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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and Kadlec (2012). The damage occurrence in structures can be detected by various methods like strain measurements, Růžek (2017), non -destructive inspections, Khan (1999), and structure health monitoring, Michalcová (2016) and Kadlec (2020). But very important issues for damage evaluation can be obtained from numerical simulations. They help to rate the severity of the next situation and inspection schedule of a structure. In connection with the use of composite materials on aircraft structures, we often encounter BVID. This topic is discussed by Šedek (2017), Liao (2015) and Wang (2019). Investigating the consequences of a collision of aircraft structures with fast-moving small objects requires a number of input parameters, which may not always be available, and which are very costly to obtain. The first goal of the work was to examine the procedure for finding the parameters of a reliable model, assuming that only the results of partial experiments will be known. The second goal was to verify the influence of the calculation parameters on the result of the impact test.

Nomenclature BVID Barely Visible Impact Damage MFH Mean Field Homogenization RVE Representative Volume Element

2. Material description The subject of interest was a 12-layer symmetrical laminate with an epoxy matrix reinforced with carbon fibres with the composition [-45/+45/0/90/0/0] S which has a thickness of 1.584 mm. The approximate mechanical properties of the initial components that served as the initial inputs to the optimization algorithm were derived from Daniel and Ishai (2006). They are shown in the Table 1. In this paper, we assume that the reinforcement and the matrix are isotropic substances.

Table 1. Properties of inclusions. Inclusion Material

Tensile modulus

Poisson’s ratio

Yield stress (MPa) 8.62 4 800

Ultimate tensile stress

Elongation at brake

(MPa) 4 300

(1)

(MPa) 47.82 4 801

(%)

Matrix Fibre

Epoxy Carbon

0.35 0.20

0.894

240 000

-

3. Experiments

V

W

U

L 0

B

B

L

Fig. 1. Specimens made from multiaxial composite.

In the introduction tensile and impact tests were performed. To measuring the modulus of elasticity, Poisson's ratio and strength, the tensile tests were performed on small samples according to ASTM D3039. The data obtained from these tests were used as main inputs for calibration process, which is described below.