铸态GH4175合金高温变形行为及热加工图研究

目的 建立铸态GH4175合金的本构模型以预测材料变形过程中的流动应力,绘制其热加工图,用于优选铸态GH4175合金热变形的工艺参数.方法 采用Gleeble-3500热模拟压缩试验机对铸态GH4175合金试样在不同的变形温度和应变速率下进行热模拟压缩试验,获得流动应力-应变曲线.结果 GH4175合金的流动应力随变形...     

组合式冷轧支承辊热装等效应力研究

为准确计算辊套和辊芯热装等效应力,首次给出了考虑辊套和辊芯尺寸、材料物理性能参数及过盈量影响的辊套和辊芯热装径向应力计算公式,在此基础上得到了不同辊套厚度及过盈量条件下热装等效应力计算公式.为了验证该理论模型,用ANSYS软件对组合式支承辊热装过程进行了数值模拟,分析了不同辊套厚度、辊套和辊芯过盈量对结合面等效应力的影响.研究结果表明:相同过盈量及辊套厚度条件下,热装过程中周向应力约为径向应力的2倍;相同辊套厚度时,过盈量每增加0.1 mm,热装等效应力增大超过20 MPa;相同过盈量时,辊套厚度每增大100 mm,热装等效应力增大约20 MPa.     

铝带冷轧机工作辊分段冷却热辊型调控功效分析

目的研究铝带冷轧机轧辊热辊型调控功效对分段冷却流量分布的影响。方法利用ANSYS有限元软件及其APDL参数化编程语言,建立工作辊温度场和热辊型轴对称仿真模型,对轧辊温度场仿真结果和实测数据进行对比分析,对轧辊基本冷却和分段局部冷却2种模式的热辊型调控效应进行了仿真分析。结果轧辊温度场仿真模型计算结果与实测结果误差较小。热辊型调控功效分析表明,二次基本冷却模式能改善轧辊中部冷却效果,减少板边处轧辊局部冷却能有效改善板边处轧辊的温降,得到了二肋浪位置附近喷嘴对二肋浪处热辊型的调控效应系数相对比例。结论热辊型调控功效分析研究结果为二肋浪等局部板形控制的分段冷却流量的确定提供了依据。     

复合包套轧制工艺对难变形高温合金GH720Li组织的影响

研究了复合包套轧制工艺对难变形高温合金GH720Li组织的影响.结果表明:采用复合包套变形可以有效控制合金的轧制温度,减少轧辊与钢锭的摩擦力,改善难变形合金的表面质量及变形组织均匀性,防止轧制过程开裂.随着轧制变形量的增大,铸态GH720Li合金粗大的柱状树枝晶组织充分破碎,热变形后合金轧态晶粒度为ASTM5级,一次γ′相尺寸约为0.46μm,同时消除了低倍粗晶现象.经过热处理后GH720Li合金晶粒度为ASTM4级,改善了强化相γ′相的大小、数量及其分布状态,获得了良好的力学性能.     

轧辊辊型曲线的计算机辅助设计

用影响函数法确定普通四辊轧机辊系的弹性变形,用有限单元法确定工作辊的热凸度,在此基础上耦合求解轧辊原始辊型曲线,与现场使用的辊型曲线对比表明:该法能较准确地快速确定轧辊的原始辊型.     

关于铝带铸轧机轧辊制造问题的探究

本文以铝带铸轧机轧辊制造问题为题,主要针对辊套与辊芯的选材、加工制造、装配以及使用的整个工程进行分析探讨,希望对铝加工厂的生产与加工有借鉴作用。     

不同轧辊尺寸下40Cr/Q345双金属环件成形过程有限元分析

目的 研究不同轧辊尺寸对40Cr/Q345双金属复合环件热辗扩成形过程的影响规律,并分析环件在辗扩变形过程中内、外层区域的协调变形机理,使辗扩完成后的双金属环件整体变形和温度分布趋于均匀。方法 基于ABAQUS有限元模拟软件,使用动态显式算法,建立双金属环件径-轴向轧制三维热-力耦合有限元模型,采用直径为70、90、110、130、150、170 mm的芯辊尺寸和直径为400、500、600、700、800 mm的驱动辊尺寸,分别研究两个主要的成形辊尺寸对双金属环件热辗扩成形过程的影响。结果 在研究的轧辊尺寸范围内,随着芯辊直径的减小,双金属环件整体温度分布趋于均匀,其变形均匀性明显提高,其中,环件外层40Cr金属塑性变形明显降低,内层Q345金属塑性变形显著升高;随着驱动辊直径的增大,环件整体温度分布均匀性有所降低,变形均匀性略有提高。结论 在双金属环件热辗扩成形过程中,较小的芯辊尺寸能够提高环件整体的温度分布均匀性,并能有效提高内层Q345金属的塑性变形程度,使环件整体变形更加均匀。较大的驱动辊尺寸会略微降低环件的温度分布均匀性,并通过改变内、外层金属的塑性变形程度使环件整体变形趋...     

