碳纤维修复管道的水压试验以及模拟验证

针对碳纤维复合材料对含缺陷管道的修复能力,专门设计了水压爆破试验:在水压试验中管道加压破裂的位置并未出现在修复区内,且修复区内管道变形量较小。接着,对加压过程进行了有限元模拟,经过模拟验证发现,两者承受的极限压力基本一致,并且在极限状态下,修复区碳纤维复合材料的应力值未超过其拉伸破坏强度。最终通过对比得出:碳纤维复合材料能有效地修复管道缺陷,恢复缺陷处的承压能力。     

低碳钢MIG焊熔滴过渡的模拟与试验研究

利用FLUENT软件模拟了低碳钢MIG焊的熔滴过渡行为,借助高速摄影系统拍摄了低碳钢MIG焊接熔滴过渡行为,分别对熔滴过渡形式、熔滴尺寸和过渡频率进行了分析,并将模拟结果与试验结果进行了对比。结果表明,焊接电流为120 A时的模拟结果为大滴过渡,不同于焊接试验的短路过渡,当焊接电流为180、220和260 A时,模拟与试验中均依次出现临界射滴过渡、射滴过渡和射流过渡。模拟结果中熔滴尺寸和过渡频率的变化趋势与焊接试验中保持一致,随着焊接电流的增大,熔滴尺寸逐渐减小,过渡频率逐渐增大。     

校正力对V形件弯曲回弹的影响

利用数值模拟方法,对V形件弯曲及卸载回弹过程进行了模拟,得到了校正力对回弹的影响规律。表明校正力的增加对回弹有很好的控制作用,但随着校正力的增加,会出现负回弹现象。进行了一系列V形件弯曲实验,并将弯曲实验的结果与数值模拟的结果进行了对比,对比结果表明,模拟值与实验值吻合良好,利用数值模拟方法可以有效地预测弯曲成形的回弹量。     

封装体中枕头效应的翘曲模拟研究

通过构建BGA封装体模型并对回流焊接过程中BGA封装体的翘曲进行模拟,采用粘弹性模型描述塑封材料随温度的变化而变化的性质,通过与实际封装体变形的测量结果对比发现,这种方法能够较好地模拟室温翘曲和回流焊中翘曲的动态演变过程,翘曲变形结果与实际测量值比较吻合。同时,对于不同的芯片堆叠方式进行了模拟对比,发现芯片与周围材料接触面积增加会导致翘曲值过大,芯片排布不对称性较高时会导致回流过程中的翘曲值变化量增大。     

铝合金薄板激光拼焊工艺及其杯突成形性能

主要研究6061铝合金激光拼焊板的工艺及成形性能,分析拼焊板在杯突试验中的成形特点以及焊缝对拼焊板的整体塑性成形的影响.杯突成形性能试验结果显示了宏观开裂发生在稍偏移焊缝中心的狭窄热影响区内;拼焊板试验杯突值低于母材杯突值;基于DYNAFORM软件数值模拟,忽略焊缝类型,仅考虑焊缝在板材上的位置.结果表明,拼焊板杯突模拟开裂容易发生在杯突顶端下沿的焊缝处,模拟结果与实际试验结果略有差异,这可能与焊缝设置有一定关系.     

快速付里叶变换在板形检测中的应用

本文简述了付里叶变换原理及其快速算法在板形检测信号处理中的应用.通过在自行研制的动态板形检测模拟试验装置上测量板带的振动信息,采用快速付里叶变换对其进行频谱分析,获得板形缺陷信息,并将分析所得结果与剖条试验中实测的板带实际板形状况对比,两者对比结果是一致的、吻合的,从而为板形检测提供了一种新方法.     

金刚石/铜复合材料导热性能的数值模拟

通过无压熔渗法制备不同金刚石颗粒粒径的金刚石/铜复合材料,研究了金刚石颗粒体积分数及粒径对复合材料导热性能的影响。采用有限元的方法对金刚石/铜复合材料导热性能进行数值模拟,建立了二维平面四颗粒及多颗粒随机分布复合材料模型,并将数值模拟结果与参考文献试验结果进行对比,同时利用激光热导仪测试了复合材料的热导率,用以验证模型的准确性。数值模拟结果表明:复合材料热导率随金刚石颗粒体积分数及粒径的增加而增加。当金刚石颗粒体积分数小于40%时,模拟结果与实验值较为吻合,在高填充下,模拟值明显高于实验值;当金刚石颗粒粒径为82.5~110μm时,模拟值与实验值较为接近。当粒径小于66μm或大于165μm时,模拟值与实验值存在一定偏差,但整体变化趋势与实验结果保持一致。     

