Tham khảo tài liệu 'volume 17 - nondestructive evaluation and quality control part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Grain size Effects of thermal or mechanical processing Distance-amplitude effects attenuation Flaw size Direction of the ultrasonic beam Information regarding standard reference blocks is available in ASTM E 127 see also the Selected References at the end of this article . Three types of standard blocks are ordinarily used for calibration or reference area-amplitude blocks distance-amplitude blocks and blocks of the type sanctioned by the International Institute of Welding IIW . These blocks must be prepared from material having the same or similar alloy content heat treatment and amount of hot or cold working as the material to be inspected to ensure equal sonic velocity attenuation and acoustic impedance in both the reference standard and the testpiece. If blocks of identical material are not available the difference between the material in the testpiece and the material used in the standard reference blocks must be determined experimentally. Area-amplitude blocks provide artificial flaws of different sizes at the same depth. Eight blocks made from the same 3 50 mm 2 in. diam round stock each 95 mm 3 I in. high constitute a set of area-amplitude blocks. The block material 3 must have the same acoustic properties as the testpiece material. Each block has a 20 mm in. deep flat-bottom hole 1 8 drilled in the center of the bottom surface Fig. 46 the hole diameters vary from to mm HI to 1 1 in. . The blocks are numbered to correspond with the diameter of the holes that is block No. 1 has a mm HI in. diam hole No. 2 has a mm HI in. diam hole and so on up to No. 8 which has a mm HI in. diam hole. Similar area- 15 amplitude blocks made from 49 mm 1 I I in. square stock are sometimes known as Series-A blocks. Fig. 46 Standard reference blocks for use in straight-beam ultrasonic inspection. a Area-amplitude block. b Distance-amplitude block. Dimensions given in inches The amplitude of the echo from a flat-bottom hole in the far field of a straight-beam
