PSI - Issue 60

Rajagurunathan M et al. / Procedia Structural Integrity 60 (2024) 517–524 Rajagurunathan and Prakash./ Structural Integrity Procedia 00 (2024) 000–000

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which occur during low velocity impact on CFRP laminates. In this numerical study, hourglass specimen of dimension 45 mm x 250 mm x 4 mm having the minimum width of 35 mm at the center as shown in Fig. 2 [John et al. (2018), Sreenath et al. (2021)] was considered. The CFRP laminates were modelled with 8 layers and two different lay-up sequences, (0/90) 2s and (0/45/-45/90) s . The translation and rotational degrees of freedom were constrained at both ends of the composite specimen. The diameter of the hemi spherical impactor is 16 mm. To reduce the computational time, the impactor was modelled as analytically rigid. The mass of the impactor was 5.2 kg and the velocity of the impactor was varied from 1 to 5 m/s. The material properties of the unidirectional carbon fiber composite laminate used in the current study are listed in Table.3 [Shi et al. (2012), Zhou et al. (2019)]. To avoid the convergence issues, the model was meshed with element size smaller than the characteristic length. Therefore, the CFRP laminates were discretized into 90000 eight-node continuum shell elements (SC8R) with 184736 nodes. The mesh size of 1 mm x 1 mm was calculated based on the characteristic length and mesh convergence study. The characteristic length of the element can be found as per the following equation: � ≤2 � �� ( � ) � ; � ≤2 �� � � ( �� ) � (15) In this study, the general contact algorithm was chosen to specify the contact behavior between the impactor and top of the laminate as well as inside the laminate. For this simulation, the cohesive surface behavior was used to predict the delamination using traction separation law and B-K criterion. The friction coefficient between the impactor and the lamina is 0.3 and between two lamina is 0.5. [Shi et al. (2012)] a) b) Fig. 2. CFRP laminate under low velocity impact: a) Geometry; b) FEA model [John et al. (2018)] Table 2: Material properties of CFRP composite laminates [Shi et al. (2012), Zhou et al. (2019)] Ply thickness = 0.5 mm Density = 1600 kg/m3 Elastic properties � = 153 GPa, � = � = 10.3 GPa ; �� = �� = 6 GPa, �� = 3.7 GPa; ν �� =ν �� =0.3,ν �� =0.4 Fracture energy �� = 91.6 N/mm, �� = 79.9 N/mm, �� = 0.22 N/mm, �� = 1.1 N/mm, Strength � = 2537 , � = 1580 ; � = 82 , � = 236 ; �� = 90 , �� = 40 Cohesive stiffness properties �� = �� = �� = 5 GPa/mm Strength � = � = � = 30 MPa Fracture toughness �� = 0.6 N/mm, ��� = ���� = 2.1 N/mm BK coefficient 1.45 4. Results and discussions During the low velocity impact process on composite laminates, the kinetic energy of the impactor will be dissipated in various forms such as elastic deformation, vibration of the laminate, damage formation due to matrix cracking, delaminations and fiber breakage etc. The energy dissipation ratio of fiber damage increases from zero with the increase in impact energy while the energy dissipation ratio of matrix damage and that of delamination decreases for the laminate with increase in impact energy. The numerical result of these five impact cases shows that