第二相对Ti-25V-15Cr-2Al-0.2C-x(x=0,2%Mo,2%Nb,02%Si)合金拉伸断裂行为的影响

研究了第二相对Ti 2 5V 15Cr 2Al 0 .2C x (x=0 ,2 %Mo,2 %Nb ,0 .2 %Si)阻燃β钛合金拉伸断裂行为的影响。结果表明 ,β晶界上析出的α相增加了合金发生沿晶断裂的趋势 ,特别是热暴露后形成的连续晶界α膜是导致合金脆性沿晶断裂的主要原因。虽然粗大的碳化物颗粒是合金中的裂纹源之一 ,但细小、弥散分布的碳化物却能显著降低合金发生脆性沿晶断裂的趋势 。

碳化物分布状态对Ti-25V-15Cr-2Al-0.2C-x合金微观组织的影响

碳化物和相是Ti-25V-15Cr-2Al-0.2C-x(x=0, 2%Mo, 2%Nb等)阻燃钛合金基体上的2种主要析出相。采用OM,SEM,TEM等方法研究了具有不同碳化物分布状态的Ti-25V-15Cr-2Al-0.2C-x合金的热处理及热暴露后的微观组织。结果表明,细小、弥散分布的碳化物颗粒不仅能细化合金的晶粒,而且能明显抑制对合金组织稳定性有害的沉淀相的析出。碳化物颗粒越细小、弥散,抑制相析出的作用就越强,合金的组织稳定性也越高。

Ti-25V-15Cr-2Al-2Mo-0.2C阻燃β钛合金的蠕变变形结构研究

采用TEM技术研究了具有不同热处理组织的Ti-25V-15Cr-2Al-2Mo-0.2C合金在540℃,250 MPa,100 h蠕变作用后的变形结构。结果表明:位错环组是合金蠕变变形结构中的典型位错组态;合金的蠕变抗力随β基体上弥散分布的第二相析出数量的增加而提高。添加微量能提高蠕变抗力的合金元素,如Si元素等,是改善合金蠕变性能的可行途径。

Effect of Processing and Composition on the Structure and Properties of P/M EP741NP Type Alloys

A study was carried out on the effects of processing and composition on the structure and properties of P/M EP741NP type alloys. The objectives of this study were to understand the role of Hf in a P/M superalloy containing high niobium used in aircraft engines and to determine the effects of extrusion and forging the powders as contrasted to HIPing （hot isostatic pressing） only. Two alloys of the P/M EP741NP composition were atomized： one alloy contained 0.26%Hfand the other was Hf free. After the as-atomized powders from both alloys were characterized, the powders were extruded into billets, forged and heat treated. After each process, the microstructures were characterized by SEM and the phases were extracted and identified by X-ray diffraction. The presence of Hf in the residues was probed by EDS （energy dispersive spectroscopy）. The alloys were given the published Russian heat treatment as well as a more conventional heat treatment more typical of western powder alloys. Tensile, creep and stress rupture mechanical property tests were run. Results of the structural behavior of the alloys after each processing step will be presented and discussed. The role of the Hfon the mechanical properties will be discussed.

钻井工具多轴高周疲劳寿命预测模型优选

针对钻井工具多轴高周疲劳问题,进行了疲劳寿命预测模型优选。结合多轴疲劳理论,分析了非比例加载条件下的多轴应力状态及多轴疲劳情况下材料开裂行为,总结了多轴疲劳模型,并推荐Dang Van模型用于判断钻井工具在特定应力下是否会发生疲劳失效。介绍了Dang Van模型的基本准则、推导原理、适用范围及疲劳极限计算公式。基于钻井现场实际应用的稳定器转向定子驱动轴实际故障验证了Dang Van多轴疲劳模型,并将其与原始平均应力模型进行了对比,结果表明,原始平均应力模型计算结果偏于保守,Dang Van模型更适用于钻井工具多轴高周疲劳寿命预测。

Effect of size and distribution of titanium carbide on microstructure and mechanical properties of Ti-25V-15Cr-2Al-0.2C-0.2Si alloy

The effect of size and distribution of titanium carbide on the microstructure and mechanical properties of non-burning β titanium alloy Ti-25V-15Cr-2Al-0.2C-0.2Si (mass fraction, %) was investigated. The microstructure of the heat-treated and exposed alloy was studied using optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). It is found that carbides with finer size and more uniform distribution can suppress the formation of α precipitates more effectively, and can especially decrease the amount of grain boundary α precipitates after long-term exposure at 540℃ (the expected application temperature). Thus, significant improvement in thermal stability can be achieved by refining carbide particles in the matrix of the alloy.

