基于晶体微观有限元方法的多相复合涂层高温摩擦应力场模拟

对高温摩擦磨损工况下多相复合涂层的热-力耦合应力场的模拟研究尚不充分。基于Voronoi多边形建立NiCr-Cr_(3)C_(2)-CaF_(2)/BaF_(2)多相复合涂层的晶体微观有限元模型,模拟复合涂层中各相的占比、分布形态和热-力学参数,求解得到热-力耦合工况下的von Mises应力和第一主应力分布。结果表明:在高温摩擦工况下,多相复合涂层的应力显著高于均匀涂层,尤其是在硬质相尖端附近易产生局部高应力区域,改善相的形态将锐角钝化能够有效缓解局部高应力现象;热-力耦合应力场与黏结相和硬质相的弹性模量密切相关,通过调节各相模量能够有效调控复合涂层的Mises应力和拉应力值。基于微观有限元方法的热-力耦合应力场模拟可为高温摩擦磨损工况下多相复合涂层的优化设计提供理论依据。

砌体填充墙RC框架基于FEAP的微观有限元分析

基于美国加州大学伯克利分校研制的有限元软件FEAP(Finite Element Analysis Program),联合应用弥散裂缝单元和离散裂缝单元,建立了砌体填充墙RC框架的精细化微观有限元模型。基于美国加州大学圣地亚哥分校UCSD的试验结果对有限元模型进行了验证,对多层砌体填充墙RC框架进行了Pushover分析,研究了填充墙的裂缝开展、刚度变化、应力发展趋势,以及填充墙与RC框架的相互作用机制,研究了砌体填充墙RC框架的失效模式和抗震性能。

基于多尺度混合有限元模型的钢框架地震时程分析

为了研究建筑结构在强震作用下的微观破坏机理以及提高建筑结构地震反应分析的精确性和可靠性,将多尺度有限元分析方法引入抗震混合试验中。根据经验将复杂结构在地震作用下表现出来的特性划分为线性,非线性以及强非线性部分,形成由宏观有限元模型模拟线性部位,微观有限元模型模拟非线性部位以及试验单元模拟用有限元单元难以模拟的强非线性部位的多尺度混合有限元模型。本文基于3层4跨Benchmark钢框架模型建立多尺度混合有限元模型进行地震反应分析。通过多尺度混合有限元模型与相应普通有限元模型之间的地震时程对比分析,验证了多尺度模型在抗震混合模拟试验中与普通有限元模型相比具有耗时相对较小同时能够得到较高精度的优越性。

金属切削过程中微观应力及宏观切削力演变规律研究

使用Python语言将Voronoi图导入ABAQUS软件,建立了二维微观切削有限元模型。考虑应变硬化效应、应变率与温度效应对切削的影响,并用Cohesive单元模拟晶粒与晶粒之间的晶界,获得了切削过程中切屑晶粒、切屑晶界和加工表面的应力变化规律。结果表明,切削过程中晶界的应力大于晶粒的应力,切屑的晶界应力大于部件的晶界应力;晶粒被挤压变得细长,切削方向上的晶界变短,非切削方向上的晶界变长。切削位置的晶界越多,切削力就相对越小,晶界越少,切削力相对越大。通过对比宏观模型的结果,推测出切削力产生波动的原因。

55NiCrMoV7模具钢锻造过程微观组织演化实验与模拟仿真

研究了55NiCrMoV7模具钢棒材镦粗和拔长过程中的微观组织演化规律。结果表明,镦粗过程中棒材心部动态再结晶体积分数达80%,而变形过渡区和死区的动态再结晶体积分数较低;拔长过程中棒材心部发生了二次动态再结晶,过渡区动态再结晶进一步发展,而死区几乎没有发生动态再结晶。基于55NiCrMoV7模具钢在变形温度850~1250℃、应变速率0.001~10 s-1下的金相组织图,建立了动态再结晶临界应变、晶粒尺寸和动力学的数学模型,并通过DEFORM-3D软件建立了棒材镦粗和拔长过程的宏微观耦合有限元模型,研究了棒材温度、应变和组织的分布规律,预测了动态再结晶晶粒尺寸和体积分数值。将预测值与实验值进行了对比,最大相对误差为11.7%。

