The working environment of aerospace engines is extremely harsh with temperature exceeding 1700℃and accompanied by thermal coupling effects.In this condition,the materials employed in hypersonic aircraft undergo abla...The working environment of aerospace engines is extremely harsh with temperature exceeding 1700℃and accompanied by thermal coupling effects.In this condition,the materials employed in hypersonic aircraft undergo ablation issues,which can cause catastrophic accidents.Due to the excellent high-temperature stability and ablation resistance,HfC exhibits outstanding thermal expansion coefficient matching that of C/SiC composites.2.5D needle-punched C/SiC composites coated with HfC are prepared using a plasma spraying process,and a high-enthalpy arc-heated wind tunnel is employed to simulate the re-entry environment of aircraft at 8 Mach and an altitude of 32 km.The plasma-sprayed HfC-coated 2.5D needle-punched C/SiC composites are subjected to long-term dynamic testing,and their properties are investigated.Specifically,after the thermal assessment ablation experiment,the composite retains its overall structure and profile;the total mass ablation rate is 0.07445 g/s,the average linear ablation rate in the thickness direction is-0.0675μm/s,and the average linear ablation rate in the length direction is 13.907μm/s.Results verify that plasma-sprayed HfC coating exhibits excellent anti-oxidation and ablation resistance properties.Besides,the microstructure and ablation mechanism of the C/SiC composites are studied.It is believed that this work will offer guideline for the development of thermal protection materials and the assessment of structural thermal performance.展开更多
Damage assessments in three dimensional (3D) textile composites subjected to mechanical loading can be performed by non-destructive and destructive techniques.This paper applies the two techniques to investigate the f...Damage assessments in three dimensional (3D) textile composites subjected to mechanical loading can be performed by non-destructive and destructive techniques.This paper applies the two techniques to investigate the fracture behavior of 3D tufted textile composites.X-ray computed tomography as a non-destructive evaluation method is appropriate to detect damage locations and identify their progression in 3D textile composites.Destructive methods such as sectioning toward observing damage provide valuable information about damage patterns.The results of this research could be utilized to evaluate the initial cause of rupture in 3D tufted composites used in aerospace structures and analyze fracture modes and damage progression.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 parametric method is developed to quantitatively represent the microstructure of 3D woven structures. Different binding patterns, such as angle interlock and orthogonal interlock with through-thickness or layer-to-l...A parametric method is developed to quantitatively represent the microstructure of 3D woven structures. Different binding patterns, such as angle interlock and orthogonal interlock with through-thickness or layer-to-layer bindings, are classified. A unit cell of 3D woven structure is defined with four constituent yarn systems represented by nine structural parameters. A mapping relationship between the 3D woven structure and corresponding representative parameters is thus established. The study indicates that four out of the nine parameters are necessary to represent a 3D woven structure with an angle interlock binding, and that five parameters are required to describe a 3D woven structure with an orthogonal interlock binding. Once the structural parameters are determined, the pattern of 3D woven structures can be unambiguously identified, and vice versa. In addition to the purpose of structure presentation, the method can be further used as a means for designing 3D woven structure to meet the performance requirements of 3D woven composites.展开更多
As one of the new structural layout in the family of woven composites, 2.5D Woven Composites（2.5D-WC） have recently attracted an increasing interest owing to its excellent properties, i.e. high specific strength and...As one of the new structural layout in the family of woven composites, 2.5D Woven Composites（2.5D-WC） have recently attracted an increasing interest owing to its excellent properties, i.e. high specific strength and fatigue resistance, in the aerospace and automobile industry. Indepth understanding of the fatigue behavior of this material at un-ambient temperatures is critical for the engineering applications, especially in aero-engine field. Here, fatigue behavior of 2.5D-WC at different temperatures was numerically investigated based on the unit cell approach. Firstly, the unit cell model of 2.5D-WC was established using ANSYS software. Subsequently, the temperature-dependent fatigue life prediction model was built up. Finally, the fatigue lives alongside the damage evolution processes of 2.5D-WC at ambient temperature（20 ℃） and unambient temperature（180 ℃） were analyzed. The results show that numerical results are in good agreement with the relevant experimental results at 20 and 180 ℃. Fatigue behavior of 2.5D-WC is also sensitive to temperature, which is partially attributed to the mechanical properties of resin and the change of inclination angle of warp yarns. We hope that the proposed fatigue life prediction model and the findings could further promote the engineering application of 2.5D-WC, especially in aero-engine field.展开更多
