The transient fracture behavior for a functionally graded layered structure subjected to an in-plane impact load

The transient fracture behavior of a functionally graded layered structure subjected to an in-plane impact load is investigated. The studied structure is composed of two homogeneous layers and a functionally gradedinterlayer with a crack perpendicular to the boundaries. The impact load is applied on the face of the crack. Fourier transform and Laplace transform methods are used to formulate the present problem in terms of a singular integral equation in Laplace transform domain. Considering variations of parameters such as the nonhomogeneity constant, the thickness ratio and the crack length, the dynamic stress intensity factors （DSIFs） in time domain are studied and some meaningful conclusions are obtained.

Influence of layer orientation and interlayer bonding force on the mechanical behavior of shale under Brazilian test conditions

The mechanical behavior of inherently anisotropic shale rocks under Brazilian test conditions are investigated in this study based on experimental studies and numerical simulations. The effects of the weak lamination planes and interlayer bonding force of these layers on the failure strength and fracture patterns are studied systematically. Numerical simulations using particle flow code in two dimensions based on the discrete element method showed a good agreement with the experimental results in the failure strength and fracture patterns. The shale revealed strong anisotropic behavior with the failure strength perpendicular to the lamination plane greater than failure strength parallel to lamination plane. The failure strength of the different interlayer bonding force against the layer orientations changed significantly. Four types of fracture patterns were observed: curved fracture, broken-linear fracture, layeractivated fracture, and central-linear fracture. The observed fracture patterns are either or a combination of tensile and/or shear fractures. Increase in interlayer bonding strength decreased the quantity of micro cracks and this directly led to reduction in the anisotropic behavior. Overall the layer orientation and interlayer bonding force of the shale thus play a very important role in the anisotropic behavior of the shale.

BOUNDARY AND ANGULAR LAYER BEHAVIOR IN SINGULARLY PERTURBED SEMILINEAR SYSTEMS

Some authors employed the method and technique of differential inequalities to obtain fairly general results concerning the existence and asymptotic behavior, as ?-n+ , of the solutions of scalar boundary value problemsIn this paper, we extend these results to vector boundary value problems, under analogous stability conditions on the solution u = u(t) of the reduced equation 0 = h(t, u) Two types of asymptotic behavior are studied, depending on whether the reduced solution u(f) has or does not have a con tinuous first derivative in (a, b) leading to the phenomena of boundary and angular layers.

Microstructure and abrasion wear behavior of Ni-based laser cladding alloy layer at high temperature

Ni-based alloy coating on 21-4-N heat-resistant steel was prepared using CO2 laser, and the high-temperature abrasion wear was tested. The microstructure of this cladding layer and its abrasion wear behavior at high temperature by changing compositions and temperatures were investigated by means of optical microscope and scanning electron microscope. Among the three compositions of cladding layer, i.e. Ni21+20%WC+0.5%CeO2, Ni25+20%WC+0.5%CeO2 and Ni60+20%WC+0.5%CeO2, the experimental results show that Ni21+20%WC+ 0.5%CeO2 cladding layer is made up of finer grains, and presents the best abrasion wear behavior at high temperature. The wear pattern of laser cladding layer is mainly grain abrasion at lower temperature, and it would be changed to adhesive abrasion and oxide abrasion at higher temperature.

Nonlinear analysis of pile load-settlement behavior in layered soil

A simplified approach is presented to analyze the single pile settlement in multilayered soil. First, a fictitious soil-pile model is employed to consider the effect of layered soil beneath pile toe on pile settlement behavior. Two approximation methods are proposed to simplify the nonlinear load transfer function and simulate the nonlinear compression of fictitious soil-pile, respectively. On this basis, an efficient program is developed. The procedures for determining the main parameters of mathematical model are discussed. Comparisons with two well-documented field experimental pile loading tests are conducted to verify the rationality of the present method. Further studies are also made to evaluate the practicability of the proposed approach when a soft substratum exists, and the results suggest that the proposed method can provide a constructive means for assessing the settlement of a single pile for use in engineering design.

Effect of the Compound Layer of Plasma Nitriding on Thermal Fatigue Behavior of 4Cr5MoSiV1 Die Steel

With the Uddeholm self restricted method, the effect of compound layer of plasma nitriding on thermal fatigue behavior of 4Cr5MoSiV1 steel was studied by the way of adding Ar during plasma nitriding to remove the compound layer. The results show that the compound layer of plasma nitriding can delay the nucleation of heat cracks and hold back the propagation of heat cracks from surface to substrate because of its high hardness and strength. On the other land, the heat checking expands faster with the compound layer on the surface than that without it. After 3000 cycles of thermal fatigue test, both heat cracks with the compound layer are wider than the another without compound layer and the number of heat cracks of the former is more from the view of cross section.

