PSI - Issue 52

Valerio Acanfora et al. / Procedia Structural Integrity 52 (2024) 340–347 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

341

2

stiffness and thickness. Composite materials offer the possibility to customize stiffness and strength characteristics based on the type of reinforcing fibers and the distribution of the reinforcing directions. However, their use is limited due to their vulnerability to low velocity impacts, like tools dropping during assembly or maintenance operation, which can cause Barely Visible Impact Damage (BVID) and severe reductions in the strength and stability of the structure [5-7]. For impacts that do not result in a complete penetration of the target, damage is initiated by matrix cracks which create delaminations at interfaces between plies with different fiber orientations [8]. To simulate the low velocity impact of a carbon fiber reinforced polymer, drop-weight testers are the most used apparatus. In this work, a 24 plies rectangular specimen with a stacking sequence of [45, -45, 0, 90, 45, -45] 2S was subjected to a 10 J energy impact. The experimental test follows the designation ASTM D 7136/D 7136-M [9]. Displacement, impact force, and different types of energy were registered, and several numerical models were developed, assuming different discretizing levels and different element formulations. Besides, in the last phase both intra-lamina and inter-lamina failures have been considered: the former are based on the Hashin criteria, whereas the latter has been implemented through a contact surface with cohesive behavior and failure option placed between each sub-laminate. The results of the numerical models were compared with experimental ones in terms of energy balance and damaged area. 2. Test case description The analyzed specimen is a 24-plies symmetric carbon fiber laminate subjected to an out-of-plane, concentrated impact using a drop-weight device with a hemispherical impactor, whose mass is 3.58 kg. The potential energy of the projectile, equal to 10 J, is defined by its drop heigh; in order to simulate the drop-weight event in the Abaqus environment, a 2.364 m/s velocity is given to the impactor. The plate is supported over its upper extremity through four guiding pins, plus a fixture base operates as a lower support. Pins are made of EPDM rubber, an M-Class rubber under ASTM standard D-1418. The thickness of each ply is equal to 0.186 mm, which means that the entire laminate thickness is 4.464 mm. The damage resistance is quantified in terms of the resulting size and type of damage in the specimen. The mechanical properties of the specimen are reported in the Table 1, while the test case geometry is shown in Figure 1.

Table 1. Mechanical properties of the material system.

Description

Symbol

Unit MPa MPa MPa MPa kJ m kJ m kJ m MPa MPa MPa MPa MPa - -

Value

Longitudinal Young’s Modulus Transverse Young’s Modulus In-plane Shear Modulus Transverse Shear Modulus

149 500

E 11 E 22

8430 4200 2520 0.33 0.55

G 12 = G 13

G 23

Poisson’s ratio Poisson’s ratio

ν 12 = ν 13

ν 23 G Ic G IIc G IIIc

Critical ERR Mode I Critical ERR Mode II Critical ERR Mode III

0.4 0.7 0.7

-2

-2

-2

Longitudinal Tensile Strength Longitudinal Compressive Strength

2143 1034

F 1 t F 1 c F 2 t F 2 c S 12

Transverse Tensile Strength

75

Transverse Compressive Strength

250

In-plane Shear Strength

95

Ply Thickness

5

mm

0.186