Hierarchical Functionally Gradient Structures of Bamboo, Barley, and Corn
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Bamboo .120
20 40 60 Culm Number ( - )
Shigeyasu Amada dots in bamboo is called the bundle sheath, which acts as fibers for the plant. These bundle sheaths are shown in the magnified photograph of corn and barley. These two plants are made of composite
Bamboo and certain other plants have excellent characteristics based on functionally gradient structures. Figure I1 shows a cross section of bamboo, corn, and barley culms. The collection of solid
5 10 Culm Number ( - ) (a) Bamboo 10 mm
(b) Corn
0.2 mm
(c) Barley
0.2 mm
Barley
Cross Section " 60
0 4 8 12 Radial Distance (mm)
(a) Bamboo
1
2
3
Radial Distance (mm)
(b) Corn
o 1
0.0 0.1 0.2 0.3 Radial Distance (mm)
(c) Barley
1
3 4 2 Culm Number (-)
Gradient Structure Figure 1. Cross section and gradient structure for (a) bamboo, (b) corn, and (c) barley.
MRS BULLETIN/JANUARY 1995
Figure 2. Gradient structure of culm diameter.
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Hierarchical Functionally Gradient Structures of Bamboo, Barley, and Corn
I GLUCOSE |
] CELLULOSE j
I MOLECULE
I
I
1 A
T
| lOnm
FIBER
| CELLULAR ]
I
I
VASCULAR
I
DIAMETER
BUNDLE
j
THICKNESS
SHEATH
I NODE DISTANCE I
1
|
1 10cm
1 mm
10/um
| 1m
SCALE Figure 3. Hierarchical structure of bamboo.
materials reinforced by fibers of the bundle sheath; the fiber strength is about 10 times that of the matrix. Furthermore, the fiber distribution is dense in the outer region and sparse in the inner region. It can be said that the fiber distribution
forms a gradient structure. The fibers in barley are sparse in the narrow cross section and are different from the fibers in corn and bamboo. The number of honeycomb-shaped cells in barley is higher on the outside than the inside region. There-
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fore, barley also has a gradient structure. These relations of the microscopic gradient structure are displayed graphically by the cross-sectional photographs. Figures la and lb present the fiber contents of bamboo and corn, respectively, with respect to radius measured from the outer radius. Figure lc gives the gradient distribution of the cell number for barley with respect to radius. These gradient features probably relate to the bending-stress distribution caused by wind, rain, and snow—the so-called environmental loads. Figure 2 shows diameter variation with respect to height from the ground. It is the macroscopic gradient structure which can adapt to the bending moment from environmental loads. Judging from macro-and microscopic features, it may be concluded that bamboo and other plants have the hierarchical gradient structure as shown in Figure 3. This unique hierarchical gradient structure generates the marvelous flexibility and strength of those plants. Reference 1. Shigeyasu Amada, Yoshinobu Itikawa, Tamotsu Munekata, Yukito Nagase, and Atsushi Kirigai, Proc. 5th Bioengineeering Div. Conf. (Jpn. Soc. Mech. Eng., 1993)
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