In recent years, there has been an increasing interest in wood properties, because wood is a commonly used and advanced building material. In this paper, the effect of anatomical characters on the transverse fracture ...In recent years, there has been an increasing interest in wood properties, because wood is a commonly used and advanced building material. In this paper, the effect of anatomical characters on the transverse fracture properties of green wood was investigated. The specific fracture energy （Gf J/m2） of ash （Fraxinus excelsior）, cherry （Prunus avium） and birch （Betula pendula） was evaluated using double edge notched tensile tests. The tests were performed on both earlywood （EW） and latewood （LW） zones in both the radial-tangential （RT） and the tangential-radial （TR） crack propagation systems. Wood anatomy and the failure patterns of each species were also investigated using environmental scanning electron microscopy （ESEM） and light microscopy （LMC）. The results showed that the Gfof RT fracture systems was around 1.5 times greater than in the TR one, whereas there were no significant differences between EW and LW zones. ESEM micrographs showed that the RT fracture system had a rougher fracture surface, while the TR had a nearly smooth and fiat fracture surface. In particular, the wood ofF. excelsior was the toughest, because of its greater percentage of rays and homogenous distribution of ray cells, while P. avium and B. pendula showed a lower Gf due to their smaller percentage of rays with a distinctive arrangement of ray cells.展开更多
Eggshells are one of the most common and well-studied biomaterials in nature and exhibit unique properties of gas conduction. However, the morphologies of eggshells at the submicro-/nano-scale and their impact on eggs...Eggshells are one of the most common and well-studied biomaterials in nature and exhibit unique properties of gas conduction. However, the morphologies of eggshells at the submicro-/nano-scale and their impact on eggshell functions remain unclear. In this work, the architecture of hen＇s eggshell at different length scales has been systematically investigated by scanning electron microscopy （SEM） and environmental SEM （ESEM）. It is found that the skeleton of calcium carbonate （CaCO3） has hierarchical structures at nano- to micro-scales： primary nano-particles of -10 Fain loosely congregate giving a porous and rough texture, and compose the upper-level morphologies including submicro spheres, nano-rods, rhombohedral-cleavage pattern and slices, which are elaborately arranged in a surface layer, palisade layer and mammillary layer along the radial direction. Accordingly, the pore system exhibits a three-level hierarchy, namely nano-scale pores （between nano-rods and primary nano-particles）, submicro-scale pores （＂bubble pores＂） and micro-scale pores （opening of ＂gas pores＂）. Further investigation shows that hen＇s eggshell regulates gas conduction through adjusting the sizes and numbers of submicro-scale ＂bubble pores＂. Based on our observations, a new description of hen＇s eggshell is presented, which amends the conventional view of micro-scale, straight and permeating ＂gas pores＂, and reveals the role of hierarchical pores in gas conduction and contamination resistance.展开更多
文摘In recent years, there has been an increasing interest in wood properties, because wood is a commonly used and advanced building material. In this paper, the effect of anatomical characters on the transverse fracture properties of green wood was investigated. The specific fracture energy （Gf J/m2） of ash （Fraxinus excelsior）, cherry （Prunus avium） and birch （Betula pendula） was evaluated using double edge notched tensile tests. The tests were performed on both earlywood （EW） and latewood （LW） zones in both the radial-tangential （RT） and the tangential-radial （TR） crack propagation systems. Wood anatomy and the failure patterns of each species were also investigated using environmental scanning electron microscopy （ESEM） and light microscopy （LMC）. The results showed that the Gfof RT fracture systems was around 1.5 times greater than in the TR one, whereas there were no significant differences between EW and LW zones. ESEM micrographs showed that the RT fracture system had a rougher fracture surface, while the TR had a nearly smooth and fiat fracture surface. In particular, the wood ofF. excelsior was the toughest, because of its greater percentage of rays and homogenous distribution of ray cells, while P. avium and B. pendula showed a lower Gf due to their smaller percentage of rays with a distinctive arrangement of ray cells.
文摘Eggshells are one of the most common and well-studied biomaterials in nature and exhibit unique properties of gas conduction. However, the morphologies of eggshells at the submicro-/nano-scale and their impact on eggshell functions remain unclear. In this work, the architecture of hen＇s eggshell at different length scales has been systematically investigated by scanning electron microscopy （SEM） and environmental SEM （ESEM）. It is found that the skeleton of calcium carbonate （CaCO3） has hierarchical structures at nano- to micro-scales： primary nano-particles of -10 Fain loosely congregate giving a porous and rough texture, and compose the upper-level morphologies including submicro spheres, nano-rods, rhombohedral-cleavage pattern and slices, which are elaborately arranged in a surface layer, palisade layer and mammillary layer along the radial direction. Accordingly, the pore system exhibits a three-level hierarchy, namely nano-scale pores （between nano-rods and primary nano-particles）, submicro-scale pores （＂bubble pores＂） and micro-scale pores （opening of ＂gas pores＂）. Further investigation shows that hen＇s eggshell regulates gas conduction through adjusting the sizes and numbers of submicro-scale ＂bubble pores＂. Based on our observations, a new description of hen＇s eggshell is presented, which amends the conventional view of micro-scale, straight and permeating ＂gas pores＂, and reveals the role of hierarchical pores in gas conduction and contamination resistance.