Microstructure and mechanical behavior of Ti/Cu/Ti laminated composites produced by corrugated and flat rolling

Ti/Cu/Ti laminated composites were fabricated by corrugated rolling(CR) and flat rolling(FR) method.Microstructure and mechanical properties of CR and FR laminated composites were investigated by scanning electron microscopy, numerical simulation methods, peel and tensile examinations. The effect of CR and FR was comparatively analyzed. The results showed that the CR and FR laminated composites exhibited different effective plastic strain distributions of the Ti layer and Cu layer at the interface. The recrystallization texture, prismatic texture and pyramidal texture were developed in the Ti layer by CR, while the R-Goss texture and shear texture were developed in the Cu layer by CR. The typical deformation texture components were developed in the Ti layer and Cu layer of FR laminated composites. The CR laminated composites had higher bond strength, tensile strength and ductility.

Effect of CuO and SnO_(2) particle size on hot extrusion deformation of AgCuOSnO_(2):Finite element simulation and experimental study

The finite element model is established according to the experimental results,and then the experimental results are verified by simulation calculation.In terms of the combination of finite element analysis and experiment,the effect of particle size of CuO and SnO_(2) on the stress,strain and microstructure of AgCuOSnO_(2) composite during hot extrusion was studied.The results illustrate that with the decrease of particle size,the dispersion of the second phase increases gradually,while the possibility of“tail shrinkage”of the billet decreases continuously;cubic CuO will evolve to fibrosis,and the degree of fibrosis will increase with the decrease of the particle size and ring clusters.Specifically,the degree of fibrosis at the middle end of the billet is higher than that at the front end,the degree of fibrosis at the front end is higher than that at the back end,and the degree of fibrosis on the surface is higher than that in the core;part of CuO fibers will bend,and the degree of buckling strength is positively correlated with the size of particles and their annular clusters.Additionally,there is fiber CuO in the front and back end of the billet that are inconsistent with the extrusion direction,and the degree of difference was negatively correlated with the particle size.

Finite element analysis of stress-strain localization and distribution in Al-4.5Cu-2Mg alloy

Finite element analysis has been carried out to understand the effect of various processing routes and condition on the microscale deformation behavior of Al–4.5 Cu–2 Mg alloy. The alloy has been developed through four different routes and condition, i.e. conventional gravity casting with and without refiner, rheocasting and SIMA process. The optical microstructures of the alloy have been used to develop representative volume elements（RVEs）. Two different boundary conditions have been employed to simulate the deformation behavior of the alloy under uniaxial loading. Finally, the simulated stress-strain behavior of the alloy is compared with the experimental result. It is found that the microstructural morphology has a significant impact on stress and strain distribution and load carrying capacity. The eutectic phase always carries a higher load than the α（Al） phase. The globular α（Al） grains with thinner and uniformly distributed eutectic network provide a better stress and strain distribution. Owing to this, SIMA processed alloy has better stress and strain distribution than other processes. Finally, the simulated yield strength of the alloy is verified by experiment and they have great agreement.

Process parameter effects on microstructure and mechanical properties of tubes processed via friction assisted tube straining method

This paper investigates process parameter effects on microstructure and mechanical properties of the tubes processed via recently developed friction assisted tube straining(FATS)method.For this purpose,design of experiment was used to arrange finite element analyses and experimental tests.Numerical and experimental tests were executed by changing rotary speed,feed rate and die angle.Taguchi design results show that increasing feed rate and decreasing rotary speed enhance Zener-Hollomon(Z)parameter and decrease average grain size,while die angle has no considerable effect.Increasing Z value reduces grain size and enhances flow stress of the processed samples,while the experiment with the highest Z value refines initial microstructure from 40 to 8μm and increases flow stress by 5 times.

