Kinetic Monte Carlo simulation of microalloying effect in Al-Ag alloys

The kinetic Monte Carlo method, which based on the Multi-States Ising Model, was applied to simulate the effect of microelements on the microstructural evolution of Al-Ag alloys during initial aging stage. The simulation results suggest that the microelements In, Sn and Be have a dramatic depression effect on the Ag clustering because of their strong tendency to co-existed with vacancies. There are no significant effects on the process of Ag clustering in Al-Ag alloys containing Li or Cd, because of little interaction between Li/Cd and Ag/vacancies. Microelements can influence the aging by interacting with vacancies and the atoms of precipitated composition, in which the former seems more important. In this model, ＂vacancy-locking＂ and ＂vacancy clusters＂ are two important mechanisms in the aging process.     

Monte Carlo simulation of extrusion die life

Due to the high cost of metal forming tools (especially in hot extrusion), one of the major goals in tool design is a longer service life. Estimation and prediction of tool life thus becomes critically important for performance evaluation of the tools. The two most dominant failure mechanisms for extrusion dies (solid, hollow, and semi-hollow dies all taken together) are fracture and wear. In the first part of the paper, a fracture mechanics based fatigue life prediction model is described. A similar treatment is then presented for wear-related failures. Fracture and wear usually coexist as failure modes, and final die breakdown occurs due to the mechanism that becomes dominant. Therefore, a competing fracture–wear model has been later developed to represent the complete die failure situation. Attempt has been made to correlate the stochastic nature of various fatigue and wear related die parameters to die life. Monte Carlo simulation has been used to predict the life distribution of a die for a given set of manufacturing conditions and mechanical properties. In comparison with actual life data from the industry, the simulated life yields very realistic predictions.     

晶粒长大介观尺度Monte Carlo方法实时模拟

提出了一个用于晶粒长大Monte Carlo模拟的实时计算新模型,基于该模型以及作者已提出的“择优转换原则”、“新结点再取向转换概率公式”等改进措施构建了一个Monte Carlo实时模拟程序,用于纯铝正常晶粒长大过程实时模拟。结果表明,Monte Carlo实时模拟程序有效地模拟了纯铝晶粒长大过程;实际时间treal与模拟时间tC。呈指数关系;模拟的晶粒长大速率与实际长大速率接近。     

Kinetic Monte Carlo simulation of physical vapor deposition of thin Cu film

A two-dimensional Kinetic Monte Carlo method has been developed for simulating the physical vapor deposition of thin Cu films on Cu substrate. An improved embedded atom method was used to calculate the interatomic potential and determine the diffusion barrier energy and residence time. Parameters, including incident angle,deposition rate and substrate temperature, were investigated and discussed in order to find their influences on the thin film morphology.     

一种ELC-BH钢板退火组织演变的Monte Carlo模拟

基于Monte Carlo方法所建立的退火模型,以一种含Nb的冷轧超低碳高强度烘烤硬化钢板(简称ELC-BH钢板)为研究对象,进行了退火组织演变的模拟和实验研究。结果表明:模拟结果较好地反映了ELC-BH实验板退火组织演变过程,特别是展示了回复阶段再结晶孕育期,证实了该模型的合理性和实用性;考虑升温、亚晶形成、析出相粒子等影响来进一步改进模型,可改善其实用效果。     

CAD model based virtual assembly simulation,planning and training

This paper reviews the state-of-the-art methodologies for developing computer-aided design (CAD) model based systems for assembly simulation, planning and training. Methods for CAD model generation from digital data acquisition, motion capture, assembly modeling, human–computer interface, and data exchange between a CAD system and a VR/AR system are described. Also presented is an integrated methodology for designing, planning, evaluating and testing assembly systems. The paper further describes the implementation of these methods and provides application examples of CAD model based simulation for virtual assembly prototyping, planning and training. Finally, the technology gaps and future research and development needs are discussed.     