Operating characteristics of a high radius pre-swirl cooling system

An experimental investigation into pre-swirl effectiveness and receiver hole discharge coefficient characteristics for a high radius injection pre-swirl cooling systems was carried out on a physically representative experimental rig with a 450 mm diameter rotor.The receiver holes and pre-swirl nozzle were located at a radius of 181 mm and 180 mm respectively.The experimental work was mainly conducted at 5 000～12 000 r/min,4 bar absolute pressure and 1.132 kg/s air supply.The maximum air supply temperature was 190 ℃.Pressure and temperature distributions in the pre-swirl system were examined with an emphasis on the velocity effectiveness of the pre-swirl system as a whole and on the discharge coefficients of the rotating 'receiver holes' in the rotor.The results showed that the velocity effectiveness increased with increasing swirl ratio resulting in reduced blade cooling flow temperature.Different seal flow configurations caused very different effectiveness at different speeds,but outflow through the inner and outer seals always gave the highest effectiveness compared other configurations.Increasing the seal flow rate reduced the effectiveness.For the coefficient of discharge,except for the low speed range,it increased with increase in swirl ratio for most speeds.

Materials and Structural Integrity Challenges for the Next Nuclear Generation

The next generation of nuclear power plants is likely to require production in limited time-scales to meet the shortfall in power generating capacity as ageing power plants are taken off-line. The reactor pressure vessel lies at the heart of a light water reactor and can take a number of years to manufacture. This paper reviews the current methods employed for the construction of these major vessels and the issues with this route of production. Possible alternatives to traditional methods are briefly reviewed and found to offer their own challenges to achieving a vessel with high demonstrable structural integrity.

Weather Impact on Heat-Related Illness in a Tropical City State, Singapore

In this article we propose a novel hurdle negative binomial (HNB) regression combined with a distributed lag nonlinear model (DLNM) to model weather factors’ impact on heat related illness (HRI) in Singapore. AIC criterion is adopted to help select proper combination of weather variables and check their lagged effect as well as nonlinear effect. The process of model selection and validation is demonstrated. It is observed that the predicted occurrence rate is close to the observed one. The proposed combined model can be used to predict HRI cases for mitigating HRI occurrences and provide inputs for related public health policy considering climate change impact.

Optimal Secondary Control of Islanded AC Microgrids with Communication Time-delay Based on Multi-agent Deep Reinforcement Learning

In this paper,an optimal secondary control strategy is proposed for islanded AC microgrids considering communi-cation time-delays.The proposed method is designed based on the data-driven principle,which consists of an offine training phase and online application phase.For offline training,each control agent is formulated by a deep neural network(DNN)and trained based on a multi-agent deep reinforcement learning(MA-DRL)framework.A deep deterministic policy gradient(DDPG)algorithm is improved and applied to search for an optimal policy of the secondary control,where a global cost function is developed to evaluate the overall control performance.In addition,the communication time-delay is introduced in the system to enrich training scenarios,which aims to solve the time-delay problem in the secondary control.For the online stage,each controller is deployed in a distributed way which only requires local and neighboring information for each DG.Based on this,the well-trained controllers can provide optimal solutions under load variations,and communication time-delays for online applications.Several case studies are conducted to validate the feasibility and stability of the proposed secondary control.Index Terms-Communication time-delay,global cost function,islanded AC microgrid,multi-agent deep reinforcement learning(MA-DRL),secondary control.

