PSI - Issue 50

Alexander Eremin et al. / Procedia Structural Integrity 50 (2023) 73–82 Alexander Eremin / Structural Integrity Procedia 00 (2019) 000 – 000

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extensometers were placed along the loading axis. Mean value of these five extensometers’ strains was used as ε comp for the analysis of compression test. One of the important issues to be taken into account during CAI testing is buckling. Linke et al. (2018) and Linke et al. (2020) have proposed a modified device that can be successfully utilized for testing of specimens nearly two times thinner than describes ASTM standard. They conclude that by modification of the upper grip the buckling phenomenon is minimized and the testing produces results that are adequate. However, the diagrams presented in the manuscripts indicate buckling and require more accurate verification.

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Fig. 1. (a) – specimen sketch with impact damage area; (b) – mask for DIC processing including virtual optical strain gages (0- 0’, 1 - 1’, 2 - 2’, 3- 3’, 4 - 4’) and a circle for evaluation of buckling induced out -of-plane displacement.

D7137 standard defines the usage of four strain gages that are used to detect the possible buckling. In the present paper buckling was monitored using full-field one-side 3D DIC that provides measurement of out-of-plane displacement. For each specimen this displacement was calculated as a mean value within the 33-mm (1/3 of the plate width) circle located in the center of the CFRP plate. In order to detect the inhomogeneity of loading along the width of the specimen 4 virtual optical strain gages were placed during postprocessing of the DIC data. Gages located at 25 mm from each side of the plate as shown in Fig. 1b. It should be noted that the sizes of the mask are smaller than the sizes of the specimen due to the areas occupied by the clamps of the testing device and offsets for the stability of DIC calculations. 3. Results and discussion 3.1. Results for drop weight impact tests The results of the impact tests are shown in Fig. 2 and Table 1. Three curves in Fig. 2 represent the specimens damaged with various energy impacts, assign in the testing settings of the machine – 8.55 J, 17.1 J and 25.65 J.