Nonlinear ultrasonic measurements for the characterization of fracture toughness in steel alloys
Open Access
- Author:
- Williams, Colin
- Area of Honors:
- Engineering Science
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Parisa Shokouhi, Thesis Supervisor
Andrea P. Arguelles, Thesis Honors Advisor - Keywords:
- Ultrasound
Fracture Toughness
Nondestructive Evaluation
Material Characterization - Abstract:
- The knowledge of “fracture toughness,” a mechanical strength parameter, is essential to ensure the operational safety of fracture-critical systems and components such as pressure vessels and pipelines. Loss of fracture toughness can be an early indicator of catastrophic failure by rapid brittle fracture. However, it is not possible to quantify fracture toughness in service for structural health monitoring (SHM). Traditional fracture toughness testing is destructive and cannot be completed in-situ. We seek to investigate the utility of nonlinear ultrasonic testing as a nondestructive alternative to traditional fracture toughness testing procedures. This research is motivated by the high sensitivity of nonlinear ultrasonic parameters to a material’s microstructure when compared to conventional (linear) ultrasonic tests. Therefore, because of their mutual dependence on microstructure, we hypothesize a correlation between the measurable nonlinear ultrasonic parameters and fracture toughness characteristics of a material. In this thesis, we investigate the existence of such a correlation in 4130 steel samples with different heat treatments and hardness values. Using the technique of Second Harmonic Generation (SHG), both surface and bulk waves were used to estimate the nonlinearity parameters of eight different tempered steel samples. These same samples were also tested destructively for their fracture toughness characteristics using Charpy V-Notch testing. We report two sets of results pertaining to bulk and surface waves. Results of nonlinear bulk wave testing indicate a correlation between the nonlinearity parameter and plate hardness values. Results for surface waves show trends between nonlinearity parameters and plate hardness values as well as wave velocity and plate hardness values. The continuation of this project will utilize numerical simulations to explore how various microstructural features influence both fracture toughness values and nonlinearity parameters with the ultimate goal of quantitative in-situ fracture toughness inspection.