织构诱发异常晶粒长大的Monte Carlo模拟

利用欧拉角表示晶粒取向的Monte Carlo方法,模拟了异常晶粒长大过程。通过Voronoi模型产生了晶粒尺寸近似符合Lognormal分布且具有立方织构的初始组织,比较了该组织中不同织构半峰宽和体积分数对晶粒长大过程的影响。模拟结果表明:随着半峰宽变大,异常晶粒长大可能性和平均晶粒尺寸都变大;织构体积分数对异常晶粒长大的影响相对较小,只在半峰宽较小且体积分数很大时,才抑制异常晶粒长大,模拟结果与实验吻合。另外,模拟组织中平均晶粒长大速度不仅受到晶界迁移率的影响,而且受到异常晶粒长大数量的影响。     

一种基于关键特性识别的综合成本公差优化模型

当前基于制造成本与质量损失的公差优化模型缺乏对制造成本与产品质量间复杂关系的考虑以及对关键特性的控制.针对这一问题,提出一种引入制造成本与质量损失的权重系数和组成环灵敏度系数的装配公差优化模型.该模型的权重系数由设计、工艺、制造以及市场调研等相关领域专家进行评判打分确定,灵敏度系数依据关键特性识别的数学模型获取.最后以某型飞机外襟翼接头为例,验证该模型的可行性和有效性.     

A multiscale coupled Monte Carlo model to characterize microstructure evolution during hot rolling of Mo-TRIP steel

A multiscale modelling framework has been proposed to characterize microstructure evolution during hot strip rolling of transformation-induced plasticity (TRIP) steel. The modelling methodology encompasses a continuum dislocation density evolution model coupled with a lumped parameter heat transfer model which has been seamlessly integrated with a mesoscale Monte Carlo (MC) simulation technique. The dislocation density model computes the evolution of dislocation density and subsequently constitutive flow stress behaviour has been predicted and successfully validated with the published data. A lumped-parameter transient heat transfer model has been developed to calculate the average strip temperature in the time domain. The heat transfer model incorporates the effect of plastic work for different strain rates in the energy conservation formulation. A coupled initial value problem solver has been developed to integrate the system of stiff ordinary differential equations in the time domain to predict dislocation density and temperature profiles simultaneously. The temporal evolution of microstructure during hot rolling of TRIP steel is simulated by the MC method incorporating thermal and dislocation density data from the continuum models. Simulated microstructural maps, kinetics of recrystallization and grain size evolution have been generated in a 200 × 200 lattice system at different strain rates and temperatures. The simulation code has been implemented in a high-performance grid computing network. The predicted temporal evolution of grain size, recrystallized fractions and flow stress have been validated with the published literature and found to be in good agreement, confirming the predictive capability of the integrated model.     

Design and simulation of assembly systems with mobile robots

This paper proposes an approach to the design and operation of assembly systems that include mobile robots. It is based on a semantic model representing the robot/resource skills along with the operations that a resource has to execute. The method is implemented in a system capable of generating the assignment of operations to the proper robotic resources. Collision free paths can be generated for the assembly system robots with the help of simulation. The method is presented in a case study from the automotive industry.     

Kinetic Monte Carlo simulation of growth of BaTiO3 thin film via pulsed laser deposition

Considering the characteristics of perovskite structure, a kinetic Monte Carlo（KMC） model, in which Born-Mayer- Huggins（BMH） potential was introduced to calculate the interatomic interactions and the bonding ratio was defined to reflect the crystallinity, was developed to simulate the growth of BaTiO3 thin film via pulsed laser deposition（PLD）. Not only the atoms deposition and adatoms diffusion, but also the bonding of adatoms were considered distinguishing with the traditional algorithm. The effects of substrate temperature, laser pulse repetition rate and incident kinetic energy on BaTiO3 thin film growth were investigated at submonolayer regime. The results show that the island density decreases and the bonding ratio increases with the increase of substrate temperature from 700 to 850 K. With the laser pulse repetition rate increasing, the island density decreases while the bonding ratio increases. With the incident kinetic energy increasing, the island density decreases except 6.2 eV〈Ek〈9.6 eV, and the bonding ratio increases at Ek〈9.6 eV. The simulation results were discussed compared with the previous experimental results.     

Atomic-scale structure of α-FeOOH containing chromium by anomalous X-ray scattering coupled with reverse Monte Carlo simulation

Quantitative X-ray structural analysis by applying anomalous X-ray scattering (AXS) has been used for characterizing the effect of chromium on the atomic-scale structure of α-FeOOH particles, which is a typical ferric oxyhydroxide in rust formed on the steel surface. The X-ray diffraction profiles showed that the fundamental structure of α-FeOOH containing chromium is similar to that of α-FeOOH particles without chromium. The realistic atomic-scale structures in α-FeOOH with and without chromium were estimated by fitting both the ordinary and environmental interference functions with model calculation using the reverse Monte Carlo (RMC) simulation technique. The results indicated that distortion of the linkage of FeO₆ octahedral structural units in α-FeOOH is induced by chromium addition, but chromium addition to α-FeOOH fundamentally is likely to be substituted for iron in α-FeOOH. The atomic-scale arrangements in α-FeOOH with and without chromium were visualized using FeO₆ octahedral units. These middle range ordering structures were correlated with the microscopic morphological change of particles by chromium addition.     

