The crushed rocks are used as a filling material in mined丒out areas of underground mining. Compared with the man-made filling materials, the crushed rocks exhibit higher compressibility and lower stability, which may...The crushed rocks are used as a filling material in mined丒out areas of underground mining. Compared with the man-made filling materials, the crushed rocks exhibit higher compressibility and lower stability, which may result in instability of surrounding rock and surface subsidence. To study the creep compaction behavior of crushed mudstones, a series of creep tests are conducted. The investigations show that the creep compaction behavior of crushed mudstones is highly dependent on the original grain composition and axial stress applied on the samples. The samples with more large particles are easier to deform at initial loading stage for more large voids existed in the samples, and exhibit greater stability than those with smaller particles when the axial stress less than the bearing capacity of uframework structure When the axial stress is higher than 20 MPa, the influences of grain composition on deformability of crushed mudstones are weakened after the samples experience repeated compression. At lower stress level, the creep behavior prefers to occur in the samples w.h smaller particles, which is mainly caused by particles flow without significant particle breakage. As the axial stress increases, the single-sized sample with smaller particle size and the well-graded sample with larger Talbol power exponent n present more unstable under the constant stress. In addition, the filling of the residual intergranular voids by small particles formed by crushing and splitting behavior is the main cause of creep deformation. Lastly, a creep equation of crushed mudstones is obtained in this paper, which can agree with the experimental results in good.展开更多
Silicon carbide ceramics were prepared with SiC powder treated by the fluidized bed opposed jet mill as raw materials, and the effects of the ultra-fine treatment mechanism on the compaction and sintering behavior of ...Silicon carbide ceramics were prepared with SiC powder treated by the fluidized bed opposed jet mill as raw materials, and the effects of the ultra-fine treatment mechanism on the compaction and sintering behavior of SiC ceramics were investigated. The results showed that the compacts had higher density and microstructure homogeneity when the sintering temperature of the compact was decreased; and that the surface microstructure, densification and mechanical properties of the sintered body could be ameliorated obviously.展开更多
The present study aims to fabricate and evaluate the mechanical properties and wear behavior of Mg metal matrix composite,reinforced by 0,1.5,3,5 and 10 vol.%B4C microparticles.Mg−B4C samples were fabricated at 450℃ ...The present study aims to fabricate and evaluate the mechanical properties and wear behavior of Mg metal matrix composite,reinforced by 0,1.5,3,5 and 10 vol.%B4C microparticles.Mg−B4C samples were fabricated at 450℃ and under different loading rates by using split Hopkinson bar(SHB),drop hammer(DH)and Instron(QS)at strain rates of 1600,800 and 0.008 s–1,respectively.The mechanical properties including microhardness,quasi-static and dynamic compressive strengths and wear behavior of samples were experimentally investigated.The results show that,the hardness of SHB and DH samples is obtained to be 20.2%and 5.7%higher than that of the QS sample,respectively.The wear rate and wear mass loss of Mg–10.0%B4C samples fabricated by SHB were determined lower than those of the QS sample by nearly 33%and 39%,respectively.The quasi-static compressive strengths of Mg−5.0%B4C are improved by 39%,30%and 29%for the SHB,DH and QS samples,respectively,in comparison with the case of pure Mg.Furthermore,it is discovered that the dynamic compressive strength of samples is 51%−110%higher than their quasi-static value with respect to the B4C content.展开更多
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
对原为沟壑的场地,经回填全风化泥质粉砂岩形成高填方地基。对高填方地基采用3000 k N·m能级强夯预处理后,打设钻孔灌注桩,通过在桩身钢筋笼主筋上安装应力计,在桩身截面和桩周土层分别埋设沉降杆、分层沉降仪,测试桩身轴力、桩身...对原为沟壑的场地,经回填全风化泥质粉砂岩形成高填方地基。对高填方地基采用3000 k N·m能级强夯预处理后,打设钻孔灌注桩,通过在桩身钢筋笼主筋上安装应力计,在桩身截面和桩周土层分别埋设沉降杆、分层沉降仪,测试桩身轴力、桩身及桩周土层沉降变化情况,得到高填方夯实地基未处理填土层桩侧负摩阻力变化规律。试验结果表明,未处理填土层桩侧摩阻力沿深度呈现"负-正"变化的现象,随着固结时间的增加,端承桩负摩阻力区段大于摩擦桩。端承桩桩侧土层提供的最大负摩阻力约是摩擦桩的1.18~2.56倍,桩周土层密实度对桩侧最大负摩阻力有影响。采用一阶负指数函数拟合得到桩身下拉荷载预测模型,随着固结时间的增加,作用于桩身的下拉荷载趋于定值,作用于端承桩的下拉荷载比摩擦桩高41.2%~55.4%,从控制负摩阻力角度推导出高填方夯实地基摩擦桩桩长设计计算方法。桩身中性点位置均随固结时间增加而逐渐下移,端承桩中性点深度较摩擦桩平均大0.7 m。展开更多
基金This research was supported by the National Natural Science Foundation of China (Grant No. 51479195)the National Key Research and Development Plan of China (2016YFC0600901)+1 种基金the Special Fund of Basic Research and Operating of China University of Mining and Technology, Beijing (Grant No. 2009QL06)the State Scholarship Fund of China.
