Abstract
In ultrasonic defect sizing using the maximum echo amplitude technique, the reflected echo signal height is taken to be related to the amount of ultrasound propagated energy which is reflected from defects and to the information contained in this reflected energy. In this investigation horizontal drilled holes of known sizes are considered in grey cast iron which is usually treated as the most difficult type of cast irons when ultrasonically inspected, due to its high sound attenuated nature. The defects sizing results obtained from grey cast iron are compared with those obtained from a steel of a similar pearlitic matrix structure as a reference material. 2, 4, 6 & 8 mm drilled holes at known depths are prepared in both grey cast iron and steel test samples. Maximum echo amplitude sizing method is adopted, using both compression wave probes & shear wave probes of 1,2,4 & 6 MHz frequencies at different scanning positions. Although the results are only limited to defect sizing in grey cast iron with reference to steel, they do
Highlights
Through the years, the majority of ultrasonic applications have been successfully directed towards detection and location of defects in cast & wrought metal parts, in addition to welded, brazed & bonded joints
Ultrasonic waves are one of the few forms of energy that can penetrate deep into the material to detect almost any type of defects and make useful estimate of defect size. These waves are relatively easy to use and has long been known to contain considerable and useful amount of information about the geometry & nature of defects [1,2]. This valuable inspection technique has been found unsuitable for material such as grey cast iron, which is known to be treated as highly attenuated material to ultrasonic waves due to its heterogeneous structure of composite nature [3,4]. i.e. In grey cast iron, the continuity of the metallic matrix is interrupted by infinite discontinuities of the non-metallic matrix component which is the graphite flakes
2-Lower defects echo signal amplitude response is the characteristics of grey cast iron compared with steel
Summary
The majority of ultrasonic applications have been successfully directed towards detection and location of defects in cast & wrought metal parts, in addition to welded, brazed & bonded joints. The effectiveness of some of these parameters is experimentally investigated in this article, with a proper interpretation of defects echo signals This hopefully will assist in yielding some of those structural parameters which have direct influence on grey cast iron ultrasonic inspection in general and defects sizing in particular. The materials involved in this research work, cover both plain-carbon steel and grey cast iron which have been carefully chosen This is in order to have pearlitic matrix (more than 90% pearlite), of similar pearlite grain size and pearlite lamination as illustrated in figure, so that matrix structure influence on ultrasonic wave propagation can be minimised as much as possible or even eliminated.
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