PSI - Issue 68

T. Fekete et al. / Procedia Structural Integrity 68 (2025) 687–693 T. Fekete et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 1. (a) Sketch of the specimen, (b) Technical drawing of the specimen

2. Specimen Preparation and Data Acquisition Tensile test specimens were manufactured using an EML-1200SV 5-axis CNC machine. The specimens are dog bone shaped. The shape of the cross section along the gauge length was rectangular, allowing for the acquisition of high-quality images during the tests. The nominal gauge section dimensions were 8 × 2 × 30 [mm×mm×mm], with a tolerance of ± 0.02 mm. The transition section between the gauge section and the cylindrical specimen head had an edge radius of 57 mm and 25 mm on each side. The size tolerance outside of the gauge section was 0.1 mm. Figure 1 illustrates the specimen sketch and technical drawing. The specimens were carefully polished to obtain smooth and homogeneous surfaces. To reduce optical reflections, natal etching was applied to the gauge section. Using solid-state laser technology, a 0.5 × 0.5 mm square grid was created on the surfaces of the gauge section (see Figure 2a). The evolution of the strain field was then monitored by taking photos of the grid during tests. The gauge section of each specimen was measured with high-precision instruments using two methods: (1) a high accuracy ( 0.005 mm) manual caliper around the center of the gauge length; (2) the CNC machine’s integrated coordinate measuring system with an accuracy of 0.0005 mm, encompassing the entire gauge length. Measurements were performed along the three lines indicated in Figure 2a for the 8 mm-wide sides and along a single line for the 2 mm-thick sides. As indicated by the data obtained from the coordinate measuring system, the thickness of the specimen exhibits a variation between 1.92 and 1.99 mm. Furthermore, at approximately 85 % of the measurement points, the thickness falls outside the manufacturing tolerance range (see Figure 2b). The mean thickness of the specimen in the interval between - 15 and - 10 mm is markedly smaller ( ≈ 1.95 mm) than in the interval between + 10 and + 15 mm ( ≈ 1.97 mm). This suggests that the specimen can be classified as asymmetric. The mean thickness of the specimen over the full gauge length is 1.967 mm, which is also outside the manufacturing tolerance range.

Fig. 2. (a) Coordinate measurement locations along 3 lines, (b) Specimen thickness along measurement lines