共查询到19条相似文献,搜索用时 266 毫秒
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基于DEFORM反传热模型表面换热系数的确定 总被引:1,自引:0,他引:1
以7075铝合金厚板淬火过程为对象,研究DEFORM反传热模型中控制参数对表面换热系数计算和温度预测精度的影响规律。结果表明,当选择实测温度曲线上的拐点温度作为温度控制点,且表面换热系数初始值接近平均换热系数时,采用反传热模型确定的表面换热系数所预测的冷却曲线与实测曲线吻合较好。在此基础上选取合理的控制参数,并确定了7075铝合金厚板淬火过程的表面换热系数,经冷却曲线预测结果与实测值对比表明,采用DEFORM反传热模型确定的表面换热系数所预测的温度场有较高精度,可以满足工程应用需要。 相似文献
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为了确定中厚板辊式淬火过程中的最佳换热系数,进行了12MnNiVR钢板淬火过程中的温度场和应力场计算.依据温度场分析提出了中厚板在淬火机高压区内淬火过程中换热系数的确定方法,并用该方法确定了不同厚度12MnNiVR钢板在高压区淬火的换热系数.应力场分析表明,在低压区采用低的换热系数,可显著降低钢板淬火过程中产生的热应力及残余应力.20mm厚12MnNiVR钢板低压区淬火,平均换热系数确定为1 kW/(m2·K),与采用8 kW/(m2·K)相比,钢板表面残余压应力与中心残余拉应力的差值可降低181.2 MPa. 相似文献
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采用改进型Jominy样品精确测定7B50合金厚板喷水淬火时样品内部的温度场(冷却曲线),并利用JMat Pro软件获得7B50合金热物性参数随温度的变化关系。以反传热原理为基础,采用ProCAST有限元软件计算得到喷水淬火时淬火表面的综合表面换热系数的变化规律。结果表明:喷水淬火时,距淬火表面6 mm处,淬火敏感温度区间(420~230°C)内的平均冷却速率为45.78°C/s;喷水淬火开始0.4 s时,综合表面换热系数达到峰值69 kW/(m~2·K),此时对应的淬火表面温度为160°C;喷水淬火初期,淬火表面中心的冷却曲线上出现"温度平台"现象,平台对应的温度范围为160~170°C,持续时间约为3 s;在温度平台持续期间,淬火表面的换热机制从核态沸腾阶段转变为对流换热阶段。 相似文献
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《热加工工艺》2020,(18)
为了测量7A85铝合金表面换热系数以及优化反传热法计算表面换热系数的偏差,利用精密测温仪(GL900)对7A85铝合金片状试样进行了淬火冷却曲线测量,测量点A和B距端面间距为20 mm和40 mm。使用激光导热仪测量了在30~500℃之间试样的比热容,并进行了线性拟合。随后通过有限差分法外推得到端面冷却曲线,进而计算出表面换热系数。结果表明,使用室温比热容数据计算得到的端面淬火冷却曲线比实际曲线高,使用线性拟合后的比热容计算得到的端面淬火温度更准确。7A85铝合金端面换热系数随着温度降低,先增大后出现波动段,最终降低,在270℃时的最大表面换热系数为2250 W·m-2·℃-1。 相似文献
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不同冷却方式下换热系数的测量与计算 总被引:9,自引:0,他引:9
为了研究不同冷却方式下的换热系数,设计了一套可以测量空冷、水淬以及不同压力下喷气淬火下冷却曲线的试验装置,试验中测量的探头采用120mm×120mm×20mm奥氏体不锈钢方板。该探头经有限元(FEM)计算验证了其一维传热特性后,用来测量上述几种冷却方式下的冷却曲线,并用反传热法(IHCM)和集中热容法(LHCM)进行换热系数的计算与分析,比较了不同压力下喷气淬火的换热系数。实验结果表明,当毕欧数Bi<0.1时集中热容法是适用的,反之则不适用;在喷气淬火时,压力越大,表面换热系数也越大。 相似文献
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通过淬火实验获得6061铝合金的冷却曲线,实验根据冷却曲线并结合数值方法获得在线淬火换热系数,运用ABAQUS有限元软件动态模拟复杂截面型材在线淬火过程。结果表明:在淬火过程中,换热系数不断变化;型材不同部位冷却速度不同,并通过淬火实验加以验证。通过ABAQUS有限元软件可以预测型材的最大残余应力;通过关键点的分析得出型材温度与应力的关系曲线。 相似文献
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基于固态相变解析模型,提出推导非等温固态相变的转变分数的新解析方法。该方法将转变起始温度和精确的温度积分引入到解析模型,从而得到扩展的解析模型。计算表明,扩展的解析模型能够准确地预测计算得到的转变分数与转变速率。扩展的解析模型与原有解析模型相比,它能够更加准确地描述相变过程的动力学行为。在转变初始温度较高的情况下,扩展的解析模型具有优越性。同时,从扩展的解析模型得到的动力学参数比原有解析模型的更合理、准确。 相似文献
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Heming Cheng Xieqing Huang Jiang Fan Honggang Wang 《Metals and Materials International》1999,5(5):445-450
The calculation of a temperature field has a great influence upon the analysis of thermal stresses and stains during quenching.