不锈钢热连轧机粗轧支持辊剥落影响因素的有限元分析

该文分析某2250不锈钢热连轧粗轧机频繁发生支持辊严重边部剥落难题的影响因素。通过理论及实际剥落断口形貌分析,指出世界上不锈钢产量最大的该生产线复杂轧制工艺条件和服役期内辊系力学行为引起的不均匀辊间接触压应力分布是该轧机轧制过程中轧辊剥落的主要原因。根据现场跟踪实测数据,采用大型通用有限元软件建立了四辊轧机辊系三维有限元模型,仿真分析了带钢宽度、轧制力、轧辊磨损对辊间接触压应力峰值和位置的影响。结果表明:随着带钢宽度和轧制力的增大,辊间接触压力峰值增幅明显,辊间接触压力分布不均匀度系数基本不变;在不同磨损阶段,当工作辊和支持辊都处于服役后期时,压力峰值、不均匀度系数显著增大,均在距轧辊辊身边部附近存在接触压应力尖峰,且此位置与实际剥落位置一致。研究结果为成功研制的新支持辊形技术投入长期稳定工业应用累计轧制600万t以上未再发生剥落提供了理论依据。     

铸态AZ80A 镁合金热加工图及高温变形行为研究

目的采用Instron5500R热模拟试验机,研究铸态AZ80A镁合金在变形温度为270~410℃、应变速率为0.001~0.5 s-1条件下的热加工图及高温变形行为。方法利用双曲正弦本构函数模型描述了铸态AZ80A镁合金的高温变形行为,计算获得了该合金的变形激活能,构建了应变量为0.3和0.6时的热加工图。结果得到了合金热变形本构模型及加工图,变形激活能为203.5k J/mol,确定了应变为0.3和0.6时的动态回复区域为与动态再结晶区域。结论铸态AZ80A镁合金在330~380℃,0.001~0.01 s-1时发生了动态结晶,这是该合金最佳的热加工工艺参数范围。     

铝/钢轧制复合有限元二次开发模拟与实验研究

目的 针对铝/钢两种金属性能差异大,轧制复合存在严重的变形不协调及结合强度低的问题,研究轧辊同径与异径及单辊驱动对复合板协调变形及结合强度的影响.方法 通过有限元二次开发进行模拟建模,并结合同步和异步轧制实验分析板翘曲机理.结果 与铝板接触的轧辊作为主驱动辊可使板变形更协调且结合强度更高,变形翘曲度为0.048,结合强度为34.2 MPa.结论 采用接触铝侧轧辊单侧驱动,双金属界面实现复合的位置更靠近轧辊出口,复合后的双金属界面间的剪应力和所受弯矩较小,制备的铝/钢复合板变形协调性更好,且结合强度更高.     

High performance 3D-analysis of thermo-mechanically loaded composite structures

This paper considers the analysis of composite structures, simultaneously loaded by mechanical and thermal loads, as often found in aerospace applications. Typically a thermal analysis providing the temperature field must precede the stress analysis, which has to account for thermal as well as for additional mechanical loads. Presently, thermal analyses are mostly carried out by finite difference methods or by 3D finite elements, whereas the stress analysis is usually performed by the use of shell elements. Thus, the temperature field has to be transferred from a finite difference or 3D finite element model to a shell finite element model. This process often requires lots of manual user interaction and can get very time consuming. The paper suggests an integrated analysis process which uses a shell finite element model throughout. Thermal lamination theories and related finite elements developed by the first author are used for the 3D thermal analysis. This leads to a reduction of the computing time by two orders of magnitude as compared to 3D finite elements whereas the accuracy of the results is nearly unaffected. The stress analysis is carried out using the same geometry model but with different mesh density. Interpolation between the different meshes can be accomplished automatically since both discretizations are defined on the same geometry. Standard shell elements based on the First order shear deformation theory (FSDT) provide the three in-plane stress components. A novel postprocessing scheme is adopted for determining all transverse stress components from the in-plane stresses and the temperature field. The postprocessing methodology is based on the extended 2D-method which utilizes the material law for transverse shear and the 3D equilibrium conditions. It is computationally very efficient and can be applied in conjunction with any standard finite element package. The interaction of thermal and stress analysis is demonstrated by the example of a composite wing box for a future large airliner.     

Finite Element Simulation on Thermal Fatigue of a Turbine Blade with Thermal Barrier Coatings

In this paper, a finite element model was developed for a turbine blade with thermal barrier coatings to investigate its failure behavior under cyclic thermal loading. Based on temperature and stress fields obtained from finite element simulations, dangerous regions in ceramic coating were determined in terms of the maximum principal stress criterion. The results show that damage preferentially occurs in the chamfer and rabbet of a turbine blade with thermal barrier coatings and its thermal fatigue life decreases with the increase of thermal stress induced by high service temperature.     

