Papers by Author: Quan Yuan

Abstract: SEM observation on an abalone shell shows that the shell is a kind of bioceramic composite consisting of inorganic aragonite sheets and organic collagen protein matter. The aragonite sheets possess long and thin shape and are divided by the collagen protein matter, which compose a kind of laminated microstructure of the shell. The fracture surface energy of the laminated microstructure is investigated and compared with non-laminated microstructure based on its representative model. It shows that the fracture surface energy of the laminated microstructure is markedly larger than that of the non-laminated microstructure and endows the shell with high fracture toughness.

Abstract: The observation of scanning electron microscope (SEM) shows that a tibia bone is a kind of bioceramic composite consisting of hydroxyapatite layers and collagen protein matters. The hydroxyapatite layers are composed of hydroxyapatite sheets. The observation also shows there is a kind of interlaced microstructure of the hydroxyapatite sheets. The maximum pullout force of the interlaced microstructure was investigated and compared with that of the parallel microstructure. It is indicated that the maximum pullout force of the interlaced microstructure with a large interlaced angle is markedly larger than that of the parallel microstructure.

Abstract: Crab carapace is a kind of biomaterial in nature. It behaves favorable strength, stiffness and fracture toughness, which are closely related to its fine microstructure. The observation of scanning electron microscope (SEM) on the carapace of a Cyclodorippoidea crab shows that the carapace is a kind of natural bioceramic composite consisting of calcite crystal layers and collagen protein matrix. The observation also shows that the calcite crystal layers consist further of long and thin calcite crystal sheets and that all the calcite crystal sheets are arranged in a kind of parallel distribution. The maximum pullout energy of the calcite crystal sheets, which is closely related to the fracture toughness of the carapace, is investigated based on the representative model of the parallel distribution. It shows that the long and thin shape as well as the parallel distribution of the calcite crystal sheets enhance the maximum pullout energy and ensure the high fracture toughness of the carapace.

Abstract: Scanning electron microscope (SEM) observation shows that fibula bone is a kind of bioceramic composite consisting of hydroxyapatite layers and protein matters. The hydroxyapatite layers are further composed of hydroxyapatite sheets. The observation also shows that the hydroxyapatite sheets possess quite large volume fraction and also have very long and thin fiber shape. The mechanism of the large volume fraction of the hydroxyapatite sheets to ensure the larger elastic modulus of the bone was investigated based on the model of the bone composite and the theory of the composite mechanics. The investigated result reveals that the large volume fraction of the hydroxyapatite sheets endows the bone with large elastic modulus.

Abstract: The observation of scanning electron microscope (SEM) shows chafer cuticle is a kind of biocomposite which possesses multiscale microstructural characteristic. Under a relative small magnification of the SEM, it is found that the cuticle consists of chitin-fiber layers and protein matrix and that the fibers in two adjacent fiber layers have different directions, which composes a kind of fiber-crossed microstructure. Under a relative large magnification, it is observed that the many chitin fibers in the crossed fiber layers are furcated fibers, which exhibits a kind of fiber-furcated microstructure. The maximum pullout force of the fiber-furcated microstructure is investigated and compared with that of the fiber-non-furcated microstructure through their representational models. It shows that the maximum pull out force of the fiber-furcated structure is distinctly larger than that of the fiber-non-furcated structure.

Abstract: The observation of scanning electron microscope (SEM) on the cuticle of Tumblebug shows that the cuticle is a kind of biocomposite consisting of chitin-fibers and collagen protein matrix. The observation also shows that there are many underpinnings in the cuticle. The underpinnings are also a kind of biological composite consisting of chitin-fiber layers and collagen protein matrixes. More careful observation indicates that the chitin-fiber layers enwrap the core of the underpinnings forming a kind of helicoidal fiber structure. The maximal pull-out force of the helicoidal fiber structure, related to the fracture toughness of the underpinnings, is theoretically and experimentally investigated and compared with that of parallel fiber structure. It shows that the maximal pull-out force of the helicoidal fiber structure is larger than that of the parallel fiber structure, which gives profitable information for the design of man-made high-performance composites and composite structures.

Abstract: The observation on conifer wood shows that wood is a kind of biocomposite consisting of wood fibers and lignin matrix. The wood fibers are embedded in the lignin matrix with parallel distribution. It is also observed that the wood fibers continuously envelop the columned branch cores in the wood forming a kind of enveloping-core fiber distribution (ECFD). The ultimate load of the composite model with the ECFD is investigated and compared with that of the composite model with non-enveloping-core fiber distribution (NECFD). It shows that the strength of the composite model with the ECFD is larger than that of the composite model with NECFD. A kind of mimetic-wood composite specimens with the ECFD is also fabricated. The test was carried out with ECFD specimens and compared with that of the composite specimens with the NECFD. The result show that the ultimate strength of the former is significantly larger than that of the latter.

Abstract: A series of tensile tests of AZ61 magnesium alloy were conducted using Gleeble-1500 thermal-mechanical material testing system to learn the effect of the test temperatures and strain rates on the mechanical properties of the alloy. It is indicated that the higher the temperature, the lower the ultimate strength and fracture stress, and the larger the plasticity. It is also revealed that the larger the strain rate is, the higher the ultimate strength of the specimens will be, and the larger the plasticity of the specimens will be. The failure mechanism of the material under high temperature was also analyzed based on the fracture observation. It shows that the high temperatures will induce microvoids or microflaws in the material.

Abstract: The effects of strain rate (SR) and heating rate (HR) on the mechanical behaviors of the tensile specimens of magnesium alloy AZ61 were experimentally investigated using a Gleeble-1500 thermal-mechanical material testing system. It showed that the higher the temperature is, the lower the ultimate strength of the specimens will be. The higher the heating rate is, the higher the ultimate strength of the specimens will be. The metallurgraphs of the fracture section of the specimens were also experimentally investigated for exploring their failure mechanism under different temperatures and heating rates. It showed that the high temperatures and high heating rates will induce microvoids in the specimens. The microvoids make the specimens failure under relative low loads.

Abstract: The mechanical response and failure of the specimens of magnesium alloy AZ61 with different heating rates (HR) and loading rates (LR) were investigated by a Gleeble-1500 thermal-mechanical material testing system. It was found that heating rate has markedly effect on the strength and plasticity of the specimens. The higher the heating rate is, the lower the strength and the smaller of the plasticity of the specimens will be. There is the relatively small effect of the loading rates on the strength and plasticity of the specimens. The metallographs of the failed specimens were also observed. It shows that there are many microvoids in the specimens near the fracture sections. These microvoids may come from the local thermal and stress inconsistency under high heating rate and loading rates and degrade the strength and plasticity of the specimens.