Penetration of the Stiffener Web to Deck Plate Weld in Orthotropic Plated Bridge Decks

This paper reports the results of experimental research the longitudinal stiffeners in an orthotropic plated bridge deck on concerning the connection between the deck plate and the web of a microscopic scale. An important number of test specimens of a weld are studied with the help of a video microscope, to detect the efficiency of the root of the weld. The second part of the paper is concerned with parametric analysis of the lack of weld penetration by using accurate finite element modelling. The results demonstrate that the weld quality often required can not always be assured, which surely has important consequence on the stresses in the weld and the fatigue resistance.

Simulation of solidification microstructure of Fe-6.5%Si alloy using cellular automaton-finite element method

3D microstructures of Fe–6.5%Si(mass fraction) alloys prepared under different cooling conditions were simulated via finite element-cellular automaton(CAFE) method. The simulated results were compared to experimental results and found to be in accordance. Variations in the temperature field and solid-liquid region, which plays important roles in determining solidification structures, were also examined under various cooling conditions. The proposed model was utilized to determine the effects of Gaussian distribution parameters to find that the lower the mean undercooling, the higher the equiaxed crystal zone ratio; also, the larger the maximum nucleation density, the smaller the grain size. The influence of superheat on solidification structure and columnar to equiaxed transition(CET) in the cast ingot was also investigated to find that decrease in superheat from 52 K to 20 K causes the equiaxed crystal zone ratio to increase from 58.13% to 65.6%, the mean gain radius to decrease from 2.102 mm to 1.871 mm, and the CET to occur ahead of schedule. To this effect, low superheat casting is beneficial to obtain finer equiaxed gains and higher equiaxed dendrite zone ratio in Fe–6.5%Si alloy cast ingots.

A Comparative Study on Linear Effective Properties Predictions of an Argillite Rock Using XFEM

The mechanical behavior of geomaterials is studied using an XFEM （extended finite element method）. Usually, the modeling of such heterogeneous material is performed either through an analytical homogenization approach, or numerically, especially for complex microstructures. For comparison, the effective properties are obtained using a classical finite element analysis （through the so-called unit cell method） and an analytical homogenization approach. The use of XFEM proposed here retains the accuracy oftbe classical finite element approach, allowing one to use meshes that do not necessarily match the physical boundaries of the material constituents. Thanks to such methods, it is then possible to study materials with complex microstructures that have non-simplified assumptions commonly used by other methods, as well as quantify the impact of such simplification. The versatility of XFEM in dealing with complex microstructures, including polycrystalline-like microstructures, is also shown through the role of shape inclusions on the overall effective properties o fan argillite rock. Voronoi representation is used to describe the complex microstructure of argillite.

Application of an acrylic vessel supported by a stainless-steel truss for the JUNO central detector

After the success of the Daya Bay experiment, the Jiangmen Underground Neutrino Observatory （JUNO） was launched to measure neutrino-mass hierarchy and oscillation parameters and to study other neutrino physics. Its central detector is set for antineutrinos from reactors, the Earth, the atmosphere, and the Sun. The main requirements of the central detector are con- tainment of 20 kt of liquid scintillator, as the target mass, and 3% energy resolution. It is about a ball-shape detector of 38.5 m with -75% coverage of PMT on its inner surface. The design of such a huge detector is a big challenge because it must meet the requirements for several different types of physics measurement and possess the feasibility and reliability in its structure and engineering, all at reasonable time and cost. One option for the JUNO central detector is a hyper-scale acrylic ball sub- merged in the water to shield the background. This paper proposes a structural scheme for such an acrylic ball that is supported by a stainless-steel truss, inspired by point-supported glass-curtain walls in civil engineering. The preliminary design of the scheme is completed and verified by finite element （FE） method using ABAQUS. FE analysis shows that the scheme can con- trol the stress level of the acrylic ball within the limit of 5 to 10 MPa, in accordance with the demand of the design objective of the central detector. The scheme is of outstanding global stability and allows various chocces on local connections. We prove that the scheme is of good feasibility and should be a reasonable option for the central detector.