一种用于电气设备状态监测的新式FBG传感器北大核心CSCD

为了监测绕组变压器的静态应力场和发生短路等故障时的动态应力变化,设计了一种用于电气设备状态监测的新式FBG传感器。该传感器由聚醚醚酮材料封装的FBG构成,通过内部圆锥形空腔结构实现将轴向应力集中于FBG敏感位置。通过仿真对不同压力强度下传感器结构的应力场部分及形变趋势进行了计算与分析,论证了设计的合理性。实验分别对静态载荷和动态冲击进行测试,结果显示,在静态压载测试中,当100 N相似文献   

千米深井大断面硐室双强壳体支护成套技术的应用

从分析深井高应力大断面巷道和硐室破碎围岩的变形破坏特点入手,指出巷道稳定性的控制机理在于及时强化失稳区围岩的残余强度,阻止初次失稳的发展,并施加高强的主动支护结构,从而使巷道进入二次稳定状态,同时采取高强的被动封闭支护技术。提出了全断面双强壳体支护设计、3S耦合协调支护设计和抗张拉强基础梁支护设计等设计方案来控制巷道变形。并对绞车房进行现场施工,支护效果良好,达到预期目标。     

用土力学的新概念解读和修正经典饱和土力学

论述了应该用有效应力的新概念代替经典有效应力原理。总应力压缩模量与渗流水等效压缩模量的曲线相似;有效应力压缩模量起加劲作用,而不是起决定性作用。土的压缩变形计算中应用有效应力原理是错误的。对于起始水力坡降,引入饱和粘性土的自由水压力衰减概念。在饱和粘性土中,自由水通道率折减不大,相对自由水压力通过一定厚度后衰减为零。所以,新概念土力学的算法接近我国规范:"对粘性土宜按水土合算计算"。还解读了地下室浮力折减、流沙陷阱等等。     

Acoustic emission from the initiation of plastic deformation of Polyethylenes during tensile tests

The acoustic emission (AE) technique has been used in the aim to detect and to observe the initiation of plasticity and damage of several Polyethylenes (PE) during tensile tests. The detection of acoustic signals originating from the deformation of the material is challenging since PE samples strongly attenuate ultrasonic waves. A weak acoustic activity has been recorded during the tests. The use of two types of PE specimens and two methodologies based on the elimination and the discrimination of spurious sources has shown that most of the AE signals truly originate from the plastic deformation of materials. We also observed that the acoustic activity increases with strain rate. Besides, some AE signals are located along the specimen length during tensile tests at high strain rate. The acoustic activity increases strongly with the crystallinity. Micro-cavities, formed before the yield point of PE samples with high crystallinity in particular, likely initiate the release of acoustic energy. In addition, some signals are collected on PE samples, which do not exhibit a formation of cavitation. Hence, the shearing of crystallites and/or the fragmentation of crystalline lamellae may also be a source of the release of acoustic energies.     

Cavitation during deformation of semicrystalline polymers

Cavitation phenomenon is observed during deformation in many semicrystalline polymers above their glass transition temperature. Numerous voids (cavities) both nanometer and micrometer size are formed inside amorphous phase between lamellae during deformation of a polymer. The cavitation is observed only in tension, never during compression or shearing. Most often used methods of voids detection are: microscopies (SEM, TEM, AFM and light microscopy), small angle X-ray scattering and measurements of density. Usually the voids are detected close to yielding or at yielding, strongly suggesting that yielding is often caused by cavitation. However, there is a competition between two processes: breaking of amorphous phase leading to cavitation and plastic deformation of lamellar crystals. Which process occurs first depends on the relation between compliances of those two phases. If the crystals are weak and defected their deformation occurs (mostly by chain slips mechanism) without cavitation. If the crystals in a polymer are thick and more perfect then the barrier for their deformation, represented by shear yielding stress, is increased and the cavitation sets in first and yielding is determined by the stress needed for cavitation. Further deformation involves deformation of crystals due to rapid local change of stress around voids. The influence of different morphological factors: crystal thickness, crystallinity degree, arrangement of crystalline elements (e.g. in spherulites), morphology of amorphous phase (free volume, entanglements, tie molecules) were analyzed. Experimental factors, such as temperature of deformation and rate of deformation influence remarkably the formation of cavities. Cavitation is generated at points where a high local triaxial state of stress is developed. Triaxiality of stress can be amplified by a notch, even very mild notch with large radius of curvature stimulates generation of cavities. Evolution of nano-cavities into micro-cavities and change of their shapes with increasing deformation were evidenced by SAXS. Initially voids are oriented perpendicularly to deformation direction, however, with increasing elongation they become oriented along deformation direction. Stress whitening is visual sign of cavitation and is caused be light scattering either by microvoids or by assemblies of nanovoids.     

