环氧绝缘的组份与工艺对低温内应力的影响

应用的改进的双圆筒测应力推广用于低温环境中内应力的测量，研究了环氧绝缘从固化温度直到低温的较宽温度范围内的内应力的出现与增长过程，说明环氧绝缘固化过程中内应力与固化反应放热峰并不是同时出现的，而是前者滞后于后者；实验再次证明了出现内应力时的温度接近固化体系的玻化温度；批出固化剂含量于低温绝缘的特点重要性和填实，增塑剂及固化温度对于降低低温内应力的作用。     

解理断裂微观准则的研究

对三点弯曲预裂纹试样断口形貌、裂尖附近微孔及残留裂纹进行了观察,并用有限元方法计算了裂尖应力应变场。结果表明,解理点距裂尖存在一个最小距离,在此距离内三轴应力度过低,仅能形成微孔而不能形成解理微裂纹,RKR模型中表述的特征距离并不存在。最小韧性取决于在最小距离上满足解理所需的最小载荷。解理的临界事件是由启裂的第二相尺寸的微裂纹向周围基体的扩展。韧性值的分散和脆性粒子在裂央前的随机分布及微观解理断裂应力的波动有关。     

韧性材料在多向动应力状态下的动强度理论

韧性材料的多向静应力状态,有最大正应力、最大剪应力等强度理论,作为强度设计计算的判断准则,而在多向动应力状态下的强度理论是什么呢?至今尚未有确切的定论。本文根据韧性材料的疲劳破坏机理,提出了在多向动应力状态下,材料的某一截面上沿某个方向首先开始破坏,主要是由于其剪应力时间历程的作用最不利所引起的,并同时考虑了该截面上的正应力时间历程的影响,建立了韧性材料在多向动应力状态下疲劳破坏截面的位置及其寿命的计算公式,作为动强度设计计算的判断准则,简称之为动强度理论。     

用边界变换法求边界近旁的应力

本文依据弹性体状态唯一性原理,提出了用边界变换法来解决边界元应力分析中边界近旁区域应力值的准确计算问题,从而避免了积分核的奇异性及边界离散化的不利影响。文中的两个简单的算例说明,边界交换法可在不改变原有边界单元划分的条件下,在边界近旁区域获得与理论值十分接近的计算结果。     

环形缺口拉伸圆杆的统一模型和断裂准则

对具有环形缺口的拉伸圆杆，以缺口尖端半径ρ，深度ｔ和张角α以及圆杆几何尺寸ａ和６为描述参量，将理想尖裂纹、钝裂纹和切口作为缺口来统一描述，给出了以ｆ＿α（ａ／ｂ）为依据的安全设计和断裂设计准则，从而使理想裂纹应力强度因子模型和切口应力集中模型得以衔接。     

工程中的非稳态温度场和热应力场问题的分析

考虑工程的非稳态温度场和热应力场问题，先后将空间域和时间域离散，从变从原理和伽辽金法导出了非稳态温度场和热应力场的有限元计算式，对工程中的一个轴对称问题进行了分析。     

纳米结构陶瓷涂层的磨削表面残余应力的X衍射测定法

磨削后的纳米结构陶瓷涂层零件表面会出现使零件强度降低的裂纹,而产生这些裂纹的原因就是磨削表面残余应力。这些表面残余应力使不同晶粒的同族晶面面间距随晶面方位及应力的大小发生有规律的变化,从而使X射线衍射谱线发生位偏移,根据位偏移的大小利用σ=K·M就可以计算出残余应力的大小。     

Comparative expression analysis of three genes from the Arabidopsis vacuolar Na^＋/H^＋ antiporter （AtNHX） family in relation to abiotic stresses

Na~ /H~ antiporters (NHX) are ubiquitous transmembrane proteins that play a key role in salt tolerance of plants. In this study, the sequence of 3 Arabidopsis NHX gene (AtNHX2―4) were compared with other AtNHX members. Putative cis-elements analysis identified elements that have been associated with stress responses. The activities of the promoters AtNHX2―4 were studied in transgenic plants carrying corresponding promoter-β-glucuronidase (GUS) fusions. The AtNHX2 promoter-GUS analysis indicated that AtNHX2 was expressed in constitutive pattern with high GUS activity in roots and leaves. AtNHX2 promoter activity was not up-regulated by NaCl or abscisic acid (ABA), in contrast to the AtNHX1 promoter which was previously studied. The AtNHX3 and AtNHX4 promoters showed tissue-specific activities. Strong GUS activity was detected in roots and vascular bundles of the stele in plants carry-ing an AtNHX4 promoter-GUS fusion, and GUS activity increased under salt stress suggesting a func-tion related to salt tolerance. Transgenic plants carrying the AtNHX3 promoter-GUS fusion showed strong GUS activity in petals, stamens and tops of siliques, suggesting a possible role of AtNHX3 in flower and seed development. Results of histochemical analysis suggested that AtNHX2―4 are involved in divergent functions and are differentially regulated under abiotic stress. The structure of AtNHX4 was predicted to include 12 transmembrane regions and a NHX domain. Overexpression of AtNHX4 in Arabidopsis transgenic lines confers greater salt tolerance than in wild type plants. These results suggest that AtNHX4 may encode a putative vacuolar NHX that plays an important role in salt tolerance.     

Reliability Based Design Optimization of Aero-Engine Spindle Ball Bearings

Aero-engine spindle ball bearings work in harsh conditions which are affected by relatively complex stresses. One of the key factors which affects bearing performance is its structure. In this paper,we used reliability based design optimization method to solve the structure design problem of aero-engine spindle ball bearings.Compared with the optimization design method, the value of equivalent dynamic load using reliability optimization design method was the least by MATLAB simulation. Also the design solutions show that the optimized structure possesses higher reliability than the original solution.     

混合式基层沥青路面动态响应测试结果特征分析

依托遂广高速公路沥青路面动态响应试验段,进行了系统采集数据的有效性分析,并基于沥青混合料、级配碎石和土体经典力学理论,评价了单后轴和双后轴货车作用下路面结构内部水平应变和竖向力学指标时程曲线的力学基本特征.研究结果表明:移动荷载作用下,沥青层层底纵向应变先后出现压—拉—压循环交变应变,沥青层层底横向应变表现为压—拉两个过程,沥青层层底纵向和横向应变应分别采用应变幅值和拉应变峰值作为路面在荷载作用下实际应变变化值,且沥青层层底横向应变测值受轮胎作用位置影响较大;同时,荷载驶离传感器后,沥青层层底水平应变响应存在明显残余应变,而土基顶面竖向压应力并不存在残余应力;双后轴货车后轴对应的路基顶面竖向压应力和沥青层层底横向应变叠加效应显著高于其他指标.现场试验证实,路面结构动态计算分析中,路基可简化为弹性体,沥青混合料材料应考虑其黏弹性特征,级配碎石过渡层应考虑其永久变形特性.