文摘The crushed rocks are used as a filling material in mined丒out areas of underground mining. Compared with the man-made filling materials, the crushed rocks exhibit higher compressibility and lower stability, which may result in instability of surrounding rock and surface subsidence. To study the creep compaction behavior of crushed mudstones, a series of creep tests are conducted. The investigations show that the creep compaction behavior of crushed mudstones is highly dependent on the original grain composition and axial stress applied on the samples. The samples with more large particles are easier to deform at initial loading stage for more large voids existed in the samples, and exhibit greater stability than those with smaller particles when the axial stress less than the bearing capacity of uframework structure When the axial stress is higher than 20 MPa, the influences of grain composition on deformability of crushed mudstones are weakened after the samples experience repeated compression. At lower stress level, the creep behavior prefers to occur in the samples w.h smaller particles, which is mainly caused by particles flow without significant particle breakage. As the axial stress increases, the single-sized sample with smaller particle size and the well-graded sample with larger Talbol power exponent n present more unstable under the constant stress. In addition, the filling of the residual intergranular voids by small particles formed by crushing and splitting behavior is the main cause of creep deformation. Lastly, a creep equation of crushed mudstones is obtained in this paper, which can agree with the experimental results in good.
文摘Silicon carbide ceramics were prepared with SiC powder treated by the fluidized bed opposed jet mill as raw materials, and the effects of the ultra-fine treatment mechanism on the compaction and sintering behavior of SiC ceramics were investigated. The results showed that the compacts had higher density and microstructure homogeneity when the sintering temperature of the compact was decreased; and that the surface microstructure, densification and mechanical properties of the sintered body could be ameliorated obviously.
文摘The present study aims to fabricate and evaluate the mechanical properties and wear behavior of Mg metal matrix composite,reinforced by 0,1.5,3,5 and 10 vol.%B4C microparticles.Mg−B4C samples were fabricated at 450℃ and under different loading rates by using split Hopkinson bar(SHB),drop hammer(DH)and Instron(QS)at strain rates of 1600,800 and 0.008 s–1,respectively.The mechanical properties including microhardness,quasi-static and dynamic compressive strengths and wear behavior of samples were experimentally investigated.The results show that,the hardness of SHB and DH samples is obtained to be 20.2%and 5.7%higher than that of the QS sample,respectively.The wear rate and wear mass loss of Mg–10.0%B4C samples fabricated by SHB were determined lower than those of the QS sample by nearly 33%and 39%,respectively.The quasi-static compressive strengths of Mg−5.0%B4C are improved by 39%,30%and 29%for the SHB,DH and QS samples,respectively,in comparison with the case of pure Mg.Furthermore,it is discovered that the dynamic compressive strength of samples is 51%−110%higher than their quasi-static value with respect to the B4C content.
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。
文摘对原为沟壑的场地,经回填全风化泥质粉砂岩形成高填方地基。对高填方地基采用3000 k N·m能级强夯预处理后,打设钻孔灌注桩,通过在桩身钢筋笼主筋上安装应力计,在桩身截面和桩周土层分别埋设沉降杆、分层沉降仪,测试桩身轴力、桩身及桩周土层沉降变化情况,得到高填方夯实地基未处理填土层桩侧负摩阻力变化规律。试验结果表明,未处理填土层桩侧摩阻力沿深度呈现"负-正"变化的现象,随着固结时间的增加,端承桩负摩阻力区段大于摩擦桩。端承桩桩侧土层提供的最大负摩阻力约是摩擦桩的1.18~2.56倍,桩周土层密实度对桩侧最大负摩阻力有影响。采用一阶负指数函数拟合得到桩身下拉荷载预测模型,随着固结时间的增加,作用于桩身的下拉荷载趋于定值,作用于端承桩的下拉荷载比摩擦桩高41.2%~55.4%,从控制负摩阻力角度推导出高填方夯实地基摩擦桩桩长设计计算方法。桩身中性点位置均随固结时间增加而逐渐下移,端承桩中性点深度较摩擦桩平均大0.7 m。
