烧结压力对铜基粉末冶金航空刹车材料的影响

通过粉末冶金的方法制备了铜基粉末冶金摩擦材料,研究了烧结压力（0．5,1．5,2．5,3．5,4．5 MPa）对材料显微组织、致密化的影响以及由此引起的材料摩擦磨损性能和行为的改变。结果表明,烧结压力由0．5MPa增加到1．5MPa,材料孔隙度显著减少,材料的摩擦因数明显减小,同时,磨损性能得到显著改善;烧结压力由1．5NPa提高到2．5MPa,材料孔隙度进一步降低,但降幅较小,材料磨损性能稍有提高;烧结压力达到2．5MPa以后,继续提高烧结压力对材料的致密化程度以及摩擦磨损性能影响不大。通过对材料进行组织观察和理论分析,阐述了烧结压力对铜基粉末冶金航空刹车材料影响规律的形成原因。     

粉末冶金航空刹车材料的选择

综述了粉末冶金航空刹车材料最基本的功能要求和特点，确定了粉末冶金航空刹车材料合适而稳定的摩擦系数，最小磨损量，不粘结，合适的物理机械性能，良好的耐温性等基本要求，并采用加权分析方法针对基本要求对Boeing-737飞机用刹车材料的选择进行了加权因子分析和研究，获得了适合Boeing-737飞机的铁铜基刹车材料，研究表明，采用加权分析方法，可以直接明了地进行材料总体选择，避免过多的筛选试难，达到事半功倍的效果。     

合金元素锌/镍对铜基粉末冶金刹车材料的影响

通过对比研究了合金元素锌和镍对铜基粉末冶金刹车材料性能的影响规律。研究结果表明：铜锡合金基体中加入少量Zn能提高材料的摩擦因数,继续增加Zn含量,摩擦因数反而降低。高转速摩擦条件下,Zn能提高材料的耐磨性能;铜锡合金基体中加入少量Ni能提高材料的摩擦因数和耐磨性能。基体中Zn、Ni含量不宜过高,Ni比Zn更有利于提高铜基刹车材料的综合性能。     

烧结温度对铁基粉末冶金航空刹车材料摩擦磨损性能的影响

研究了不同烧结温度(900,930,950,980,1020℃)对飞机铁基粉末冶金刹车材料材料显微组织、致密化和摩擦磨损性能的影响。借助于材料组织结构、摩擦试验后的材料表面观察及理论分析,阐述了材料组织结构及摩擦磨损变化的机制。结果表明:900℃的试样由于烧结不够充分,材料密度较低,珠光体的数量较少,硬度低,耐磨性差,经过摩擦试验后,摩擦材料表面大面积剥落和点蚀比较严重,材料磨损量较大,磨屑以大块状及条状为主;930℃试样的材料密度增加,珠光体数量增加,硬度及耐磨性增加,经摩擦试验后,试样表面比较光滑,但仍有大量的点状剥落,材料磨损量较900℃的试样有所降低;当烧结温度由950℃升高至1020℃时,由于原子扩散的加剧,材料的基体具有足够强度,珠光体的数量显著增加,显著提高了材料的耐磨性,经摩擦试验后,材料表面生成了完整的氧化膜,材料的磨损量变化不大,相对于950℃和980℃的试样而言,1020℃时的材料摩擦表面出现更少的点状脱落并形成了多层叠加的工作层。     

铁基粉末冶金刹车材料烧结压力的研究

采用粉末冶金法,制备了铁基粉末冶金航空刹车材料,借助光学显微镜、硬度仪及摩擦磨损试验机等仪器研究了烧结压力对该材料组织、力学性能及摩擦磨损性能的影响.结果表明:当烧结压力由1.6 MPa增至2.2 MPa时,材料在塑性变形过程中将产生晶格畸变能,使得作用在材料上的压力有所降低,同时,材料屈服极限的存在也将会消耗一部分应力,原子扩散速度缓慢提高;烧结压力提高到2.8 MPa时,原子扩散过程加快,作用在材料上的应力大大地超过材料的屈服极限,进而发生塑性变形,有效地消除了材料内部的孔隙,显著提高了材料的致密化,同时,材料力学性能和摩擦磨损性能提高;继续提高烧结压力至3.2 MPa,材料密度和硬度略有降低,摩擦磨损性能变化不显著,说明烧结压力为2.8 MPa足以保证材料具有优良的综合性能.     