DYNAMIC BEHAVIOR OF PILES EMBEDDED IN TRANSVERSELY ISOTROPIC LAYERED MEDIA

Dynamic behavior of single pile embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's function for ring loads. The influence of soil anisotropy on the dynamic behavior of piles is examined through a series of parametric studies.

Dynamic behavior of single-layer latticed cylindrical shells subjected to seismic loading

The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.

燃料电池气体扩散层表面液相涌出行为

燃料电池流道内的两相分布特性对于提升燃料电池水管理能力至关重要,探究多液滴在流道表面流动行为利于优化结构及运行条件。使用流体体积(Volume of Fluid)法对液态水从气体扩散层(Gas diffusion layer)涌出到流道内的动态过程进行模拟,研究流道内气体流速、GDL表面接触角和水孔间距对水涌出过程和流动行为影响。结果表明,液滴在GDL表面经历了生长、分离、传输和碰撞凝并等过程。气体流速明显影响压降和液滴分离周期,随着气体流速增加,压降增加,液滴分离周期从14.7 ms降至4.7 ms,水去除能力显著增强,高气体流速造成液滴形态和流动情况不稳定。GDL表面润湿性改变了表面张力,影响液滴形态和流动,显著影响水覆盖率,随着接触角增大,GDL表面平均水覆盖率从20.03%降至9.01%;水孔间距对液滴碰撞周期影响大,小水孔间距时液滴在生长中发生凝并,大液滴飞溅造成流道内气流速度下降,压降和GDL表面水覆盖率产生大波动;大水孔间距时,流道内速度场受影响明显,前一液滴获得大速度后发生碰撞更易造成液滴飞溅,导致最大水孔间距时水覆盖率下降,从16.84%(D=0.8 cm)骤降至14.69(D=1.2 cm)。研究结果为流道表面接触角,GDL孔隙分布、进气条件等参数优化提供理论指导和技术借鉴,改善质子交换膜燃料电池水传输能力提高工作效率。

Cr_(3)C_(2)/WC的添加对Stellite 12熔覆层耐磨耐蚀性的影响

目的 提高Stellite 12熔覆层的耐磨耐蚀性能。方法将Stellite 12合金粉末与碳化物(Cr_(3)C_(2)、WC)混合,采用激光熔覆技术在H13钢板上制备复合熔覆层。通过超景深显微镜和XRD分析其显微组织和物相,通过显微硬度测试、摩擦磨损试验和电化学腐蚀试验,分别评价熔覆层的硬度、耐磨性和耐蚀性,并通过超景深显微镜对磨痕形貌进行分析。结果添加碳化物后,熔覆层的微观组织以柱状晶和树枝晶为主,物相主要由γ-Co固溶体和碳化物(M23C6、M7C3)组成;Cr_(3)C_(2)的添加使得熔覆层的硬度降低,由610HV0.2降至530HV0.2,但耐磨性得到提高,磨损量由0.45 mm^(3)降至0.33 mm^(3),下降了28%,耐蚀性得到提高,腐蚀电位由-0.385 V增加到-0.264 V,腐蚀电流密度由9.269×10^(-10)A/cm^(2)降至1.496×10^(-10)A/cm^(2),极化电阻由3.982×10^(7)Ω·cm^(2)提升至2.424×10^(8)Ω·cm^(2),提高了1个数量级;WC的添加使其硬度由610HV0.2提高至750HV0.2,磨损深度变浅,磨损量由0.45 mm3降至0.19 mm^(3),下降了43%,但耐腐蚀性有所降低。3种熔覆层的磨损机制主要为磨粒磨损和黏着磨损。结论WC的添加可以有效提高熔覆层的硬度和耐磨性,但耐腐蚀性有所降低;添加Cr_(3)C_(2)后,耐蚀性得到显著提高,耐磨性略微提升,但硬度降低。

