Experimental method for and defect tolerance of fixed plate theoretical research on based on damage mechanics

An experimental method and a theoretical analysis based on continuum damage mechan- ics are applied for the defects tolerance of fixed plate. The defects type studied in this article is scratch, which is considered a typical defect on fixed plate according to the engineering practice. The general approach to the defects tolerance analysis of scratched fixed plate is presented. The method of fatigue life prediction for standard notched specimens has been established on the basis of continuum damage mechanics. For the purpose of obtaining the influence law of fatigue life in consequence of scratches, fatigue experiments of standard notched specimens and scratched specimens have been done. Evalu- ation of the fatigue life of scratched fixed plate has been carried out. And the value of scratch defects permissible to the condition of safety service life has been worked out. According to the results of the- oretical calculations, the fatigue experiment of scratched fixed plate has been performed. The outcome shows that the theoretical prediction tallies with the experimental results.     

Storage life of silicone rubber sealing ring used in solid rocket motor

It is urgent to carry out detailed research on storage performance of rubber sealing ring to get the criterion for its storage life. This paper acquires material ageing regularity by theoretical analysis and experimental confirmation. On this condition, failure mode and failure criterion of typical sealing structure is studied, and the failure mechanism is found. Thus by analyzing the stress distribution, the relationship between ageing state and sealing condition is established. Rationalization proposal is put forward and storage life of sealing ring is evaluated. The research mentionedabove has special reference to the design of sealing structures and can provide reference for prolonging their service life.     

Preliminary experiment on spontaneous ignition performances of cavity-based strut flameholder

The thermal-structural response and low cycle fatigue life of a three-dimensional (3D) channel wall nozzle with regenerative cooling were numerically investigated by coupling the finite volume fluid-thermal method, nonlinear finite element thermal-structural analysis and local strain methods. The nozzle had a high area ratio (nozzle exit area divided by throat area) under cyclic working loads. Parametric studies were carried out to evaluate the effects of channel structural parameters such as channel width, channel height, liner thickness and rib width. Results showed that the integrated effects of three-dimensional channel structure and load distribution caused serious strain, which mainly occurred at the intersectant regions of liner wall on the gas side and the symmetric planes of channel and rib. The cooling effect and channel structural strength were significantly improved as the channel width and height decreased, leading to substantial extension of the nozzle service life. On the other hand, the successive decrease in liner thickness and rib width apparently increased the strain amplitude and residual strain of channel wall nozzle during cyclic work, significantly shortening the service life. The present work is of value for design of the channel wall nozzle to prolong its cyclic service life.      

STRATOSPHERIC LIGHTER-THAN-AIR POWERED PLATFORM

A feasibility study has been carried out on a high altitude (20km) superpressurcd PLTA(powered lighter-than-air) platform, which has a long service life and larger payload than that of a large artificial satellite. This PLTA platform has an electric propulsion system to cope with wind flow for position keeping and its thruster is driven by solar power acquired through solar cells. Solar energy is to be stored for night use in regenerative fuel cells. The study is focused on energy balance and hull structure analysis of the platform. This platform is particularly capable of conducting high resolution remote sensing and telecommunications relay. This platform can replace a number of ground-based telecommunications relay facilities and can guarantee reasonable radio frequency intensity enough to secure good telecommunications quality. The altitude where the platform resides is the least windy area in the lower stratosphere at a height from which one can have a direct line of sight on the ground within a 1,     

基于静强度分布的复合材料疲劳寿命分布的预测模型(英文)

The reasons of the static strength dispersion and the fatigue life dispersion of composite laminates are analyzed in this article. It is concluded that the inner original defects, which derived from the manufacturing process of composite laminates, are the common and major reason of causing the random distributions of the static strength and the fatigue life. And there is a correlative relation between the two distributions. With the study of statistical relationship between the fatigue loading and the fatigue life in the uniform confidence level and the same survival rate S-N curves of material, the relationship between the static strength distribution and the fatigue life distribution through a material S-N curve model has been obtained. And then the model which is used to describe the distributions of fatigue life of composites, based on their distributions of static strength, is set up. This model reasonably reflects the effects of the inner original defects on the static strength dispersion and on the fatigue life dispersion of composite laminates. The experimental data of three kinds of composite laminates are employed to verify this model, and the results show that this model can predict the random distributions of fatigue life for composites under any fatigue loads fairly well.     

