铸造模拟关键热参数的反求优化及应用研究

铸造过程数值模拟技术已经得到广泛应用,想要获得准确的模拟结果,就需要输入准确的条件参数。然而,通过实验直接测量条件参数却比较困难,部分条件参数甚至无法直接测量获得。应用DOE设计方法进行重力砂铸凝固模型热物性参数敏感性实验,以实验实测温度曲线作为反算优化的初始输入条件,按热物性参数敏感性由高到低依次用ProCAST铸造模拟软件对数值模型的材料热属性、边界散热参数、界面传热系数等热物性关键参数进行反算优化,并将优化获得的热参数进行凝固模拟验证。结果表明,反算优化后的热参数可以准确匹配实测结果,达到无需直接测量而优化条件参数的目的。     

TiB2/A356复合材料薄壁零件熔模铸造研究

利用TiB2和A356热物性的文献值,根据颗粒均匀分散于基体类型复合材料热物性的计算准则确定了10％TiB2/A356铝基复合材料的热物性参数,并将其用于实际生产中某航空零件熔模铸造的数值模拟.通过浇注实验验证了数值模拟结果与实际的一致性和热物性参数的可靠性,在此基础上通过模拟与实验结合的方式改进了浇注工艺,消除了缩松缩孔缺陷,提高了铸件质量.     

铸造用型砂热物性参数研究及校正

型砂的热物性参数对铸造凝固过程数值模拟结果有很大影响,得到准确的型砂热物性参数对提升铸造数值模拟的准确性意义重大.本文通过现场试验测得了实际铸造型砂的降温曲线,在仿真模拟软件中对型砂热物性参数进行反算优化,并与现场实测的降温曲线匹配拟合,最终确定出与现场匹配的型砂热物性参数用于今后的数值模拟计算中,提升数值模拟准确性,...     

钢液导热系数对大型钢锭凝固过程的影响

数值模拟是提高大型钢锭质量、优化浇铸工艺、降低实验费用和帮助缺陷诊断分析的重要手段之一.模拟结果是否可靠很大程度上取决于数学模型假设是否合理,合金热物性参数和边界条件的设置是否准确等因素.利用ProCAST铸造模拟软件,分析了钢液导热系数对钢锭充型和凝固过程中的温度分布、凝固时间和缩孔、疏松的影响规律.结果表明,导热系数的提高显著缩短钢锭整体凝固时间,增加钢锭中心产生缺陷的可能性,因此有必要在模拟计算之前准确测量该物性参数.另外,对于在同一模具中浇铸具有不同物性参数的各类合金,该结果为了解其凝固规律提供了参考.     

AZ91D镁合金反重力铸造充型及凝固过程计算机模拟

给出了AZ91D镁合金的相关热物性参数，采用ProCAST铸造模拟软件对镁合金力学试棒反重力铸造充型与凝固过程进行了模拟，并通过反重力铸造工艺实验对模拟结果进行了验证。结果表明：铸造模拟软件ProCAST可用于镁合金铸件反重力铸造充型及凝固过程的模拟，能够提供较为准确的流场、温度场等信息，实现缺陷及其位置的预测。     

镐形截齿感应热处理后硬度组织分布的计算机模拟及实验验证

采用梅尼尔模型与有限元模拟相结合的方法,对感应热处理后截齿的硬度以及组织进行了预测预报.并对模拟结果进行了实验验证.在模拟过程中以普通加热近似处理感应加热,通过合理选择钢的热物性参数、换热系数,表明模拟结果和实验结果有很好的一致性.     