小冲杆试验中摩擦系数及试样厚度对载荷-位移曲线及断裂位置的影响

基于Gurson弹塑性损伤理论,应用大型有限元软件ABAQUS对小冲杆试验全过程进行模拟,通过0.5mm厚试样载荷-位移曲线的模拟值与试验值对比,确保有限元模型参数的准确性,进而得出钢珠与试样间的摩擦作用对载荷-位移曲线及断裂位置的影响,以及试样厚度对断裂位置的影响。     

孔隙率对SiC_p/Al复合材料热导率影响

通过无压渗透方法制得不同孔隙率SiCp/Al复合材料,采用了有限元数值模拟方法并与实验相结合研究了孔隙率对复合材料热导率的影响,并与MEMA模型计算值进行了对比。结果表明:通过改变无压浸渗温度和时间,可以制备出2.8%~9.4%范围内可调的含孔隙复合材料;在有限元数值模拟中,当孔隙率为小于6%时,热导率下降较快,反之,下降平缓。含孔隙复合材料有限元数值模拟值和实验结果较吻合,有一定的参考价值。随着孔隙率的增大,MEMA模型计算值和有限元模拟值的偏差越大。     

锥形件一次成形凸模底部不破裂成形条件研究

针对锥形件在一次成形时凸模底部容易破裂的缺陷,分析了锥形件变形特征和成形机理,定义了锥形件一次成形中,锥壁上质点靠模位移最大点为关键点,得出了锥形件一次成形至极限条件,凸模底部不破裂的计算条件,利用Dynaform软件对锥形件一次成形进行数值模拟,将计算值与模拟值进行对比,得出相对误差,分析计算条件的适用性。利用实验验证计算值的适用性,将计算值与实验值进行对比,同时给出计算条件的修正系数,其相对误差均小于22%,修正后的计算条件对于判断凸模底部不破裂更为适用。     

3D FEM simulations and experimental validation of plastic deformation of pure aluminum deformed by ECAP and combination of ECAP and direct extrusion

Rigid-viscoplastic 3D finite element simulations (3D FEM) of the equal channel angular pressing (ECAP), the combination of ECAP + extrusion with different extrusion ratios, and direct extrusion of pure aluminum were performed and analyzed. The 3D FEM simulations were carried out to investigate the load–displacement behavior, the plastic deformation characteristics and the effective plastic strain homogeneity of Al-1080 deformed by different forming processes. The simulation results were validated by microstructure observations, microhardness distribution maps and the correlation between the effective plastic strain and the microhardness values. The 3D FEM simulations were performed successfully with a good agreement with the experimental results. The load–displacement curves and the peak load values of the 3D FEM simulations and the experimental results were close from each other. The microhardness distribution maps were in a good conformity with the effective plastic strain contours and verifying the 3D FEM simulations results. The ECAP workpiece has a higher degree of deformation homogeneity than the other deformation processes. The microhardness values were calculated based on the average effective plastic strain. The predicted microhardness values fitted the experimental results well. The microstructure observations in the longitudinal and transverse directions support the 3D FEM effective plastic strain and microhardness distributions result in different forming processes.     

Large-scale three-dimensional simulation of Ostwald ripening

Large-scale three-dimensional simulations of Ostwald ripening were carried out using a multiphase-field model for accurate and efficient computation of multiparticle diffusional interaction in order to clarify coarsening kinetics in systems with finite particle fractions. The simulations were performed on 400³ grid systems in a particle fraction range of 0.25–0.86, where the initial microstructures with 20,000–100,000 solid particles in a liquid matrix evolve into structures with 1500–3000 particles. The simulation results were carefully analyzed and compared with those from the previous simulations and experiments, which have data range relevant to the present simulation range. The present results are in excellent agreement with the simulations by Akaiwa and Voorhees at low particle volume fractions, with the recent results from the 3-D reconstruction of serial sections at high fractions and with the grain size distribution of ideal grain growth at very high fractions.     

Molecular Dynamics Study of Tension Process of Ni-Based Superalloy

To understand the atomistic mechanisms of tension failure of Ni-based superalloy,in this study,the classical molecular dynamics(MD) simulations were used to study the uniaxial tension processes of both the Ni/Ni_3 Al interface systems and the pure Ni and Ni_3 Al systems.To examine the effects of interatomic potentials,we adopted embedded atom method(EAM)and reactive force field(ReaxFF) in the MD simulations.The results of EAM simulations showed that the amorphous structures and voids formed near the interface,facilitating further crack propagation within Ni matrix.The EAM potentials also predicted that dislocations were generated and annihilated alternatively,leading to the oscillation of yielding stress during the tension process.The ReaxFF simulations predicted more amorphous formation and larger tensile strength.The atomistic understanding of the defect initiation and propagation during tension process may help to develop the strengthening strategy for controlling the defect evolution under loading.     

