The theoretical calculation formulas for the plane strain fracture toughness of mode Ⅰand Ⅱcracks of ceramic materials are deduced in this paper by using the nonlocal elasticity theory and maximum tensile stress cri...The theoretical calculation formulas for the plane strain fracture toughness of mode Ⅰand Ⅱcracks of ceramic materials are deduced in this paper by using the nonlocal elasticity theory and maximum tensile stress criterion The deduced formulas, which are independent of crack geometry,bear a relation to material parameters.It is shown through experiment that the theoretical value of fracture toughness is the lower limit of testing value. The theoretical calculation formulas for fracture toughness relate the macro-mechanical performance of materials with the micro-structural parameters and,therefore, are beneficial to fully understanding the physical mechanism of material rupture.展开更多
The fracture toughness and fracture work of A12O3/SiC prismatic ceramic composites was evaluated in this paper, which showed the fracture energy was improved greatly. Based on the observation 'for crack propagat...The fracture toughness and fracture work of A12O3/SiC prismatic ceramic composites was evaluated in this paper, which showed the fracture energy was improved greatly. Based on the observation 'for crack propagation and fracture morphology, the fracture behavior of the prismatic composites was analyzed. In the bending test, the composites displayed a non-catastrophic behavior and a graceful failure with reasonable load-carrying capability.展开更多
ZrB_2-SiC based ultra-high temperature ceramic（UHTC） struts were firstly proposed and fabricated with the potential application in the combustor of scramjets for fuel injection and flame-holding for their machinabil...ZrB_2-SiC based ultra-high temperature ceramic（UHTC） struts were firstly proposed and fabricated with the potential application in the combustor of scramjets for fuel injection and flame-holding for their machinability and excellent oxidation/ablation resistance in the extreme harsh environment. The struts were machined with electrospark wire-electrode cutting techniques to form UHTC into the desired shape, and with laser drilling to drill tiny holes providing the channels for fuel injection. The integrated thermal-structural characteristic of the struts was evaluated in high-temperature combustion environment by the propane-oxygen free jet facility, subject to the heat flux of 1.5 MW/m^2 lasting for 300 seconds, and the struts maintained integrity during and after the first experiment. The experiments were repeated for verifying the reusability of the struts. Fracture occurred during the second repeated experiment with the crack propagating through the hole. Finite element analysis（FEA） was carried out to study the thermal stress distribution in the UHTC strut. The simulation results show a high thermal stress concentration occurs at the hole which is the crack initiation position. The phenomenon is in good agreement with the experimental results. The study shows that the thermal stress concentration is a practical key issue in the applications of the reusable UHTC strut for fuel injection structure in scramjets.展开更多
Background Ceramic bearing surfaces have been introduced to prevent osteolysis after total hip arthroplasty （THA）,but little is known about the difference in clinical and radiological results between pure alumina an...Background Ceramic bearing surfaces have been introduced to prevent osteolysis after total hip arthroplasty （THA）,but little is known about the difference in clinical and radiological results between pure alumina and sandwich alumina bearings.The purpose of this study was to analyze the results obtained with third-generation alumina-on-alumina THA with two different designs both in liner and femoral stem fixation after a minimum follow-up of 4.2 years.Methods The results of 195 primary alumina-on-alumina THAs in 167 patients were evaluated.The procedures were performed between January 1998 and October 2006.Three patients died and 11 patients were lost to follow-up,leaving a total of 153 patients （181 hips） available for study.In the 88 group A patients,107 hips were implanted using pure alumina bearings with cementless femoral stems.These patients were followed for （6.84±1.49） years.In the 65 group B patients,74 hips were implanted using sandwich alumina ceramic bearings with cemented femoral stems.These patients had a follow-up period of （7.73±1.60） years.Patients in both groups were evaluated clinically and radiographically.Results One ceramic liner fracture occurred in group A and five took place in group B （P 〈0.05）,four of them revised for liner fracture.In each group,one acetabular shell migration happened without liner breakage and two hips developed deep infections,and all these six hips received revisions.Nine femoral components loosened in group B,with seven undergoing revisions.Kaplan-Meier survivorship at 5 years for revision of any component for any reason in group A was 96.26% compared to 90.54% in group B （P 〈0.05）.Better function was determined in group A （average Harris hip scores：92.13±2.85） than in group B （average Harris hip scores：86.03±4.21） and the difference was significant （P 〈0.05）.Squeaking was not recorded in either group.Conclusions The sandwich design of the acetabular bearings can not reduce the migration rate in ceramic bearings but increase the liner fracture rate compared to pure ceramic liners.The high loosening rate in fluted and taped designed cemented stems with sandwich liners warrant caution to their use.展开更多
文摘The theoretical calculation formulas for the plane strain fracture toughness of mode Ⅰand Ⅱcracks of ceramic materials are deduced in this paper by using the nonlocal elasticity theory and maximum tensile stress criterion The deduced formulas, which are independent of crack geometry,bear a relation to material parameters.It is shown through experiment that the theoretical value of fracture toughness is the lower limit of testing value. The theoretical calculation formulas for fracture toughness relate the macro-mechanical performance of materials with the micro-structural parameters and,therefore, are beneficial to fully understanding the physical mechanism of material rupture.
