动力蓄电池包挤压失效仿真与实验

为提高动力蓄电池包挤压仿真的精度，将延性损伤准则引入到有限元仿真，通过单轴拉伸试验、纯剪切试验与缺口件拉伸试验与有限元仿真，获得了某动力蓄电池包结构所用材料6061-T6铝合金的延性损伤参数。型材三点弯曲试验、动力蓄电池包挤压试验与有限元仿真的结果表明：输入延性损伤参数的有限元仿真结果与试验结果误差小，能较为准确地模拟铝合金损伤对结构承载性能的影响；不考虑材料失效的结果与试验结果误差较大。     

A stiffness parameter and truncation error criterion for adaptive path following in structural mechanics

We explore a truncation error criterion to steer adaptive step length refinement and coarsening in incremental-iterative path following procedures, applied to problems in large-deformation structural mechanics. Elaborating on ideas proposed by Bergan and collaborators in the 1970s, we first describe an easily computable scalar stiffness parameter whose sign and rate of change provide reliable information on the local behavior and complexity of the equilibrium path. We then derive a simple scaling law that adaptively adjusts the length of the next step based on the rate of change of the stiffness parameter at previous points on the path. We show that this scaling is equivalent to keeping a local truncation error constant in each step. We demonstrate with numerical examples that our adaptive method follows a path with a significantly reduced number of points compared to an analysis with uniform step length of the same fidelity level. A comparison with Abaqus illustrates that the truncation error criterion effectively concentrates points around the smallest-scale features of the path, which is generally not possible with automatic incrementation solely based on local convergence properties.     

积分中值屈服准则解析厚板轧制椭圆速度场

为解决非线性Mises比塑性功率积分困难以及由此导致的轧制功率解析式难以获得的问题,本文通过建立并利用线性比塑性功率表达式对提出的椭圆速度场进行能量分析,得到了轧制力能参数的解析解.文中通过对变角度屈服函数求积分中值,构建了一个新的屈服准则,它是主应力分量的线性组合,在π平面上的轨迹是逼近Mises圆的等边非等角的十二边形,其基于Lode参数表达式的理论结果也与实验数据吻合较好.同时,根据厚板轧制时金属流动速度从入口到出口逐渐增大的特点,提出了水平速度分量满足椭圆方程的速度场,该速度场满足运动许可条件.通过相应的轧制能量分析,获得了基于线性屈服准则的内部变形功率以及基于应变矢量内积法上的摩擦功率与剪切功率.在此之上,通过泛函的极值变分导出了轧制力矩、轧制力以及应力状态系数的解析解,并与现场实测数据进行了对比,结果表明利用本文提出的屈服准则与速度场所建立的轧制力矩与轧制力模型与实测值吻合较好,其中轧制力误差小于5.3%,轧制力矩误差在6%左右.     

Stabilisation of stochastic differential equations driven by G-Brownian motion via aperiodically intermittent control

ABSTRACT

As an emerging field, the G-Itô stochastic calculus plays an important role in describing the model uncertainty. Many interesting works have been done on stochastic differential equations driven by G-Brownian motion (G-SDEs). Among the theories and applications of G-SDEs, the stability is the vital important one. In this paper, we investigate the stabilisation for G-SDEs based on G-Lyapunov function and aperiodically adaptive intermittent controller. As an application, the sufficient conditions are established for the stabilisation of stochastic Cohen–Grossberg neural networks driven by G-Brownian motion (G-SCGNNs). Finally, an example is provided to illustrate the obtained results.     

Hand hygiene and surface cleaning should be paired for prevention of fomite transmission

Touching contaminated surfaces might lead to the spread of pathogens, that is, the fomite transmission route. Although hand- and surface-hygiene practices are potentially important non-pharmaceutical interventions for the fomite route, the two interventions have been mostly studied separately in the literature. In this study, we develop a new conceptual model based on the law of mass action, analyze the temporal diffusion of contaminated surfaces and hands, and verify the model with simulations in an assumed norovirus outbreak in a buffet restaurant. A quantitative hygiene criterion is developed for the required frequency of surface disinfection and hand hygiene to control the fomite transmission in indoor environments. To eliminate surface contaminations, the product of pathogen-removal rates (including hygiene and natural death) on hands and surfaces must be no smaller than that of the human hand and surface contact frequency (ie, the net removal product must be non-negative). When the net removal product is negative, the number of contaminated surfaces and hands would show a logistic growth trend and finally approach the equilibrium. Our approach sheds light into how to optimize the combined use of hand hygiene and environmental decontamination for the best effectiveness under different settings.     

基于AIC信息准则的Delta T声发射源定位方法

疲劳断裂是金属结构中的主要失效形式,而金属结构中的早期疲劳断裂信号通常难以检测。TOA方法是常用的声发射定位源方法,但是声波传播过程中波速变换和路径的复杂性对其结果影响很大。运用Delta T声发射源定位方法,用断铅实验模拟声发射源,用AIC信息准则对到达时间进行优化,通过使用差值求源点坐标和图像处理的方法,求得声发射源坐标。通过在平板上的实验,比较两种源定位方法在不同结构中的定位结果,分析定位误差,结果表明图像处理方法更为优秀。     

Modeling the effects of loading scenario and thermal expansion coefficient on potential failure of cryo-compressed hydrogen vessels

A multiscale thermomechanical model for a simplified Type-3 cryogenic, compressed-hydrogen (H₂) storage vessel is described in this paper. The model accounts for the temperature-dependent elastic-plastic behavior of the vessel's carbon/epoxy composite overwrap and aluminum alloy liner. The homogenized thermo-elastic-plastic behavior for the individual laminae of the vessel layup is obtained using an incremental Eshelby-Mori-Tanaka approach associated with a micromechanical failure criterion to predict laminar failure while a standard elastic-plastic constitutive model is used to describe the behavior of the typical aluminum alloy assumed for the liner. The vessel's response to external loadings is modeled using a finite element method. Four loading scenarios, representing four thermomechanical cycles applied to the vessel, are analyzed to evaluate constituent and laminar stresses as well as the associated failure criterion during the cycle according to these scenarios. The model can provide helpful guidance to mitigate thermal stresses by selecting a suitable loading scenario, optimizing the layup, and tailoring the thermomechanical properties of the resin matrix.     

不同应力状态下的高强钢板断裂机理及预测

板料成形过程的宏观断裂行为依赖于其微观断裂机理，因此成形过程模拟中的断裂准则的准确选择对于断裂预测具有重要意义。以高强钢TRIP780板料为研究对象，设计从剪切到拉伸应力状态的五种断裂试验，结合宏观拉伸试验和扫描电子显微镜（Scanning electron microscope，SEM）分析研究不同应力状态下TRIP780板料的断裂机理，得到不同应力状态下正应力和切应力与断裂机理的关联关系，引入正应力与切应力的影响构建MMC断裂准则，应用于板料压剪应力区间的断裂行为预测。结果表明，反映断裂机理的MMC准则能适用于板料压剪和拉剪变形应力状态下断裂失效的准确预测。