Ph.D. (Engg): Ultrasonic Guided Wave-based Inspection of Additively Manufactured Components

Layered structural components, such as laminated composites and those made via Additive Manufacturing (AM), are widely used in aerospace and automotive industries due to their various advantages. The layer-wise approach allows for intricate and multifunctional designs, but their performance depends on factors such as joining technique, material properties, manufacturing conditions, and service environments. These layered components are susceptible to defects like delamination, debonding, porosity, residual stress, cracks, and surface roughness, affecting mechanical performance. In AM, process parameters like laser power, scan speed, layer thickness, hatch spacing, scan strategies, solidification strategies, and build chamber conditions impact the quality of the produced parts. Optimizing these parameters and using in-process monitoring systems can minimize these defects. This thesis focuses on developing an ultrasonics-based monitoring system for AM processes.
This work involves the modeling and analysis of wave propagation in multi-layered structures. For this purpose, three different approaches based on the modeling of interlayer interface bonding have been formulated. The developed models allow for the analysis of different levels of interface bonding, including perfect bonding and complete debonding. The AM components are idealized as one-dimensional higher-order planar frame structures. The equations of motion are derived from Hamilton’s principle, and the Fourier transform-based Spectral Finite Element Method (FSFEM) is used to perform the spectral analysis and the spectral elements formulation. The FSFEM formulation results in the dispersion curves and responses in frequency domain, which is transformed into the time domain by performing the inverse Fast Fourier Transform. A concept of effective thickness is introduced to match the cut-off frequencies in the dispersion curves obtained from the developed approaches with those of exact Lamb waves, which are used in determining the shear correction factors necessary for higher-order frame formulations.
The developed models undergo two levels of validation involving the validation of the dispersion curves, and time-domain responses. Reference dispersion curves are computed from open-source software for dispersion curve computation, while the reference time-domain responses are obtained from experiments and the Finite Element simulations.
Further, this thesis focuses on examining the interaction of ultrasonic-guided waves (UGW) with two types of defects – porosity and delamination/debonding. The impact of porosity is analyzed through porosity-dependent constitutive models. Various levels of delamination/debonding are numerically simulated by varying the interface bonding strength in the defect region. Additionally, the Semi-analytical Finite Element Method is employed to perform spectral analysis of defective structural waveguides with complex geometry, where the impact of various defect parameters, such as size, depth, and orientation, have been investigated. Further, the developed FSFEM models are employed to solve inverse problems for material property characterization, porosity estimation, and interface bonding strength characterization. Ultimately, these models provide a framework for analyzing the dynamic behavior of multi-layered structures, offering insights into the interaction of UGW with defects.

All are welcome.

Speaker :   Anoop Kumar Dube

Research Supervisor : Prof. S. Gopalakrishnan FNAE FASc, FIMechE, CEng