Numerical Simulation of Laser Induced Elastic Waves in Response to Short and Ultrashort Laser Pulses.

Author

Alireza ZareiFollow

Date of Award

5-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Automotive Engineering

Committee Chair/Advisor

Srikanth Pilla

Committee Member

Gang Li

Committee Member

Rahul Rai

Committee Member

Morteza Sabet

Abstract

In an era of intensified market competition, the demand for cost-effective, high-quality, high-performance, and reliable products continues to rise. Meeting this demand necessitates the mass production of premium products through the integration of cutting-edge technologies and advanced materials while ensuring their integrity and safety. In this context, Nondestructive Testing (NDT) techniques emerge as indispensable tools for guaranteeing the integrity, reliability, and safety of products across diverse industries.

Various NDT techniques, including ultrasonic testing, computed tomography, thermography, and acoustic emissions, have long served as cornerstones for inspecting materials and structures. Among these, ultrasonic testing stands out as the most prevalent method, owing to its versatility, accuracy, portability, and cost-effectiveness. However, traditional ultrasonic testing presents inherent limitations, all of which are directly or indirectly related to the need for contact with the structure. Therefore, Laser Ultrasonic Testing (LUT) has been introduced as a noncontact NDT technique, harnessing lasers and optical devices for wave generation and detection. In LUT, the material acts as an emitting transducer, and the ultrasonic waves are generated through the photoacoustic effect. LUT's non-contact nature eliminates the need for coupling mediums, enhances inspection speed, and enables automation and application in hostile environments (e.g., radioactive, high-pressure, high-temperature).

Yet, LUT encounters its own hurdles. Low signal-to-noise ratios (SNRs) due to the low amplitude of generated waves, and the intricacies of wave generation and propagation pose significant challenges. Meeting these challenges requires precise simulations to understand the mechanisms behind laser-induced wave generation, optimize laser parameters, and explore innovative solutions. Therefore, this dissertation delves into the accurate modeling and simulation of laser-induced elastic waves in both isotropic and composite materials. Additionally, it presents a novel approach to addressing the challenges faced by LUT. Initially, a new theory of thermoelasticity capable of capturing intricacies due to ultrafast heating of material using short and ultrashort laser pulses is presented. Next, the root cause of numerical solution issues in simulating laser-induced elastic waves is explored, and a new guideline for spatial discretization of the domain is proposed. Subsequently, simulations are verified by analytical results. Furthermore, a new model for light absorption in composite materials, considering distinct optical absorptivities for different constituents, is proposed. Lastly, the dissertation thoroughly examines the effects of laser beam shaping on wave convergence and unveils the dynamics of laser-induced elastic waves in composite materials.

Recommended Citation

Zarei, Alireza, "Numerical Simulation of Laser Induced Elastic Waves in Response to Short and Ultrashort Laser Pulses." (2024). All Dissertations. 3634.
https://open.clemson.edu/all_dissertations/3634