Local-Micro-Zone-Wise Time-Resolved Integrated Digital Image Correlation for Evaluating the Mechanical Properties of Welding Joints

Abstract: The comprehensive determination of mechanical properties of heterogeneous objects such as welding joint remains challenging in various scientific fields. This paper develops a Local-micro-zone-wise Time-resolved Integrated Digital Image Correlation (LTIDIC) method, which can self-divide different regions of the material and get the multiple elastic–plastic parameters of each region through parameter inversion simultaneously, including elastic modulus, yield strength, hardening coefficient, and hardening exponent. First, the principle and process of the LTIDIC method are demonstrated, and the method of automatically dividing regions is introduced. Then, the reliability of the LTIDIC is analyzed and optimized, based on evaluating the influence of the correlation criteria, the area size, the noise type, and the number of pictures on the results of parameter inversion. Finally, a uniaxial tensile test was performed on the friction stir welding joint of aluminum alloy 6061T6 thin plate sample, and the distribution of multiple mechanical parameters was measured by the LTIDIC method. The results show that the modulus in the weld zone ranges between 30 and 70 GPa, with the lowest modulus in the thermo-mechanical affected zone and the highest modulus in the heat affected zone. The yield strength in the weld zone ranged from 75–115 MPa. The elastic modulus distribution shows an asymmetric W-shape, and the plastic parameters generally show a decreasing trend from the weld nugget to both sides. The feasibility and accuracy of the LTIDIC method were verified by comparing the consistency with the localized DIC method. The proposed method can obtain multiple elastic–plastic parameter distributions in different areas of material simultaneously through a single tensile experiment and provide important experimental data for the evaluation of mechanical properties of heterogeneous materials similar to welding joints. Highlights: 1. The developed LTIDIC method can obtain multiple elastic–plastic parameter distributions including elastic modulus, yield strength, hardening coefficient, and hardening exponent simultaneously through a single tensile experiment. 2. Automatically identify areas of heterogeneous materials with different mechanical properties. 3. The parameter inversion error is less than 1% by analyzing the factors that affect parameter identification. It can effectively reduce the influence of random noise on the inversion and improve the accuracy of the results.