铜基粉末冶金刹车闸片磨损形貌演变研究

采用多功能销-盘摩擦磨损试验机,开展铜基粉末冶金/Q235-B摩擦副的摩擦磨损试验,在载流和无载流的工况下,研究接触压力(0.4、0.7、1.0和1.3 MPa)对铜基粉末冶金材料闸片磨损表面形貌的影响。结果表明：在无载流工况下,随着接触压力的增大,摩擦因数和磨损率均缓慢上升,试样表面损伤加剧,粗糙度升高,主要的损伤机制为磨粒磨损和剥层;在载流工况下,0.4 MPa时的摩擦因数和磨损率最大,损伤最严重,粗糙度最高,当接触压力增大到0.7 MPa后,表面形貌损伤的变化趋势与无载流工况一致,磨损机制在磨粒磨损和剥层的基础上增加了电弧烧蚀;载流工况下材料表面的粗糙度普遍高于无载流工况下,表面损伤更为严重。     

铁基粉末冶金刹车材料加压烧结冷却水流量研究

对于铁基粉末冶金刹车材料而言,加压烧结冷却过程中冷却水流量是保证材料获得优良综合性能的关键参数之一.通过粉末冶金方法制备了铁基刹车材料,研究了空冷和不同水流量(12 L/s、27 L/s、40 L/s)条件下,材料组织、力学性能及摩擦磨损性能的变化规律.通过光学显微镜和扫描电镜分析了材料性能变化规律的形成原因.结果表明:冷却水流量与冷却时间及冷却速度并不是简单的正比例关系,当冷却水流量为27 L/s时,冷却所用时间最短,材料冷却速度最大,材料组织以片状珠光体和粒状珠光体为主,其它条件下材料的组织主要为片状珠光体,但材料力学性能随冷却水流量变化不显著,同时,当冷却速度为27 L/s和40 L/s时,材料具有最大的密度;摩擦因数比较稳定,材料表面形成了完整的氧化膜,磨损量最小.     

飞机防滑刹车过程的视景仿真研究

将视景仿真技术应用到飞机防滑刹车系统中.利用Multigen Creator建立飞机及机场的三维实体模型,然后用OpenGVS进行场景管理,实现了刹车系统在其控制律下的运动,使刹车过程可视化,对缩短系统研制周期等起着重要作用.     

机轮刹车振动的仿真与试验分析

为研究飞机机轮刹车振动规律,以机轮刹车系统为研究对象,采用振型叠加法,运用大型有限元软件ABAQUS对机轮刹车振动进行了仿真,通过模态分析和动力响应分析,计算出前30阶固有频率和模态,得到了加载条件下的加速度响应曲线。并在刹车试验台架上进行机轮刹车振动试验,对比分析表明有限元计算结果与试验结果基本一致,验证了仿真模型的有效性,得出刹车装置主要部件的加速度响应曲线。通过仿真和试验结果初步得到了刹车振动规律,并为机轮刹车系统设计和改进提供了依据。     

粉末冶金闸瓦主要制动参数的仿真计算研究

采用热-机耦合方法,利用Marc软件,在经过准确性验证的粉末冶金闸瓦踏面制动计算模型上,专门针对粉末冶金闸瓦的主要制动参数摩擦体脱落面积和不同初始制动速度下闸瓦摩擦系数变化偏差范围(±0.04或±0.03)对制动试验结果的影响进行了验证性的仿真计算研究.仿真计算结果表明,闸瓦摩擦体脱落10%,车轮踏面最高温度增加52℃,制动距离未发生明显变化;不同初始制动速度下闸瓦摩擦系数变化偏差范围对车轮踏面的最高温度和制动距离影响较小,偏差范围设置合理.     