文摘The fracture toughness and fracture work of A12O3/SiC prismatic ceramic composites was evaluated in this paper, which showed the fracture energy was improved greatly. Based on the observation 'for crack propagation and fracture morphology, the fracture behavior of the prismatic composites was analyzed. In the bending test, the composites displayed a non-catastrophic behavior and a graceful failure with reasonable load-carrying capability.
基金Funded by the Major Research Plan of the National Natural Science Foundation of China(No.91216302)the Major State Basic Research Development Program of China(973 Program)(No.2015CB655200)the National Natural Science Foundation of China(Nos.11672088,11472092,and 11502058)
文摘ZrB_2-SiC based ultra-high temperature ceramic（UHTC） struts were firstly proposed and fabricated with the potential application in the combustor of scramjets for fuel injection and flame-holding for their machinability and excellent oxidation/ablation resistance in the extreme harsh environment. The struts were machined with electrospark wire-electrode cutting techniques to form UHTC into the desired shape, and with laser drilling to drill tiny holes providing the channels for fuel injection. The integrated thermal-structural characteristic of the struts was evaluated in high-temperature combustion environment by the propane-oxygen free jet facility, subject to the heat flux of 1.5 MW/m^2 lasting for 300 seconds, and the struts maintained integrity during and after the first experiment. The experiments were repeated for verifying the reusability of the struts. Fracture occurred during the second repeated experiment with the crack propagating through the hole. Finite element analysis（FEA） was carried out to study the thermal stress distribution in the UHTC strut. The simulation results show a high thermal stress concentration occurs at the hole which is the crack initiation position. The phenomenon is in good agreement with the experimental results. The study shows that the thermal stress concentration is a practical key issue in the applications of the reusable UHTC strut for fuel injection structure in scramjets.
文摘Background Ceramic bearing surfaces have been introduced to prevent osteolysis after total hip arthroplasty （THA）,but little is known about the difference in clinical and radiological results between pure alumina and sandwich alumina bearings.The purpose of this study was to analyze the results obtained with third-generation alumina-on-alumina THA with two different designs both in liner and femoral stem fixation after a minimum follow-up of 4.2 years.Methods The results of 195 primary alumina-on-alumina THAs in 167 patients were evaluated.The procedures were performed between January 1998 and October 2006.Three patients died and 11 patients were lost to follow-up,leaving a total of 153 patients （181 hips） available for study.In the 88 group A patients,107 hips were implanted using pure alumina bearings with cementless femoral stems.These patients were followed for （6.84±1.49） years.In the 65 group B patients,74 hips were implanted using sandwich alumina ceramic bearings with cemented femoral stems.These patients had a follow-up period of （7.73±1.60） years.Patients in both groups were evaluated clinically and radiographically.Results One ceramic liner fracture occurred in group A and five took place in group B （P 〈0.05）,four of them revised for liner fracture.In each group,one acetabular shell migration happened without liner breakage and two hips developed deep infections,and all these six hips received revisions.Nine femoral components loosened in group B,with seven undergoing revisions.Kaplan-Meier survivorship at 5 years for revision of any component for any reason in group A was 96.26% compared to 90.54% in group B （P 〈0.05）.Better function was determined in group A （average Harris hip scores：92.13±2.85） than in group B （average Harris hip scores：86.03±4.21） and the difference was significant （P 〈0.05）.Squeaking was not recorded in either group.Conclusions The sandwich design of the acetabular bearings can not reduce the migration rate in ceramic bearings but increase the liner fracture rate compared to pure ceramic liners.The high loosening rate in fluted and taped designed cemented stems with sandwich liners warrant caution to their use.
