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Viscoelastic composite materials
Published in Roderic S. Lakes, Viscoelastic Solids, 2017
Most composites of biological origin exhibit a rich hierarchical structure [9.5.1]. Hierarchical solids contain structural elements which themselves have structure. Human compact bone is a natural composite which exhibits a complex hierarchical structure [9.5.2, 9.5.3] as shown in Fig. 9.7. In bone, the presence of proteinaceous or polysaccharide phases can give rise to significant viscoelasticity, as discussed in §7.10. Observe in Fig. 7.15 that the loss tangent of compact bone attains a broad minimum over the frequency range associated with most bodily activities. The mineral phase of bone is crystalline hydroxyapatite (Ca10(PO4)6(OH)2) which is virtually elastic; it provides the stiffness of bone [9.5.4]. On the microstructural level are the osteons [9.5.5], which are large (~200-μm diameter) hollow fibers composed of concentric lamellae and of pores. The lamellae are built of fibers, and the fibers contain fibrils (smaller fibers). At the ultrastructural level (nanoscale) the fibers are a composite of the mineral hydroxyapatite and the protein collagen, which has a triple helix structure. Specific structural features have been associated with properties such as stiffness via the mineral crystallites [9.5.2], creep via the cement lines between osteons [9.5.6], and toughness via osteon pullout at the cement lines [9.5.7]. Lacunae are ellipsoidal pores with dimensions on the order 10 μm which provide spaces for the osteocytes (bone cells) which maintain the bone and allow it to adapt to changing conditions of stress by mediating growth or resorption of bone in response to stress. Haversian canals contain blood vessels which nourish the tissue, and nerves for sensation. Flow of fluid within the pore space in bone is important in the nutrition of bone cells. Stress-generated fluid flow can give rise to mechanical damping in bending or in tension-compression via the Biot mechanism. Two-level hierarchical analytical models involving the osteon as a large fiber have been used to understand anisotropic elasticity [9.5.8] and viscoelasticity [9.5.9] of bone.
The formation mechanism of microcracks and fracture morphology of wood during drying
Published in Drying Technology, 2023
Yufa Gao, Zongying Fu, Feng Fu, Yongdong Zhou, Xin Gao, Fan Zhou
The fracture morphology of the microcrack in the cross-section, TL plane and RL plane was observed from three directions by using X-ray CT, as shown in Figure 7(a). As it can be seen from Figure 7(b), the cracks in the cross-section originated in the latewood and propagated along the R direction. The earlywood and latewood were arrayed in parallel and series in the T and R directions, respectively. In the R direction, shrinkage was the average among the independent earlywood and latewood. The T shrinkage was affected by a combination of earlywood and latewood, which were mutually constrained by each other. The shrinkage of the earlywood was less than that of the latewood. In other words, the shrinkage of latewood of surface layer was limited not only by the subsurface layer but also by the earlywood within the same annual ring. As a result, the latewood was subjected to larger drying stresses than that of earlywood, which leads to cracks originating in the latewood. The propagation of the crack in the L direction is presented in Figure 7(c). It can be seen that the ray tissue and cell middle lamella between the tracheids were destroyed. The cell middle lamella between the tracheids with lower strength was damaged under drying stress, followed by the crack developing longitudinally. As illustrated in Figure 7(d), the relatively clean surface of RL plane was produced since the cells were separated in the middle lamella. The cross-field regions could be distinguished and relatively complete.
Surface treated Pteris vittata L. pinnae powder used as an efficient biosorbent of Pb(II), Cd(II), and Cr(VI) from aqueous solution
Published in International Journal of Phytoremediation, 2018
Smruthi G. Prabhu, Govindan Srinikethan, Smitha Hegde
Calcium chloride (CaCl2) precipitates pectin or pectic acid (Nin-Chuan and Xue-Yi 2012). Pectin is the major component of the middle lamella and a minor component of the primary cell wall of a cell. Pectin of the middle lamella was affected by the action of CaCl2, consequently leading to further disintegration of the plant tissue resulting in smaller particle size. Removal of organic compounds and volatiles by CaCl2 contributed to the modification of topological features of CPV.
Exploring design principles of biological and living building envelopes: what can we learn from plant cell walls?
Published in Intelligent Buildings International, 2018
Yangang Xing, Phil Jones, Maurice Bosch, Iain Donnison, Morwenna Spear, Graham Ormondroyd
There are up to three major layers that can be distinguished in plant cell walls: the primary cell wall, the secondary cell wall (where present), and the middle lamella. The middle lamella is the first layer formed during cell division. This outermost layer is rich in pectin and joins together adjacent plant cells. The thin, flexible and extensible primary cell wall is formed after the middle lamella while the cell is growing and is the major textural component of plant-derived foods.