Theory of Economic Life Prediction and Reliability Assessment of Aircraft Structures

The theory of economic life prediction and reliability assessment of aircraft structures has a significant effect on safety of air-craft structures.It is based on the two-stage theory of fatigue process and can guarantee the safety and reliability of structures.According to the fatigue damage process,the fatigue scatter factors of crack initiation stage and crack propagation stage are given respectively.At the same time,mathematical models of fatigue life prediction are presented by utilizing the fatigue scatter factors and full scale test results of aircraft structures.Furthermore,the economic life model is put forward.The model is of sig-nificant scientific value for products to provide longer economic life,higher reliability and lower cost.The theory of economic life prediction and reliability assessment of aircraft structures has been successfully applied to determining and extending the structural life for thousands of airplanes.     

THE COMPLEX-VARIABLE-VARIATIONALMETHOD FOR ANALYSING FINITEINTERNALLY CRACKED PLATESAND ITS APPLICATION

In this paper, a whole field solution to finite internally cracked plates is derived by complex variable method, where the equations of equilibrium and compatibility, the single value condition of displacements and the traction-free condition on crack surfaces are satisfied exactly. The stress intensity factors of finite plates with central crack or eccentric crack or cracks emanating from a hole are calculated by using minimum potential energy principle to treat the boundary conditions excluding those on crack surfaces. As an application of the method to engineering problems, the computation about a finite rivet joint stiffened plate with cracks emanating from a hole is also performed. The numerical results show that the method presented in this paper gives rapid convergence and is much time-saving in computations.     

Foreign Object Damage to Fan Rotor Blades of Aeroengine Part Ⅱ： Numerical Simulation of Bird Impact

Bird impact is one of the most dangerous threats to flight safety. The consequences of bird impact can be severe and, therefore, the aircraft components have to be certified for a proven level of bird impact resistance before being put into service. The fan rotor blades of aeroengine are the components being easily impacted by birds. It is necessary to ensure that the fan rotor blades should have adequate resistance against the bird impact, to reduce the flying accidents caused by bird impacts. Using the contacting-impacting algorithm, the numerical simulation is carded out to simulate bird impact. A three-blade computational model is set up for the fan rotor blade having shrouds. The transient response curves of the points corresponding to measured points in experiments, displacements and equivalent stresses on the blades are obtained during the simulation. From the comparison of the transient response curves obtained from numerical simulation with that obtained from experiments, it can be found that the variations in measured points and the corresponding points of simulation are basically the same. The deforming process, the maximum displacements and the maximum equivalent stresses on blades are analyzed. The numerical simulation verifies and complements the experiment results.     

Tribological evaluation of surface modified H13 tool steel in warm forming of Ti–6Al–4V titanium alloy sheet

The H13 hot-working tool steel is widely used as die material in the warm forming of Ti–6Al–4V titanium alloy sheet. However, under the heating condition, severe friction and lubricating conditions between the H13 tools and Ti–6Al–4V titanium alloy sheet would cause difficulty in guaranteeing forming quality. Surface modification may be used to control the level of friction force, reduce the friction wear and extend the service life of dies. In this paper, four surface modification methods(chromium plating, TiAlN coating, surface polishing and nitriding treatment)were applied to the H13 surfaces. Taking the coefficient of friction(CoF) and the wear degree as evaluation indicators, the high-temperature tribological behavior of the surface modified H13 steel was experimentally investigated under different tribological conditions. The results of this study indicate that the tribological properties of the TiAlN coating under dry friction condition are better than the others for a wide range of temperature(from room temperature to 500 C), while there is little difference of tribological properties between different surface modifications under graphite lubricated condition, and the variation law of CoF with temperature under graphite lubricated is opposite to that under the dry friction.     

Infrared radiation signature of exhaust plume from solid propellants with different energy characteristics

The infrared radiation signature of the plume from solid propellants with different energy characteristics is not the same. Three kinds of double-base propellants of different energy characteristics are chosen to measure the infrared spectral radiance from 1000 cm 1 to 4500 cm 1 of their plumes. The radiative spectrum is obtained in the tests. The experimental results indicate that the infrared radiation of the plume is determined by the energy characteristics of the propellant. The radiative transfer calculation models of the exhaust plume for the solid propellants are established. By including the chemical reaction source term and the radiation source term into the energy equation, the plume field and the radiative transfer are solved in a coupled way. The calculated results are consistent with the experimental data, so the reliability of the models is confirmed. The temperature distribution and the extent of the afterburning of the plume are distinct for the propellants of different energy characteristics, therefore the plume radiation varies for different propellants. The temperature of the fluid cell in the plume will increase or decrease to some extent by the influence of the radiation term.     

