考虑界面端应力奇异性的螺栓连接支承面接触压力计算模型

将螺栓连接支承面接触问题简化为集中载荷和力矩耦合作用的有限刚度平头压模接触问题,利用BOGY特征值方程,分析双材料界面端应力奇异性发生的几何条件;依据GLADWELL接触力学理论,构建集中载荷和力矩耦合作用下平头压模接触压力计算模型,利用此模型分析螺栓预紧力、装配间隙和被连接件材料对螺栓连接支承面接触压力分布的影响规律。结果表明：在规定预紧力范围、装配等级和常用被连接件材料下,螺栓连接支承面不会发生退让接触,而界面端部出现明显的应力奇异性,其中预紧力变化对界面端应力奇异性强度影响不明显,但装配间隙和被连接件材料的变化对界面端应力奇异性强度影响显著;当被连接件材料弹性模量大于螺栓材料时,支承面内侧应力奇异性强度大于外侧,反之内侧应力奇异性强度明显小于外侧。此外,以平头压模为算例,采用有限元法验证了构建模型的准确性。     

低温BOG压缩机气缸螺栓预紧研究

采用有限元方法对BOG压缩机气缸螺栓进行了模拟计算,得到了预紧螺栓在压力、温度载荷作用下的应力和接触状态.分析了材料属性、预紧力矩值、螺栓排列方式及螺栓个数等对螺栓连接性能的影响.研究结果表明,当气缸和缸盖采用奥氏体不锈钢材料时预紧力矩应比常温下取得大,而采用Ni35时常温下的预紧力矩即可以满足要求;预紧力矩取值越大,被连接件结合越紧密,但同时螺栓的应力也越大;螺栓排列越靠气缸内侧时,所需预紧力越小;而螺栓个数的选取应兼顾气缸密封状态和螺栓应力状态.     

大口径法兰三维力学有限元分析

建立了螺栓法兰联接大口径法兰的三维有限元模型，在考虑垫片非线性和接触非线性的基础上，研究了预紧工况和承压工况下螺栓、垫片等元件的受载与变形情况。研究表明螺栓外侧应力与预紧力成正比且随着内压的升高而增加：螺栓内侧应力与预紧力成正比但随着内压的升高而降低；法兰偏转量对垫片和螺栓的应力影响较大，随着内压的升高法兰偏转量增加，垫片变形量减小但不均匀性增加。     

基于ABAQUS的螺栓预紧分析

对扭矩法控制螺栓预紧力进行理论分析,建立了螺栓三维模型.通过前处理软件将网格模型导入ABAQUS软件,运用面面接触分析螺栓预紧状态,计算出不同参数对接触面应力大小及分布影响;就预紧力矩的精确控制提出几点建议.     

切向加载下螺栓连接复合板的失效分析*

极限载荷和孔周应力是导致螺栓连接复合板失效的主要因素。基于Hashin失效准则和有限元模型建立螺栓连接复合板的渐进损伤有限元模型,通过位移载荷响应讨论预紧力、界面摩擦因数和孔隙变化对极限载荷的影响,分析不同铺层角下孔周应力分布规律。结果表明：随预紧力增大,螺栓连接复合板极限载荷先增大后减小,随摩擦因数增大,螺栓连接复合板极限载荷逐渐增大;不同孔隙下准线性阶段位移载荷响应基本一致,孔隙对极限载荷的影响主要体现在滑移阶段及剪切变形阶段;孔隙增大会减小螺栓与螺孔间的有效接触面积,影响螺栓连接的压力分布和强度;纤维铺层方向与应力分量同向时可有效减少外载荷导致的该方向应力分量的变化,且主应力分量皆在承压区域达到其最小值;应力分量方向与纤维铺层方向相同且该方向无外载荷作用时,应力分量随着角度从承压区到非承压区递增变化。     

螺栓及其预紧力对大型转盘轴承接触载荷分布的影响北大核心

研究了转盘轴承钢球的简化方法以及螺栓预紧力的模拟方法,建立了无螺栓和有螺栓转盘轴承的简化模型,并对其进行了静力学仿真分析。结果表明:有螺栓模型的接触载荷最大值略大于无螺栓模型的接触载荷最大值,随着螺栓预紧力的增大,接触载荷分布越来越均匀,螺栓预紧力对接触载荷分布的影响越来越小;钢球与沟道之间的最大接触载荷与螺栓预紧力成反比。     

螺栓与孔间隙对紧螺栓连接板孔周应力的影响

为研究螺栓与孔间隙对单搭接单螺栓连接板孔周应力水平的影响规律,基于弹性力学方法建立螺栓连接板孔周应力分析模型,讨论影响孔周应力水平的各种因素;以单搭接单螺栓连接板为对象,建立螺栓连接板的参数化有限元模型;通过算例分析螺栓与孔间隙变化对紧螺栓连接孔周应力水平的影响。结果表明:当圆孔直径与螺栓直径之比值在1～1.3之间时,孔周应力平均水平沿圆孔深度方向逐渐降低;但是螺栓与孔间隙对板上表面和下表面的孔周应力作用规律不同,在板上表面或孔中间位置,孔周应力随孔隙增大而减小,在板下表面位置,孔周应力分布呈开口向上的抛物线;当圆孔直径与螺栓直径之比值在1.1～1.2之间时,孔周应力不受孔隙大小影响。     

多螺栓连接结构预紧力实验研究

开展多螺栓连接结构预紧力实验研究,获得了其在纯拧紧力矩作用下的预紧力及其响应规律。研究采用应变片测试方法,首先对单螺栓连接结构进行了预紧力实验,获得了不同拧紧力矩条件下螺杆上的轴向应变、轴向应力及预紧力,并通过与经验公式计算结果比较,验证了预紧力测试方法的合理性。在此基础上,开展了多螺栓连接结构预紧力实验研究。为比较相同拧紧力矩条件下,多螺栓连接结构与单螺栓连接结构预紧力水平间的差异,定义了预紧力比例因子K_(pro)。实验结果表明,由于螺栓组内部各螺栓间的相互影响,其预紧力水平明显低于单螺栓结构,并与螺栓拧紧状态相关。就本文所采用的多螺栓连接结构而言,在拧紧力矩较低、螺栓尚未完全拧紧时,K_(pro)为0.7~0.8,其预紧力水平为单螺栓结构的0.7~0.8倍;当拧紧力矩较高、螺栓处于稳定的拧紧状态时,K_(pr)为0.6左右,其预紧力约为单螺栓结构的0.6倍。     

螺栓及其预紧力对大型转盘轴承接触载荷分布的影响

研究了转盘轴承钢球的简化方法以及螺栓预紧力的模拟方法,建立了无螺栓和有螺栓转盘轴承的简化模型,并对其进行了静力学仿真分析。结果表明:有螺栓模型的接触载荷最大值略大于无螺栓模型的接触载荷最大值,随着螺栓预紧力的增大,接触载荷分布越来越均匀,螺栓预紧力对接触载荷分布的影响越来越小;钢球与沟道之间的最大接触载荷与螺栓预紧力成反比。     

承受拉力的高强度螺栓预紧力的设定

以某港口机械回转支承高强度螺栓为例,对高强度螺栓的工作拉力、总拉力、应力大小、工作预紧力及其关系等进行了计算与分析,给出在承拉状态下,高强度螺栓预紧力的计算公式。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.