非等厚度四点弯曲试样环向应力理论研究

针对四点弯曲试样标准为等厚度直梁试样，不能真实模拟管件曲梁结构的真实工况，设计了一种外壁为完整的一段圆弧，内壁为一直线段和两段对称圆弧构成的非标准、非等厚度的四点弯曲试样。根据非等厚度的四点弯曲试样结构及其力学模型，推导出了其外壁任意一点环向拉应力与试样加载载荷之间的理论计算公式，建立了该四点弯曲试样的有限元力学计算模型。计算结果表明，文中推导出的理论公式计算出的最大环向应力与有限元法的计算结果误差的绝对值为0.06%~0.33%，几乎没有误差，充分证明了理论公式的准确性，该理论公式为非等厚度四点弯曲的应力腐蚀开裂试验加载参数提供了简便的计算方法。

Theoretical Research on Circumferential Stress of Four-point Bending Specimen of Unequal Thickness

Straight beam specimens of equal thickness,which are standard four-point bending specimens,cannot be used to simulate the real working condition of the curved-beam structure of pipes.Therefore,a non-standard four-point bending specimen of unequal thickness was designed,which has a complete arc as the outer wall and a straight-line segment combined with two symmetrical arcs as the inner wall.Based on the structure and mechanical model of a four-point bending specimen with unequal thickness,a theoretical formula to calculate the circumferential tensile stress at any arbitrary point on the specimen’s outer wall from the load of the specimen was derived.Further,a finite element mechanics calculation model for this four-point bending specimen was established.The results show that the absolute error of the maximum circumferential stress calculated by the theoretical formula derived in the paper was 0.06%～0.33%compared to the result by the finite element method.This indicates that there is almost no error,which fully proves the accuracy of the theoretical formula.The theoretical formula provides a simple method for calculating load parameters of stress-corrosion cracking experiments with the four-point bending specimen of unequal thickness.