多轴条件下基于细观结构模型的泡沫金属屈服与破坏行为研究

发布时间：2019-01-02 09:06

【摘要】：泡沫金属具有质轻、比强度高、吸能效率高等优良性能,在航空航天、交通运输和吸能减震等领域有广阔的应用前景。泡沫金属及其复合结构在应用时承受多轴复杂加载工况,发生大变形甚至破坏断裂行为,因此,多轴加载下泡沫金属屈服面和破坏面的正确表征显然十分必要。然而,由于泡沫金属多轴试验特别是多轴拉伸试验数据非常少,数据离散大,因此泡沫金属屈服面表征存在争议,而且多轴加载下泡沫金属破坏面研究几乎空白。针对这些存在的问题,本文基于3D Voronoi细观模型,采用优化的无量纲参数和被验证的基体材料参数,开展三轴等比例加载数值仿真实验,研究多轴加载条件下泡沫金属屈服和破坏行为,并定量研究相对密度、形状不规则度以及胞壁厚度分布等参数对泡沫金属屈服面和破坏面的影响。具体包括:(1)建立泡沫金属细观模型有限元模型并验证其合理性。根据泡沫铝单轴试验确定基体材料参数。采用无量纲方法探究质量缩放、单元尺寸与类型以及加载速率等参数对计算精度和效率的影响,并推荐了优化的无量纲参数,这些参数对类似的Voronoi细观结构的非线性数值分析具有一定的参考价值。(2)提出适合泡沫金属三轴加载的初始屈服判据。基于能量观点,综合考虑多轴加载下不同荷载的影响以及单轴加载屈服条件,选取单轴压缩屈服状态(0.2%塑性应变)的无量纲塑性耗散功作为初始屈服判据。该判据避免采用单一等效应力或静水压定义屈服状态,更加合理地确定出泡沫金属多轴加载初始屈服点。(3)开展三轴等比例数值仿真实验,研究多轴加载泡沫金属屈服面特性。根据屈服面的拉伸压缩不对称性,提出双参数(单轴压缩和拉伸屈服强度)归一化方法,发现归一化的屈服面不受相对密度影响。并定量研究了相对密度、形状不规则度以及胞壁厚度分布等参数对泡沫金属屈服面和归一化屈服面的影响。(4)研究多轴加载泡沫金属破坏面特性。提出峰值应力破坏判据,进行应力表征破坏面的研究,定量分析了相对密度、形状不规则度及胞壁厚度分布等参数对泡沫金属破坏面的影响。初步探究了应力三轴度对破坏时等效塑性应变的影响。
[Abstract]:Foamed metal has many excellent properties, such as light weight, high specific strength, high energy absorption efficiency and so on. It has a broad application prospect in aerospace, transportation and energy absorption and shock absorption. The foam metal and its composite structure are subjected to complex multiaxial loading conditions, resulting in large deformation and even fracture behavior. Therefore, it is necessary to characterize the yield surface and failure surface of foam metal under multiaxial loading. However, because the data of multiaxial test, especially the multiaxial tensile test, are very few and the data are discrete, the characterization of foam metal yield surface is controversial, and the study on the failure surface of foam metal under multiaxial loading is almost blank. Aiming at these problems, based on 3D Voronoi mesoscopic model, the optimized dimensionless parameters and the verified matrix material parameters are adopted to carry out the numerical simulation experiment of triaxial and equal proportion loading. The yield and failure behaviors of foam metals under multiaxial loading were studied. The effects of relative density, shape irregularity and cell wall thickness distribution on the yield and failure surfaces of foam metals were studied quantitatively. The main contents are as follows: (1) the finite element model of foam metal meso model is established and its rationality is verified. The matrix material parameters were determined according to the uniaxial test of aluminum foam. The dimensionless method is used to study the effects of the parameters such as mass scaling, cell size and type, loading rate on the calculation accuracy and efficiency. The optimized dimensionless parameters are recommended. These parameters have certain reference value for nonlinear numerical analysis of similar Voronoi mesoscopic structures. (2) the initial yield criterion suitable for triaxial loading of foam metals is proposed. Based on the view of energy, considering the influence of different loads under multiaxial loading and the yield condition of uniaxial loading, the dimensionless plastic dissipation work of uniaxial compression yield state (0.2% plastic strain) is selected as the initial yield criterion. The criterion avoids the use of a single equivalent stress or hydrostatic pressure to define the yield state, and determines the initial yield point of multiaxial loading of foam metal more reasonably. (3) Triaxial numerical simulation experiments are carried out. The yield surface characteristics of multiaxial loaded foam metal are studied. Based on the asymmetry of tensile compression of yield surface, a biparameter (uniaxial compression and tensile yield strength) normalization method is proposed. It is found that the normalized yield surface is not affected by relative density. The effects of relative density, shape irregularity and cell wall thickness distribution on the yield surface and normalized yield surface of foam metal were studied quantitatively. (4) the failure surface characteristics of multiaxial loaded foam metal were studied. The failure criterion of peak stress is put forward and the failure surface characterized by stress is studied. The influence of relative density, shape irregularity and cell wall thickness distribution on the failure surface of foam metal is analyzed quantitatively. The effect of triaxiality of stress on the equivalent plastic strain during failure is preliminarily investigated.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.21;TB383.4

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