Monte Carlo simulation of stress corrosion cracking on a smooth surface of sensitized stainless steel type 304

Stress corrosion cracking (SCC) on a smooth surface of structural metal materials occurs by initiation and coalescence of micro cracks, subcritical crack propagation and multiple large crack formation or final failure under combination of material, stress and corrosive environment. In this paper, a Monte Carlo simulation of the SCC process is proposed based on stochastic properties for micro crack initiation and concepts in fracture mechanics for crack coalescence and propagation. The procedure is as follows: The possible number of grain-sized micro cracks which can be initiated is set for a given space and initiation times for all cracks are assigned by random numbers based on exponential distribution. Sites and sizes of cracks are assigned by uniform random numbers and normal random numbers, respectively. Coalescence and propagation of cracks are determined based on fracture mechanics. The emphasis in the model is put on the influence of semi-elliptical surface cracks. Numerical simulations are carried out based on the results of creviced-bent-beam tests for sensitized stainless steel type 304 under high-temperature and high-purity water containing dissolved oxygen and the influence of micro crack initiation rate and coalescence condition on the simulation results is discussed.     

基于蒙特卡洛的模糊层次分析法在埋地管线腐蚀影响因素分析中的应用

针对埋地管线风险评估,结合管线外腐蚀影响因素众多的特点,确定出影响管线外腐蚀的十八个基本因素,建立了外腐蚀影响因素的层次结构图.应用基于蒙特卡洛的模糊层次分析法对这些影响因素进行定量分析,明确界定出这些腐蚀影响因素的相对权重,为今后制定埋地管线外腐蚀的防护措施提供参考.     

A calibrated Monte Carlo approach to quantify the impacts of misorientation and different driving forces on texture development

A calibrated Monte Carlo (cMC) approach, which quantifies grain boundary kinetics within a generic setting, is presented. The influence of misorientation is captured by adding a scaling coefficient in the spin flipping probability equation, while the contribution of different driving forces is weighted using a partition function. The calibration process relies on the established parametric links between Monte Carlo (MC) and sharp-interface models. The cMC algorithm quantifies microstructural evolution under complex thermomechanical environments and remedies some of the difficulties associated with conventional MC models. After validation, the cMC approach is applied to quantify the texture development of polycrystalline materials with influences of misorientation and inhomogeneous bulk energy across grain boundaries. The results are in good agreement with theory and experiments.     

焊接热影响区微观结构演化的蒙特卡罗计算机模拟方法

焊接热影响区是影响焊接性能的主要区域。焊接热影响区的晶粒长大常常导致焊接热影响区成为性能薄弱的环节,对焊接热影响区晶粒长大的研究一直是焊接接头的重要研究课题。焊接热影响区微观结构演化与诸多因素密切相关,是一个复杂的过程。运用适当的计算机方法进行模拟,完成对晶粒生长的完全预测,具有重要的意义,可以为优化焊接工艺参数,提高焊接质量提供依据。在此对在模拟焊接热影响区微观结构的演化时采用的基本方法进行综述。     

微量杂质对高纯铝再结晶影响的Monte Carlo模拟

将微量杂质对再结晶的阻碍作用转化为再结晶自由能变化,从而建立微量杂质作用下的能量转化模型。采用Monte Carlo方法实现能量转化模型的数值模拟,结果表明,微量杂质元素含量的波动对再结晶晶粒长大的影响很大。并与高纯铝实验结果进行了对比,对比表明模拟结果与实验结果很吻合。     

蒙特卡罗模拟和实验验证纳米薄膜晶粒生长的厚度效应

利用各向异性的蒙特卡罗方法模拟了纳米薄膜在退火过程中的晶粒生长。模拟结果显示,纳米薄膜的厚度效应并非体现在晶粒生长的整个过程中,而是仅当平均晶粒尺寸达到厚度的0.8～1.2倍时才明显表现出来。为描述这种晶粒生长的动力学过程,需要对Burke方程添加一个与晶粒平均尺寸和薄膜厚度之比相关的因子进行修正。Ni/SiO2纳米多层薄膜晶粒生长的试验结果证明了修正方程的合理性。通过比较溶质拖曳、第二相拖曳和厚度效应的动力学方程,提出了一个更为普遍适用的动力学方程。