GB/T 18852-2002 in English

《GB/T 18852-2002无损检测 超声检验 测量接触探头声束特性的参考试块和方法》由TC56（全国无损检测标准化技术委员会）归口，主管部门为国家标准化管理委员会。
本标准推荐两种金属参考试块、半圆阶梯试块（HS试块）和横孔试块（SDH试块）。本标准为接触探伤中使用的探头在固体内产生的声场提供了测定方法。

This Standard introduces two metal reference blocks, the hemi-step (HS) and the side-drilled-hole (SDH) blocks. This Standard establishes procedures for measuring the sound field or beam profiles produced by search units in contact tests. The search units include straight beam, angle beam (refracted compressional and refracted shear), focused beam and dual element search units. The diameter or the side dimension of the search unit shall be no greater than 25 mm. The methodology of this Standard provides guidelines for search units to be used for different metals including forged or rolled steel, aluminum or titanium alloy products. The frequency range of the search units used in this Standard extends from 1 MHz to 15 MHz, where 1 MHz to 5 MHz is best suited for steels and 5 MHz to 15 MHz is best for fine grain structured alloys such as aluminum products. If this Standard is to be used for material other than steels, users should be aware of the fact that the wave velocities in these materials may be different from that of steels and the angle beam search units are normally designed based on the steel applications. Snell’s law of refraction is described in this Standard so that correct refraction angles in other materials can be calculated. This Standard applies to angle beam search units of all practical angles (0° to 70°), and to focused and dual element search units. This Standard does not address the use of surface (Rayleigh) wave search units.
The procedures in this Standard can be used in whole, or in part, with other standards. For testing materials which are very thick or very thin, the present reference blocks may be made proportionally larger or smaller to accommodate different search unit beam sizes. This Standard does not address the estimation of equivalent defect sizes which will require reference blocks with flat-bottom-holes. This Standard establishes no acceptance criteria; but does establish the technical basis for criteria that may be defined by user parties.

Foreword II
Introduction III
1 Scope 1
2 Normative References 2
3 Symbols and Abbreviations 2
3.1 Symbols 2
3.2 Abbreviations 3
4 Descriptions of the Reference Blocks 3
4.1 Hemi-step (HS) block 3
4.2 Side-drilled hole (SDH) block 4
5 Techniques and Procedures 4
5.1 Straight beam search units (normal probe) 4
5.2 Angle beam search unit (angle probe) 5
5.3 Dual element search unit (twin crystal probe) 7
Appendix A (Normative) Time Base Calibration 18
Appendix B (Normative) Time of Flight (TOF) Beam Profile 20
Appendix C (Informative) Skew (or Squint) Angle, Far Field and Near Field Resolution 22