PSI - Issue 35

Jarmil Vlach et al. / Procedia Structural Integrity 35 (2022) 132–140 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 2. Dimensions of specimens. Name

Unit

Small sample

Large sample

Length (L) Width (W)

(mm) (mm) (mm) (mm) (mm) (mm)

250 25 50 28 20 150

250 100

Tab length (B)

50

Deformed length (L 0 )

150

Extension control dimension (U) Contraction control dimension (V)

- -

Control point

a

b

Fig. 2. (a) Impact model; (b) Deflection under impactor.

For impact model validation, impact tests were done. They were performed on large samples according to the ASTM D7316 (Fig. 2a). The impactor with the diameter of 12.5 mm was used. Dimensions of samples are given in Table 2. During the experiment, quantities such as the impact velocity and the deflection of the sample under the impactor were observed (Fig. 2b). Subsequently, damage was detected by C-scan (Fig. 5b) and photographs (Fig. 5a) were taken of depicting the typical character of the damage to the samples so that it can be compared with the results of the simulations in Fig 5c.

4. Calibration of FE model 4.1. Optimization overview

To make reliable predictions in impact tests, it was necessary to tune the parameters of the model so that it’s response to the force load corresponds to the reference experiments. Unlike analytical calculation, the finite element (FE) model is always sensitive to the size of the element, the chosen formulation, and the method of solution. For this case, all optimization steps were performed on a model with a continuum shell elements with size of 1.5 mm. The optimization of the parameters took place in two phases in relation to the performed experiments. In the first step the stiffness was optimized, in the second step the strength. The optimization was performed on a model that corresponded to the tensile test specimens. The measuring points from which the deformation values were read are shown in Fig. 1. The choice of optimization method was made regarding the efficiency and speed of the calculation. 4.2. Schema of optimization While the stiffness optimization was performed using ABAQUS/Standard, the strength optimization was performed using ABAQUS/Explicit. To optimize the stiffness, MFH was used, where the parameter was the volumetric concentration of fibres. To optimize the strength of composite, the RVE method with the parameter of fibre strength was utilised.