基于圆筒内硬球颗粒的致密化过程涉及应力传递与堆积结构的耦合作用,是颗粒介质研究中的一个难点问题,为此,采用MTS 858 Mini Bionix Ⅱ型力学性能测试仪,通过改变压力、颗粒粒径、剪切速率等参数,对循环扭转剪切作用下的致密化行为进...基于圆筒内硬球颗粒的致密化过程涉及应力传递与堆积结构的耦合作用,是颗粒介质研究中的一个难点问题,为此,采用MTS 858 Mini Bionix Ⅱ型力学性能测试仪,通过改变压力、颗粒粒径、剪切速率等参数,对循环扭转剪切作用下的致密化行为进行实验研究。研究结果表明:颗粒介质致密化过程表现为快速致密和缓慢致密2个阶段,体积分数的演化过程满足双指数项关联函数,即φ(t)=φ0+A1(1-exp(-t/t1))+A2(1-exp(-t/t2))(其中,φ0为系统初始体积分数,A1和A2为拟合系数,t1和t2分别为快速和缓慢致密过程的特征时间);系统经历快速堵塞过程后,进入颗粒缓慢重排过程;在循环剪切过程中,颗粒体积分数的涨幅Δφ在体积分数达到0.604时发生由降转升的转变;增大压力、粒径与圆筒直径之比(d/D)以及剪切速率均有利于提高致密化程度,循环扭转剪切作用比纯剪切和垂直振动作用的致密化效率更高。展开更多
Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian ...Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases （or degradation degree increases） significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.展开更多
Deformation and fatigue of extruded Mg-8.0 Gd-3.0 Y-0.5 Zr(GW83, wt%) magnesium(Mg) alloy were experimentally investigated under cyclic torsion using tubular specimen fabricated along the extrusion direction. The cont...Deformation and fatigue of extruded Mg-8.0 Gd-3.0 Y-0.5 Zr(GW83, wt%) magnesium(Mg) alloy were experimentally investigated under cyclic torsion using tubular specimen fabricated along the extrusion direction. The controlled shear strain amplitudes ranged from 0.606% to 4.157%. Twinning and detwinning of extension twins are observed to take place during cyclic torsion and the shear stress-shear strain hysteresis loops display a perfectly symmetric shape at all tested strain amplitudes. Marginal cyclic softening is observed when the shear strain amplitude is higher than 1.732%. The strain-life fatigue curve shows two kink points, corresponding to the shear strain amplitude of 1.040% and 1.732%, respectively.When the shear strain amplitude is higher than the upper kink point, early fatigue crack is found to initiate on the maximum shear plane. When the strain amplitude is lower than the lower kink point,fatigue cracking is parallel to the maximum tensile plane. At an identical equivalent strain amplitude,the fatigue life under pure shear is much higher than that under tension-compression. The fatigue life of extruded GW83 alloy is much higher than that of extruded AZ31 B alloy at the same plastic strain energy density.展开更多
文摘基于圆筒内硬球颗粒的致密化过程涉及应力传递与堆积结构的耦合作用,是颗粒介质研究中的一个难点问题,为此,采用MTS 858 Mini Bionix Ⅱ型力学性能测试仪,通过改变压力、颗粒粒径、剪切速率等参数,对循环扭转剪切作用下的致密化行为进行实验研究。研究结果表明:颗粒介质致密化过程表现为快速致密和缓慢致密2个阶段,体积分数的演化过程满足双指数项关联函数,即φ(t)=φ0+A1(1-exp(-t/t1))+A2(1-exp(-t/t2))(其中,φ0为系统初始体积分数,A1和A2为拟合系数,t1和t2分别为快速和缓慢致密过程的特征时间);系统经历快速堵塞过程后,进入颗粒缓慢重排过程;在循环剪切过程中,颗粒体积分数的涨幅Δφ在体积分数达到0.604时发生由降转升的转变;增大压力、粒径与圆筒直径之比(d/D)以及剪切速率均有利于提高致密化程度,循环扭转剪切作用比纯剪切和垂直振动作用的致密化效率更高。
基金supported bythe National Natural Science Foundation of China(Grant Nos.50579006,50639010 and 50909014)
文摘Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases （or degradation degree increases） significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.
基金the support of the National Natural Science Foundation of China(51601112)Shanghai Rising-Star Program(17QB1403000,16QB1402800)+1 种基金support by National Natural Science Foundation of China(11572191)support from the National Science Foundation(CMMI-1762312).
文摘Deformation and fatigue of extruded Mg-8.0 Gd-3.0 Y-0.5 Zr(GW83, wt%) magnesium(Mg) alloy were experimentally investigated under cyclic torsion using tubular specimen fabricated along the extrusion direction. The controlled shear strain amplitudes ranged from 0.606% to 4.157%. Twinning and detwinning of extension twins are observed to take place during cyclic torsion and the shear stress-shear strain hysteresis loops display a perfectly symmetric shape at all tested strain amplitudes. Marginal cyclic softening is observed when the shear strain amplitude is higher than 1.732%. The strain-life fatigue curve shows two kink points, corresponding to the shear strain amplitude of 1.040% and 1.732%, respectively.When the shear strain amplitude is higher than the upper kink point, early fatigue crack is found to initiate on the maximum shear plane. When the strain amplitude is lower than the lower kink point,fatigue cracking is parallel to the maximum tensile plane. At an identical equivalent strain amplitude,the fatigue life under pure shear is much higher than that under tension-compression. The fatigue life of extruded GW83 alloy is much higher than that of extruded AZ31 B alloy at the same plastic strain energy density.