凝固模拟在球铁飞轮工艺优化中的应用

应用MAGMAsoft对四种不同结构球铁飞轮的不同工艺方案进行凝固模拟，根据凝固模拟结果和实际试生产铸件外观缺陷及内部缩松情况，提出不同改进工艺方案并逐个进行凝固模拟，选择最佳方案用于生产。优化后的工艺方案投入批量生产后，球铁飞轮的缩孔、缩松缺陷达到用户要求。     

Modified looping technique for remeshing of forming simulations with free surface folding

In finite element simulations of forming processes with a complex geometry, free surface folding phenomenon is likely during simulations when die design or the size of initial billet is inappropriately determined. In such cases, free surface geometry becomes so acute that mesh generation may be impossible with a conventional looping technique automatically. In order to solve this kind of problem, looping technique was modified to generate boundary elements for the acute geometry with a better mesh quality. The developed technique was implemented to the in-house bulk metal forming simulation program CAMPform and applied for forming simulations of ring gear forging and nosing in which surface folding defects occur. It was found that folding phenomenon was successfully handled with the currently developed algorithm and suitable process conditions to eliminate the free surface folding were determined through numerical simulations.     

Misorientation dependence of intrinsic grain boundary mobility: simulation and experiment

Both experimental and atomistic simulation measurements of grain boundary mobility were made as a function of temperature and boundary misorientation using the same geometry that ensures steady-state, curvature-driven boundary migration. Molecular dynamics simulations are performed using Lennard–Jones potentials on a triangular lattice. These simulations represent the first systematic study of the dependence of intrinsic grain boundary mobility on misorientation. The experiments focus on high purity Al, with 〈111〉 tilt boundaries, which are isomorphic to those examined in the simulations. Excellent agreement between simulations and experiments was obtained in almost all aspects of these studies. The boundary velocity is found to be a linear function of the curvature and the mobility is observed to be an Arrhenius function of temperature, as expected. The activation energies for boundary migration varies with misorientation by more than 40% in the simulations and 50% in the experiments. In both the simulations and experiments, the activation energies and the logarithm of the pre-exponential factor in the mobility exhibited very similar variations with misorientation, including the presence of distinct cusps at low Σ misorientations. The activation energy for boundary migration is a logarithmic function of the pre-exponential factor in the mobility, within a small misorientation range around low Σ misorientations.     

Loading path optimization of tube hydroforming process

Optimization methods along with finite element simulations were utilized to determine the optimum loading paths for closed-die and T-joint tube hydroforming processes. The objective was to produce a part with minimum thickness variation while keeping the maximum effective stress below the material ultimate stress during the forming process. In the closed-die hydroforming, the intent was also to conform the tube to the die shape whereas in the T-joint design, maximum T-branch height was sought. It is shown that utilization of optimized loading paths yields a better conformance of the part to the die shape or leads to a higher bulge height. Finite element simulations also revealed that, in an optimized loading path, the majority of the axial feed needs to be provided after the tube material yields under the applied internal pressure. These results were validated by conducting experiments on aluminum tubes where a good correlation between the experimental results and simulations were obtained.     

Monte Carlo simulation of grain growth with the full spectra of grain orientation and grain boundary energy

Monte Carlo simulations of grain growth were performed for two-dimensional polycrystals with crystallographic orientations being assigned to individual grains in terms of randomly generated Euler angles. Individual grain boundaries were characterized based on the orientation relationships of grains across them and grain boundary energies were given with a continuous function of deviation angle from the exact coincidence orientation relationships. The physical and technical significance of the conditions of the orientation change in the simulations is discussed in terms of the degree of the probablistic nature of the simulation. The simulations showed the following characteristic features: (1) the energy spectra make the grain size distribution more symmetric; (2) they make the average grain growth rate smaller; and (3) the fraction of low energy boundaries increases with grain growth. These results are discussed with respect to local boundary configurations and the nature of the present model.     

Physical and mathematical simulation of liquid steel mixing zone in one strand continuous casting tundish

This paper presents the results of computer simulations and laboratory experiments carried out to describe the formation of the transient zone during continuous casting of slabs. The facility under investigation was a one strand tundish. Computer simulations of liquid steel flow were performed using the commercial program Ansys-Fluent. For the validation of the numerical model and verification of the hydrodynamic conditions occurring in the examined tundish furniture variants, obtained from the computer simulations, a water model of the tundish was employed. During laboratory tests simulating the process of steel flowing through the tundish, step type Residence Time Distribution curves were recorded. In order to obtain a complete hydrodynamic picture in the tundish furniture variants tested, the computer simulations were performed for both isothermal and non-isothermal conditions. In order to explain the phenomena occurring in the tundish working space, the Buoyancy number (Bu) has been calculated.