闸瓦踏面制动热过程的仿真研究

建立了闸瓦与机车车轮的踏面制动摩擦接触数学模型,确定了模型的初始条件,位移、力学等边界条件,并计算了制动过程中车轮对外换热系数,最后利用Marc有限元软件,采用热-机耦合方法对闸瓦踏面制动热过程进行了仿真计算。仿真计算后得出的车体动能变化、制动距离、车轮踏面温升变化曲线等结果与理论分析相符,并基本接近于1：1制动试验结果,验证了所构建模型和所选用计算方法的正确性。     

铜基粉末冶金摩擦材料高温疲劳磨损规律

研究了高速列车用铜基粉末冶金多孔摩擦材料的高温摩擦磨损性能。在PlintTE77高温疲劳试验机上对该材料进行了高温磨损性能测试 ,工况分别为 :室温 ,10 0℃ ,2 0 0℃ ,3 0 0℃ ,3 5 0℃ ,5 0 0℃ ;法向载荷为 :2 0 0N ,45 0N ,等12种工况 ;振动频率为 :4Hz ;移动幅值为 :± 5mm ;并对摩擦后的磨痕进行了SEM分析 ,发现 :(1)在 2 0 0N ,3 0 0℃时出现了粘压的多源弧形裂纹 ,这和冲击时的沿树枝晶裂纹截然不同 ;(2 )在 45 0N ,3 0 0℃时 ,磨痕表面出现了球状的石墨颗粒层 ,这起到了极好的润滑作用 ,使得 3 0 0℃时磨损较低。 (3 )在 45 0N ,3 5 0℃时 ,有沿磨痕方向的长条裂纹出现 ;(4 )在不同荷载 5 0 0℃时 ,发生了负磨损 ,即摩擦材料粘附到对偶材料上 ,由于新的氧化面的形成摩擦系数是最高的。根据以上分析粗略拟合了该材料的磨损规律     

不同温度下铜基粉末冶金摩擦材料往复滑动磨损规律

研究不同温度下高速列车用铜基粉末冶金摩擦材料磨损特征。在PlintTE77高温疲劳试验机上对该材料进行磨损性能测试 ,工况分别为室温、10 0℃、2 0 0℃、3 0 0℃、3 5 0℃、5 0 0℃ ,法向载荷为 2 0 0N、45 0N等 12种工况 ,振动频率为 4Hz ,滑动幅值为± 5mm。并对摩擦后的磨痕进行Scanelectro mirror (SEM)分析。发现①在 2 0 0N、3 0 0℃时出现碾压的多源弧形裂纹 ,这和冲击时的沿树枝晶裂纹截然不同。②在 45 0N、3 0 0℃时 ,磨痕表面出现球状的石墨颗粒层 ,这起到了极好的润滑作用 ,使得 3 0 0℃时磨损较低。③在 45 0N、3 5 0℃时 ,有沿磨痕方向的长条裂纹出现。④在不同载荷 5 0 0℃时 ,发生粘附现象 ,即摩擦材料粘附到对偶材料上。根据以上分析用最小二乘法粗略拟合了该材料的磨损规律     

Deep drawing with anti-lock braking system (ABS)

In this study, for improving the formability and LDR a new method deep drawing with anti-lock braking system (ABS) was developed. The system is based on the blank sliding from the flange into the die cavity continually, which is controlled by the blank holder gap (BHG) and, at the same time by ABS, which moves up and down vertically, conducting anti-lock braking to the blank with the interval of very short time. The experimental results for AI99.8 aluminium sheet showed that higher drawing height and LDR of the cup can be achieved by the use of ABS. It was found that the new system increased surface quality and decreased ear in the top corners of the cup.     

Thermal modeling of drilling process in titanium alloy (Ti-6Al-4V)

Abstract

In drilling in titanium alloys, heat trapped in a hole adversely affects tool life, hole surface quality and integrity. Therefore, modeling temperature distribution in drilling is vital for effective heat dissipation and improving quality of drilled surfaces. The existing numerical and finite element models consider only frictional heat, whereas the effect of shear heat generation and tertiary heat generation is neglected. In the present work, a comprehensive thermal model of the drilling process is developed by considering all heat generated in shear, friction and tertiary zones. The drill cutting edges are divided into a series of independent elementary cutting tools (ECT). The calculated heat flux loads are applied on an individual ECT in the finite element model to determine the temperature distribution and the maximum temperature around the cutting edge. The temperature in the drill was also measured experimentally with the help of an Infrared (IR) camera. The results of numerical simulations lie within the error of ～8.75% when compared to the prior studies, and ～5.41% when compared to our experimental work. The thermal model gives the temperature distribution, and the maximum temperature observed at the corner of cutting edge was 604.2°C at a cutting speed of 35?m/min.     

