Effective-Medium Theory for Two-Phase Random Composites with and Interfacial Shell

According to the Bruggeman theory and Maxwell-Garnett theory, the effective dielectric constant of a two-phase random composite with an interfacial shell is presented. The nonlinearity of the theory is obvious. Especially, the theory is suited to study the dielectric properties of two-phase random composites with a spherical interfacial shell. The theoretical results on dielectric properties of polystyrene-barium titanate composites with an interfacial shell are in good agreement with experimental data.

RANDOM MICROSTRUCTURE FINITE ELEMENT METHOD FOR EFFECTIVE NONLINEAR PROPERTIES OF COMPOSITE MATERIALS

Some theoretical methods have been reported to deal with nonlinear problems of composite materials but the accuracy is not so good. In the meantime, a lot of linear problems are difficult to be managed by the theoretical methods. The present study aims to use the developed method, the random microstructure finite element method, to deal with these nonlinear problems. In this paper, the random microstructure finite element method is used to deal with all three kinds of nonlinear property problems of composite materials. The analyzed results suggest the influences of the nonlinear phenomena on the effective properties of composite materials are significant and the random microstructure finite element method is an effective tool to investigate the nonlinear problems.

Dynamic thermo-mechanical coupled response of random particulate composites:A statistical two-scale method

This paper focuses on the dynamic thermo-mechanical coupled response of random particulate composite materials. Both the inertia term and coupling term are considered in the dynamic coupled problem. The formulation of the problem by a statistical second-order two-scale （SSOTS） analysis method and the algorithm procedure based on the finite-element difference method are presented. Numerical results of coupled cases are compared with those of uncoupled cases. It shows that the coupling effects on temperature, thermal flux, displacement, and stresses are very distinct, and the micro- characteristics of particles affect the coupling effect of the random composites. Furthermore, the coupling effect causes a lag in the variations of temperature, thermal flux, displacement, and stresses.

Alveolar Ridge Preservation Utilizing Composite (Bioceramics/Collagen) Graft: A Cone-Beam Computed Tomography Assessment in a Randomized Split-Mouth Controlled Trial

Background: The vast percentage of the alveolar bone resorption process happens within the first 12 to 24 weeks post extraction;however, this phenomenon is chronic, and the alveolar ridge continues to resorb. In order to prevent this reduction or at least recompense the loss of bone dimensions, the alveolar ridge preservation (ARP) technique was developed. Objectives: This research studied the vertical and horizontal bone dimensional changes as a result of non-molar teeth extraction alone against extraction with alveolar ridge preservation utilizing composite (bioceramics/collagen) graft by cone-beam computed tomography radiographies analyses. Material and Methods: This research was a randomized split-mouth controlled trial. 12 patients need extraction of the maxillary non-molar teeth were enrolled and allocated into 2 groups. 12 sockets after atraumatic extraction were filled with a composite graft in the role of the test group, 12 sockets left to unassisted healing after atraumatic extraction without any graft materials in the role of the control group. Two CBCT radiographs were taken at baseline and at 4 months after extraction for comparison. Both vertical and horizontal resorptions of the alveolar ridge were analyzed between test and control group by CBCT radiographs. Results: 4 months after extraction, there was a mean of vertical alveolar bone resorption compared with the baseline (0.56 ± 0.15 mm) in the test group and (1.47 ± 0.30 mm) in the control group. Whereas it was a mean of horizontal alveolar bone resorption compared with the baseline (0.90 ± 0.16 mm) in the test group and (2.26 ± 0.30 mm) in the control group. Therefore, there was a significant difference between the two groups. Conclusions: Within the limitations of this research, we demonstrated that the osteogen-plug technique significantly decreased the reduction of the bone dimensional in comparison to the tooth extraction alone, and showed that the dimensional change of the alveolar ridge after tooth extraction was minimized by using an osteogen-plug.

Stochastic Second-Order Two-Scale Method for Predicting the Mechanical Properties of Composite Materials with Random Interpenetrating Phase

In this paper,a stochastic second-order two-scale(SSOTS)method is proposed for predicting the non-deterministic mechanical properties of composites with random interpenetrating phase.Firstly,based on random morphology description functions(RMDF),the randomness of the material properties of the constituents as well as the correlation among these random properties are fully characterized through the topologies of the constituents.Then,by virtue of multiscale asymptotic analysis,the random effective quantities such as stiffness parameters and strength parameters along with their numerical computation formulae are derived by a SSOTS strategy combined with the Monte-Carlo method.Finally,the SSOTS method developed in this paper shows an excellent computational accuracy,and therefore present an important advance towards computationally efficient multiscale modeling frameworks considering microstructure uncertainties.

