Papers by Author: Bin Chen

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.

Abstract: Scanning electron microscope (SEM) observation showed that femur bone is a kind of bioceramic composite consisting of hydroxyapatite layers and protein matters. The hydroxyapatite layers are further composed of hydroxyapatite fiber sheets. The observation also showed that the hydroxyapatite fiber sheets possess very thin fiber shape. The thickness of the hydroxyapatite fiber sheets is within nanometer scale. The mechanism of the high fracture strength of the bone was investigated based on the microstructural characteristics of the hydroxyapatite fiber sheets and the theory of fracture mechanics. The result reveals that the thin fiber shape of the hydroxyapatite fiber sheets endows the bone with high fracture strength.

Abstract: Scanning electron microscope (SEM) observation shows that the shell of a Unio douglasiae is a kind of bioceramic composite consisting of laminated aragonite and organic materials. The aragonite layers further consist of thin and long aragonite fibers. The aragonite fibers possess high density in the shell and their diameter is within nanometer scale. The mechanism of the high modulus and high strength of the shell were investigated based on the observed nanometer structure of the aragonite fibers and the rule of mixtures Young’s modulus as well as the Griffith criterion. It reveals that the high density and the nanometer scale of the aragonite fibers endow the shell with high modulus and fracture strength.

Abstract: Tooth 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 a mature tooth shows that the tooth is a kind of natural bioceramic composite consisting of hydroxyapatite layers and collagen protein matrix. The observation also shows that the hydroxyapatite layers consist of long and thin hydroxyapatite sheets and that all the hydroxyapatite sheets are arranged in a kind of parallel distribution. The maximum pullout energy of the hydroxyapatite sheets, which is closely related to the fracture toughness of the tooth, 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 hydroxyapatite sheets increase the maximum pullout energy and enhance the fracture toughness of the tooth.

Abstract: Scanning electron microscope (SEM) observation on a mature shankbone shows that the bone is a kind of bioceramic composite consisting of hydroxyapatite sheets and collagen protein matrix. The observation also shows that there are many holes in the bone and that the hydroxyapatite sheets near by these holes helicoidally round these holes forming a kind of helicoidally-rounded-hole microstructure (HRHM). The maximum pullout force of the HRHM is investigated and compared with that of non-helicoidally-rounded-hole microstructure (NHRHM). It shows that the HRHM could markedly increase the maximum pullout force of the hydroxyapatite sheets compared to the NHRHM and therefore enhance the fracture toughness of the bone.

Abstract: The observation of scanning electron microscope (SEM) showed that a tibia bone is a kind of bioceramic composite consisting of hydroxyapatite layers and collagen protein matrix. All the hydroxyapatite layers are parallel with the surface of the bone and consist of numerous hydroxyapatite sheets. The observation also showed there is a kind of intercrossed microstructure of the hydroxyapatite sheets. In which the hydroxyapatite sheets in an arbitrary hydroxyapatite layer make a large intercrossed angle with the hydroxyapatite sheets in its adjacent hydroxyapatite layers. The maximum pullout force of the intercrossed microstructure, which is closely related to the fracture toughness of the bone, was investigated and compared with that of the parallel microstructure of the sheets through their representative models. Result indicated that the maximum pullout force of the intercrossed microstructure is markedly larger than that of the parallel microstructure.

Abstract: The microstructures of a whangee (a kind of bamboo) were observed with a scanning electron microscope (SEM). It showed that the whangee is a kind of natural cellular biocomposite consisting of countless bamboo cells. The bamboo cells are columnar and all of them are parallel with the surface of the bamboo. The observation also showed that the walls of the bamboo cell are a kind of fiber-reinforced biocomposite with bamboo fiber-spiral mcirstructure. Based on the SEM observation, a kind of biomimetic composite with the fiber-spiral structure was fabricated. The fracture toughness of the composite was investigated and compared with that of the conventional composite with parallel-fiber structure. It showed that the fracture toughness of the biomimetic composite is markedly larger than that of the conventional composite.

Abstract: A scanning electronic microscope (SEM) was used for observing the microstructures of a Cockle shell. It showed that the shell is a kind of natural bioceramic composite consisting of aragonite sheets and organic collagen matrix. The aragonite sheets are further composed of aragonite fibers. The aragonite fibers are of long and thin shape and compose various reinforced microstructures, which include a kind of fiber-intersected reinforced one. The fiber-intersected reinforced microstructure was employed as the design example for the structure of man-made fiber-reinforced composite, a kind of fiber-reinforced composite with the fiber-intersected reinforced structure was biomimetically fabricated. The fracture toughness of the biomimetical composite was tested and compared with that of the conventional composite with fiber-parallel structure. It indicated that the fracture toughness of the biomimetical composite is markedly larger than that of the fiber-parallel composite.

Abstract: A scanning electron microscope (SEM) was used for the observation of the microstructures of a chafer cuticle. It showed that the cuticle is a kind of biocomposite consisting of complected chitin-fiber plies and sclerous protein matrix. The observation also showed that there are many holes in the cuticle and the complected fibers continuously reel these holes forming a kind of fiber-complected and reeled microstructure. Based on the SEM observation, a kind of biomimetic composite laminate with complected and reeled structure was fabricated with a special mould and process. The ultimate strength of the obtained biomimetic composite laminate was experimentally investigated and compared with that of the conventional drilling-hole composite laminate. It showed that the ultimate strength of the biomimetic composite laminate is markedly larger than that of the drilling-hole composite laminate.