DDA方法中材料本构关系的研究

发布时间：2019-06-16 15:06

【摘要】：非连续变形分析(Discontinuous Deformation Analysis,DDA)数值方法擅长模拟不连续材料体的变形破坏和大位移力学行为,它已经在岩体结构破坏失稳模拟等方面得到了广泛的应用。目前,DDA方法中采用的本构模型是线弹性本构模型,不能模拟材料的非线性应力-应变响应,这是导致计算结果不够真实的一个重要因素。本文从材料本构关系的角度出发,在DDA方法中实现了弹脆性本构模型、损伤本构模型和Johnson-Cook本构模型,从而能更好地采用DDA方法模拟不同材料的非线性应力-应变响应力学行为。首先,将岩石力学领域比较常用的弹脆性本构模型引入到DDA方法中。弹脆性本构模型参数较少,DDA实现较为简单,其实现基于DDA方法的子块体节理面开裂算法。子块体节理面开裂算法本身已经被成功应用于模拟诸多静态和动态岩石力学问题,比如巴西劈裂和凿岩爆破等。在弹脆性本构模型的应用上,模拟了方件压缩试验,并讨论了残余应力系数对模拟结果的影响。其次,从损伤角度出发,将弹性损伤本构模型引入到DDA方法中。采用不同的加载历史,模拟长杆单元模型的应力-应变关系,并与理论应力-应变曲线进行对比,从而验证损伤本构模型在DDA方法中实现的正确性。模拟了方件压缩试验,并讨论了允许开裂时的损伤值与子块体节理面开裂算法中单元开裂边数对模拟结果的影响。当允许开裂时的损伤值为0.8和开裂3条边(采用三角形划分子块体单元),模拟结果与其他数值模拟方法得到的结果最为接近。而后,将能够描述金属材料应力-应变响应的Johnson-Cook本构模型引入到DDA方法中,并将长杆单元模型的应力-应变响应模拟结果与实验结果进行对比,探讨了不同加载率条件下参考应变率的取值。在此基础上,模拟了长杆模型的拉伸试验,其结果与实验结果和有限元模拟结果较为接近。最后,将弹脆性本构模型、弹性损伤本构模型以及Johnson-Cook本构模型运用到弹体侵彻试验的DDA模拟中。与采用线弹性本构模型模拟的结果相比,发现DDA方法对弹体侵彻这类复杂力学问题的模拟能力明显提高。
[Abstract]:The numerical method of discontinuity deformation analysis (Discontinuous Deformation Analysis,DDA) is good at simulating the deformation and failure and large displacement mechanical behavior of discontinuous materials, which has been widely used in the simulation of failure and instability of rock mass structures. At present, the constitutive model used in DDA method is linear elastic constitutive model, which can not simulate the nonlinear stress-strain response of materials, which is an important factor that leads to the unreal calculation results. In this paper, the elastic-brittle constitutive model, damage constitutive model and Johnson-Cook constitutive model are realized in DDA method from the point of view of material constitutive relation, so that the nonlinear stress-strain response mechanical behavior of different materials can be better simulated by DDA method. Firstly, the elastic-brittle constitutive model, which is commonly used in rock mechanics, is introduced into DDA method. The elastic-brittle constitutive model has fewer parameters and the implementation of DDA is relatively simple. The crack algorithm of subblock joint surface based on DDA method is realized. The subblock joint cracking algorithm itself has been successfully applied to simulate many static and dynamic rock mechanics problems, such as Brazilian fracturing and rock drilling blasting. In the application of elastic-brittle constitutive model, the compression test of square parts is simulated, and the influence of residual stress coefficient on the simulation results is discussed. Secondly, from the point of view of damage, the elastic damage constitutive model is introduced into DDA method. The stress-strain relationship of the long bar element model is simulated by using different loading history and compared with the theoretical stress-strain curve to verify the correctness of the damage constitutive model in DDA method. The compression test of square parts is simulated, and the influence of the damage value of allowable cracking and the number of element cracking edges in the crack algorithm of subblock joint surface on the simulation results is discussed. When the damage value is 0.8 and the cracking three sides are allowed to crack (using triangular molecular block element), the simulation results are most close to those obtained by other numerical simulation methods. Then, the Johnson-Cook constitutive model, which can describe the stress-strain response of metal materials, is introduced into the DDA method, and the simulation results of stress-strain response of the long rod element model are compared with the experimental results, and the values of the reference strain rate under different loading rates are discussed. On this basis, the tensile test of the long bar model is simulated, and the results are close to the experimental results and the finite element simulation results. Finally, the elastic-brittle Constitutive Model, Elastic damage Constitutive Model and Johnson-Cook Constitutive Model are applied to the DDA simulation of missile penetration test. Compared with the simulation results of linear elastic constitutive model, it is found that the simulation ability of DDA method for the penetration of projectiles into such complex mechanical problems is obviously improved.
【学位授予单位】：西南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB301

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