Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure,...Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.展开更多
An experimental study was conducted to investigate the behavior of composite concrete beams damaged and cracked under pure torsion, and then repaired by external strengthening. This was achieved using high strength Ca...An experimental study was conducted to investigate the behavior of composite concrete beams damaged and cracked under pure torsion, and then repaired by external strengthening. This was achieved using high strength Carbon Fiber Reinforced Polymer (CFRP) laminates bonded with epoxy four composite modify reactive powder concrete (MRPC) I-beams. Different types of section (Solid & with opening) were tested to obtain the effect of amount of CFRP laminate on beams ultimate torque behavior, angle of twist and failure modes. The results obtained showed that a significant effect of external high strength CFRP laminates on effectively restore of section solid, the range of 89.8% to 91.2% of ultimate torsional strength effectively restored as well as effectively restoring of section opening by 83.48% - 86.67% of ultimate torsional strength. The repaired beams give high efficiency in ultimate torsional strength, and indicate that the adopted technique gives a good torsional strength.展开更多
Physical properties of composite propellants used in solid rocket motors change significantly with age. To predict the margin of safety and to reevaluate the remaining service life, the structural integrity analysis o...Physical properties of composite propellants used in solid rocket motors change significantly with age. To predict the margin of safety and to reevaluate the remaining service life, the structural integrity analysis of solid propellant grains of aged rocket motors is performed at various stages of their life span. To have the reliable results from these analyses, it is mandatory to use the current physical properties of the propellant at the time of analysis. Change in physical properties due to aging is more significant at exposed surfaces. Traditional methods of assessing current physical properties may not truly rep resent the properties of the batch. The paper presents a novel technique to measure the stress strain response at the exposed surface of propellant grain using a miniature-testing device. This specially designed device is able to measure the stress response while the propellant surface is compressed at a constant rate. This measured stress strain behavior is then co-related with the physical properties measured by routine tensile tests of the similar type of propellant which is aged artificially. It is observed that there exists an excellent correlation between the measured stress values by the sensor and physical properties measured by uni-axial tensile test. This nondestructive technique provides properties of propellant grains of all the motors in the batch comprehensively. The technique is safe as well as economical as compared to the traditional methods.展开更多
基金financially supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20110006110025)the National Natural Science Foundation of China(No.U1134102)
文摘Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.
文摘An experimental study was conducted to investigate the behavior of composite concrete beams damaged and cracked under pure torsion, and then repaired by external strengthening. This was achieved using high strength Carbon Fiber Reinforced Polymer (CFRP) laminates bonded with epoxy four composite modify reactive powder concrete (MRPC) I-beams. Different types of section (Solid & with opening) were tested to obtain the effect of amount of CFRP laminate on beams ultimate torque behavior, angle of twist and failure modes. The results obtained showed that a significant effect of external high strength CFRP laminates on effectively restore of section solid, the range of 89.8% to 91.2% of ultimate torsional strength effectively restored as well as effectively restoring of section opening by 83.48% - 86.67% of ultimate torsional strength. The repaired beams give high efficiency in ultimate torsional strength, and indicate that the adopted technique gives a good torsional strength.
文摘Physical properties of composite propellants used in solid rocket motors change significantly with age. To predict the margin of safety and to reevaluate the remaining service life, the structural integrity analysis of solid propellant grains of aged rocket motors is performed at various stages of their life span. To have the reliable results from these analyses, it is mandatory to use the current physical properties of the propellant at the time of analysis. Change in physical properties due to aging is more significant at exposed surfaces. Traditional methods of assessing current physical properties may not truly rep resent the properties of the batch. The paper presents a novel technique to measure the stress strain response at the exposed surface of propellant grain using a miniature-testing device. This specially designed device is able to measure the stress response while the propellant surface is compressed at a constant rate. This measured stress strain behavior is then co-related with the physical properties measured by routine tensile tests of the similar type of propellant which is aged artificially. It is observed that there exists an excellent correlation between the measured stress values by the sensor and physical properties measured by uni-axial tensile test. This nondestructive technique provides properties of propellant grains of all the motors in the batch comprehensively. The technique is safe as well as economical as compared to the traditional methods.
