Energy Resolved Neutron Imaging for Strain Reconstruction Using the Finite Element Method.

Area of Science:

• Materials Science
• Neutron Scattering
• Computational Mechanics

Background:

• Residual strain analysis is crucial for material performance and integrity.
• Nondestructive techniques are highly desirable for in-situ material characterization.
• Existing methods may lack the spatial resolution or applicability for complex strain fields.

Purpose of the Study:

• To develop and validate a novel pulsed neutron imaging technique for residual strain reconstruction.
• To enable nondestructive analysis of strain fields with high spatial resolution.
• To improve the accuracy and robustness of strain mapping in polycrystalline materials.

Main Methods:

• Utilizing a finite element method (FEM) approach for strain reconstruction.
• Employing a least squares method constrained by equilibrium conditions to ensure a well-posed problem.
• Validating the technique with simulated data (cantilevered beam) and experimental data (ring-and-plug sample).
• Comparing results with conventional constant wavelength neutron strain measurements.

Main Results:

• Successful reconstruction of residual strain from Bragg edge images using the novel FEM technique.
• Demonstrated high spatial resolution in strain field mapping.
• Validation of the method against simulated and experimental data, showing good agreement with conventional methods.
• Tikhonov regularization further enhanced the reconstruction quality.

Conclusions:

• The developed pulsed neutron imaging technique based on FEM is effective for nondestructive residual strain analysis.
• The method provides a powerful tool for characterizing strain fields in polycrystalline materials with high resolution.
• The inclusion of equilibrium constraints and Tikhonov regularization improves the reliability and accuracy of strain reconstruction.