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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3.2. Results for compression after impact tests Compression testing yields stress-strain curves the maximum value of which is a residual compressive strength (Fig. 4a). One specimen was tested for each energy value. The compression strength for the specimen impacted by 8.55 J is 253.4 MPa with a 0.62% of compressive strain at failure. The specimen impacted by the nominal energy of 17.1 J showed CAI the strength of 173.2 MPa and strain of 0.35%. The results of the third specimen (25.65 J) are 192.0 MPa and 0.63%. Elasticity moduli of the impacted specimens are estimated as 47.14 GPa, 46.26 GPa and 45.71 GPa correspondingly. Due to the low thickness of the specimens the compressive loading origins buckling. Thus the additional bending stresses were combined with compression-induced. Stress-strain curves contain the inflection points which are located similarly for all specimens at ~0.18%. This confirms that the general deformation behavior is mainly governed by the thickness of the specimen but not a damage severity. In order to qualitatively and quantitatively study the deformation processes 3D DIC was employed. The dependencies of out-of-plane displacement normalized to [0,1] for all specimens are presented in Fig. 4b. Besides the deformed shapes and strain fields are presented in Figs. 5,6, and 7. Left-side images demonstrate the shape of specimen deformation at different time steps of loading and the right-side show corresponding longitudinal strain fields. For all specimens the first image is for low value of compression strain (CS=0.11-0.13%). The second image corresponds to the loading step when out-of-plane displacement (OPD) reaches 50% of maximum (i.e. OPD=0.5). The third image is captured just prior to failure, i.e OPD=1. This sequence helps to study the deformation behavior of the compressively loaded plate from the beginning of loading up to failure.

(a)

(b)

Fig. 4. (a) compression loading curves of orthotropic [0/90] 5S CFRP with various energy impact damages; (b) normalized out-of-plane displacements ( w/w max ) of CFRP plates under compression.

The first specimen after the 8.55 J impact during the first step of loading experiences small homogeneous deflection at 0.11% longitudinal strain (Fig. 5a). The second and the third specimens (17.1 and 25.65 J) are showing non-uniform deflection (Fig. 6a and 7a) while the impacted area is distinctly revealed. Above described corresponds to the first linear stage of the loading curves in Fig. 4a.