Effect of PyC Interface Thickness on the Heat-stability of Cansas-ⅡSiC_(f)/SiC Composites

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.

A novel compilation method of comprehensive mission spectrum of aero-engine maneuvering load based on use-related mission segment

Comprehensive Mission Spectrum(CMS)of an aero-engine can reflect the usage characteristics of the engine.It can provide load input for engine life prediction and accelerated mission test.In this paper,a novel compilation method of CMS of aero-engine maneuvering load based on mission segment is proposed.Firstly,the use-related Typical Mission Segment(TMS)of maneuvering load is divided and identified according to spectral characteristics.Secondly,the mathematical model of different kinds of TMS are established based on stochastic process theory.Finally,the CMS of maneuvering load is compiled based on TMS.The proposed method can accurately quantify the compilation of CMS.The compiled CMS shows good agreement with the original load spectrum.According to damage consistency inspection,the compiled CMS is consistent with the damage caused by the original load spectrum in terms of low cycle fatigue.

Effect of Particle Size Distribution on Radiative Heat Transfer in High-Temperature Homogeneous Gas-Particle Mixtures

The weighted-sum-of-gray-gas(WSGG)model and Mie theory are applied to study the influents of particle size on the radiative transfer in high temperature homogeneous gas-particle mixtures,such as the flame in aero-engine combustor.The radiative transfer equation is solved by the finite volume method.The particle size is assumed to obey uniform distribution and logarithmic normal(L-N)distribution,respectively.Results reveal that when particle size obeys uniform distribution,increasing particle size with total particle volume fraction fvunchanged will result in the decreasing of the absolute value of radiative heat transfer properties,and the effect of ignoring particle scattering will also be weakened.Opposite conclusions can be obtained when total particle number concentration N0 is unchanged.Moreover,if particle size obeys L-N distribution,increasing the narrowness indexσor decreasing the characteristic diameter Dˉwith the total particle volume fraction fvunchanged will increase the absolute value of radiative heat transfer properties.With total particle number concentration N0 unchanged,opposite conclusions for radiative heat source and incident radiation terms can be obtained except for radiative heat flux term.As a whole,the effects of particle size on the radiative heat transfer in the high-temperature homogeneous gas-particle mixtures are complicated,and the particle scattering cannot be ignoring just according to the particle size.

Extension of continuous scanning laser Doppler vibrometry measurement for complex structures with curved surfaces

The continuous Scanning Laser Doppler Vibrometry(SLDV)developed on the base of the galvanometer scanner system has made it possible to quickly obtain the full field vibration responses within a rectangular area of the structure.In this paper,an arbitrary continuous scanning path generating method for Continuous Scanning Laser Doppler Vibometry(CSLDV)is further put forward in order to allow the CSLDV suitable for testing structures featured by complex shapes not just for regular areas.In the first step,the relationship between position of laser spot and the driving voltages of galvanometer scanner system has been described by a mathematical modeling.Then,a novel arbitrary scanning path generating strategy based on CSLDV is presented by deforming a normalization rectangular scanning path to an arbitrary continuous scanning path.The mapping relation between the normalization rectangular scanning path and arbitrary continuous scanning path is established using the reference points.In the second step,a compressor blade with curved surface was taken as an example for modal test using the proposed method.At the same time,a validated experiment was performed in SLDV.The results show the mode shapes derived from the extended CSLDV are in agreement with those from SLDV and the Modal Assurance Criterion(MAC)between the two are all greater than 0.96.They also demonstrate the feasibility and effectiveness of the proposed method for CSLDV test and show strong potential on further practical engineering applications.

An Elasticity Model Considering Grain Boundaries and Tensile Orientations for Directionally Solidified Superalloys

In order to investigate the elastic properties of directionally solidified(DS)superalloys,an elasticity model called boundaries elastic model(GBE model),considering grain boundaries and tensile orientations,is proposed in this paper.Two assumptions are adopted in the GBE model:(1)The displacement of grains,which moves along the perpendicular direction,is restricted by the grain boundaries;(2)Grain boundaries influence region(GBIR)is formed around the grain boundaries.Based on the single crystal(SC)calculation method of elastic properties,the GBE model can well predict macroscopic equivalent elastic modulus(Young’s modulus)of DS superalloys under different tensile orientations effectively.To demonstrate the correctness of the GBE model,3D finite element simulation is adopted and tensile experiments on a Ni3Al?base DS superalloy(IC10)along five tensile orientations are carried out.Meanwhile,the grain boundaries are observed by light microscopy and transmission electron microscope(TEM).Therefore,the GBE model is proved to be feasible by comparing the simulated results with the experiments.

