Investigation of the friction coefficient evolution and lubricant breakdown behaviour of AA7075 aluminium alloy forming processes at elevated temperatures

The lubricant behaviour at elevated temperatures was investigated by conducting pin-on-disc tests between P20 tool steel and AA7075 aluminium alloy. The effects of temperature, initial lubricant volume, contact pressure and sliding speed on the lubricant behaviour(i.e. evolutions of the coefficient of friction(COF) and the breakdown phenomenon) were experimentally studied. The evolutions of COF at elevated temperatures consisted of three distinct stages with different friction mechanisms. The first stage(stage Ⅰ) occurred with low friction when the boundary lubrication was present. The second stage(stage Ⅱ) was the transition process in which the COF rapidly increased as the lubricant film thickness decreased to a critical value. In the final plateau stage(stage Ⅲ), lubricant breakdown occurred and intimate contact at the interface led to high friction values. At the low friction stage(stage Ⅰ), the value of COF increased with increasing temperature. The increase in temperature, contact pressure and sliding speed as well as the decrease in initial lubricant volume accelerated the lubricant breakdown.

Exploration of Infection Prevention and Control Practice of Designated Hospitals in During Corona Virus Disease 2019 Epidemic Period

Corona Virus Disease 2019(COVID-19)is a new infectious disease that appeared in whan in December 2019 Since January23,the national health and fitmess commission has required hospitals to be designated in accordance with the principle of"concentrating patients,experts,resources and treatment".Designated hospitals are often the strength of the general hospital and general hospital complex layers of various kinds of personnel,campus area is large,multi-channel,ordinary outpatient accepts people more,for emergency and severe cases treatment in patients with normal difficulty pressuure big,suspected/confirmed cases,combined with the COVID-19 occurred when the traditional holiday,the country launched the emergency response since,process reform faces a difficult labor,shortage of mampower,protective shortages,short time limit,and many other difficulties,hospital infection prevention and control is facing unprecedented pressure.In this paper,the West China-Guang'an Hospital,Sichuan University(Guang'an people's hospital)as a designated hospital,on the basis of the relevant scheme of the national health committee,epidemic prevention and control of the actual,combined with comprehensive hospital leadership,mampower allocation,protection,security,patient management,disinfection isolation,preview triage,preventive measures,training,monitoring,etc.,with practical experience summary for the COVID-19 diring the hospital infection prevention and control to improve the practice exploration.

Orbital stability of two-component peakons

We prove that the two-component peakon solutions are orbitally stable in the energy space.The system concerned here is a two-component Novikov system,which is an integrable multi-component extension of the integrable Novikov equation.We improve the method for the scalar peakons to the two-component case with genuine nonlinear interactions by establishing optimal inequalities for the conserved quantities involving the coupled structures.Moreover,we also establish the orbital stability for the train-profiles of these two-component peakons by using the refined analysis based on monotonicity of the local energy and an induction method.

民机机身结构耐撞性研究的进展与挑战

应急着陆场景下的民机耐撞性与乘员安全直接相关,是民机安全性的重要体现,其中机身结构耐撞性是民机结构强度领域内的研究热点.机身结构耐撞性是复杂的非线性冲击动力学问题,涉及到结构的大变形、断裂失效与动态接触等.运输类飞机适航标准对机身结构耐撞性做出了明确规定,要求通过合理的设计,避免乘员承受过于严酷的冲击载荷,维持客舱内大质量体的有效约束,保持乘员的可生存空间以及维持乘员应急撤离通道的可用等,相关的设计需要通过实验方法或经验证的分析方法进行评估.论文对民机机身结构耐撞性研究中的几个关键问题,如紧固件和机械连接结构的冲击动力学行为,高效吸能元件与吸能结构设计方法,机身结构耐撞性评估的实验与数值方法等近年来的研究情况进行了分析,总结了主要研究进展,并分析了当前研究面临的主要挑战.

Changing the strategy and culture of stroke awareness education in China: implementing Stroke 1-2-0

This project implemented the Stroke1-2-0 stroke awareness programme across China and investigated its impact over a 2-year period.We initiated the Stroke1-2-0 educational campaign and Stroke1-2-0 special task forces(STF)across the nation.Massive media coverage,community-based educational sessions with videos and other related materials and induction of Stroke1-2-0 STF were the major means of promotion.We delivered a survey at the end of 2016 and 2018 to evaluate the impact of our effort.A total of 3066 participants responded to the first survey in 2016,and 15207 participants responded in 2018 across China.The acceptance rate for Stroke1-2-0 versus FAST(an English-language stroke awareness tool)was 50.2%versus 19.1%in 2016,and changed significantly to 82.2%versus 8.0%in 2018(p<0.001).Stroke1-2-0 was well accepted by all ages and by people with different academic qualifications.Only 6.5%of survey respondents were aware that there was a therapeutic window for thrombolytic therapy in 2016,but this awareness increased significantly to 32.8%in 2018.Only 12.6%of people in 2016 indicated that they would send patients with stroke to the nearest hospital capable of performing thrombolytic therapy,but there was a nearly threefold increase(52.5%)in this number by 2018.More than 1000 major hospitals joined the Stroke1-2-0 STF,and more than 20000‘stroke warriors’have joined our stroke awareness improvement effort so far.Stroke1-2-0 stroke awareness programme is well-implemented and accepted,and is generating profound improvement in stroke awareness in China.

