磁粉探伤用环形试件的几何尺寸

根据磁偶极子链近似理论对Betz环的分析结果，推导出下列关系：（m-1）／mlnm=2（h-a）／Dln（D／D-2h）（其中m=D／d，D-环外径，d-环内径，a-小孔半径，h-小孔埋藏深度），从而得悉：D、d、a、h中只有3个是独立的。由上式的数值计算证明：英国的BS6072-1981标准试件设计合理，而日本的儿SG0565-1982中B型对比试件的内径过小，无法达到环的使用目的，给出了改进后的合理内径尺寸。

Geometrical Dimensions of a Testing Ring for Magnetic Particle Inspection

Abstract： On the basis of the analytical result of Betz＇s ring by the approximate theory of magnetic dipole chains, the function below was derived for the magnetization of a testing ring through the threading-bar technique： （m-1）/mlnm=2（h-a）/Dln（D/D-2h）（in which, m=D/d, D-outer diameter of the ring, d-inner diameter of the ring, a-radius of the little hole, h-buried depth of the little hole）. Whereby it is known that only three among D, d, a and h are independent. The digital calculation from this formula proved that the design of the British standard testing ring BS 6072-1981 was reasonable, and that the core diameters of the Japanese comparing blocks Type B, JISG 0565-1982 were too small to reach their employed target. The rational sizes of the inner diameters after innovation were given in the present paper.