基于多模态神经网络流量特征的网络应用层DDoS攻击检测方法

农业设备、传感器和监控系统与网络的连接日益紧密,给农村配电网带来了新的网络安全挑战。其中,分布式拒绝服务(DDoS)攻击是一种常见的网络威胁,对农村配电网的安全性构成了严重威胁。针对农村配电网的特殊需求,提出一种基于多模态神经网络流量特征的网络应用层DDoS攻击检测方法。通过制定网络应用层流量数据包捕获流程并构建多模态神经网络模型,成功提取并分析了网络应用层DDoS攻击流量的特征。在加载DDoS攻击背景下的异常流量特征后,计算相关系数并设计相应的DDoS攻击检测规则,以实现对DDoS攻击的有效检测。经试验分析,所提出的方法在提取DDoS攻击相关特征上表现出色,最大提取完整度可达95%,效果明显优于对比试验中基于EEMD-LSTM的检测方法和基于条件熵与决策树的检测方法。

纳米结构BCC-Al_(0.5)CoCrFeNi_(0.4)高熵合金在氯化钠溶液中的电化学腐蚀行为

采用电化学测试并结合对合金表面膜的细致表征,研究Al_(0.5)CoCrFeNi_(0.4)高熵合金(HEA)在3.5%NaCl(质量分数)溶液中的电化学腐蚀行为。结果表明,Al_(0.5)CoCrFeNi_(0.4) HEA主要由富含Al、Ni的B2相和富含Cr、Fe的A2相组成。在电化学极化作用下,合金表面均匀地形成了一层富含Cr的超薄钝化膜。随着外加电位的增加,保护膜在两相界面处破裂,随后B2相优先溶解。最后,在HEA表面形成三层结构的表面膜:内层富集Cr、中间层富集Fe,外层富集Al和Ni。内层和中间层的形成可归因于Cr物种的高稳定性和Fe的选择性溶解,而腐蚀产物的沉积形成表面膜外层归因于B2相的溶解。

计及出行行为调整的综合能源系统双层博弈优化策略

针对园区综合能源系统中各个主体的利益难以兼顾及新能源汽车出行计划临时变动会对系统运行带来不利影响的问题,提出了考虑车主出行行为调整的电热氢综合能源系统双层博弈优化运行策略。首先,建立以能源运营商(IESO)、负荷聚合商(ULA)和新能源汽车负荷聚合商(NEVLA)为主体的Stackelberg-Shapley双层博弈框架;其次,将双层博弈框架嵌入两阶段模型预测控制滚动调度模型中,并在第1阶段引入惩罚博弈机制,抑制车主按照个人意愿无序改变充电计划的行为;最后,联合沙丘猫优化算法与CPLEX求解器对博弈模型进行求解。仿真结果表明:所提策略与无惩罚博弈机制的滚动优化运行策略及考虑惩罚博弈机制的单断面优化运行策略对比,能源运营商的收益分别提高了4.43%、7.75%,负荷聚合商的剩余价值分别提高了6.48%、12.18%,电动汽车负荷调度成本分别减少了13.64%、4.43%,验证了所提策略具有更好的系统运行经济性。

镍基高温合金U720Li在750℃不同氧化阶段的恒温氧化行为

航空发动机涡轮盘服役温度的不断升高,对材料的抗氧化性能提出了更严苛的要求。U720Li合金是一种具有较高承温能力的涡轮盘用镍基高温合金,其长期服役温度高达750℃。阐明该合金在服役温度下的氧化行为,对延长涡轮盘的服役寿命具有重要意义。本文采用静态增重法测定了锻态U720Li合金在750℃的氧化动力学曲线,用XRD、SEM-EDS等手段分析了不同氧化阶段的氧化膜形貌、结构及元素分布。结果表明,U720Li合金在其服役温度下具有优异的抗氧化性能,在750℃的恒温氧化动力学曲线大致遵循立方规律,达到了完全抗氧化级别。分析认为,U720Li合金在氧化初期生成了疏松的γ-Cr_(2)O_(3),随着氧化的进行,γ-Cr_(2)O_(3)层不断剥落,氧化膜变得更加连续致密并形成复杂多层结构,且在氧化膜附近基体内形成γ'贫化层。在稳定氧化阶段,氧化膜更加连续致密并形成规整的双层结构,包括致密的α-Cr_(2)O_(3)外氧化层和α-Al_(2)O_(3)内氧化层。连续致密的α-Cr_(2)O_(3)和α-Al_(2)O_(3)层的形成能够有效阻止氧的内扩散及合金元素的外扩散,保障了U720Li合金的优异抗氧化性能。