Investigation on Combustion Characteristics in Channel with Obstacles for Internal Combustion Wave Rotor

This paper establishes a simplified test system for internal combustion wave rotor with a single channel and designs different intensifying combustion obstacles and arrangements. Moreover, this paper analyzes the intensifying effect of obstacles on combustion process of the internal combustion wave rotor from the stable operation range, pressure gain and flame progression process perspective. The results show that the range of inlet velocity under stable operation of the internal combustion wave rotor narrows after the addition of obstacles, and the corresponding velocity values substantially reduce while the flame propagation speed can be improved by 2 - 4 times. At the rotation rate of 1500 rpm, the pressure gain increases significantly during the combustion process. These results provide technical supports for further research and application of the internal combustion wave rotor.

A comprehensive set of criteria for evaluating thermal management systems of aerial vehicles

Thermal management has become a significant concern in the design of advanced air vehicles.However,an effective evaluation method is needed when designers need to evaluate aircraft thermal management systems comprehensively.This paper proposes an evaluation method in which several evaluation directions concerned with thermal management systems(TMSs) are put forward to form an evaluation index system.The effect of temperature control,heat sink utilization efficiency,energy utilization efficiency,flight performance penalty,thermal endurance,space occupancy ratio,and economy are chosen as the direction of evaluation for TMS,considering its primary function,system performance,and impact on aerial vehicles.This method is comprehensive,intuitive,and user-friendly,along with the intensely subjective user-defined weight parameters,which provide rational metrics for thermal management techniques involved in aerial vehicles.The evaluation method could potentially be helpful for designers to comprehensively analyze the performance of aircraft thermal management systems and provide a basis for practical application.Two examples are provided to demonstrate the application of the method to evaluating TMS comprehensively.

Calculation Model of Effective Thermal Conductivity of a Spiral-wound Lithium Ion Battery

This paper proposed an analytical model which can calculate the effective thermal conductivity (ETC) of a spiral-wound Lithium-ion battery (Li-ion battery). It bases on a two-dimensional energy balance with both radial and spiral heat transfer, as well as internal thermal contact resistance (TCR) considered simultaneously and studies the influence of winding layers and winding tension on the ETC. Results show that the analytical data are in good agreement with the numerical results. With the winding layers decreased and the winding tension enhanced, the ETC of Li-ion battery increases gradually. The radial temperature in Li-ion battery is also investigated which demonstrates a relatively higher temperature when considering the internal TCR.

Pilot Combustion Characteristics of RP-3 Kerosene in a Trapped-Vortex Cavity with Radial Bluff-Body Flameholder

The structure of the trapped-vortex cavity and radial flameholder can maintain stable combustion under severe conditions,such as sub-atmospheric pressure and high inlet velocity.This article reports a complete study of combustion characteristics for this design.The flow field of the physical model was obtained by numerical simulation.The pilot combustion characteristics,including the combustion process,combustion efficiency,and wall temperature distribution,were studied by experiments.The pilot combustion can be divided into three modes under different fuel flow rates and inlet conditions.In“cavity maintained(CM)”mode,pilot flame exists at both sides of the cavity zone,rotating with the main vortex.In“cavity-flameholder maintained(CFM)”mode,the combustion process occurs both inside the cavity and behind the flameholder.While in“flameholder maintained(FM)”mode,the cavity will quench,and the combustion is maintained by the radial flameholder only.Due to the difference in the flow field,the flame pattern and propagation direction vary under different combustion modes.The combustion efficiency,influenced by combustion modes,shows an increase-decrease-increase curve.The wall temperature distribution is also affected;the cavity wall temperature decreases under large fuel flux while the temperature of the burner-back plate continues to rise to a maximum value.

Prediction of combined cycle fatigue life of TC11 alloy based on modified nonlinear cumulative damage model

The nonlinear cumulative damage model is modified to have high prediction accuracy when the high-low cycle stress frequency ratio m is large(m500).The low cycle fatigue(LCF)tests,high cycle fatigue(HCF)tests and combined high and low cycle fatigue(CCF)tests of TC11 titanium alloy were carried out,and the influencing factors of CCF life were analysed.The CCF life declines with the decrease of the ratio of high-low cycle stress frequency m.Both linear and nonlinear cumulative damage models are used to predict the CCF life.The CCF life prediction error of the linear cumulative damage model is great and the predictions tend to be overestimated,which is dangerous for engineering application.The accuracy is relatively high when the high-low cycle stress frequency ratio m500.The accuracy of nonlinear cumulative damage model is higher than that of linear model when the high-low cycle stress frequency ratio m500.Based on the relationship between high cycle average stress rmajor and material yield limit rp,0.2,a correction term is added to the nonlinear cumulative damage model and verified,which made the modified model more accurate when m500.

