Materials 2022 , 15 , 663
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rugated and flat layers; see Table 1), the geometric parameters of the five-layer corrugated cardboard (5EB; see Table 2) and the results of four-point bending tests for six boards made of various combinations of component papers. In this paper, the above experimental data were the starting point for in-depth studies on the cause of the difference in the bending stiffness of samples bent with a positive and negative moment. The geometric characteris- tics of the corrugated layers are also shown in Figure 3. It was assumed that the shape of wavy layers is described by a trigonometric function with the amplitude h i and the period 2 π / p i .
Table1. Stiffness moduli for individual flat layers of corrugated board.
Stiffness Modulus E 1 inMD(Nmm − 2 )
Mode ID
Liner 1
Liner 2
Liner 3
Board1 Board2 Board3 Board4 Board5 Board6
5700 6690 5700 5700 6690 5700
6460 5200 6460 5720 5200 5730
5650 5520 5650 5650 5520 5520
Table2. Geometrical parameters of corrugated layers.
Layer
Period (mm)
Height (mm)
Take-Up Factor
1.262 1 1.362 1
FluteE FluteB
3.40 6.10
1.20 2.58
1 Length of medium to liner ratio.
Figure3. Five-layer corrugated board–waves geometry.
Since in the adopted calculation model (details will be discussed in the next subsection), only flat layers affect the machine direction (MD) bending stiffness, therefore only the MD stiffness moduli for liners only for all six boards are listed in Table 1. The corrugated layers play the role of keeping the liners at the right distance to ensure adequate bending stiffness. The geometry of the separated, undulating layers is presented inTable 2. In the geometrical description of the corrugated board, however, the thickness of the
individual layers should also be taken into account, see Figure 4. Therefore, the total height of the corrugated cardboard 5EB is:
N ∑ i = 1
t 1 2
t 3 2
( h ∗ i )+
,
(1)
H =
+
where h ∗ i are the distances between the central axes of the liners. So the corrected E-flute height is: h ∗ 1 = h 1 + 0.5 t 1 + 0.5 t 2 + t 4 , (2)
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