Accurate ex situ deformation measurement using an ultra-stable two-dimensional digital image correlation system

Area of Science:

• * Experimental Mechanics
• * Materials Science
• * Optical Measurement Techniques

Background:

• * In situ two-dimensional digital image correlation (2D-DIC) is widely used but limited in specific applications like long-term monitoring or unusual loading conditions.
• * Ex situ 2D-DIC measurements, requiring specimen repositioning or camera relocation, introduce potential errors that need quantification and minimization.
• * Accurate deformation measurement is crucial for understanding material behavior and structural integrity.

Purpose of the Study:

• * To identify and discuss potential error sources in ex situ 2D-DIC measurements.
• * To develop and validate an ultra-stable 2D-DIC system for mitigating these errors.
• * To quantify the strain accuracy of the proposed ex situ 2D-DIC system.

Main Methods:

• * Detailed analysis of error sources in ex situ 2D-DIC.
• * Development of an ultra-stable 2D-DIC system using active imaging and a bilateral telecentric lens.
• * Comparison of the new system with a regular 2D-DIC setup on an unstrained sample and application in residual stress measurement via hole-drilling.

Main Results:

• * The ultra-stable 2D-DIC system demonstrated invariance to ambient lighting variations and minor out-of-plane motions.
• * Comparative analysis confirmed the high fidelity of surface strain measurements using the new system.
• * Ex situ residual stress measurements using the developed system showed good agreement with applied stresses.

Conclusions:

• * The proposed ultra-stable 2D-DIC system effectively minimizes errors associated with ex situ measurements.
• * The system achieves high-fidelity deformation measurements, suitable for practical ex situ testing.
• * This advancement expands the applicability of 2D-DIC for challenging deformation analysis scenarios.