Statistical Analyses of the Strengths of Particulate Reinforced Metal Matrix Composites(PRMMCs)Subjected to Multiple Tensile and Shear Stresses

For design and application of particulate reinforced metal matrix composites(PRMMCs),it is essential to predict the material strengths and understand how do they relate to constituents and microstructural features.To this end,a computational approach consists of the direct methods,homogenization,and statistical analyses is introduced in our previous studies.Since failure of PRMMC materials are often caused by time-varied combinations of tensile and shear stresses,the established approach is extended in the present work to take into account of these situations.In this paper,ultimate strengths and endurance limits of an exemplary PRMMC material,WC-Co,are predicted under three independently varied tensile and shear stresses.In order to cover the entire load space with least amount of weight factors,a new method for generating optimally distributed weight factors in an n dimensional space is formulated.Employing weight factors determined by this algorithm,direct method calculations were performed on many statistically equivalent representative volume elements(SERVE)samples.Through analyzing statistical characteristics associated with results the study suggests a simplified approach to estimate the material strength under superposed stresses without solving the difficult high dimensional shakedown problem.

Composite Likelihood for Bilinear GARCH Model

In this study, we focus on the class of BL-GARCH models, which is initially introduced by Storti & Vitale [1] in order to handle leverage effects and volatility clustering. First we illustrate some properties of BL-GARCH (1, 2) model, like the positivity, stationarity and marginal distribution;then we study the statistical inference, apply the composite likelihood on panel of BL-GARCH (1, 2) model, and study the asymptotic behavior of the estimators, like the consistency property and the asymptotic normality.

Light scattering effect of submicro-textured Ag/Al composite films prepared at lower substrate temperatures

We present a new and practical approach for preparing submicro-textured silver and aluminum （Ag/Al） double-structured layers at low substrate temperatures. The surface texturing of silver and aluminum double-structured layers was performed by increasing the deposition temperature of the Al layers to 270℃. The highly submicro-textured silver and aluminum double-structured layers were prepared by thermal evaporation on quartz glasses and their surface microstructure, light scattering properties, and thermal stability were investigated. Results showed that the highly submicro-textured Ag/Al composite films prepared at low substrate temperatures used as back reflectors not only can enhance the light scattering and have good thermal stability, but also have good adhesion properties. In addition, their fabrication is low cost and readily carried out.

太阳电池阵弧形基板结构振动分析及优化设计

针对弧面型太阳电池阵新型基板结构,在满足结构安全的前提下以多参数轻量化设计为目标。本文基于等效板理论获得弧形太阳电池阵基板的各向异性等效性能参数,建立新构型太阳电池阵基板的三维有限元数值模型,并通过正弦扫频振动试验验证了模型的可靠性,进而初步实现了结构薄弱区域定位。最后结合工程实际,基于参数化建模结合多目标迭代优化的方法,分析结构在典型随机振动载荷作用下的最大应力随各特征参数的变化规律,从而获得满足结构安全条件下的补强优化方案,相比于原始结构,可使面板最大应力下降21%,若加强结构为单向无纬布,结构最大应力可进一步下降15.6%,为新构型太阳电池阵基板的轻量化设计提供支撑。

基于随机森林算法的异常发热复合绝缘子分类模型

不同类型异常发热复合绝缘子对应的检修决策、应急处理手段各不相同,因此迫切需要建立复合绝缘子异常发热类型识别方法。该文分析了表面积污、护套老化受潮和芯棒酥朽发热复合绝缘子的表面中轴线温度曲线,并定义了7个温度特征量对复合绝缘子异常发热状态进行表征。此外,该文提出了基于随机森林算法的异常发热复合绝缘子分类型模型,并使用现场和实验室拍摄的异常发热复合绝缘子红外图像构建温度特征量样本集。采用SMOTE算法对芯棒酥朽复合绝缘子温度特征量进行数据增广、10折交叉验证选择决策树个数。模型测试结果显示,表面积污、护套老化受潮和芯棒酥朽复合绝缘子的分类精确率均在85%以上。

金属橡胶复合隔振器的动静态性能

设计一种对称式金属橡胶与线弹簧复合的隔振器,基于整体隔振,考虑安装板的柔性因素,建立相应的等效线性动力学模型.通过准静态力学试验,分析线弹簧刚度、金属橡胶密度和加载位移对金属橡胶复合隔振器准静态性能的影响.同时,进行随机振动试验,研究金属橡胶复合隔振器在整体隔振中的隔振性能.试验结果表明,复合样件的刚度特性趋向于线性效果.金属橡胶复合隔振器在谐振点处的峰值衰减是线弹簧隔振器的5倍以上,且系统的随机振动响应在频段0.12~2.00 kHz内都有较大程度的衰减.