Carbon fiber reinforced silicon carbide(C_(f)/SiC)composites are widely used in aerospace for their excellent mechanical properties.However,the quality of the machined surface is poor and unpredictable due to the mate...Carbon fiber reinforced silicon carbide(C_(f)/SiC)composites are widely used in aerospace for their excellent mechanical properties.However,the quality of the machined surface is poor and unpredictable due to the material heterogeneity induced by complex removal mechanism.To clarify the effects of fiber orientation on the grinding characteristics and removal mechanism,single grit scratch experiments under different fiber orientations are conducted and a three-phase numerical modelling method for 2.5D C_(f)/SiC composites is proposed.Three fiber cutting modes i.e.,transverse,normal and longitudinal,are defined by fiber orientation and three machining directions i.e.,MA(longitudinal and normal),MB(longitudinal and transverse)and MC(normal and transverse),are selected to investigate the effect of fiber orientation on grinding force and micro-morphology.Besides,a three-phase cutting model of 2.5D C_(f)/SiC composites considering the mechanical properties of the matrix,fiber and interface is developed.Corresponding simulations are performed to reveal the micro-mechanism of crack initiation and extension as well as the material removal mechanism under different fiber orientations.The results indicate that the scratching forces fluctuate periodically,and the order of mean forces is MA>MC>MB.Cracks tend to grow along the fiber axis,which results in the largest damage layer for transverse fibers and the smallest for longitudinal fibers.The removal modes of transverse fibers are worn,fracture and peel-off,in which normal fibers are pullout and outcrop and the longitudinal fibers are worn and push-off.Under the stable cutting condition,the change of contact area between fiber and grit leads to different removal modes of fiber in the same cutting mode,and the increase of contact area results in the aggravation of fiber fracture.展开更多
Engineering structures made of ceramic matrix composites(CMCs)usually suffer from cyclic loads during service,which could lead to disastrous failures.This work focuses on the fatigue behavior of a 2.5D C/SiC composite...Engineering structures made of ceramic matrix composites(CMCs)usually suffer from cyclic loads during service,which could lead to disastrous failures.This work focuses on the fatigue behavior of a 2.5D C/SiC composite under tension–tension cyclic loading.Experiments of the 2.5D C/SiC composite are firstly carried out to determine the fatigue lifetime of the material at different stress levels.The fracture surfaces examined by a scanning electronic microscope indicate that the damage mechanisms under cyclic loading are closely related to crack propagation,fiber/matrix interfacial degradation,and fiber breakage.Considering the damage evolution of fibers and interfacial resistance,a micromechanical model is adopted to describe the fatigue behavior of 2.5D C/SiC composite,and the numerical results are compared with the experimental results.Further,a sensitivity analysis is performed as a function of the interfacial shear stress,fiber Weibull modulus,and fiber strength.The calculation of sensitivity factors shows that the variations of the fiber Weibull modulus and fiber strength have the most significant influence and,thereafter,the variation of interfacial shear stress.展开更多
基金financially supported by the National Key R&D Program of China(No.2022YFB3-401900)the National Natural Science Foundation of China(No.U21A20134)the Shandong Provincial Natural Science Foundation(Excellent Young Fund,No.ZR2022YQ48).
文摘The working environment of aerospace engines is extremely harsh with temperature exceeding 1700℃and accompanied by thermal coupling effects.In this condition,the materials employed in hypersonic aircraft undergo ablation issues,which can cause catastrophic accidents.Due to the excellent high-temperature stability and ablation resistance,HfC exhibits outstanding thermal expansion coefficient matching that of C/SiC composites.2.5D needle-punched C/SiC composites coated with HfC are prepared using a plasma spraying process,and a high-enthalpy arc-heated wind tunnel is employed to simulate the re-entry environment of aircraft at 8 Mach and an altitude of 32 km.The plasma-sprayed HfC-coated 2.5D needle-punched C/SiC composites are subjected to long-term dynamic testing,and their properties are investigated.Specifically,after the thermal assessment ablation experiment,the composite retains its overall structure and profile;the total mass ablation rate is 0.07445 g/s,the average linear ablation rate in the thickness direction is-0.0675μm/s,and the average linear ablation rate in the length direction is 13.907μm/s.Results verify that plasma-sprayed HfC coating exhibits excellent anti-oxidation and ablation resistance properties.Besides,the microstructure and ablation mechanism of the C/SiC composites are studied.It is believed that this work will offer guideline for the development of thermal protection materials and the assessment of structural thermal performance.
文摘Damage assessments in three dimensional (3D) textile composites subjected to mechanical loading can be performed by non-destructive and destructive techniques.This paper applies the two techniques to investigate the fracture behavior of 3D tufted textile composites.X-ray computed tomography as a non-destructive evaluation method is appropriate to detect damage locations and identify their progression in 3D textile composites.Destructive methods such as sectioning toward observing damage provide valuable information about damage patterns.The results of this research could be utilized to evaluate the initial cause of rupture in 3D tufted composites used in aerospace structures and analyze fracture modes and damage progression.
