ASTM E1816-12
应用电磁声传感器 (EMAT) 技术进行超声检测的标准方法

Standard Practice for Ultrasonic Testing Using Electromagnetic Acoustic Transducer (EMAT) Techniques

被代替

标准号

ASTM E1816-12

发布

2012年

发布单位

美国材料与试验协会

替代标准

ASTM E1816-18

当前最新

ASTM E1816-18(2022)

 

 

引用标准

ANSI/ASNT CP-189 ASTM E114 ASTM E1316 ASTM E1774 ASTM E494 ASTM E543 ASTM E587 ASTM E797

适用范围

5. Significance and UseTop Bottom

5.1 Since EMAT techniques are noncontacting, they should be considered for ultrasonic examinations in which applications involve automation, high-speed examinations, moving objects, applications in remote or hazardous locations, and applications to objects at elevated temperatures or objects with rough surfaces. This practice describes procedures for using EMAT techniques as associated with the ultrasonic method to detect flaws for both surface and volumetric examinations as well as to measure thickness.

5.2 The uniqueness of the electromagnetic acoustic transducer technique for ultrasonic examination basically lies in the generation and reception of the ultrasonic waves. Otherwise, conventional ultrasonic techniques and methodologies generally apply.

5.3 An EMAT generates and receives acoustic waves in a material by electromagnetic means; electrically conductive or ferromagnetic materials can be examined. In its simplest form, an EMAT as a generator of ultrasonic waves is basically a coil of wire, excited by an alternating current, and placed in a uniform magnetic field near the surface of a material. For conductive materials, eddy currents are induced as a result of the alternating current. Due to the magnetic field, these eddy currents experience Lorentz forces that in turn are transmitted to the solid by collisions with the lattice or other microscopic processes. These forces are alternating at the frequency of the driving current and act as a source of ultrasonic waves. If the material is ferromagnetic, additional coupling mechanisms play a part in the generation of ultrasonic waves. Interactions between the dynamic magnetic field generated by the alternating currents and the magnetization associated with the material offer a source of coupling, as do the associated magnetostrictive influences. Reciprocal processes exist whereby all of these mechanisms lead to detection. Fig. 3 depicts the mechanisms (forces), along with associated direction, for electromagnetic ultrasound generation.

Note 1???j8201;=8201;current in a single conductor, Bo8201;=8201;magnetization from external magnet, Fm8201;=8201;magnetic force (ferromagnetic material), Fms8201;=8201;magnetostrictive force (ferromagnetic material), and FL8201;=8201;Lorentz force (conductive material).

FIG. 3 Mechanisms of Electromagnetic Ultrasound Generation

5.4 The EMAT can be used to generate all ultrasonic modes of vibration. As with conventional ultrasonic techniques, material types, probable flaw locations, and flaw orientations determine the selection of beam directions and modes of vibration. The use of EMATs and selection of the proper wave mode presuppose a knowledge of the geometry of the object; the probable location, size, orientation, and reflectivity of the expected flaws; the allowable range of EMAT lift-off; and the laws of physics governing the propagation of ......

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