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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6

CS=0.11%

(a)

NOPD=0.03

CS=0.28%

(b)

NOPD=0.5

CS=0.61%

(c)

NOPD=1

Fig. 5. Changes in the shape and longitudinal strain fields within the compression of the plate impacted by 8.55 J. Figures are rotated by 90° counterclockwise.

According to the stress-strain curves in Fig. 4a the transition to the less stiff behavior associated with buckling occurs at ~0.18% of longitudinal strain. However, using DIC the buckling (i.e. rapid increase of out-of-plane displacements) initiates at ~0.15% of longitudinal strain. Subsequently the normalized value of out-of-plane displacement increases with a higher rate. The shapes of the plates and longitudinal strains fields when the NOPD reaches 0.5 are shown in Figs. 5b, 6b, and 7b. Wherein total compression strain for different specimens reaches 0.28, 0.25 and 0.2% for 8.55, 17.1 and 25.65 J respectively. The first specimen (Fig. 5b) demonstrates a bell-shape due to impact damage presence and delamination of the adjacent layers. Longitudinal strain fields show localization of tensile strains due to deflection of the plate towards the observer. The third specimen (Fig. 7b) similar to the first one experiences tensile strains and deflects towards the imaging system. However, due to the larger damaged area the magnitude of strain is lower as well as out-of-plane displacements (3.2 mm against 2.8 mm). The second specimen (Fig. 6b) deflects in the opposite direction, thus the longitudinal buckling-induced bending strains are compressive. Longitudinal strains prior to failure of the first specimen (Fig. 5с) are concentrated within the fairly large a rea in the center of the plate. The shape of the plate is very smooth without any jumps in deformation that evidences small and non-deep damages after impact. For the central red colored area of the second specimen is inherent a speckle damage that can result in possible errors during DIC processing. However the obtained data indicate that deflection is not homogeneous and the deformed shape contains the impact indent and longitudinal areas partly fractured after impact testing.