厚壁半球形液压缸的强度计算及其与圆筒形液压缸对比分析

半球形液压缸是缸梁一体式压力机的主要承力构件，它与传统的三梁四柱式液压机的圆筒形液压缸相比，结构上和受力状态都发生很大的改变，从而使承压能力有近一倍的提高。导出半球形液压缸强度计算公式，对于厚壁球壳，最薄弱区域是球的内壁，在该处有最大的经(纬)向拉应力与代数值最小(绝对值最大)的径向压应力。按照Tresca 强度准则或Mises强度准则均可算出数值相同的最大当量应力，强度计算公式表明该应力应小于或等于材料的许用应力。并将该式与圆筒形液压缸强度计算公式进行对比，在相同条件下(相同许用应力、相同内压及相同内半径)，计算结果表明，半球形液压缸的壁厚要远小于圆筒形液压缸，减重效果明显。

Strength Calculation of Thick-walled Hemispherical Hydraulic Cylinder and Comparative Analysis with Cylindrical Hydraulic Cylinder

Hemispherical hydraulic cylinder is the key part of hydraulic press with unity of cylinder and beam(HPUCB). Comparing with the cylindrical hydraulic cylinder used in traditional three beams four pillars hydraulic press, it can support approximately two times liquid pressure due to the significant changes in structure and stress state. Strength calculation equation for hemispherical hydraulic cylinder is derived. For the thick-walled spherical shell, the weakest zone is located on the inner wall where the algebraic value of radial stress is smallest(the absolute value is largest) and the latitudinal tensile stress and longitude tensile stress are biggest. The equivalent stresses calculated through 3rd strength theorem or 4th strength theorem are the same, and it should be less than the allowable stress of the material. Comparing with strength calculation equation between hemispherical hydraulic cylinder and cylindrical hydraulic cylinder under the condition of the same liquid pressure, the same inner radius and the same allowable stress, it can be seen that thickness of hemispherical hydraulic cylinder is much less than the cylindrical hydraulic cylinder, and the effect of reducing weight is obvious.