Processes in heat dynamics and modelling of friction and wear (dry and boundary friction)

Theoretical postulates of heat dynamics and modelling of friction and wear are formulated based on a system of equations including basic dependences of friction behaviour on load, velocity, time and temperature.     

端面泵浦热传导各向异性激光棒温场特性研究

了解决LD端面泵浦热传导各向异性激光介质产生的热效应问题,建立了端面绝热、侧面冷却的Nd:YVO4晶体热模型。考虑到Nd:YVO4为热传导各向异性材料,而光纤耦合LD输出光束有着超高斯分布的特点,利用特征函数法和常数变异法得到了超高斯光束端面泵浦热传导各向异性激光介质温度场的一般解析表达式。并定量分析了超高斯泵浦光阶次、泵浦功率以及光斑尺寸对于Nd:YVO4晶体温度场的影响。新的各向异性介质热传导方程求解方法具有计算量小、精度高等特点。研究结果表明：若LD输出功率为30W,光学聚焦耦合器的传输效率为82%时,4阶超高斯光束端面泵浦掺钕离子质量分数为0.5%的Nd:YVO4晶体,泵浦面获得528.95C的最大温升。所得结果可用于LD端面泵浦热传导各向异性激光介质全固态激光器热稳腔的设计之中,对于提高激光器性能具有了理论指导作用。     

Non-destructive characterization of deer (Cervus Elaphus) antlers by X-ray microtomography coupled with image analysis

X-ray microtomography coupled with image analysis was tested as a non-destructive alternative method for the textural characterization of the trabecular part of deer antlers ( Cervus Elaphus ). As gas adsorption and mercury intrusion cannot be applied on this soft and spongy material, its pore texture was, up to now, determined from histological sections that give only two-dimensional information. In this work, X-ray microtomography is used to scan entire or half pieces of antlers and three-dimensional image analysis is performed in order to assess the differences between samples collected at various antler locations. Results clearly show a porosity profile along the sample diameter. The pore size distribution is showed to be dependent on the sample original site.     

硫酸铝和蔗糖合成ALN纳米粉实验研究

利用硫酸铝和蔗糖合成ALN纳米粉,通过X射线衍射仪对实验产物进行物相分析,以确定产物的物相组成。采用PhilipsEM420分析电子显微镜观察ALN颗粒粒度为50nm,同时对合成机理进行了研究。通过实验结果表明该方法可行。     

Surface grinding of carbon fiber reinforced plastic (CFRP) with an internal coolant supplied through grinding wheel

Carbon fiber reinforced plastic (CFRP) is widely used in the aerospace industry due to its high specific strength and elastic modulus. When cutting CFRP with tools such as an endmill, problems such as severe tool wear, delamination, and burrs in the CFRP can arise. Grinding, on the other hand, is supposed to improve the quality of the machined surface and tool life, according to its machining property. However, the amount of heat generated during grinding is still a considerable problem in that it is significantly higher than the temperature with conventional cutting. In order to achieve the high performance machining of CFRP, this study aims to show the effect of supplying an internal coolant through the grinding wheel on the surface of the CFRP. Face grinding of CFRP using a cup-type grinding wheel was conducted. Vitrified aluminum oxide grinding wheel was used. Three different coolant supply systems were tested: dry grinding, coolant supply using an external nozzle, and coolant supplied internally through the grinding wheel. The results showed that matrix resin loading on grinding wheel was significantly reduced by the internal coolant supply. Hence, the grains of the grinding wheel were able to cut the fibers sharply, without delamination or burr formation on the ground surface, and surface roughness was reduced compared to the machined surface with endmill. The internal coolant supplied through the grinding wheel showed greater cooling ability, and markedly reduced grinding temperature, keeping it lower than the glass-transition temperature of the matrix epoxy resin of CFRP. Because the coolant was supplied to the grinding point directly through pores in the grinding wheel, chips were eliminated from the pores, and coolant supply was sufficient to cool the ground surface.