Fe-25Mn-3Si-3Al TWIP钢等温压缩流变应力的研究

 在Gleeble-1500D热模拟试验机上采用等温压缩试验研究了高锰奥氏体Fe-25Mn-3Si-3Al TWIP钢在变形温度为900~1100℃，变形速率为0.01~1s-1条件下的热变形行为。研究结果表明，Fe-25Mn-3Si-3Al钢热变形流变应力曲线呈现明显的动态再结晶特征，出现了一个明显的流变应力峰值，峰值之后流变应力逐渐降低，呈现稳态流变。双曲正弦形式的Arrhenius方程可以较好地描述Fe-25Mn-3Si-3Al钢的热变形行为，通过线性回归分析计算出Fe-25Mn-3Si-3Al钢的热变形流变应力本构方程，得出试验钢的热变形激活能QHW为432.95kJ/mol。  

尾砂胶结充填体的破坏机理及其损伤本构方程

本文从细观力学角度，分析了尾砂胶结充填体的物理组成，单轴压缩时的破坏机理，并运用损伤力学方法建立了其本构方程。结果表明，理论曲线与实验曲线吻合得较好。  

Approximation of Nonlinear Unloading Effects in the Strain Rate Dependent Deformation Analysis of Polymer Matrix Materials Utilizing a State Variable Approach

An experimental and analytical program is carried out to explore key behaviors in the loading and unloading behavior of polymers. Specifically, the effects of strain rate and hydrostatic stresses on the nonlinear portions of the deformation response are examined. Tension, compression, and shear load only and load/unload tests are conducted on a representative polymer across a range of strain rates, and key features of the experimental results are identified. To conduct a preliminary exploration of how the key features of the deformation response could be simulated analytically, a previously developed set of constitutive equations, which were developed to analyze the strain rate dependent, nonlinear deformation of polymers including the effects of hydrostatic stresses, were modified in order to approximate key features of the nonlinear unloading behavior observed in the polymer. The constitutive relations are based on state variable constitutive equations originally developed for metals. The nonlinear unloading observed in the experiments is approximated by reducing the unloading modulus of the material as the effective inelastic strain is increased. The effects of the hydrostatic stress state on the unloading modulus are also simulated analytically. To examine the revised formulation, the loading and load/unload responses of the representative polymer in tension, compression, and shear are examined at several strain rates. Results computed using the developed constitutive equations were found to correlate reasonably well with the experimental data.  

1Cr17Ni1双相不锈钢的热变形行为及其热加工图

运用Gleeble-3800热模拟试验机研究了1Cr17Ni1马氏体-铁素体双相不锈钢在变形温度为950～1150℃、应变速率为0.1～10 s－1条件下的热压缩变形行为。运用双曲正弦函数构建了本构方程，得到了表观激活能为391.586 kJ/mol，并基于动态材料模型绘制了1Cr17Ni1钢不同应变量下的热加工图。观察变形后的组织形貌得到较低温度下发生动态回复与动态再结晶，较高温度只发生动态回复，综合热加工图与变形后组织得到最佳热变形工艺：热加工温度范围为950～1000℃、热加工变形速率范围为0.1～0.3和5～10 s－1。  

Modelling the high temperature flow behaviour of sintered Cu–28Zn pre-alloyed powder compacts considering the effect of strain

In the field of the deformation process modelling, constitutive equations tend to be utilised as a calculation basis for the estimation of the materials’ flow responses. This holds also for powder metallurgy products. Hence, in this study, the flow behaviour of sintered Cu–28Zn pre-alloyed powder compacts was investigated by a collection of isothermal hot compression tests in the temperature range of 550–850°C at strain rates of 0.001, 0.01, 0.1 and 0.5?s^?1 up to the true strain of 0.6. For the sintered part with a predefined porosity of 9.4%, the impacts of the temperature and strain rate on the deformation behaviour were shown by the Zener–Hollomon parameter in an exponent-type equation. As a result, a model was developed to predict the high temperature flow behaviour of the Cu–28Zn pre-alloyed powder compact. The results indicated that the strain-dependent constitutive equations are in good conformity with the experimental results.  

900MPa级析出强化钢高温变形行为

针对900 MPa级析出强化型热轧高强钢,利用Gleeble-3800热模拟试验机研究其在变形温度为950~1 150℃、变形速率为0.1~10 s-1条件下的压缩变形行为。根据应力-应变曲线图获得峰值应力,并用双曲正弦方程描述热压缩变形过程中的试验钢峰值应力与Zener-Hollomon参数的关系。回归分析得到方程中变形激活能及其他材料变形参数,并对试验在高温条件下的流变应力本构方程并对其进行了验证。结果表明,采用该本构方程计算出的流变应力值与试验所得应力值非常接近,为估算成形时所需的最大载荷及设备选取提供参考。  

热轧低碳钢高温变形行为与显微组织

采用 Gleeble-1500试验机对低碳钢进行热变形试验,获得了真应力-真应变曲线,进而研究了变形温度为900~1200℃,应变速率为0·1~10 s－1对材料热变形行为的影响。通过非线性回归获得了材料在不同变形条件下的材料常数,建立材料的热变形本构方程,进而分析了热变形低碳钢的微观组织演变及极限压缩率的变化规律。结果表明：基于热变形方程真应变为0·5时的热变形激活能Q为216·95 kJ/mol,利用该本构方程计算的峰值应力与试验得到的应力-应变曲线的峰值应力吻合较好；应变速率1 s－1,变形温度1100℃下的显微组织较其他温度相比都要细小、均匀,此时其极限压缩率最大可以达69％,可在此工艺条件下实现较大的塑性变形,且变形后具有较好的综合力学性能。  

20CrMnTiH钢唯象本构模型及动态再结晶行为

采用Gleeble-3800热模拟试验机对20CrMnTiH钢进行了等温热压缩试验,研究了该钢在变形温度为850~1150℃、应变速率为0.01~10 s-1条件下的高温热变形行为,运用数学回归方法和热力学不可逆原理,建立了20CrMnTiH钢应变补偿的唯象本构方程和动态再结晶模型,并对该应变补偿的唯象本构模型进行了有效验证.在真应力-真应变曲线中,变形温度和应变速率对20CrMnTiH钢的流变应力影响显著,表现出正的应变速率敏感性和负的温度敏感性;由本构模型计算得到的流变应力值与试验值两者之间有很好的相关性(R=0.97664),平均相对误差为5.5442%;在应变硬化速率与流变应力关系曲线中,利用单一参数法和求解拐点法获得了不同变形条件下动态再结晶的临界应力σc和临界应变εc值,建立了临界应力、临界应变和Zener-Hollomon参数的数学模型ε≥εc=0.0079 lnZ-0.15323,且临界应变εc随着温度补偿应变速率因子Z的增加而增加.  

Effect of Laminar Cooling on Phase Transformation Evolution in Hot Rolling Process

 In the hot rolling processes, it always uses the laminar cooling system to control the cooling of plate and get the microstructure of different constitution. To investigate the effect of temperature variation due to the cooling pattern, rolling speed and thickness of plate on the microstructure evolution, a thermal-mechanical coupled FE model has been established. A set of constitutive equations of phase transformation is implemented into the commercial FE solver MARC through the user defined subroutine CRPLAW, and the temperature field is calculated by another user defined subroutine FILM. The effect of cooling pattern, rolling speed and thickness of plate on the temperature variation is numerically studied. Furthermore, the effect of temperature variation on the evolution of each phase transformation is investigated for various cooling pattern.