高速冲击下子午线轮胎胎面胶的本构模型

在室温下,运用分离式Hopkinson压杆对子午线轮胎胎面胶进行高速冲击破坏试验(应变速率为2 000~5 400s~(-1)),得到了胎面胶在高速冲击下的应力-应变曲线;通过修正MooneyRivlin本构模型,构建了适用于高应变速率并具有脆性特征的动态本构模型,并通过非线性拟合得到了动态本构模型的拟合参数。结果表明:胎面胶呈现非线性应力-应变关系,屈服应力随应变速率的增加由89 MPa增至345 MPa,具有应变速率强化效应与脆性断裂特征;本构模型计算得到的应力-应变与试验值比较吻合,验证了动态本构模型的可靠性。     

动态冲击载荷下无氧铜的力学性能研究

利用分离式Hopkinson压杆实验装置(SHPB)对无氧铜进行了常温下不同应变率(2 500 s-1~15 500 s-1)的动态力学性能进行了测试,得到常温下无氧铜的真实应力-真实应变曲线,并分别通过Power-Law本构模型和JohnsonCook本构模型对其进行了拟合。结果表明:无氧铜在受到动态压缩载荷的作用时,其塑性流动应力对应变率并没有表现出敏感的趋势,但对于材料的屈服应力则在应变率高于14 000 s-1时明显增加,同时材料的应变强化效果降低,另外,相较于Johnson-Cook本构模型,Power-Law本构模型能够更准确的预测无氧铜在高应变率下的塑性流动应力。     

铜基粉末冶金多孔材料在高应变率下的力学性能及本构关系

通过实验得出铜基粉末冶金摩擦材料在高应变率下的应力应变曲线，建立该材料的本构模型。在分离式Hopkinson压杆(SHPB)上进行了该材料在10^2/s-10^3/s应变率范围内的冲击试验，弹速范围为4m／s-15m／s，在透射杆上采用半导体应变计技术；在MTS实验机上做了该材料在10^-4s/10^-3/s应变率范围内的准静态实验，分别在应变为0．005、0．01、0．02、0．035时卸载再加载，以验证该材料的粘弹塑性特征。通过分析动态和静态实验曲线，发现该材料在应变率300/s和准静态时有应变硬化效应，但在500/s以上却反映出应变软化效应，得出该材料为含损伤非线性粘弹塑性材料，故提出用适应于脆性材料的粘弹塑性模型和粘塑性项的组合本构模型来拟合该材料应变弱化段的本构方程。所得结果可推广应用于类似烧结合金的材料。     

车用双相高强钢的动态力学性能及本构模型的对比

通过不同应变速率(0.001～500 s^-1)下的室温拉伸试验,研究了车用HC340/590DP、HC700/980DP双相高强钢的动态力学性能;分别采用Johnson-Cook模型、Swift-Hockett/Sherby模型,以及将Swift-Hockett/Sherby模型引入到Ludwik模型中的修正模型对2种钢的流动应力-应变曲线进行拟合,对比分析3种本构模型的拟合结果。结果表明：随着应变速率的增加,2种钢均表现出增强增塑现象;Johnson-Cook模型、Swift-Hockett/Sherby模型和修正Ludwik模型的拟合度平均值分别为0.950,0.999,0.997;修正Ludwik模型既具有各应变速率间应力耦合的特点,又保持了高拟合精度,可以准确描述车用双相高强钢的动态流变行为。     

7075铝合金热压缩动态软化行为的本构模型

在应变速率为0.01～10 s-1、温度为250～450℃的条件下,采用Gleeble-1500型热模拟试验机对7075铝合金进行了高温热压缩试验,得出其变形过程中的真应力-真应变曲线;通过拟合回归分析得出了该合金高温变形过程中的本构模型并对其应变行为进行了预测。结果表明:在峰值应力之前,Fields-Backofen本构模型预测值与试验值比较吻合;在加入软化因子之后,模型的预测值更接近试验值。     

TC4-DT钛合金材料动态力学性能及其本构模型

利用同步组装的高温分离式Hopkinson压杆试验装置,对TC4-DT钛合金材料分别进行了常温下不同应变率（930~9700s-1）和应变率为5000s-1时不同温度下（20~800℃）的动态力学性能测试,获得了各种冲击载荷下的应力-应变曲线。试验数据表明,TC4-DT材料具有应变率增塑效应且存在着临界应变率值,当应变率高于此值时应变率敏感性增强明显,此外随着材料加热温度的升高,软化效应减弱。利用试验所得的数据拟合了基于Power-Law和Johnson-Cook两种热-黏塑性本构方程且获得这两种动态本构模型参数,并将所得的两种拟合曲线与试验所得数据进行对比分析,结果表明两曲线吻合度都较好,此外还对这两种曲线的拟合精度进行对比,对比结果表明两种模型的拟合误差相差不大,但是Power-Law模型拟合精度要略优于Johnson-Cook模型的拟合精度。     

