PSI - Issue 38

S. Spanke et al. / Procedia Structural Integrity 38 (2022) 220–229

227

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Author name / Structural Integrity Procedia 00 (2021) 000±000

When comparing the larger symmetric system RVE SYM M1 with the fiber distribution model RVE57 MG 2, it is clear that the RVE57 RMG 2 model forms higher von Mises stresses along the stress paths. To illustrate this relationship, the maximum von Mises stresses for the tension and shear load steps are shown in Table 1.

Table 1. von Mises stresses load step 1-6.

Load step

RVE SYM M1 von Mises [MPa]

RVE RMG 2

Absolute deviation von Mises [MPa]

Relative deviation

von Mises [MPa]

[%]

1 2 3 4 5 6

76.40 76.30

120.10 121.20 2400.12 302.00 190.40 115.00

43.70 44.90

57.19 58.85

2399.59 141.40

0.53

0.02

160.60 101.71

113.58 114.66

88.70 86.70

28.58

33.07

3.2. E ff ective homogenized material parameters of the unidirectional layer

The numerically calculated material parameters of the RVE systems are validated with a 4-point bending test. The developed 4-point bending test rig is shown in Figure 6.

(a) 4-point bending testing machine

(b) Test specimen

Fig. 6. (a) 4-point bending testing machine; (b) Test specimen.

The experimental tests on the maximum stressed edge fiber of the test specimens are evaluated according to the Bernoulli bending beam theory. The experimental tests are carried out with three di ff erent crosshead speeds v 1 = 1 mm / s , v 2 = 0 . 18 mm / s and v 3 = 0 . 011 mm / s . No viscoelastic e ff ect was observed in the CFRP test spec imens. With the same test setup, this was di ff erent for pure resin specimens made of RIM 935, where a strain rate dependent material behavior was observed. For this reason, the matrix of the RVE models was mapped with a strain rate-dependent material behavior. Figure 7 shows the results of the experimental tests and the RVE systems with dif ferent fiber orientations for the homogenized e ff ective sti ff ness value in the fiber direction and transverse to it. The RVE systems are built with symmetrical and random fiber distributions. The symmetrical RVE systems include the unit cell (RVE57 EH) and the larger symmetrical system (RVE57 SYM). The unit cell consists of one fiber in the center of the RVE space and quarter fibers in the corners. The random fiber distributions are constructed using the Random Microstructure Generator (RVE57 RMG) and the Random Distribution Generator (RVE57 RDG). The test specimens and the RVE systems are unidirectional and have a fiber volume fraction of 57 %.