航空涡轮发动机主轴使用寿命实验研究

本文论述了航空涡轮发动机主轴损伤换算比的确定方法。根据线性累积疲劳损伤理论和S-N曲线,采用不同寿命主轴的剩余寿命对比试验,可获得飞行换算率A_p。预定安全标准循环寿命除以A_p,就可以获得发动机主轴的使用寿命(小时)。本文进一步介绍了在机动飞行和螺旋载荷掺合作用下目标寿命的确定方法。     

飞机结构可靠性分析的若干问题

 本文提出了计算飞机结构在使用中破坏率的一组基本公式,估计了各种因素对结构可靠性的影响。本文指出,英国皇家航空研究院工程科学数据活页所建议的破坏率为10~(-7)/h量级,置信水平为95％的匹配是不合适的。对几个重要影响因素的数据处理,本文发展了新的方法,得到了若干新的结果。     

结构可靠性定寿模型

 本文提出一新的结构可靠性定寿模型,它综合考虑了安全寿命设计、损伤容限设计和无损检测的可靠性。根据该模型可以合理确定结构具有高可靠度的使用寿命和检修周期。     

固体火箭发动机使用寿命的确定

本文论述了一种新的推进剂老化试验方法:即使用不同年分火药在一种高温下进行加速老化,定期进行发动机试验,用发动机内弹道性能参数和对火药理化性能要求作为失效判定标准,根据不同年分火药和失效时间的关系,可以计算火药的使用寿命.文中提出了一种简便的计算加速因子和火药使用寿命的方法,概括地介绍了有关试验结果.     

概率损伤容限分析模型研究

提出了一种新的概率损伤容限分析模型,它由a-t随机裂纹扩展模型和基于寿命失效准则的破坏概率可靠性分析模型组成。该模型弥补了现有概率损伤容限分析模型的不足,并便于工程应用。     

TC4锻件机械加工与焊接的研制与应用

“钛合金在飞机上的综合应用”是“九五”期间重点科研课题。课题的研究目的是通过典型零件的率先使用,突破飞机在重要承力构件上的钛合金综合应用技术,为新一代歼击机的钛合金综合应用做好技术储备。用钛合金替代合金钢制造飞机结构零件,可以显著减轻飞机质量,提高飞机的推重比;同时还可以提高飞机结构的抗热能力,使飞机进入更高的飞行范围,从而提高飞机结构的可靠性和使用寿命。     

结构破坏危险率与使用寿命的关系

在结构疲劳寿命服从双参数Ｗｅｉｂｕｌ分布假设的基础上,通过结构细节疲劳额定值的概念给出了结构破坏危险率与使用寿命的关系式,并通过实例计算得出了破坏危险率－寿命曲线。     

桨叶可靠性分析方法

本文给出二维疲劳裂纹扩展门槛值分布函数,建立二维应力—门槛值干涉模型。该模型可用于含初始缺陷或意外损伤的螺旋桨叶无限寿命可靠性分析和设计,得到桨叶可靠度与初始裂纹尺寸之间的函数关系式。考虑到随使用时间增长,桨叶遭受意外损伤的可能性将不断增大,损伤的程度也不断加重,文中还给出桨叶在无限寿命条件下的检修周期。该方法也可用于其它含裂纹构件以及复合材料桨叶的无限寿命可靠性分析和检修周期确定。      

飞机消耗寿命计算方法研究

对飞机单机疲劳寿命监控使用的飞机消耗寿命计算的各主要技术问题做了相应的论述、推导和证明;提出了３种飞机消耗寿命计算方法;建立了飞机消耗寿命与设计使用寿命之间的换算关系,为飞机单机疲劳寿命监控课题的消耗寿命计算和剩余寿命计算提供了一个既简单又适用的方法。     

战术导弹火箭发动机经济性分析

本文以某型地空导弹为例,从寿命期费用的角度,对战术导弹采用液体火箭发动机(LRE)和固体火箭发动机(SRE)时的经济性进行了定性的和部分定量的分析,并对战术导弹动力装置的更新进行了讨论.