摘地震动持时会显著影响结构累积损伤和破坏水平,但目前抗震设计中,对地震动持时对结构响应的影响考虑不足。为研究地震动持时对结构损伤的影响,文中采用谱匹配并结合小波变换方法,从日本强震动数据库(K-NET)中匹配得到115条不同持时的地震动记录,计算了2种恢复力模型下的地震动损伤谱,并综合分析了地震动持时、屈服强度折减系数和结构自振周期等因素对结构损伤谱的影响。然后,该文从美国太平洋地震工程研究中心(Pacific Earthquake Engineering Research Center,PEER)选取了585条不同场地条件、具有不同持时的天然地震动记录,综合考虑地震动持时、屈服强度折减系数、结构恢复力模型以及场地条件影响,采用差分进化算法建立了损伤谱预测模型计算公式。与已有预测模型的对比研究表明,文中模型相对误差降低了40%以上,能够更好地预测考虑持时的地震动损伤谱,且具有更高精度。研究结果可为考虑地震动持时效应的结构抗震设计和损伤评估等提供参考。
文摘探究聚-γ-谷氨酸(γ-PGA)对直播稻抗倒伏性、产量和品质的影响,为高产优质的水稻栽培技术提供理论依据和技术参考。于2022和2023年在湖北省武穴市花桥镇开展田间试验,采用双因素裂区设计,以直播方式水直播(W)和旱直播(D)为主区,不施加γ-PGA发酵液(P0)和施加25 kg hm–2γ-PGA发酵液(P1)为副区,共4个处理,对水稻抗倒伏能力相关指标、产量、稻米品质进行测定。结果表明,施加γ-PGA能分别使水、旱直播下水稻第一基节茎粗增加10.3%~10.6%和7.5%~13.3%,第二基节茎粗增加10.5%~11.8%和8.2%~17.5%,茎秆壁厚增加23.7%~27.9%和12.5%~22.0%,抗折能力提高37.3%~52.7%和50.8%~54.5%,弯曲力矩提高3.8%~7.6%和4.1%~5.9%,折断弯矩提高37.3%~52.7%和50.8%~54.5%,倒伏指数降低21.9%~29.1%和30.2%~32.2%。施加γ-PGA能改变水稻的茎秆强度,提高产量和稻米品质。
