滑带土长距离剪切强度及对滑坡启动的影响

滑带土的长距离剪切强度及其变化规律是滑坡启动的主要控制性因素之一,但是目前的常规直剪和三轴剪切试验还无法实现长距离剪切。为了研究滑带土的长距离剪切强度变化规律及对滑坡启动的影响,以四川省达县青宁乡滑坡为例,取其滑带土进行环剪试验,获得滑带土的长距离剪切强度变化规律,并与滑坡过程和运动特征进行对比分析。结果表明,滑带土长距离剪切强度变化规律与滑坡的启动过程较为吻合,滑坡首先受到降雨等因素触发开始变形和缓慢滑动,此时滑带土受到滑体的剪切,由于剪缩效应孔隙水压力迅速增大,导致剪切强度迅速减小,当小于某一临界值时,滑体开始加速并快速滑动。研究结论对类似的研究有一定的参考价值,可以为滑坡的预测预报和防治提供理论依据。

具有高品质因数的剪切力扫描近场光学显微镜在液体中的生物成像(英文)

基于剪切力的探针-试样间距控制扫描近场光学显微镜用于生物材料在液体中的成像比在空气中难得多。液体的黏性阻尼和软的试样表面要求更高的力检测灵敏度。最近我们试验成功的压电双晶片剪切力检测器结合力反馈技术,可以大幅度提高双晶片的机械谐振品质因数,从而改善在粘滞液体中力检测灵敏度。当双晶片在它的某一本征频率下被激励,通过调节一个适当的反馈力,它的机械谐振品质因数在水中可以从40增强到103,因此成像灵敏度获得显著改善。上述力检测技术被用于一些生物试样在液体环境下的拓扑和近场光学成像。所得到的力、相位和光学图像显示了高的成像质量和分辨率。实验结果证明上述装置尤其适宜于近场光学显微镜在生物领域的应用。

有限元中弹性连接单元的刚度矩阵

针对常用有限元软件中弹性连接单元的刚度矩阵开展研究。类似普通梁单元刚度矩阵的分析方法,将弹性连接单元的空间受力状态分解为伸缩、弯曲和扭转三种独立的模式进行分析,并提出两种方式推导弯曲受力模式下的刚度矩阵。对于弯曲受力状态下的刚度矩阵,明确了MIDAS中弹性连接单元输入参数包括弯曲和剪切刚度系数、弹性连接长度和剪切距离比R在刚度矩阵中的表现形式,给出了其刚度矩阵的理论表达式;阐明了剪切距离比R的力学意义,即用以考虑弹性支承两端因剪力传递的弯矩,其对结构的影响只体现在杆端位移结果中,杆端力始终满足静力平衡条件而不受R的影响,并且在R取0.5时,MIDAS中弹性连接的单元刚度矩阵与普通欧拉梁单元的刚度矩阵最为接近。同时通过分析对比,明确了ANSYS和ABAQUS中弹性连接单元的弯剪效应是独立的,这与MIDAS中弹性连接单元在不考虑剪切距离比R时的特性一致。研究成果既有助于理解弹性连接单元刚度矩阵,又为其工程应用提供了参考。

Analysis of strain variation in cross shear zone of plate during snake hot rolling

In order to study the distribution of equivalent and shear strain of aluminum alloy plate during snake hot rolling, several coupled thermo-mechanical finite element models(FEM) are established. Effects of speed ratio and offset distance on strain distribution of the plate are analyzed. The length of cross shear zone is defined to have a better understanding of the deformation characteristic in cross shear zone, which is the essential difference from symmetrical rolling in deformation zone. The results show that the equivalent strain and shear strain of lower part both increase with the increase of speed ratio, while the upper part decreases; the equivalent strain through the whole thickness decreases with ascending offset distance, while the shear strain of lower part increases. The length of cross shear zone quickly increases with ascending speed ratio and slightly decreases with ascending offset distance. The "positive" and "negative" cross shear zones are formed with the increase of speed ratio and offset distance, respectively. The value of the sensitivity coefficient of speed ratio is an order of magnitude bigger than the offset distance. However, the shear strain at center point increases with the ascending speed ratio and offset distance for different mechanism. As speed ratio increases, the asymmetry of the distribution of equivalent is becoming larger and the shear strain is generated in the same direction in cross shear zone. The FEM results agree well with experimental results.

对剪切线条痕迹的分析利用

本文主要研究了剪切工具线条痕迹的形成规律、形态特征,分析了造痕工具的结构特点,找出了进行工具种类、规格的推断方法。