多源中高分辨率影像协同下时间合成窗口对农作物识别的影响

【背景】中高空间分辨率(≤30 m)影像是在耕地破碎、种植结构复杂的中国南方开展农作物遥感识别研究的重要数据。然而,要克服中高分辨率传感器重访周期较长以及南方多云雨天气的影响,对影像进行时间窗口合成以协同使用多源中高分辨率遥感数据,是获取时空连续农作物制图结果的必要保障。由于不同卫星影像获取的周期不同,且不同农作物物候季相节律存在较大差异,如何选择影像合成时间窗口是农作物准确识别的关键前提。【目的】通过探究影像合成时间窗口对于农作物识别的影响机制,为大尺度复杂农作物种植结构制图提供重要参考依据。【方法】以农作物类型多样且云雨天气频繁的湖北省江汉平原为研究区,通过协同Landsat-8和Sentinel-2A/2B卫星影像,设置7种时间合成窗口(15、20、25、30、40、50和60 d)情景,分别从影像的覆盖度、不同农作物时序光谱特征以及不同农作物分类精度等角度,深入分析影像时间合成窗口对农作物遥感识别的影响。【结果】在影像20 d时间合成窗口的情景下,江汉平原农作物(冬油菜、冬小麦、水稻、稻虾田和其他作物)的总体分类精度最高,为93.13%。对比而言,在影像较短时间合成窗口(如15d)的情景下,时间序列密集但高质量影像覆盖度较低,农作物总体分类精度较低(90.91%);而在影像较长时间合成窗口(如60 d)的情景下,影像覆盖度高但时间序列稀疏,导致农作物识别的关键物候信息丢失,降低了总体分类精度(86.06%)。此外,不同农作物的识别效果受影像时间合成窗口的影响程度不同,依次为其他作物>冬油菜>水稻>冬小麦>稻虾田。其他作物类内时序光谱特征变异性较大,因此对时间窗口极其敏感。油菜准确识别的关键物候期为开花期,该时期长度较短,影像合成时间超过30 d会极大降低其识别效果,主要体现为与小麦的混淆。区分稻虾田与单季稻的关键物候期为稻虾田的稻闲季淹水期,其持续时间较长,受时间合成窗口影响较小。【结论】影像时间合成窗口20d时可兼顾高质量影像覆盖度和捕获农作物识别的关键物候特征,但不同作物识别的最优时间合成窗口受到作物关键物候期影响。研究结果可为多源中高分辨率影像协同下时间合成窗口的选择提供理论参考和方法支撑,进而有效服务于宏观尺度农作物高精度遥感制图研究。

随机疲劳下复合材料剩余刚度-剩余强度关联模型及寿命预测

剩余刚度和剩余强度作为描述复合材料疲劳损伤程度最常见的方法,在应用过程中都存在各自的优缺点。刚度试验成本低,但缺少明确的失效判据使得其实际工程中的应用受到限制,强度虽然存在天然的失效判据,但破坏性试验导致试验成本较高。考虑复合材料结构大多在随机交变载荷下服役,如噪声、振动等。本文通过复合材料常幅疲劳数据推导了随机疲劳下的剩余强度曲线,提出了一种随机载荷下的剩余刚度-强度关联模型,减少了试验时间和成本,并通过关联模型预测了结构随机疲劳寿命,预测值与试验值具有较好的一致性。

融合随机统计规律与优化思想的成分数据预测方法研究

频率分布序列预测是成分数据研究中一类重要的问题。融合频率分布所具有的统计规律性与优化思想。文章采用灰色预测理论与最优化方法相结合的预测方法,以期望与均值的预测值之间差异最小化为目标,设置历史经验约束与成分数据约束的组合为约束条件,构建二次规划数学预测模型,并通过某专业学生专业核心能力频率分布结构数据进行实证分析,验证了所提预测模型的有效性。结果表明,所提预测模型的平均绝对误差为0.0416,均方根误差为0.0460,方向余弦为0.9824,与球坐标变换预测结果相比具有更好的预测精度,预测模型是可行的。研究表明,所提预测模型具有较好的预测精度,可以有效解决频率分布序列预测问题,同时对成分数据的分量中含有0或1的预测问题提供了一个新的研究思路。