In-situ observation and finite element analysis of fretting fatigue crack propagation behavior in 1045 steel

In this paper fretting fatigue crack behavior in 1045 steel is studied by in-situ observation and finite element analysis.in-situ fretting fatigue experiments are conducted to capture real-time fretting fatigue crack formation and propagation process.The fretting fatigue tests under different load conditions are carried out,then the lifetime and fracture surface are obtained.The crack propagation rates under different loading conditions are measured by in-situ observations.With in-situ observation,crack initiation location and direction are analyzed.Finite element model is used to calculate J-integral which then is applied to fitting with experimental crack growth rate,and establishing crack growth rate model.From fitted S-N curve,it turns out that smaller load ratio leads to higher lifetime.Crack initiates slightly below the point equivalent to line contact of the contact surface in different test conditions,and crack direction shows no obvious relationship with load parameters.The established crack growth rate model well agrees with the test results.

Very-large eddy simulation of the rotational effects on turbulent flow in a ribbed channel

For the simplified model of the internal cooling passage in the turbine blade of an aero-engine,the present study applies a newly developed turbulence modeling method,very-large eddy simulation(VLES),for analyzing rotational effects on the characteristics of complex turbulent flow.For comparison,not only are the delayed detached eddy simulation(DDES)method(recognized as one of the most popular hybrid Reynolds-averaged Navier-Stokes–large eddy simulation(RANS-LES)methods)and the LES method used with the same numerical setup,but also three RANS turbulence models,including the k-ωshear stress transport(SST),standard k-ε,and Reynolds stress models,are applied to analyze the flow structure in the ribbed channel(whether rotating or stationary).Complex turbulent flows in a square ribbed channel at high Reynolds number of 100000 in the stationary state and different rotational numbers(Ro)between 0.1 and 0.4 are simulated and analyzed in detail.The comparisons show that when compared with the experimental data the VLES method works best in both the stationary and rotating states.It can capture unsteady flow characteristics such as wall shear layer separation and the vortex structure resulting from the rib disturbance.The DDES method can only capture the larger-scale vortex structures,and its predictions of the time-averaged velocity differ considerably from experiments,especially in the stationary state.With a relatively coarse grid,satisfactory prediction cannot be achieved in either rotating or stationary state by the LES method with wall-adapting local eddy-viscosity(WALE)and dynamic Smagorinsky models.The three RANS models perform poorly in both the stationary and rotating states.The results demonstrate the advantages of the VLES method in analyzing the unsteady flow characteristics in the ribbed channel at high Reynolds numbers for both stationary and rotating conditions.On that basis,the study uses the VLES method to analyze the flow evolution under different rotational numbers,and the rotational effects on the fluid mechanisms are analyzed.

Viscoplastic constitutive model of a nickel-based superalloy under multiaxial loading conditions

Based on Chaboche constitutive model,a viscoplastic constitutive model of nickel-based alloy under multiaxial loading is proposed by introducing Lemaitre damage model and non-proportional hardening factor.Lemaitre damage model can characterize the effect of microscopic defects on the fatigue behavior and non-proportional hardening factor is used to describe non-proportional hardening phenomenon.Subsequently,the stress–strain hysteresis loops at room and high temperatures under different loading conditions are simulated by the proposed constitutive model.Comparison between experiments and simulations confirms that the proposed model can reasonably predict the fatigue behavior of nickel-based alloy under different multiaxial loadings.At last,the fatigue life predictions under different multiaxial loadings are investigated,and comparison between experiments and simulations verifies the accuracy of the proposed model.

Mission segment division of the whole aeroengine loading spectrum based on flight actions

This paper studies on a division method of the whole aeroengine loading spectrum flight mission segment and rotor speed mission segment,which is based on the actual flight actions and related to the flight operations of aeroengine and is suitable for the variable-speed aeroengines such as turbojet and turbofan.Through the research,the aeroengine loading spectrum operation-related mission segments can be divided,which can provide important data basis for the life research on the structures which are sensitive to flight maneuver(such as the main shaft,large gearbox and installation section),lay a foundation for the simulation,compilation and prediction of the whole aeroengine loading spectrum.Firstly,based on the summary of basic flight actions in actual flight,the division of flight mission segment was realized by programming.Moreover,the aeroengine rotor speed mission segments,associated with flight actions and missions,were divided based on the flight mission segment division results.Besides,the efficiency and accuracy of the mission segment division results were verified by adopting measured loading spectrum data.Finally,the characteristics of speed mission segment division results were compared and analyzed in tables and figures.The comparison results show that the characteristics of similar speed mission segments are similar,while the characteristics of different speed mission segments are different.And the shapes of similar mission segments vary to the change of flight actions and operations,which can reflect the operation-related feature of the segments.