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特定反射体的超声回波波幅与探头所放置表面的曲率半径 R 有关。因此常规的校正方法需要一套与工件的多种表面曲率相适应的试块。为此着手研究一种可以减少或取消制作这些曲面试块的校正技术。用锻钢件加工了一些表面曲率半径 R 为3～40吋(76.2～1016毫米)的试块。用纵波和横波平面接触式探头探查了这些试块内的平底孔和横孔。反射体(距离为4～8.5吋)处于探头声束的远场区。在这样的条件下,对于大 R,回波波幅与 R 无关。R 小于临界半径 R_c 时,回波波幅随 R 的减小而降低。R_c 值则根据探头特性和耦合层声阻抗的不匹配而推算出来。根据比值 R/R_c,提出了表示曲面试块与平面试块中相同反射体回波波幅之间关系的一种经验修正系数。
The ultrasonic echo amplitude of a particular reflector is related to the radius of curvature, R, of the surface on which the probe is placed. Therefore, the conventional calibration method requires a set of test pieces that are adapted to the various surface curvatures of the workpiece. To this end, we started to study a correction technique that can reduce or cancel the production of these surface test blocks. Forged pieces were machined with test coupons with a surface radius R of 3 to 40 inches (76.2 to 1016 mm). Plane and transverse holes were probed with longitudinal and transverse plane contact probes. The reflector (4 to 8.5 inches) is in the far field of the probe beam. Under such conditions, for large R, echo amplitude has nothing to do with R. When R is less than the critical radius R_c, the amplitude of the echo decreases as R decreases. The value of R_c is deduced from the mismatch between the probe characteristics and the acoustic impedance of the coupling layer. According to the ratio R / R_c, an empirical correction coefficient is proposed that represents the relationship between the echo amplitude of the curved reflector and the same reflector in the planar test block.