随机复合材料结构非线性热-力耦合模拟的统计高阶多尺度方法

对于具有复杂随机细观构造的复合材料结构的非线性热-力耦合问题的随机多尺度建模和计算仍是一个具有挑战性的问题。本文发展了一个新的统计高阶多尺度方法,克服了随机多尺度问题直接模拟时巨大的计算量,实现了具有随机复合材料结构非线性热-力耦合问题的数值模拟。借助统计多尺度渐近分析和泰勒级数方法,本文严格推导了可以精确分析随机复合材料结构宏-细观尺度非线性热-力耦合响应的统计高阶多尺度计算模型。然后,通过局部误差分析证明了统计高阶多尺度计算模型中高阶校正项在保持计算模型局部能量和动量守恒的重要意义。进一步,建立了可以高效模拟随机复合材料结构非线性热-力耦合行为的具有离线和在线两阶段的时空多尺度算法。最后,通过数值实验验证了统计高阶多尺度方法的计算高效率和高精度。

复合多尺度注意熵在旋转机械多工况损伤识别中的应用

针对传统旋转机械损伤识别方法存在模型精度低和抗噪性差的问题,提出了一种基于复合多尺度注意熵(CMATE)和随机森林(RF)的旋转机械多工况损伤识别方法。首先,提出了一种新的测量时间序列复杂度的非线性动力学工具——复合多尺度注意熵;然后,利用CMATE提取旋转机械振动信号的损伤特征,其表征了旋转机械不同工况下的损伤特性;接着,将损伤特征输入至基于随机森林构造的多类别分类器中,进行了损伤识别;最后,采用滚动轴承-齿轮箱、齿轮箱和离心泵3种旋转机械数据集,并分别构造了9种工况和20种工况的多工况损伤数据集,对该损伤识别方法进行了实验研究。研究结果表明:该旋转机械损伤识别方法分别取得95%、97%和100%的识别准确率,在准确率和特征提取效率两方面优于其他的非线性动力学工具;并且在0 dB、1 dB、2 dB和3 dB这4种不同信噪比的噪声干扰下,依然取得了不错的损伤识别结果,证明了该模型具有可观的抗噪性;同时,该损伤识别方法能够稳定地识别旋转机械的不同负载和转速下的损伤,平均识别准确率分别达到了97.2%和93.5%,具有较好的实际应用潜力。

复合材料小尺寸不规则孔隙随机分布算法

以碳纤维/环氧树脂复合材料中的孔隙为研究对象,建立一种可以生成小尺寸不规则孔隙的随机分布算法。首先利用Matlab软件对复合材料的微观形貌图像进行处理,以获取小尺寸不规则孔隙的尺寸分布统计数据。然后以该统计数据为依据,采用改进的邻点融合法,通过C++编程建立小尺寸不规则孔隙随机分布算法。最后将孔隙微观形貌图和随机分布算法生成的孔隙分布图进行对比分析,结果表明本文算法生成的孔隙与实际孔隙的形状和分布基本相同,证明了小尺寸不规则孔隙随机分布算法的有效性和合理性。

河南省铁路-航道货运多层复合网络鲁棒性研究

发展铁水联运是优化调整运输结构、促进物流业降本增效的重要手段之一,为深入理解和把握河南省铁水联运网络的网络性能,有针对性地优化调整铁水联运网络布局、提升联运效益,运用复杂网络理论,对河南省铁路-航道货运网络进行了拓扑分析和鲁棒性研究。一方面,对铁路网、航道网以及二者相结合的复合网络进行拓扑分析,得出航道网兼具显著的小世界特性和无标度特性,铁路网则具有显著的无标度特性;另一方面,选取网络效率和最大连通子图相对大小作为评价指标,针对3种网络的有效性和连通性进行鲁棒性研究,得出鲁棒性强弱依次为复合网络、铁路网络、航道网络,表明发展铁水联运的重要性和优越性;最后,针对河南省综合运输网络构建优化,提出具体保障措施和运营建议。

复合材料压力容器的概率和非概率可靠性设计

考虑复合材料压力容器结构中各参数和载荷的随机性或区间性,利用基于概率的网格法得到其纤维强度发挥系数随机函数的计算表达式。建立了该类压力容器的可靠性分析模型,并分别应用随机因子法和区间因子法导出了纤维强度的均值、标准差和离差的计算表达式,利用概率的和非概率的可靠度计算方法,实现了该类压力容器的概率和非概率的可靠性设计,并考察了结构各不确定性参数的波动对容器厚度设计尺寸的影响。算例结果表明:概率和非概率的可靠性设计结果均可满足安全要求,且比传统的安全系数法结果更为精确与合理;概率方法相比非概率方法,其结果相对误差较小,但计算过程较为复杂。