研究目的
To evaluate large plastic deformations of metals, especially for thin metal foils and for the forming at high temperatures, using a simple non-contacting technique, digital image correlation (DIC) with laser speckles.
研究成果
The DIC technique with laser speckles was validated as a reliable non-contacting method for measuring large plastic deformations of metals, including thin foils and high-temperature forming. It provided accurate stress-strain curves and full-field strain distribution without the need for surface preparation with paints.
研究不足
The decorrelation in rapid and out-of-plane movements was not considered, leading to large deviations in measured nominal strains in the yielding stage. The decorrelation at high temperatures, such as thermal disturbance and background radiation, was also not considered, affecting measurement accuracy.
1：Experimental Design and Method Selection:
The study used digital image correlation (DIC) with laser speckles to measure large plastic deformations of metals. The methodology included the use of a multithreaded reliability-guided DIC (RG-DIC) method for displacement field calculation and strain field determination based on Green-Lagrange strains.
2：Sample Selection and Data Sources:
Tensile samples were prepared from phosphorous-deoxidized copper (JIS C1220P-O), low carbon steel (JIS SPCC), aluminum alloy (JIS A5052-O), and pure titanium (JIS TR270C-O) foils. Aluminum alloy (JIS A1050-O) tubes were used for high-temperature tests.
3：List of Experimental Equipment and Materials:
A Zwick/Roell Z005 tensile testing machine with a red laser source, a digital camera (PENTAX K-50) with 90 mm fixed focal lens, and a glass heater for high-temperature tests were used.
4：Experimental Procedures and Operational Workflow:
Uniaxial tensile tests were conducted at room temperature and 400 °C. The speed of the crosshead was set to 1 mm/min for most samples and 0.5 mm/min for others. Images were captured and post-processed using Ncorr for DIC analysis.
5：5 mm/min for others. Images were captured and post-processed using Ncorr for DIC analysis.
Data Analysis Methods:
5. Data Analysis Methods: Displacement and strain fields were calculated using Ncorr, with Green-Lagrange strains derived from displacement fields. True strain was calculated from its relationship with Green-Lagrange strain.
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