5083铝合金宽应变率下拉压力学性能及其本构模型描述

发布时间：2019-01-06 05:27

【摘要】：随着5083铝合金在制造业中广泛的应用,尤其高速列车和船舶行业的发展,要求对其在高速碰撞、大塑性变形等条件下具有良好的力学性能。同时,材料的屈服应力、加工硬化率等参数也必然会在不同加载速率、温度等条件下发生改变。因此,研究分析5083铝合金在动态载荷下相关力学性能,对工程结构的设计和碰撞问题的数值计算有着重要意义。本文通过MTS材料试验机、INSTRON动态材料试验机和分离式霍普金森试验系统,针对5083铝合金材料进行准静态实验以及中、高应变率加载下的力学拉伸和压缩实验,实验得到了在较宽应变率(2×10-/s-7×103/s)下的5083铝合金应力应变曲线。实验结果表明：该材料在同一实验条件下所得到的应力应变曲线,其强化阶段的拉伸曲线总是低于压缩曲线。不同应变率下的拉伸和压缩在不同加载情况下的屈服应力基本相同,并且屈服应力随着应变率不同而有所变化,当加载应变率低于10/s时,材料的屈服应力呈现出负应变率效应,之后随着应变率的升高,屈服应力呈现出正应变率效应。进入屈服阶段之后有着较明显的幂率形式的应变硬化规律,加工硬化率随着应变率有所降低,呈典型的FCC金属特征。基于以上实验结论,本文归纳总结了近年来各种可用于描述5083铝合金冲击实验本构关系的模型,针对描述5083铝合金的动态本构关系最常用的Johnson-Cook模型(JC模型)进行改进,由于该模型并没有考虑到细观层面的损伤机理,通过分析了该类材料的动态损伤机理,并结合延性金属的损伤理论和微观断裂机理方面的研究,对5083铝合金动态软化现象在理论机理上进行了合理解释,并引入本构方程。通过实验曲线与所得模型曲线的对比,拟合良好,表明该模拟具有很好的适用性。该研究能够对该材料的工程应用提供有效的科学依据、分析模型和必要的参考。研究过程中发现,原有的Johnson-Cook本构模型虽然形式简单,物理参数较少,但由于此模型属于半经验半物理型的本构模型,缺点在于对加工硬化率随应变和应变率增加或者减少的力学行为描述不足。因此,本文对多晶FCC材料在宽应变率下的塑性流动行为进行了系统的分析,讨论5083铝合金在宽应变率下的反常屈服行为和加工硬化率降低的实验现象,产生以上现象的变形机制为两相合金元素在不同应变率下的竞争结果。基于位错动力学概念及热激活理论,并结合合金元素对金属的强化机制,引入Copley和Kear的强化模型,重构了Zerilli-Armstrong本构模型,通过对实验曲线和拟合结果的比较,证实该模型较Johnson-Cook本构模型有着更好的拟合效果。通过实验曲线和模型所得曲线的对比,该模型拟合良好,表明此模型具有更好的预测此类材料的塑性流动应力的能力。
[Abstract]:With the wide application of 5083 aluminum alloy in manufacturing industry, especially the development of high-speed train and ship industry, it is required to have good mechanical properties under the condition of high speed collision and large plastic deformation. At the same time, the yield stress, work hardening rate and other parameters will change under different loading rate and temperature. Therefore, it is of great significance to study and analyze the mechanical properties of 5083 aluminum alloy under dynamic load for the design of engineering structures and the numerical calculation of impact problems. In this paper, by means of MTS material testing machine, INSTRON dynamic material testing machine and split Hopkinson test system, the quasi-static test and mechanical tensile and compression tests of 5083 aluminum alloy under medium and high strain rate loading are carried out. The stress-strain curves of 5083 aluminum alloy were obtained at a wide strain rate (2 脳 10-/s-7 脳 103 / s). The experimental results show that the stress-strain curves obtained under the same experimental conditions are always lower than the compression curves in the strengthening stage. The yield stress of tension and compression under different strain rates is basically the same under different loading conditions, and the yield stress varies with the strain rate. When the strain rate is less than 10 / s, The yield stress of the material shows a negative strain rate effect, and then with the increase of the strain rate, the yield stress presents a positive strain rate effect. After entering the yield stage, there is a more obvious law of strain hardening in the form of power rate, and the work hardening rate decreases with the strain rate, which is typical of FCC metal. Based on the above experimental results, this paper summarizes various models that can be used to describe the constitutive relations of 5083 aluminum alloy in impact tests in recent years, and improves the Johnson-Cook model (JC model), which is the most commonly used model to describe the dynamic constitutive relations of 5083 aluminum alloy. Because the damage mechanism of meso-level is not taken into account in this model, the dynamic damage mechanism of this kind of material is analyzed, and the damage theory of ductile metal and the microscopic fracture mechanism are studied. The theory and mechanism of dynamic softening of 5083 aluminum alloy were explained and constitutive equation was introduced. The comparison between the experimental curve and the model curve shows that the simulation has good applicability. The research can provide effective scientific basis, analysis model and necessary reference for the engineering application of the material. In the course of the study, it is found that the original Johnson-Cook constitutive model is simple in form and few in physical parameters, but it belongs to the semi-empirical and semi-physical constitutive model. The drawback is that the mechanical behavior of work hardening rate increases or decreases with strain and strain rate. Therefore, the plastic flow behavior of polycrystalline FCC materials at wide strain rate is systematically analyzed, and the abnormal yield behavior of 5083 aluminum alloy at wide strain rate and the experimental phenomenon of reducing work hardening rate are discussed. The deformation mechanism of the above phenomenon is the result of competition of two-phase alloy elements at different strain rates. Based on the dislocation dynamics concept and thermal activation theory, combined with the strengthening mechanism of alloy elements, the strengthening model of Copley and Kear is introduced to reconstruct the constitutive model of Zerilli-Armstrong. The experimental curves and fitting results are compared. It is proved that this model has better fitting effect than Johnson-Cook constitutive model. By comparing the experimental curve with the curve obtained from the model, the model is fitted well, which indicates that the model has a better ability to predict the plastic flow stress of this kind of material.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG146.21

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