B280VK钢动态力学性能及其本构模型研究

通过对B280VK低合金高强钢在应变率分别为0.003、20、80、180和530/s下进行高速拉伸试验,对其不同应变率下的动态力学性能进行研究,得到不同应变率下B280VK低合金高强钢的应力-应变曲线,并对不同应变率下的材料延伸率、流变应力、抗拉强度以及显微组织变化进行了分析。试验结果表明,随着材料应变率的升高,B280VK低合金高强钢的流变应力、屈服强度和抗拉强度均增大。另外,基于Johnson-Cook本构模型,建立该B280VK低合金高强钢应变率相关性塑性变形本构模型,本构方程模拟结果与试验结果吻合程度较为良好。     

6013-T4铝合金在不同温度和应变速率下的动态力学行为及数值模拟

采用分离式霍普金森压杆装置对6013-T4铝合金在不同温度(25,200,300℃)和应变速率(1 000,2 000,3 000,4 000,5 000s-1)下进行了动态压缩试验,研究了该铝合金在冲击载荷作用下的动态力学行为,并采用试验拟合得到的Johnson-Cook本构方程,对动态冲击试验进行了数值模拟。结果表明:6013-T4铝合金具有明显的应变速率和应变硬化效应,动态流变应力随变形温度的升高而减小;室温下合金的屈服强度对应变速率不敏感,但随变形温度的升高,屈服强度的应变速率敏感性增强;基于室温准静态与不同温度和应变速率下的动态真应力-真应变曲线,确定了铝合金的Johnson-Cook本构方程;不同温度和应变速率下真应力-真应变曲线的数值模拟结果与本构方程拟合和试验结果均吻合的较好。     

高应变速率下SiCp/Al复合材料的动态力学性能及其本构关系

利用分离式Hopkinson压杆试验装置对体积分数15％SiCp/Al复合材料进行动态压缩试验,研究了该复合材料在500～2000 s-1高应变速率下的动态力学性能及其显微组织演变;基于试验数据,通过包含与应变速率和塑性应变相关的绝热温升软化项的Johnson-Cook本构模型对应力-应变曲线进行预测,并将模型预测结果与试验结果进行对比.结果表明:复合材料的应变速率强化效应不明显,但是该材料具有显著的应变强化效应;随着应变速率的增加,复合材料的变形类型由均匀变形向局部化变形转变,增强相颗粒破裂严重,绝热剪切带在局部区域形成并扩展;采用包含绝热温升软化项Johnson-Cook本构模型计算得到的应力-应变曲线与试验结果间的相对误差小于17％.     

含硼不锈钢的热变形行为

在304不锈钢成分基础上,添加了质量分数1.96％的硼元素,采用真空感应熔炼技术制备含硼不锈钢,对该钢进行单道次热压缩试验,研究了该钢在900～1150℃ 和应变速率0.1～10 s-1条件下的热变形行为;根据试验数据,基于Arrhenius方程并结合5次多项式拟合建立该钢的热变形本构模型,对加工硬化率-真应力曲线进行分析确定该钢发生动态再结晶的临界条件.结果表明:在试验参数下热压缩后,含硼不锈钢的流变应力-应变曲线为典型的动态再结晶型,软化机制以动态再结晶为主;随着变形温度的升高或应变速率的减小,试验钢的峰值应力及其对应的真应变降低;采用所建立的热变形本构方程计算得到的真应力-真应变曲线与试验测得的相吻合,平均相对误差绝对值为2.76％,说明该本构模型能够准确预测含硼不锈钢的热变形行为;变形温度较高、应变速率较小时,该钢较易发生动态再结晶.     

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.     

Limits of topographic measurement by the scanning tunnelling and atomic force microscopes

Parameters describing the topographic character of a surface (height, surface wavelength, slope and curvature) can be derived from equivalent sinusoidal profiles. The response of a surface-measuring instrument may be modelled in terms of instrument parameters such as stylus radius, and scanning range and resolution. The performance of the instrument may then be mapped as a zone in amplitude-wavelength (AW) space to show the sinusoidal profiles it is capable of measuring. In a first-order analysis the STM and AFM are considered as equivalent to contact-stylus instruments with a notional stylus radius equal to the tip radius plus the gap. Comparisons between different instruments and types of instrument are readily made by mapping in AW space. The error arising from convolution of the sinusoidal profile with that of the finite tip may be quantified and plotted as contours in AW space.