PSI - Issue 61

T. Stoel et al. / Procedia Structural Integrity 61 (2024) 206–213

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T. Stoel et al. / Structural Integrity Procedia 00 (2023) 000 – 000

Another modification of the initial model is an adjustment of the material parameters. Therefore, tensile, compression and shear tests in accordance with DIN EN ISO 527-5, DIN EN ISO 14126, and ASTM D7078 for 2 mm UD CFRP laminates with an epoxide matrix and high tenacity fibers as well as two different fiber volume fractions f = {60, 70} % were carried out. The empirically determined mechanical properties of the materials used for the numerical model are given in Table 1. Table 1: Empirically determined mechanical material properties of the investigated UD CFRP in dependence of fiber volume fraction f Mechanical property Symbol Unit f = 60 % f = 70 % Elasticity modulus, longitudinal ∥ MPa 123339 160691 Elasticity modulus, transverse ⊥ MPa 7748 9854 Poisson’s ratio, longitudinal ∥⊥ – 0.29 0.29 Poisson’s ratio, transverse ⊥⊥ – 0.38 0.38 Shear modulus, longitudinal ∥⊥ MPa 4098 6574 Shear modulus, transverse ⊥⊥ MPa 3611 5349 Tensile strength, longitudinal ∥ MPa 1995.7 2516.6 Compressive strength, longitudinal ∥ MPa 1062.3 1398.1 Tensile strength, transverse ⊥ MPa 49.3 41.9 Compressive strength, transverse ⊥ MPa 149.5 183.2 Shear strength, longitudinal ⊥∥ MPa 62.1 81.1 It is shown that in general the values of elasticity and shear modulus as well as the strength parameters increase with higher fiber volume fraction. An exception is the tensile strength in the transverse direction which is mostly influenced by the properties of the matrix. Here the value for a high fiber volume fraction decreases, which can be explained by an increasing embrittlement of the material. Fracture energy values were not empirically determined. Therefore, the values determined by Camanho et al. (2007) were used for the laminate with a fiber volume fraction of f = 60 %. For the laminate with f = 70 % a linearly proportional relationship between the fracture energies and the respective tensile and compressive strength parameters was estimated. It was checked that a variation of the fracture energy values of ± 25 % does not significantly affect the numerically determined blanking force B . The fracture energy values used are listed in Table 2. Table 2: Measured fracture energies by Camanho et al. (2007) for f = 60 % and estimated fracture energies for f = 70 % Mode Symbol Unit f = 60 % f = 70 % Fiber tension ft kJ/m² 81.5 102.8 Fiber compression fc kJ/m² 106.3 139.9 Matrix tension mt kJ/m² 0.277 0.235 Matrix compression mc kJ/m² 0.788 0.966 2.3. Geometry and meshing The process was modeled using Abaqus/explicit 6.14-6. The developed near-net-shape blanking model consists of the four tool components punch, blank holder, counter punch and die as well as the CFRP laminate. The cutting line geometry is equivalent to a square with a length of 29.98 mm. Therefore, it is sufficient to model only a quarter of the total geometry using two symmetry planes (see Figure 2a). All tool components were assumed to be rigid and were modeled as analytical rigid shells (R3D4). The laminate was modeled as a three-dimensional deformable body. The relative die clearance was set to = 0.5 % ≙ ͳͲ ρ of the laminate thickness of 2 mm. To reduce the number of elements and therefore computational time, the laminate size was reduced. It was determined that a minimum clamped