Abstract
It has been shown that nonlinear ultrasonics can be more sensitive to local incipient defects, such as a fatigue crack, than conventional linear ultrasonics. Therefore, there is an increasing interest in utilizing nonlinear ultrasonics for structural health monitoring and nondestructive testing applications. While the conditions, which are the necessary conditions that should be satisfied for the generation of nonlinear harmonic components, are extensively studied for distributed material nonlinearity, little work has been done to understand the necessary conditions at the presence of a localized nonlinear source such as a fatigue crack. In this paper, the necessary conditions of nonlinear ultrasonic modulation generation in a plate-like structure are formulated specifically for a localized nonlinear source. Then, the correctness of the formulated necessary conditions is experimentally verified using ultrasounds obtained from aluminum plates.
Highlights
Due to a high sensitivity to micro defects such as a fatigue crack, nonlinear ultrasonic techniques, which look for nonlinear characteristics of ultrasounds, have gained prominence in structural health monitoring (SHM) and nondestructive testing (NDT) applications [1,2,3,4]
The condition (NCs), which are necessary for the generation of nonlinear ultrasonic components are necessary condition (NCs), which are necessary for the generation of nonlinear ultrasonic components formulated for a localized nonlinear source
The suitability of the necessary conditions (NCs) is validated through the are formulated for a localized nonlinear source
Summary
Due to a high sensitivity to micro defects such as a fatigue crack, nonlinear ultrasonic techniques, which look for nonlinear characteristics of ultrasounds, have gained prominence in structural health monitoring (SHM) and nondestructive testing (NDT) applications [1,2,3,4]. Nonlinear ultrasonic techniques use nonlinear components, such as harmonics and modulations, which are generated from the interaction of ultrasounds with nonlinear sources such as material degradation and fatigue cracks. One of the essential steps for using guided wave based nonlinear ultrasonic techniques on plate, rod, and pipe structures is matching the necessary conditions (NCs) for the generation of the nonlinear components. The NCs, which must be satisfied for the creation of nonlinear components due to distributed material nonlinearity are provided by de Lima and Hamilton [5,6]. There is a large volume of literature utilizing the NCs for the distributed material nonlinearity to characterize material properties and degradations [8,9,10,11,12,13]
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