Experimental and modelling study of interaction between friction and galling under contact load change conditions

The galling process remains one of the least understood phenomena in metal forming.The transfer of material from a work-piece onto the tool surface can cause an evolutionary increase in friction coefficient(COF)and thus the use of a constant COF in finite element(FE)simulations leads to progressively inaccurate results.For an aluminium work-piece,material transfer,which has history and pressure dependency,is determined by a dynamic balance between the generation and ejection of wear particles acting as a‘third body’abrasive element at the contact interface.To address this dynamic interactive phenomenon,pin-on-disc tests between AA6082 and G3500 were performed under step load change conditions.The COF evolutions,morphologies of the transfer layer and its cross-section were studied.It has been found that contact load change will disequilibrate and rebuild the dynamic balance and high load will increase the generation and ejection rate of third body and vice versa.Moreover,based on the experimental results,an interactive model was developed and presented to simulate the dynamic formation process of the aluminium third body layer under load change conditions,enabling multi-cycle simulations to model the galling distribution and friction variation.

Fixed-interval smoothing of an aeroelastic airfoil model with cubic or free-play nonlinearity in incompressible flow

Fixed-interval smoothing,as one of the most important types of state estimation,has been concerned in many practical problems especially in the analysis of flight test data.However,the existing sequential filters and smoothers usually cannot deal with nonlinear or high-dimensional systems well.A state-of-the-art technique is employed in this study to explore the fixed-interval smoothing problem of a conceptual two-dimensional airfoil model in incompressible flow from noisy measurement data.Therein,the governing equations of the airfoil model are assumed to be known or only partially known.A single objective optimization problem is constructed with the classical Runge–Kutta scheme,and then estimations of the system states,the measurement noise and even the unknown parameters are obtained simultaneously through minimizing the objective function.Effectiveness and feasibility of the method are examined under several simulated measurement data corrupted by different measurement noises.All the obtained results indicate that the introduced algorithm is applicable for the airfoil model with cubic or free-play structural nonlinearity and leads to accurate state and parameter estimations.Besides,it is highly robust to Gaussian white and even more complex heavy-tailed measurement noises.It should be emphasized that the employed algorithm is still effective to high-dimensional nonlinear aeroelastic systems.

A review of high‐velocity impact on fiber‐reinforced textile composites: Potential for aero engine applications

Considerable research has indicated that fiber‐reinforced textile composites are significantly beneficial to the aerospace industry,especially aero engines,due to their high specific strength,specific stiffness,corrosion resistance,and fatigue re-sistance.However,damage caused by high‐velocity impacts is a critical limitation factor in a wide range of applications.This paper presents an overview of the development,material characterizations,and applications of fiber‐reinforced textile composites for aero engines.These textile composites are classified into four ca-tegories including two‐dimensional(2D)woven composites,2D braided composites,3D woven composites,and 3D braided composites.The complex damage me-chanisms of these composite materials due to high‐velocity impacts are discussed in detail as well.

Tax Burden,Institutional Environment and Foreign Direct Investment Flow:From the Perspective of Asymmetric International Tax Competition

The global economic uncertainty is mounting.Governments need to respond with supporting measures for long-term external environment changes as they lower tax burden to attract working capital.Based on the asymmetric tax competition theory,this paper constructs a theoretical model of tax burden,institutional transaction costs and FDI flow.It is found that one country’s strength of institutional environment makes its equilibrium tax rate higher than that of another within certain limits of market size.Based on the data of 199 countries and regions from 2005 to 2018,this paper conducts an empirical analysis,proving that favorable institutional environment narrows the negative impact of tax burden on FDI fl ow.Moreover,it is showed that in small-market,low-income countries and regions,tax burden level has a larger negative impact on foreign direct investment(FDI)when institutional environment produces no positive impact;in large-market,high-income countries,the negative impact of tax burden is relatively weak but the institutional environment shows largely positive impact.This paper contributes some policy recommendations on how to make use of and improve institutional environment to meet challenges and impacts of the international economic climate.