考虑非均匀应力分布的大型筒节轧制力计算模型

为了准确计算筒节轧制力,建立一种基于切块法的考虑筒节不均匀应力分布的轧制力计算模型。根据轧制过程中筒节和轧辊的几何关系,精确计算筒节内外表面的接触弧长;根据筒节非对称轧制条件,考虑非均匀分布的张应力和切应力,建立筒节轧制变形区(前滑区、搓轧区和后滑区)的力平衡微分方程;基于有限元软件Marc研究大型筒节轧制的轧透性条件。对某厂3 700 mm筒节轧机典型产品进行仿真,结果表明模型计算结果与实测结果误差小于10%,满足工业应用要求;为了满足轧制过程稳定性和异步轧制条件,筒节轧制压下量Δh>20 mm,上下轧辊速比1<v2/v1<1.02;上下轧辊速比对平均切应力影响较大,压下量对平均切应力的影响较小。

压应力非均匀分布下螺栓连接件垂向刚度研究

首先选取2块等厚度且半径足够大的圆盘型被连接件为研究对象,其轴向压缩变形体可等效为2个空心圆锥体。通过假设其垂直于螺栓轴的横向压应力非均匀分布并呈四次多项式分布以及假设横向压应力均匀分布,分别推导了其轴向压缩变形体的刚度计算公式。依据研究模型选择了不同尺寸和不同材料的螺栓连接,并建立其详细的有限元模型,并对其进行理论以及有限元对比分析计算,得出了当被连接件等效压缩体可简化为空心圆锥体时更精确的轴向压缩刚度计算公式。

聚乙烯管材残余应力的定性和定量评价

研究了冷却速度、挤出速度和拉伸比等不同挤出工艺对管材物理性能及残余应力的影响,结果表明,随着冷却和挤出速度的增加,PE管材纵向回缩率增大,静液压和SCG破坏时间逐渐降低。通过盲孔应变法研究了不同挤出工艺对管材内外层的释放应变和残余应力分布的影响,研究表明,采用理想化的均匀分布模型不适用于残余应力的定量评价,采用非均匀应力分布模型计算得到的管材外层的残余应力随着冷却和挤出速度的增加而增大,而管材内层的残余应力变化较小,由于管材沿壁厚方向冷却速度的不均匀,内外层残余应力分布存在差异。最终,通过对管材内中外层分别进行拉伸、密度和结晶度等物理性能试验,进一步证明了盲孔法定量评价残余应力的有效性。同时试验发现,当挤出拉伸比太高时,分子链取向严重,管材纵向回缩率增大,静液压和耐SCG性能下降,管材外层残余应力的最大值为14.6 MPa,与材料拉伸屈服强度相比,提高了50%。

井眼附近地应力数值模型研究

针对井眼周围岩石的受力情况,通过ANSYS有限元分析软件建立了7个二维数值模型,分析研究了均匀地应力和不同的远场应力对井眼及周围产生的影响,分析了井眼内和井眼外岩石的杨氏模量的差异和钻井过程中流体压力对其所产生的影响。在均匀地应力条件下,地应力的大小和方向是均匀地变化的,应力的非均匀性是井眼附近的应力轨迹发生变化的最主要原因。在非均匀地应条件下,井眼周围的应力轨迹会变为椭圆形。地应力的非均匀性以及岩石强度参数(如杨氏模量)的变化,对于井眼附近的地应力等值曲线形状的改变起着非常重要的作用。钻井液的压力以及非均匀地应力影响着井眼内外的应力变化。

Effect of non-uniform stress characteristics on stress measurement in specimen

There is a remarkable difference in stress distribution between a specimen and a plate removed from the specimen.The plate presents a uniform stress distribution whereas the specimen presents a non-uniform stress distribution.Firstly,the real stress distributions in plates with thickness of 30,40 and 50 mm and then in the specimens were obtained through simulation and X-ray surface stress measurement.Secondly,in order to study the impact of specimens shapes and processing ways on the results accuracy,two irregular shapes (parallelogram and trapezoid) and two processing ways (saw and electron discharge machining (EDM)) were compared and analyzed by simulation and experiment using layer removal method,then the specimen effects on measurement results were evaluated.The results show that:1) the non-uniform stress distribution characteristics of the specimen near the surface of the cut is significant,the range of non-uniform stress distribution is approximately one-thickness distance away from the cut,and it decreases gradually along the depth;2) In order to ensure the stability in the results,it is suitable to take the specimen plane size 2-3 times of its thickness;3) Conventional processing methods have little effect on experimental results and the average deviation is less than 5%.

Stress analytical solution for plane problem of a double-layered thick-walled cylinder subjected to a type of non-uniform distributed pressure

The stress state around circular openings,such as boreholes,shafts,and tunnels,is usually needed to be evaluated.Solutions for stresses,strains and ultimate bearing capacities of pressurized hollow cylinder are common cases.Stress analytical method for plane problem of a double-layered thick-walled cylinder subjected to a type of non-uniform pressure on the outer surface and uniform radial pressure on the inner surface is given.The power series method of complex function is used.The stress analytical solution is obtained with the assumption that two layers of a cylinder are fully contacted.The distributions of normal and tangential contact stress along the interface,tangential stress on the inner boundary and stresses in the radial direction at θ=0°,45° and 90°,are obtained.An example indicates that,when the elastic modulus of the inner layer of a double-layered thick-walled cylinder is smaller than that of the outer layer,the tangential stress is smaller than that in the corresponding point for a traditional cylinder composed of homogeneous materials.In that way,stress concentration at the inner surface can be alleviated and the stress distribution is more uniform.This is a capable way to enhance the elastic ultimate bearing capacity of thick-walled cylinder.