Abstract
In view of the early fatigue damage of high-strength steel FV520B, a nonlinear ultrasonic detection was performed on two types of fatigue samples using nonlinear Lamb waves. The experimental results indicated that the ultrasonic nonlinear parameter is highly sensitive to early fatigue damage in high-strength FV520B. For plate specimens, the ultrasonic nonlinear parameter increased with the number of fatigue cycles. Scanning electron microscopy (SEM) observations of the fatigue specimens revealed that as the number of fatigue cycles increased, the microstructure of the material gradually deteriorated, and the ultrasonic nonlinear parameter increased. For notched specimens, the ultrasonic nonlinear parameter increased as the size of the main crack increased. SEM observations of the fracture indicated that the ultrasonic nonlinear parameters were more consistent with the equivalent microcrack length (defined as the sum of microcrack lengths in the statistical area), as compared with the length of the main crack. It was determined that the nonlinear effect of the Lamb wave is related to the equivalent microcrack length inside the material and that the ultrasonic nonlinear parameter can effectively characterize the fatigue damage state of high-strength FV520B.
Highlights
High-strength FV520B is often used to make centrifugal compressor impellers
Erefore, the study of ultrasonic nondestructive testing technology for the early fatigue damage of high-strength FV520B is of great significance
The growth of the main crack on the surface of the notch of the fatigue specimen was observed under the optical microscope, including the crack morphology and the length of the main crack. e notched sample was cut off using an Instron universal material testing machine, and its section was observed under Scanning electron microscopy (SEM)
Summary
High-strength FV520B is often used to make centrifugal compressor impellers. A centrifugal compressor is an important energy conversion device and is widely used in the petroleum, chemical, metallurgy, natural gas transmission, aero-engine, and mine ventilation industries, and in other important fields [1,2,3]. e impeller is an integral part of the centrifugal compressor associated with high rotational speeds and complex loading. e impeller often generates small vibrations at high frequencies; it is prone to fatigue failure [4, 5]. e accidents caused by fatigue failure are often catastrophic and can cause massive losses.erefore, the study of ultrasonic nondestructive testing technology for the early fatigue damage of high-strength FV520B is of great significance.For most well-designed engineering components, the early damage of the material (before the formation of macrocracks) accounts for more than 80% of the component life [6]. High-strength FV520B is often used to make centrifugal compressor impellers. E impeller is an integral part of the centrifugal compressor associated with high rotational speeds and complex loading. Erefore, the study of ultrasonic nondestructive testing technology for the early fatigue damage of high-strength FV520B is of great significance. While the existing nondestructive testing technology, which includes linear ultrasonic testing technology, is effective for the detection of macrodefects in materials, it is less sensitive to early damage (e.g., dislocation structure and microcracks) to the materials before macrocracks appear in the fatigue process. Recent studies have shown that the degradation of the early mechanical properties of materials can trigger ultrasonic nonlinear effects [7]. Jhang and Kim [8] conducted nonlinear ultrasonic testing research on SS41 and SS45 medium-carbon steel under tensile and fatigue loading, respectively, and analyzed the high-order harmonics in the process of ultrasonic propagation. Walker et al [10] used a nonlinear
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