Inverse and centreline segregation formation in twin roll cast AZ31 magnesium alloy

Two microstructure defects formed in the twin roll cast AZ31 strips were investigated: inverse and centreline segregations. A two-dimensional finite element thermal–fluid–stress model was employed to study the thermomechanical response of the AZ31 strip during twin roll casting process. The results showed that the key parameter for centreline segregation is the mushy zone thickness at centreline. For inverse segregation, the interaction between the yy peak stress at the centreline in the mushy zone and the solidified shell on the roll surface is the determinant parameter. The modelling results suggested increasing the setback distance decreases the risk of both defects. Moreover, scaling up the caster reduces the propensity to inverse segregation but appears to have a minor effect for centreline segregation formation.     

Failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting. Part II: Thermal stress analysis by FEA

A martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting and used as a glass roller failed prematurely after six rolling campaigns. A previous fractographic investigation showed that the failure of the roll was caused by thermal stresses associated with microstructural embrittlement of the steel casting. Crack nucleation took place on the internal surface of the roll and the crack propagated by ductile intergranular mode. In the present work, the thermal stresses distribution was investigated by a thermal elastic–plastic model using finite element analysis in order to associate the crack growth with the thermal history of the roll during service. The proposed methodology based on the assessment of thermal stresses by finite element analysis together with coupled thermal–mechanical non-linear modelling and calculations using non-linear elastic–plastic fracture mechanics allowed a better understanding of the stable and unstable growth of a longitudinal crack until the premature failure of the roll during its cooling to room temperature after the sixth campaign. The stable and unstable crack growth and the thermal history of the roll (heating up, glass rolling and cooling operations during the six campaigns of the roll) could be related using the proposed calculation.     

Thermal stress dependence of magnetic hysteretic processes in core–shell nanoparticles

The control of thermal stresses in the core–shell structures is an important task in order to understand their temperature dependent magnetization processes. This paper is dedicated to a theoretical and micromagnetic study of the thermal stresses on the hysteretic processes in core–shell nanoparticles. The analytical model can predict the thermal and elastic behavior of the core–shell nanoparticle supposed to a forced cooling process. The temperature and thermal stresses values obtained by direct computation from the analytical model were used to evaluate the magneto-elastic energy of the core–shell system. A micromagnetic model was used to compute the equilibrium positions of the particle magnetization as function of the applied field. The model allows an evaluation of the increase of the particle coercive field and of the blocking temperature as an effect of the thermal stress.     

冷弯成形过程参数化仿真

为了缩减U型槽钢系列产品设计周期,可借助参数化设计实现槽钢模型分析的调整。利用有限元软件ANSYS提供的APDL语言,采用有限元方法对U型钢辊弯成形过程进行仿真,将参数化设计的思想融入有限元结构分析,实现了有限元建模和分析参数化,给出了这一方法与基本步骤。结果表明,这种方法极大地减少了有限元分析的工作量,提高了工作效率。研究表明,提出的参数化有限元法对辊弯U型槽钢实用、可行,为辊弯成形数值模拟探索出了一种高效、快捷、实用的新方法。     

基于 Deform-3 D 的汽车摆臂辊锻制坯模拟优化研究

分析了某汽车摆臂的结构,提出用铝合金棒料进行三道次辊锻制坯的工艺,采用Deform-3D软件对其辊锻制坯过程进行有限元模拟研究,用正交试验的方法对坯料温度、辊锻模预热温度和辊锻模转速的参数组合进行了优化,为此种类型摆臂的开发、设备的选择提供了理论依据。     

Thermal shock and thermal fatigue study of ceramic materials on a newly developed ascending thermal shock test equipment

A test equipment was designed to study thermal shock and thermal fatigue of ceramic materials subjected to fast heating (ascending). The equipment was designed to generate thermal stress in a test specimen by heating one surface of it by an oxy-hydrogen flame while cooling the opposite surface. The sample cracked when thermal stress exceeded its mechanical strength. The in situ crack formation was detected by an acoustic emission system coupled to the set up. The hot zone temperature was measured by an infra red pyrometer. The equipment was also designed to run thermal fatigue test cycles in automatic mode between two selected temperatures. The temperature and thermal stress distribution in the test specimen were modelled using finite element software. The effect of temperature distribution of the top and bottom surfaces on thermal stresses was studied. It was observed that the thermal stress is very sensitive to the temperature distribution on the top surface and maximum near the periphery of the top surface. This was in agreement with the experimental results in which the cracks were originated from the periphery of top surface. It was also observed that the failure temperature was higher for thicker samples.     

三辊斜轧空心减径的辊形设计及实验验证

以三辊斜轧空心减径过程中辊形对轧制过程的影响规律为研究对象,对无缝钢管三辊斜轧空心减径过程进行分析研究,建立了辊型的数学模型.利用有限元软件分析辊形曲线对成形过程的影响,并在某三辊实验轧机上进行实验分析,将实验结果与有限元模拟结果进行对比和分析.结果表明,当减径量小于10 mm时,入口锥角为2.5°的辊型对应的轧件在接近均整变形区金属流动十分平缓和均匀,轧件前端面也从三角形截面逐步变为圆截面;当减径量在14 mm左右,采用入口锥角为3.5°的辊型时轧件的质量较好.