钛合金保载疲劳失效特征及敏感性判定方法

钛合金在航空发动机上使用时存在保载疲劳失效现象。钛合金保载疲劳寿命显著低于普通疲劳寿命且其断裂特征有别于普通疲劳。本文通过系统的实验研究,从疲劳断口、二次裂纹以及应变积累等方面总结了保载疲劳的失效特征。研究对象涵盖了保载敏感性强、弱以及无的钛合金类型。利用上述总结的特征,给出了判定钛合金保载疲劳失效及敏感性强弱的方法。

The friction of diamond-like carbon coatings in a water environment

Diamond-like carbon(DLC)coatings are known to provide beneficial mechanical and tribological properties in harsh environments.Their combination of high wear resistance and low friction has led to their extensive use in any number of industries.The tribological performance of a DLC coating is varied however,and the frictional response is known to be strongly dependent on the surrounding environment,as well as the material composition and bonding structure of the DLC coating.This paper presents an up-to-date review on the friction of DLC coatings in a water environment,with a special focus on transfer layer formation and tribochemistry.

A computationally efficient method for identification of steady state in time series data from ship monitoring

Most applied time series are non-stationary,or exhibit some kind of non-stationarity for at least parts of the time series.For time series analyses or mathematical modeling purposes,the non-stationarities can be difficult to handle.Therefore,identification of stationary and non-stationary behavior is of great practical interest in time series analysis.In this study a robust and computationally efficient method to identify steady state parts of time series data is presented.The method is based on the class of deterministic trend models using a sliding window,and is focused towards being easy to implement,efficient and practical in use and to preserve data completeness.To demonstrate the performance of the steady state identifier,the method is applied on different sets of time series data from two ships equipped with systems for in-service monitoring.The method is shown to be reliable and practical for identifying steady state parts of time series data,and can serve as a practical preprocessing tool for time series data analysis.

Influence of Turbulators in Blade Cooling Passages on Film Hole Discharge Coefficients

This paper details the results of a joint project between Rolls-Royce Deutschland (RRD) and the Northwestern Polytechnical University of China (NWPU). The objective of the project was the determination of the influence of tabulators in turbine blade cooling passages on film hole discharge coefficients (Cd coefficients). A large-scale plexiglas model was used by the NWPU to measure the turbulator influence on Cd coefficients for a wide range of different geometrical parameters, Reynolds numbers and cooling flow off take ratios. RRD specified the comprehensive test matrix and analysed the test data. The CFD code FLUENT was used by RRD for numerical simulation of the test cases with the main objective to support the interpretation of observed trends. Both, experimental and numerical results will be presented in this paper for a selection of test configurations.

AITEB - An European Research Project on Aero-thermodynamics of Turbine Endwalls and Blades

The paper delivers an overview on the European research project AITEB - Aerothermal Investigations on Turbine Endwalls and Blades, which started in year 2000 in the course of the 5. Framework Programme (GROWTH). The aim is to submit an integrated technology and design tool package for the advanced, aerothermal highly loaded design of turbines, especially: Experimental/numerical investigation on heat transfer and film-cooling in separated flow for highly loaded blades including advanced trailing edge cooling Heat transfer/ improved cooling of turbine endwalls: Experimental/numerical work on cooling of turbine endwalls, shrouds and recessed blade tips. Optimised CFD-process (drawing-grid-modelling-postprocessing-risk assessment) in order to derive the 'best practice' to use CFD as a time effective tool. After most of the project life, an overview on the project is delivered. Experimental results of test series at various test sites are compared to numerical simulations of the industrial and university partners.

The development of a high-performance Ni-superalloy additively manufactured heat pipe

Additively manufacturing(AM)has been used to manufacture fine structures with structured/engineered porosity in heat management devices.In this study,laser powder bed fusion(LPBF)was used to manufacture a high-performance Ni-superalloy heat pipe,through tailoring LPBF process parameters to fabricate thin wall and micro-channel.By using novel laser scanning strategies,wick structure heat pipes with maximised surface-area-to-volume ratio,fine features size around 100µm,and controlled porosity were successfully fabricated.Microscopy and X-ray microtomography(micro-CT)were used to investigate the 3D structure of the void space within the pipe.Wick test results showed that most of the heat pipes made by LPBF had better performance than the conventionally manufactured pipes.This study also investigated the influences of the process parameters on the porosity volume fraction and the feature size.The results showed that LPBF process could fabricate thin structure due to the change of melt pool contact angle.The relationship between process parameters and bead size reported in this study could help design and manufacture heat pipe with complex fine structure.