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Module 2: DIC and crack tip fields

Module 2: DIC and crack tip fields

This module will focus on the application of digital image correlation (DIC) to the study of crack tip fields.

For this module, we will use an image-based technique to determine the deformation fields in solid media. This method is called Digital Image Correlation (DIC). The method's premise is to embed or emboss a random pattern of high-contrast markers that move with the material, and to compare their current states to a reference state. Once the spatial distribution of marker deformations is determined, kinematic quantities of interest such as strain tensors, etc. can be used to answer mechanics questions.

Readings

Week 1

A general introduction to DIC as a method, with a specific implementation

Fracture notes from Grutzik provide an overview of both stress concentration via the Ingliss solution and the full expressions or the stress fields. If you don't understand Continuum Mechanics sufficiently to interprete these expressions, we can discuss in detail in the class :)

I strongly encourage you to review the NCORR manual. Section 2.10 will prove particularly useful if you intend to elaborate your analysis, and measure stress fields from the deformation data.

Exercises

Week 1

1. Form new groups.

2. Install NCORR on a PC with one of your group member's accounts. Each account will require a separate install, but once installed, it should always work with that sign in

3. Download and process the image samples from NCORR. Use the hole in the plate dataset to familiarize yourself with the software, the speckle pattern, and calculation of strains. You should work with the documentation in-hand, so you have a clear idea of what each of the software `knobs' does in the experiment.

4. Write a script that allows you to calculate the deformation gradient tensor components from the displacement fields for the hole-in-the-plate data. Make sure that this will work with your data, so you can re-use it at a later date.

5. Write a script that allows you to calculate the 1st Piola-Kirchhoff stress fields for the hole in the plate data for a Hookean solid or a neo-Hookean solid (see e.g. Hs or nHs, normalized by a modulus. Make sure that this will work with your data, so you can re-use it at a later date.