PSI - Issue 75

Lewis Milne et al. / Procedia Structural Integrity 75 (2025) 419–425

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L.Milne et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 1. Henry Royce dual-gauge length high strain rate specimen: a) dimensions (mm); b) tensile test set-up in Zwick HTM 5020 machine; c) speckle pattern on the specimen from left to right – too coarse, too fine, too sparse, good quality.

speckle pattern using RS Pro Matt Black spray paint. The speckle pattern was applied by hand by lightly releasing the nozzle of the spray can and quickly passing the jet over the specimens at a distance of 30cm. Naturally, there was a variation in the size and quality of the speckles produced, so if the pattern was not of su ffi cient quality it was cleaned and repainted. Examples of the pattern quality are given in Fig. 1c. In high strain rate test, the load is applied to a machine with a slack rod, allowing the crosshead to accelerate up to the desired test rate before impacting the specimen. As the speed at impact is the controlled parameter, there is some level of variability in the actual test strain rate, which must be taken into account during processing. Tests were carried out at 0.2, 2, 6 and 18 m / s, which corresponds to nominal strain rates of 10, 100, 300, and 900 s − 1 respectively in the smaller gauge section of the specimen. The machine was not capable of carrying out accurate tests at lower rates than 0.2m / s. Force was measured using a 50 kN Kistler load cell, with a sampling rate of 500 kHz.

3. Experimental data processing

To process the DIC data, Zeiss Inspect Correlate was used. All of the DIC images were imported into the software as a single project. The image scale was set using a calibration test piece, and the timestep between each image was evaluated based on the framerate. A surface component was created on the speckled specimen surface (see Fig. 2a) to evaluate displacement and strain values. Two probes were defined – one within the small gauge section to measure strain, and one within the large gauge section to measure velocity. Additionally, a virtual extensometer of length 20mm was placed along the gauge section. A representative DIC plot with the measurement probes and extensometer is presented in in Fig. 2a. To correct for any relative motion between the camera and the test rig, deformations were