不同材料的室温单轴应变循环特性和棘轮行为研究

通过对U71Mn轨道钢和316L不锈钢室温下单轴应变控制和应力控制循环的实验研究，就两种材料的应变循环特性和棘轮行为进行研究和比较。讨论应变循环下应变幅值和平均应变的大小及其历史对应变循环特性的影响以及应力循环下应力幅值和平均应力的大小及其历史对棘轮行为的影响，同时还讨论了应变循环与应力循环间的交互作用。研究中着重对两种材料的循环特性进行比较，得到一些有助于进行合理本构描述的结果。     

6061铝合金室温与150℃单轴棘轮行为实验研究

在室温和150℃温度下对6061铝合金开展了系统的单轴应变控制循环和单轴非对称应力控制循环实验,讨论了6061铝合金的单轴应变循环特性和单轴棘轮行为。研究表明,6061铝合金的单轴应变循环特性受到应变幅值和平均应变及其加载历史等因素的影响;单轴棘轮行为依赖于应力幅值、平均应力及其加载历史,并随应力幅值和平均应力的增大而增加。     

聚醚醚酮的室温单轴棘轮行为

在室温下对聚醚醚酮(PEEK)进行一系列非对称应力控制的单轴循环棘轮变形试验,研究了应力水平、加载历史、应力速率和峰值应力保持时间对PEEK棘轮行为的影响规律。结果表明：PEEK在非对称应力循环加载下产生了明显的棘轮行为,棘轮应变包含可恢复的黏弹性应变和不可恢复的黏塑性应变;棘轮应变和棘轮应变速率均随着应力水平的增加而增大;PEEK的棘轮行为具有明显的加载历史效应,高平均应力的加载历史会抑制后续低平均应力循环过程中棘轮变形的发生,低平均应力的加载历史对后续高平均应力循环过程中的棘轮变形影响不大;PEEK的棘轮行为具有明显的时间相关特性,应力速率越低、峰值应力保持时间越长,棘轮应变越大。     

PE100管的室温单轴应变循环行为与棘轮效应

在室温下对聚乙烯(PE100)管分别进行了单轴拉伸试验、扭转对称应变循环试验和单轴棘轮效应试验,探讨了不同应变速率下PE管的应力-应变响应,分析了循环应变幅、应变幅历史对应变循环特性的影响以及均值应力和幅值应力及其加载历史对PE100管棘轮变形的影响。结果表明:PE100是一种率相关循环软化材料,无论应变循环特性还是单轴棘轮行为,两者都强烈依赖于当前的载荷条件和既往加载历史;PE100管存在产生循环硬化的对称扭转应变幅阈值,其值为5%,当PE100管经历大于该阈值的循环后再经历后续小应变幅循环时会发生一定程度的硬化,但静置后这种硬化现象又会消失,表现出时效恢复特性。     

U75VG钢轨钢与温度相关的循环塑性变形行为

采用单轴拉伸试验和循环塑性变形试验研究了U75VG钢轨钢在不同温度(25,300,600℃)时的单轴拉伸性能以及循环塑性变形行为。结果表明:在应变控制循环载荷下,25℃时U75VG钢轨钢表现出循环软化特性,300℃时在动态应变时效作用下表现出循环硬化特性,600℃时动态应变时效作用消失,表现出更明显的循环软化特性;在应力控制循环载荷下,U75VG钢轨钢在不同温度下均表现出明显的棘轮行为特征,棘轮应变速率随平均应力或应力幅的增加而增大,在300℃时棘轮应变演变呈现出准安定状态,在600℃时随着平均应力或应力幅的增加棘轮应变加速增大。     

316L不锈钢温度相关与非比例强化的粘塑性本构模拟

高温动态应变时效影响316L不锈钢的力学行为,且材料在非比例加载条件下,表现出明显的非比例附加强化特性。基于McDowell粘塑性模型和Chaboche温度相关本构模型,将非比例度嵌入短程背应力模量与各向同性强化模型,提出了一个考虑温度相关与非比例附加强化的粘塑性本构模型,合理描述了室温及873 K下316L不锈钢在单轴、纯扭、比例及非比例加载路径的应力应变响应,得到了与试验一致的结果。     

多种循环加载制度下Q235材料性能试验

对Q235钢进行了变应力载荷幅值及不同预变形和载荷保持时间等条件下的循环加载试验,并分析了其力学响应和材料性能。研究结果表明：Q235钢在应力控制的循环加载过程中表现出明显的循环软化特性和棘轮效应,棘轮应变的大小主要取决于载荷水平;当循环载荷逐级增大时,前期的变形会导致后期的棘轮应变增大;而当循环载荷逐级减小时,后期的棘轮应变值取决于最大载荷时的棘轮应变,且棘轮应变率接近于零;当预变形的响应应力峰值小于后期控制应力峰值时,预变形对材料的棘轮效应具有抑制作用,且预变形量越大,抑制效果越明显;载荷保持时间延长会使材料的棘轮应变增大,棘轮应变率增大,从而加速材料失效。     

热处理U71Mn钢轨钢的棘轮行为及其本构模型

通过单轴拉伸试验、对称应变循环疲劳试验和非对称应力循环疲劳试验,研究了热处理U71Mn钢轨钢的循环特征和棘轮行为;基于试验结果,对Abdel-Karim-Ohno循环塑性本构模型进行修正,并将模拟结果与试验结果进行对比。结果表明:试验钢表现出初始循环软化特性;在非对称应力循环载荷下,试验钢产生了明显的棘轮行为,棘轮应变随应力幅、平均应力和峰值应力的增加而增加,棘轮应变率随峰值应力的增加而增加,当峰值应力不超过950MPa时,棘轮应变率随循环周次的增加快速减小至稳定值,当峰值应力超过950MPa时,棘轮应变率先减小后增大;大多数工况下采用所建立的修正Abdel-Karim-Ohno循环塑性本构模型得到的棘轮应变与试验值的平均相对误差约为9.8%,说明该模型能够较好地预测热处理U71Mn钢轨钢在应力循环工况下的棘轮行为。     

316L钢中温环境下应力控制的低周疲劳行为研究(二)

通过对316L钢在420℃环境下应力控制的低周疲劳实验，揭示和分析了316L钢在420℃环境下的弹性模量、全应变范围、塑性应变范围、塑性应变能及平均应变随加载历史和名义应力范围的变化特性，为以后的寿命评估模型提供依据。     

退火处理对紫铜棘轮行为的影响

对未退火硬态紫铜和退火处理得到的软态紫铜进行室温应变控制对称循环和应力控制非对称循环变形试验,研究了退火处理对紫铜显微组织和棘轮行为的影响.结果表明:退火处理会增大紫铜的晶粒尺寸,影响紫铜的循环软/硬化特性;两种状态紫铜均表现出明显的棘轮行为,且其棘轮行为依赖于外加应力水平;应力幅的增大会显著影响硬态紫铜棘轮演化第Ⅲ阶...     

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.