In this paper, a 42CrMo steel cylinder was used an example for investigation. From the TTT diagram of the 42CrMo steel, the
CCT diagram was simulated by mathematical transformation, and the volume fraction of phase constituents was calculated. The
thermal physical properties were treated as functions of temperature and the volume fraction of phase constituents. The rational
approximation was applied to the finite element method. The temperature field with phase transformation and non-linear surface
heat-transfer coefficients was calculated using this technique, which can effectively avoid oscillationin the numerical solution
for a small time step. The experimental results of the temperature field calculation coincide with the numerical solutions. 相似文献
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自然对流条件下非稳态相变过程数值模拟 总被引:5,自引:0,他引:5
利用PHOENICS软件计算流场与温度场的功能,针对金属熔化与凝固过程的特点,依据单相统一控制方程,采用焓孔隙度方法,模拟了自然对流条件下相变的过程;并用经典的金属镓熔化过程基准实验进行了验证,良好的一致性表明,该程序能可靠地用于模拟金属相变过程的温度场、流场及确定相变前沿的位置。 相似文献
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In the heat treatment of steel, uneven cooling in variably introduces residual stresses in the workpiece. These residual stresses
can combine with the thermomechanical stresses encountered in operation to cause premature fatigue failure of the material.
A prediction of the residual and thermoelastoplastic stresses developed during heat treatment would be beneficial for component
design.
In this article a numerical model is developed to predict the thermoelastoplastic and residual stresses during rapid cooling
of a long solid cylinder. The total strains developed during cooling of the cylinder comprise elastic, thermal, and plastic
strains and strains due to phase transformation. For plastic deformation an extension of Jiang’s constitutive equations developed
by Jahanian is adopted. The properties of the material are assumed to be temperature dependent and characterized by nonlinear
strain hardening.
For phase transformation two parts are considered: nucleation according to Scheil’s method and phase growth according to Johnson
and Mehl’s law. For martensitic transformation, a law established by Koisteinin and Marburger is used. Non-additivity of pearlitic
and bainitic nucleation suggested by Manning and Lorig is taken into account by means of a correction factor to Scheil’s summation
of the transition from pearlitic to bainitic.
The effect of phase transformation and temperature dependence of material properties is investigated. It is shown that by
neglecting the temperature dependency and phase transformation in numerical calculations, the results are underestimated.
The numerical results are compared with the available experimental data in the literature, and good agreement is observed. 相似文献
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贝氏体相变理论—两个一级相变耦合的模型 总被引:2,自引:0,他引:2
建立了一种贝氏体相变的Ginzburg-Landau理论模型,该模型设计了贝氏体相变的一种耦合机制,即转变过程包含两个一级相变,一个具有重构特征,另一个为位移相变。由数值计算结果,建议了一种扩散诱导形核机制及扩散伴随伴移生长机制。 相似文献
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X. LiuF. Zhong 《金属学报(英文版)》2000,13(3):901-910
1.IntroductionBainite,discoveredinsteelmorethansixdecadesago[1],nowhasbecomeanenlargedtermofphysicalmetallurgyandmateriasscience.Itcharacterisesaseriesofphase-transformationproductsformedintherangeofintermediatetemperaturenotonlyinsteelbutalsoinothernonferrousalloysystemsandeveninsomeoxideceramics[2l.Beingofgreatpracticalandtheoreticalimportance,ithasbeenextensivelyinvestigatedanddeeplyconsideredI3.However,someessentialaspectsarestillhighlycontroversialI4].Theexistingtheorlesofthetwoschools,… 相似文献
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S Jahanian 《Journal of Materials Engineering and Performance》1995,4(6):737-744
A theoretical model was developed to predict the thermoelastoplastic and residual stresses developed in a round steel bar
during induction hardening. For numerical analysis, a quasi- static, uncoupled thermoelastoplastic solution based on the hyperbolic
sine law of Tien and Richmond was formulated. The properties of the material were assumed to be temperature dependent. The
phase transformation was considered in the numerical calculation, and the results were compared with the case where phase
transformation is avoided. The cylinder was heated rapidly; once the temperature of the outer surface exceeded the transformation
temperature, the cylinder was rapidly cooled. Accordingly, in the numerical calculation, only the area at the vicinity of
the outer surface was assumed to transform to martensite. The results showed that the compressive residual stresses at the
vicinity of the outer surface were considerably higher than the tensile stresses at the center. 相似文献