轮胎骨架材料带束层的有限元分析

使用ABAQUS有限元分析软件,考虑了轮胎材料的非线性、接触非线性及轮胎结构非线性等因素,建立了195/65R15半钢子午线轮胎三维有限元分析模型。探讨充气工况和静负载工况下轮胎及轮胎骨架材料带束层受力变形的情况,并对带束层不同部位帘线的受力及胎肩部位变形情况进行了分析。结果表明,带束层帘线径向受力分布与轮胎接地区域应力分布相似,按照中心轴线对称分布,最大值出现在胎肩位置,约为142N;通过带束层帘线在胎肩部位变形分析可知,帘线在胎肩部位最大周向变形量约为16mm。     

大断面煤层巷道交叉点支护技术研究

新元煤业东辅运大巷2号联络巷与回风大巷的交叉点是新掘巷道与原有巷道贯通后形成的交叉点,新掘巷道的扰动影响打破原有巷道围岩应力平衡状态,导致巷道交叉点处围岩的松动圈变大,巷道变形,提出全锚索（7.3 m锚索）＋密集点柱进行支护,加打9根12 m锚索进行补强的新型支护方案,通过对施工完成后的交叉点表面位移及顶板离层进行观测,可知：该支护技术满足交叉点支护强度的需要,能有效的控制巷道变形,取得较好的支护效果,保证了矿井通风、行人等安全需要。     

Pd-20W合金的热压缩变形行为和显微组织

采用Gleeble-3500热模拟试验机对Pd-20W合金进行热压缩试验,研究了合金在变形温度1000~1200 ℃、应变速率0.001~1.000 s^-1条件下的流变应力以及变形过程中的显微组织。结果表明,合金的流变应力在变形初期随着真应变的增大快速上升,出现峰值应力后逐渐下降并达到稳态或略有下降。该合金热压缩变形的流变应力行为可用Zener-hollomon参数来描述,拟合计算得到了该材料的形变激活能等参数,获得流变应力的本构方程。热压缩变形后合金组织呈现一定程度的协同变形特征,晶界动态再结晶趋势增强,合金的主要软化机制为动态再结晶,表现出典型的应变诱发晶界形核机制特点。     

均匀化处理对挤压态Mg-Al-Zn-0.1Y合金热变形行为及织构的影响

利用250～400℃、0.01～10 s^-1 Gleeble 3500热模拟机等温热压缩试验研究了均匀化处理对稀土Y微合金化挤压态Mg-Al-Zn合金热变形行为的影响,利用电子背散射衍射(EBSD)研究了均匀化热处理对其热变形织构的影响。建立了挤压态和均匀化处理态Mg-Al-Zn-0.1Y镁合金的Arrhenius型本构方程,绘制了代表稳态流动的0.5应变加工图。研究了均匀化热处理对合金热加工图的影响,发现均匀化处理拓宽了合金低温可加工区,提升了合金的低温可加工性,确定了挤压态合金的适宜加工区为(325～375℃、0.01～0.1 s^-1)和(350～375℃、1～10 s^-1),均匀化热处理态合金的适宜加工区为(275～325℃、0.01～0.1 s^-1)。均匀化热处理提升了合金的动态再结晶能力,弱化了挤压态合金热变形基面织构强度,提升了软取向部分比例,提高了挤压态镁合金的热成形性。     

基于分形曲线的分区扫描策略对激光熔化沉积基板变形的影响

目的 研究新型扫描策略,减小激光熔化沉积过程中基材的变形。方法 首先,采用分形曲线作为全域扫描策略,通过激光熔化沉积试验研究了1种传统扫描策略与3种分形扫描策略的基板变形。其次,提出将分形扫描策略和分区扫描策略相结合,按照分形曲线的走向扫描各个分区,形成基于分形曲线的分区扫描策略,通过激光熔化沉积试验研究了1种传统分区扫描策略与3种基于分形曲线的分区扫描策略的基板变形。结果 无论是全域扫描还是分区扫描,基板的4条边均发生了竖直向上的翘曲变形。在扫描路径的终点附近,基板的变形量最大。全域扫描策略下,基板的最大变形量分别为：光栅式扫描7.5mm,Peano曲线3.3 mm,Sierpinski曲线2.5 mm,Lebesgue曲线3.8 mm。分区扫描策略下,基板的最大变形量分别为：光栅式顺序7.5 mm,Hilbert曲线顺序3.5 mm,Sierpinski曲线顺序3.2 mm,Lebesgue曲线顺序5.4 mm。结论 基于分形曲线的分区扫描策略可以显著减小基板变形,还可以灵活地调节扫描线段的方向和数量,在综合考虑扫描线设计的灵活性和变形量的情况下,基于Sierpinski曲线的分区...