Energies 2021 , 14 , 1095
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of 50% ± 2%, TAPPI standard T402 was used. In Figure 4, the full histories of the box measurements are presented. The histories represent the force versus displacement data obtained from the strength testing machine [37]. Note that good repeatability of the histories of the measurements was observed.
Table1. Experimental ultimate loads of boxes tested in the study with different perforation types.
Mean Ultimate Load ± 2 Standard Deviations (N)
No.
Type of Perforation Ultimate Load (N)
1033.0 1078.0 1003.0 1009.0 1050.0 974.7 1017.3 1007.0 933.6
1 2 3 4 5 6 7 8 9
25 × 75
1020 ± 77.8
50 × 50
1002.0 ± 98.4
10 11 12 13 14
987.8 979.6 944.9 899.1 880.2
75 × 25
939.3 ± 95.6
Figure 4. Measurements from a box compression test machine [37] for FEFCO 201 box with different perforations: ( a ) 25 × 75, ( b ) 50 × 50and ( c ) 75 × 25.
The experimental results, namely, the mean ultimate loads computed from the peak forces (presented in Figure 4 and Table 1), were used to verify the approach proposed in the paper, see Equation (23). According to the proposed method, the critical buckling loads from the first buckling mode of all box panels (computed separately; with and without perforations) were computed via the FE model to use them in Equation (23). In Supplementary Materials, the data were attached, which feed the Equation (23), and served to compute the estimations of the ultimate loads of boxes with perforations. In Table 2, the material constants were demonstrated, which were the input for the constitutive law used in the FEM computations. Apart from the mean values, in order to show the uncertainty of the data, the minimum and maximum values were also presented. Moderate scatter of the material constants was observed.
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