大型铸钢件热物性参数确定及在凝固模拟中的应用

为确定大型铸钢件砂型热物性参数,对17.5t铸钢试件进行了测温实验;将确定后的热物性参数应用于300t快锻机下横梁铸件凝固过程的模拟。结果表明,400℃时,砂型导热系数最小;温度大于600℃时,砂型比热随温度升高而增大的速度减小。优化设计下横梁铸件冷铁及补贴有利于补缩,可防止缩孔缩松。     

热物性对球铁件温度场数值模拟精度的影响

采用正交计算的方法研究了热物性 对球铁件凝固过程温度数值模拟精度的影响，得到了热物性值对数值模拟精度影响的主次顺序，并通过合理选到热物性值显著提高，数值模拟分析的精度。     

U75V钢轨轧制模拟物性参数的测定及研究

对U75V钢轨钢变形模拟所需物性参数进行了测定及研究。利用热模拟试验机研究了不同的温度、应变速率、应变下的变形抗力,确定了U75V钢变形抗力的数学模型。经过理论计算与试验数据的对比,发现误差较小。采用顶杆法测量了U75V钢轨钢的各个温度区间内的平均热膨胀系数;采用非稳态法测量了U75V钢的热扩散率和热导率,利用待测样品与参考样品比较的方法测量了比热容;利用动态测量方法—敲击共振法测量了U75V钢的杨氏模量、剪切模量和泊松比。这些物性参数可以为工艺计算和数值模拟提供重要参考。     

ZG30Cr06A热物性参数的测定及在铸造CAE中的应用

应用射线吸收、激光脉冲等方法测定了新型合金ZG30Cr06A的热物性参数,并应用MAGMAsofl和ABAQUS等X2AE软件对该材质柱窝零件铸造工艺进行了优化设计以及应力分布分析.CAE模拟分析结果与生产实际吻合.     

SIMULATION OF TEMPERATURE AND THERMAL STRESS FIELD IN LASER MILLING PROCESSING

The physical model of temperature field and thermal stress field are established in this paper,on which the numerical simulation with the assuming physical and laser milling parameters have been finished. The laser milling process can be explained.     

TIG arc characteristics in different atmospheres (part 1)

Summary

The physical properties of gases such as density, thermal and electrical conductivity, as well as ionisation potential, determine to a great extent the operational characteristics of welding arcs. These properties may vary widely for different gases. As a result, arc voltage, heat output, mean radius, thermal profile, performance and other parameters which influence bead geometry (shape, width and penetration) depend on the chemical composition of the shielding gas. Rather complex physical models have been proposed to explain and quantify the effects of shielding gas chemical composition on welding arc performance. The influence of arc atmosphere may also be easily predicted by empirical methods. However, only changes in arc operational parameters and weld bead geometry due to variations in gas composition appear in the literature. This article presents an optical study of the TIG welding arc, based on a digital system of image capture and welding parameter recording, during arc operation. Variations in arc aspect, dimensions and electrical parameters were observed, and the results related to the physical properties of gases and mixtures used, as well as forecasts by theoretical models.     

SIMULATION OF SOLIDIFICAFION BEHAVIOR IN SPRAY DEPOSITED PREFORM Ⅱ.Calculation Results For Al-Cu Alloy

根据本文作者提出的喷射沉积成型沉积体内的凝固模型,对典型的Ａｌ－Ｃｕ合金进行了计算分析。结果表明,工艺参数和材料的热物性对沉积体内的凝固过程有明显影响。     

雾化喷射沉积成型凝固过程模拟Ⅱ.Al-Cu合金的计算结果

根据本文作者提出的喷射沉积成型沉积体内的凝固模型,对典型的Al-Cu合金进行了计算分析结果表明,工艺参数（如沉积速率和沉积时雾化锥的温度）和材料的热物性（如界面换热系数）对沉积体内的凝固过程有明显影响在沉积热力学条件（沉积前雾化锥的热力学状态）相同的情况下,沉积表面的温度随工艺参数和材料热物性发生显著变化所以,必须以沉积表面温度的变化作为工艺控制的参考、以往提出的以沉积前雾化锥热力学状态作为工艺控制标准的原则需要重新加以考虑     

由形核过冷度研究Ga熔体原子团尺寸变化的滞后性

DSC测试表明,Ga的形核过冷度随其熔体高温保温时间的延长而增大,随熔体降温后保温时间的延长而减小,表现出明显的滞后性.通过对熔体温度与熔体中原子团尺寸之间关系的热力学和动力学研究,得到了金属熔体原子团中的原子数随温度变化的关系式,获得了确定熔体温度变化后其形核温度变化滞后幅度的方法,确定的Ga的形核温度变化滞后幅度与实验结果相吻合,其误差只有3.9%—4.8%.     

