Nagasawa, Kaneko and Adachi, Journal of Advanced Mechanical Design, Systems, and Manufacturing, Vol.13, No.1 (2019)
directly while the quasi-static bending was examined (Nagasawa, et al., 2014). Recently, Nagasawa et al. investigated the relaxation characteristics of bending moment resistance of 0.3 mm thickness white-coated paperboard during a folding motion from an initial position up to various tracking angles, and through the bending test by the use of the bending moment measurement apparatus (CST-J-1, 2013), the relaxation of the bending moment resistance was investigated by an exponential coefficient of logarithmic function which was independent to the normalized indentation depth and the tracking angle (Nagasawa, et al., 2014; 2015). Furthermore, a creep-recovery (release) response of folded angle during returning back was also approximated by a logarithmic function of elapsed time. Seeing the effect of rotational velocity on the release angle when the holding (stopping) time was kept in 0s at the tracking position, the initial release angle decreased with the rotational velocity (Nagasawa, et al., 2016). Here, the initial release angle was determined at the time when the reaction force of folding becomes zero. However, in that report, the effect of holding (stopping) time at the tracking position on the released behavior was not discussed. Therefore, the combination effect of the rotational velocity during folding/unfolding process and the hold time at the tracking position on the release behavior was investigated in this work. Firstly, the time-dependent behavior of release angle was reviewed under the specified rotational velocity of fixture 0.2 rps (revolution per second) (1.26 rad ή s ) when varying the hold time, and some coefficients of logarithmic approximation of release angle was discussed. Secondly, the initial released angle (when the rotation force of folding becomes zero) was investigated when both the rotational velocity and the holding (stopping) time were varied in a certain range.
2. Experimental condition and method 2.1 Initial creasing of specimen for pre-processing
Figure 1 illustrates viewpoints of a paperboard. The prepared white-clay-coated paperboard (basis weight U =228~237 g m 2 ) had a thickness of t =0.3 (0.297~0.303) mm. Table 1 shows the analysis result of fiber size and pulp combination ratio. Regarding the mechanical properties of the paperboard, the in-plane tensile test properties in the Machine Direction of paper making (MD, the principal axis direction with reference to the fiber grain direction), were shown in Table 2. The specimens were kept in a room which had a temperature of 296 K and a humidity of 50 %RH. The test pieces were prepared as 5 pieces of rectangle-shaped white-coated paperboard, which had a width of 15 mm, length of 60 mm, for each condition.
Top view (top side)
Coated surface (top side)
Sectional view (top side)
Coated side
Coated layer
Machine direction (MD)
Interfaces
Laminated pulp layers
None-coated side (b)
10 P m
(c)
100 P m
(a)
Sectional view (back side)
Uncoated surface (back side)
Figure 1 Outline of coated paperboard. (a) Schematic illustration. (b) SEM sectional view. (c) Top side SEM sectional view. The paperboard is composed of multiple plies and the coated top layer and the uncoated back layer are generally different (strong or tough) from the middle layer. When scoring the out-of-plane (top or back side) by the use of round-edge punching tool, the bonded interfaces of pulp layers apt to be de-laminated. This de-lamination is used for folding the paperboard without any breaking of outside layers. Table 1 Size of fiber and pulp combination ratio of coated paperboard 230 (measured by Kajaani-FS300) L-BKP: Broad-leaved lumber (hard wood), bleaching kraft pulp; N-BKP: Needle-leaved lumber (soft wood), bleaching kraft pulp; N-TMP: Needle-leaved, thermal mechanical pulp; L(n): based on number of fibers in each fibrillation index class; L(l): based on length weighted number of fibers in each fibrillation index class; L(w): based on weight-weighted number of fibers in each fibrillation index class; CWT: Wall thickness of cell; Width: average width of fiber. Unit Pulp combination ratio /% Projected length of fiber /mm Size / P m Section area / P m 2 Item L-BKP N-BKP N-TMP L(n) L(l) L(w) Width CWT CSA Value 83.1 16.9 0.0 0.45 0.88 1.36 18.2 4.6 206.2
© 2019 The Japan Society of Mechanical Engineers
[DOI: 10.1299/jamdsm.2019jamdsm0004]
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