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the Research Fund for the Doctoral Program of Higher Education and the Shanghai Key Discipline Project
文摘A parametric method is developed to quantitatively represent the microstructure of 3D woven structures. Different binding patterns, such as angle interlock and orthogonal interlock with through-thickness or layer-to-layer bindings, are classified. A unit cell of 3D woven structure is defined with four constituent yarn systems represented by nine structural parameters. A mapping relationship between the 3D woven structure and corresponding representative parameters is thus established. The study indicates that four out of the nine parameters are necessary to represent a 3D woven structure with an angle interlock binding, and that five parameters are required to describe a 3D woven structure with an orthogonal interlock binding. Once the structural parameters are determined, the pattern of 3D woven structures can be unambiguously identified, and vice versa. In addition to the purpose of structure presentation, the method can be further used as a means for designing 3D woven structure to meet the performance requirements of 3D woven composites.
基金supported by Jiangsu Innovation Program fo Graduate Education (No. KYLX_0237)
文摘As one of the new structural layout in the family of woven composites, 2.5D Woven Composites（2.5D-WC） have recently attracted an increasing interest owing to its excellent properties, i.e. high specific strength and fatigue resistance, in the aerospace and automobile industry. Indepth understanding of the fatigue behavior of this material at un-ambient temperatures is critical for the engineering applications, especially in aero-engine field. Here, fatigue behavior of 2.5D-WC at different temperatures was numerically investigated based on the unit cell approach. Firstly, the unit cell model of 2.5D-WC was established using ANSYS software. Subsequently, the temperature-dependent fatigue life prediction model was built up. Finally, the fatigue lives alongside the damage evolution processes of 2.5D-WC at ambient temperature（20 ℃） and unambient temperature（180 ℃） were analyzed. The results show that numerical results are in good agreement with the relevant experimental results at 20 and 180 ℃. Fatigue behavior of 2.5D-WC is also sensitive to temperature, which is partially attributed to the mechanical properties of resin and the change of inclination angle of warp yarns. We hope that the proposed fatigue life prediction model and the findings could further promote the engineering application of 2.5D-WC, especially in aero-engine field.
基金supported by the National Natural Science Foundation of China(No.51922066)the Key Research and Development Plan of Shandong Province(Nos.2019JMRH0307,2020CXGC010204)。
文摘Carbon fiber reinforced silicon carbide(C_(f)/SiC)composites are widely used in aerospace for their excellent mechanical properties.However,the quality of the machined surface is poor and unpredictable due to the material heterogeneity induced by complex removal mechanism.To clarify the effects of fiber orientation on the grinding characteristics and removal mechanism,single grit scratch experiments under different fiber orientations are conducted and a three-phase numerical modelling method for 2.5D C_(f)/SiC composites is proposed.Three fiber cutting modes i.e.,transverse,normal and longitudinal,are defined by fiber orientation and three machining directions i.e.,MA(longitudinal and normal),MB(longitudinal and transverse)and MC(normal and transverse),are selected to investigate the effect of fiber orientation on grinding force and micro-morphology.Besides,a three-phase cutting model of 2.5D C_(f)/SiC composites considering the mechanical properties of the matrix,fiber and interface is developed.Corresponding simulations are performed to reveal the micro-mechanism of crack initiation and extension as well as the material removal mechanism under different fiber orientations.The results indicate that the scratching forces fluctuate periodically,and the order of mean forces is MA>MC>MB.Cracks tend to grow along the fiber axis,which results in the largest damage layer for transverse fibers and the smallest for longitudinal fibers.The removal modes of transverse fibers are worn,fracture and peel-off,in which normal fibers are pullout and outcrop and the longitudinal fibers are worn and push-off.Under the stable cutting condition,the change of contact area between fiber and grit leads to different removal modes of fiber in the same cutting mode,and the increase of contact area results in the aggravation of fiber fracture.
基金The financial supports from the National Science Foundation of China(10802022,10872049)The Key-grant Project of Chinese Ministry of Education(309014 )+1 种基金The sponsors from Shanghai Educational Development Foundation(08CG39)Shanghai Rising-Star Program(08QA14008)
基金This paper is supported by the Jiangsu Natural Science Foundation(BK20170022).
文摘Engineering structures made of ceramic matrix composites(CMCs)usually suffer from cyclic loads during service,which could lead to disastrous failures.This work focuses on the fatigue behavior of a 2.5D C/SiC composite under tension–tension cyclic loading.Experiments of the 2.5D C/SiC composite are firstly carried out to determine the fatigue lifetime of the material at different stress levels.The fracture surfaces examined by a scanning electronic microscope indicate that the damage mechanisms under cyclic loading are closely related to crack propagation,fiber/matrix interfacial degradation,and fiber breakage.Considering the damage evolution of fibers and interfacial resistance,a micromechanical model is adopted to describe the fatigue behavior of 2.5D C/SiC composite,and the numerical results are compared with the experimental results.Further,a sensitivity analysis is performed as a function of the interfacial shear stress,fiber Weibull modulus,and fiber strength.The calculation of sensitivity factors shows that the variations of the fiber Weibull modulus and fiber strength have the most significant influence and,thereafter,the variation of interfacial shear stress.
