Dual-Frequency Rayleigh Wave Source Modeling
Open Access
- Author:
- Boddie III, Gerald
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 03, 2021
- Committee Members:
- Clifford Jesse Lissenden, III, Thesis Advisor/Co-Advisor
Judith Todd Copley, Committee Member
Christopher Kube, Committee Member
Edward William Reutzel, Committee Member - Keywords:
- Line array source
Rayleigh waves
FEA
laser ultrasound
dual-frequency
additive manufacturing
nondestructive evaluation
signal processing - Abstract:
- Metallic additive manufacturing (AM) produces designs with complex geometries and specified material properties. Yet, current quality assurance (QA) and characterization methods limit ubiquitous adaption of a promising manufacturing technique. Various post-processing methods exist for defect detection and material characterization. However, destructive and post-processing methods do not facilitate real-time corrective feedback control. Thus, realizing real-time corrective control requires the AM inspection process to be shifted from post-process to in-situ. Furthermore, improving material characterization requires a better understanding of the AM material's microstructure. Rayleigh waves provide an non-destructive, non-contact source capable of nonlinear testing of AM microstructure and multiple layer in-situ inspection. Therefore, this thesis focuses on investigating a non-destructive non-contact ultrasonic source capable of generating a dual-frequency Rayleigh wavefield. Designing a source containing two identical adjacent individual sources generates a dual-frequency Rayleigh wavefield capable of in-situ inspection and nonlinear ultrasonic QA testing. Currently laser ultrasonic testing (LUT) allows for the in-situ inspection of a metallic AM part’s surface and nonlinear LUT facilitates microstructural interrogation, and thus material characterization. However the laser generation source must be manipulated to generate the desired ultrasound. Specifying the laser source generates ultrasound containing necessary features for non-contact, nondestructive nonlinear LUT of an AM part. Combining two individual line-array-sources (LASs) generates a nonlinear dual-frequency wavefield by overlapping the individually generated wavefields. Overlapping individual wavefield results in wave interference or wave mixing, when analyzing the system in a linear or nonlinear domain. Yet, appropriate nonlinear LUT depends on high amplitudes of the waves generated in the linear domain, primary waves, because the energy present in the higher harmonics generated in nonlinear domains arises from the energy present in the primary waves. Therefore, this thesis restricts the numerical analysis of the ultrasound produced by various LAS designs to a linear analysis, and focuses on the design of individual LASs. To design this ultrasonic source this thesis focuses on (i) efficient and accurate implementation of finite elements and parallel processing in a commercial Finite Element Analysis (FEA) software ABAQUS, (ii) identifying and determining appropriate values of influential geometric parameters of an individual LAS to determine high amplitude locations in the resulting wavefield. Individual LAS investigations utilize FEA tools and MATLAB to develop a signal processing method to interpret results and decide on appropriate design for adjacent LASs. Thus, this thesis conducts preliminary FEAs to investigate the effect of varying the length of a 4 MHz LAS from 2, 4, 6, 8 mm on the resulting energy distribution and subsequent FEA(s) to investigate 4 and 6 MHz LAS wavefield energy distributions. The FEAs provide both qualitative and quantitative results that assist in both individual and dual LAS designs. Furthermore FEA and MATLAB signal-processing facilitate individual analyses of wavefield energy distributions generated by various independent LASs. The quantitative results from the preliminary simulations convey that a 6 mm length 4 MHz LAS generates the highest energy wavefield and is therefore an appropriate length for the remainder of the LAS simulations. Moreover, the quantitative results from the 4 and 6 MHZ LAS wavefield studies highlights that the distance between two LASs should be minimized because a LAS generated wavefield exhibits a high rate of decreasing energy, due to spreading, in a direction transverse to propagation. Thus considerations and insights from both qualitative and quantitative results facilitate the design of a dual-line-array-source (DLAS). Specifically, for this thesis the 4 and 6 MHz DLAS is designed to generate a dual-frequency Rayleigh wavefield, which can be validated experimentally and numerically in future work.