The effect of the pyrolytic carbon(PyC)interface thickness on the heat-stability of CansasⅡSiC_(f)/SiC composites under Ar up to 1500℃was studied in detail.After the heat treatment at 1500℃for 50 h,the interface bo...The effect of the pyrolytic carbon(PyC)interface thickness on the heat-stability of CansasⅡSiC_(f)/SiC composites under Ar up to 1500℃was studied in detail.After the heat treatment at 1500℃for 50 h,the interface bonding strength of the thin interface(about 200 nm)decreases from 74.4 to 20.1 MPa(73.0%),while that of the thick interface(about 2μm)declines from 7.3 to 3.2 MPa(52.7%).At the same time,the decline fraction of strength of the composites with the thin interface is 12.1%,less than that with the thick interface(42.0%).The fiber strength also decreases after heat treatment,which may be due to the significant growth ofβ-SiC grains and critical defects.The different heat-stability of the interface with the thin and thick thickness might be related to the inconsistency of the degree of the graphitization of PyC.Compared with the composites with the thick interface,the composites with the thin interface remained higher tensile strength after heat treatment due to the better interface bonding strength.The interface with strong bonding strength could protect the fiber by postponing the decomposition of amorphous phases SiC_(x)O_(y) and hindering the generation of fiber defects.展开更多
A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Th...A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Then,some data points in the original load spectrum are added between the peak and valley values.Finally,the filtering spectrum is obtained.The proposed method can reflect the path information of the original load spectrum.In addition,it can also eliminate the noise in the signal and improve the efficiency of signal processing,which is of practical significance for the research of aero-engine.展开更多
To make better use of 2.5D C/SiC composites in industry, it is necessary to understand the mechanical properties. A finite element model＇of 2.5D composites is established, by considering the fiber undulation and the ...To make better use of 2.5D C/SiC composites in industry, it is necessary to understand the mechanical properties. A finite element model＇of 2.5D composites is established, by considering the fiber undulation and the porosity in 2.5D C/SiC composites. The fiber direction of warp is defined by cosine function to simulate the undulation of warp, and based on uniform strain assumption, analytical model of the elastic modulus and coefficient of thermal expansion （CTE） for 2.5D C/SiC composites were established by using dual- scale model. The result is found to correlate reasonably well with the predicted results and experimental results. The parametric study also demonstrates the effects of the fiber volume fraction, distance of warp yarn, and porosity in micro-scale on the mechanical properties and the coefficients of thermal expansion.展开更多
A new unified macro- and micro-mechanics failure analysis method for composite structures was developed in order to take the effects of composite micro structure into consideration. In this method, the macro stress di...A new unified macro- and micro-mechanics failure analysis method for composite structures was developed in order to take the effects of composite micro structure into consideration. In this method, the macro stress distribution of composite structure was calculated by commercial finite element analysis software. According to the macro stress distribution, the damage point was searched and the micro-stress distribution was calculated by reformulated finite-volume direct averaging micromechanics （FVDAM）, which was a multi-scale finite element method for composite. The micro structure failure modes were estimated with the failure strength of constituents. A unidirectional composite plate with a circular hole in the center under two kinds of loads was analyzed with the traditional macro-mechanical failure analysis method and the unified macro- and micro-mechanics failure analysis method. The results obtained by the two methods are consistent, which show this new method＇s accuracy and efficiency.展开更多
基金Funded by the National Science and Technology Major Project(No.2017-IV-0005-0042)the China Postdoctoral Science Foundation(No.2021M691566)。
文摘The effect of the pyrolytic carbon(PyC)interface thickness on the heat-stability of CansasⅡSiC_(f)/SiC composites under Ar up to 1500℃was studied in detail.After the heat treatment at 1500℃for 50 h,the interface bonding strength of the thin interface(about 200 nm)decreases from 74.4 to 20.1 MPa(73.0%),while that of the thick interface(about 2μm)declines from 7.3 to 3.2 MPa(52.7%).At the same time,the decline fraction of strength of the composites with the thin interface is 12.1%,less than that with the thick interface(42.0%).The fiber strength also decreases after heat treatment,which may be due to the significant growth ofβ-SiC grains and critical defects.The different heat-stability of the interface with the thin and thick thickness might be related to the inconsistency of the degree of the graphitization of PyC.Compared with the composites with the thick interface,the composites with the thin interface remained higher tensile strength after heat treatment due to the better interface bonding strength.The interface with strong bonding strength could protect the fiber by postponing the decomposition of amorphous phases SiC_(x)O_(y) and hindering the generation of fiber defects.
基金This work was supported by the National Basic Research Program of China,National Nature Science Foundation of China(No.51675266)the Foundation Research Funds for the Center in NUAA(Nos.NJ20160038,NS2017011)Foundation of Graduate Innovation Center in NUAA(No.kfjj20170220)。
文摘A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Then,some data points in the original load spectrum are added between the peak and valley values.Finally,the filtering spectrum is obtained.The proposed method can reflect the path information of the original load spectrum.In addition,it can also eliminate the noise in the signal and improve the efficiency of signal processing,which is of practical significance for the research of aero-engine.
基金Funded by the National Basic Research Program of China,National Natural Science Foundation of China(No.51075204)Aeronautical Science Foundation of China(No.2012ZB52026)+1 种基金Research Fund for the Doctoral Program of Higher Education of China(No.20070287039)NUAA Research Funding(No.NZ2012106)
文摘To make better use of 2.5D C/SiC composites in industry, it is necessary to understand the mechanical properties. A finite element model＇of 2.5D composites is established, by considering the fiber undulation and the porosity in 2.5D C/SiC composites. The fiber direction of warp is defined by cosine function to simulate the undulation of warp, and based on uniform strain assumption, analytical model of the elastic modulus and coefficient of thermal expansion （CTE） for 2.5D C/SiC composites were established by using dual- scale model. The result is found to correlate reasonably well with the predicted results and experimental results. The parametric study also demonstrates the effects of the fiber volume fraction, distance of warp yarn, and porosity in micro-scale on the mechanical properties and the coefficients of thermal expansion.
基金co-supported by National Basic Research Program of China, National Natural Science Foundation of China(No. 51075204)Aeronautical Science Foundation of China (No.2009ZB52028, No. 2012ZB52026)+1 种基金Research Fund for the Doctoral Program of Higher Education of China (No. 20070287039)NUAA Research Funding (No. NZ2012106)
文摘A new unified macro- and micro-mechanics failure analysis method for composite structures was developed in order to take the effects of composite micro structure into consideration. In this method, the macro stress distribution of composite structure was calculated by commercial finite element analysis software. According to the macro stress distribution, the damage point was searched and the micro-stress distribution was calculated by reformulated finite-volume direct averaging micromechanics （FVDAM）, which was a multi-scale finite element method for composite. The micro structure failure modes were estimated with the failure strength of constituents. A unidirectional composite plate with a circular hole in the center under two kinds of loads was analyzed with the traditional macro-mechanical failure analysis method and the unified macro- and micro-mechanics failure analysis method. The results obtained by the two methods are consistent, which show this new method＇s accuracy and efficiency.