基于BERT的多视角事件日志修复

在业务流程执行过程中,由于信息系统故障或者人工记录出错等问题导致事件日志中数据的丢失,从而产生缺失的事件日志,使用这种缺失日志会严重影响业务流程分析结果的质量。针对这种缺失日志的修复问题,现有研究大部分仅从数据视角或者行为视角进行展开,很少从数据和行为相融合的视角开展事件日志的修复工作。提出了一种基于BERT模型的多视角事件日志修复方法。该方法利用双层BERT模型,从数据和行为融合的视角训练模型,通过BERT模型的预训练任务((masked attribute model,MAM)和(masked event model,MEM))以及Transformer编码块的注意力机制捕获输入属性的双向语义信息和长期依赖关系,使用微调策略进行模型训练,以预测的形式修复事件日志中的缺失值。最后,通过公开可用的数据集进行评估分析,结果表明,该方法在修复事件日志方面表现良好。

斜坡非均匀弧形滑动下管道力学行为研究

目前尚未建立准确描绘斜坡三维非均匀圆弧滑动下探究管道力学行为的模型。为此,基于强度折减理论,利用2D平面应变有限元模型确定斜坡失稳滑动面,基于2D平面应变有限元模型的斜坡滑动轨迹,纳入非均匀三角函数型表征的滑坡位移函数,建立含有滑坡真实滑动面的3D有限元模型。基于中缅油气管道的工程案例及参数取值范围,充分分析8种无量纲因素对管道轴向拉伸应变行为的影响。研究结果表明:减小埋深、增大壁厚、根据径厚比设计管道穿越斜坡位置、合理把关回填土力学性能等措施,能极大地降低管道在轴向失效的可能性;通过控制管道壁厚能有效减小土壤内摩擦角和运行内压带来的影响。研究结论可为穿越斜坡段敷设的管道设计工作提供理论指导。

云环境下跨层级间歇故障行为建模与量化分析

间歇故障具有随机性,复杂的机理与表现会导致传统诊断方法不再有效,尤其是对于云计算环境,因为长时间运转、高负载运行以及集群规模大等因素致使间歇故障易感性居高。针对此问题,提出了一种基于跨层级间歇故障传播行为的建模与量化分析方法。该方法对间歇故障行为演化进行跟踪并量化分析,包括发现并记录故障在云环境不同层级的传播,构建传播路径,量化间歇故障对结构级、固件、超特权、特权和用户层级的影响,以及故障模型参数对系统影响的比较,以为云环境下间歇故障诊断策略提供辅助诊断信息和指导。

基于数值模拟的新拌混凝土竖直泵送流动行为

借助数值模拟研究了3种流动性的混凝土在竖直向上泵送时的管内流动行为,分析了混凝土内部压力和流速的分布规律.结果表明:泵送压力主要受润滑层性质的影响,其纵向分布与管壁阻力沿程变化规律有关,截面中心的泵送压力略高于管壁处;混凝土在管内的流动存在“前进—扩散—滞留堆积—汇聚”的行为特征,并据此分析了润滑层的形成和粗骨料的迁移,解释了泵送离析和堵管的原因.

孔洞形状对层状岩石力学特性影响的FDEM数值模拟研究

为揭示孔洞形状对层状岩石力学性质和破坏模式的影响,采用有限元-离散元耦合数值模拟方法(FDEM)开展系列数值模拟研究。首先,阐述FDEM模拟层状岩石的基本原理,然后,开展不同层理倾角完整试样的单轴压缩模拟,并与试验结果进行对比验证。最后,对含有圆形、椭圆形、三角形、矩形和方形孔洞的层状岩石试样(β为0°、30°、45°、60°和90°)进行单轴压缩模拟研究。研究结果表明:对于不同孔洞形状的试样,抗压强度和试样破坏程度随层理倾角的增大呈V字型变化趋势,且均在层理倾角为0°时抗压强度取得最大值,在90°时破坏程度最为严重;孔洞的存在严重削弱了试样的力学性能,且削弱幅度与孔洞形状密切相关,其中方形和圆形孔洞对抗压强度的削弱能力最弱。将含不同形状孔洞试样的破坏模式随层理倾角的变化主要分为穿层理面拉剪混合破坏(β=0°)、沿层理面与穿层理面混合拉剪破坏(β=30°)、沿层理面剪切破坏(β=45°和60°)和沿层理面拉剪劈裂破坏(β=90°)。