Thermal and metal transfer behaviours in pulsed current gas metal arc weld deposition of Al–Mg alloy

Abstract

The control of pulsed current gas metal arc (GMA) welding is highly critical owing to the simultaneous influence of the pulse parameters on thermal and metal transfer behaviours of the process. An analytical model has been developed to provide a theoretical understanding of the influence of pulse parameters on the behaviour of metal transfer and thermal characteristics in pulsed current GMA welding using Al–Mg filler wire. The variations in thermal and metal transfer behaviours with changes in pulse parameters have been satisfactorily analysed considering a summarised influence of pulse parameters defined by a dimensionless factor &phis; = (I _b/I _p)ft _b, proposed previously. A large number of process parameters have been considered, as a result of using four different GMA welding power sources. The hypothesis has been verified using some previously reported experimental results. The theoretical model may be useful in the control of pulse parameters to achieve desired behaviours of thermal and metal transfer under different conditions of weld fabrication, thereby facilitating more universal application of GMA welding.     

基于BP神经网络的镁合金晶粒尺寸及流变应力模型

通过等温压缩试验研究了热变形条件对AZ61B镁合金再结晶晶粒尺寸及其流变应力的影响,并采用人工神经网络方法分别建立了动态再结晶晶粒尺寸及流变应力的模型。利用反向传播算法对网络进行试探性训练研究,得到了最佳参数。结果表明,所建立的网络模型具有优良的性能,能精确预测AZ61B合金热变形条件下的再结晶晶粒尺寸及流变应力。     

Modeling of particles impacting on a rigid substrate under plasma spraying conditions

Finite-element methods have been applied for the spreading process of a ceramic liquid droplet impacting on a flat cold surface under plasma spraying conditions. The goals of the present investigation are to predict the geometrical form of the splat as a function of process parameters, such as initial temperature and velocity, and to follow the thermal field developing in the droplet up to solidification. A nonlinear finite-element procedure has been extended to model the complex physical phenomena involved in the impact process. The dynamic motion of the viscous melt in the drops as constrained by elastic surface tensions and in interaction with the developing contact with the target has been coupled to transient thermal phenomena to account for the solidification of the material. A model is used to study the impact of spherical particles of liquid ceramic of given temperature and velocity on a flat, cool rigid surface. The deformation of the splat geometry as well as the evolution of the thermal field within the splat are followed up to the final state and require adaptive discretization techniques. The proposed model can be used to correlate flattening degrees with the initial process parameters.     

凝固模拟热物性参数数据库系统的研究与开发

针对凝固模拟中热物性参数数据量大、种类多,数据查找困难、更新不便的问题,研究开发了一套热物性参数数据库系统.系统包括参数录入、数据更新、数据查询和液固相线温度计算模块,实现了对参数数据的集中有效管理.     

On cracks and delaminations of thermal barrier coatings due to indentation testing: Experimental investigations

Rockwell indentation testing as a method of establishing the interfacial fracture toughness of thermal barrier coatings is investigated. To this end, indentation tests have been systematically performed on coatings with yttria-stabilized zirconia top coat deposited by electron beam physical vapor deposition. Specimens in “as-coated” condition and after heat treatment in air have been studied. Unexpectedly, indentation of the heat-treated samples resulted in smaller delaminations than the as-coated samples, suggesting an increase in fracture toughness for coatings subjected to elevated temperatures. Careful image analyses of the cross-section of the indented area show that the ceramic top coat undergoes a complex damage evolution during indentation that is altered by thermal treatment. The consequences of this are discussed and we note that care must be taken when evaluating fracture parameters for multilayered structures based on indentation testing.