基于微观结构的颗粒增强复合材料力学性能数值分析

发布时间：2018-01-06 04:33

本文关键词：基于微观结构的颗粒增强复合材料力学性能数值分析　出处：《上海交通大学》2015年博士论文　论文类型：学位论文

【摘要】：颗粒增强金属基复合材料具有高强度、高弹性模量、耐磨损和导电导热性能好等特点,广泛应用于航空航天、电子、汽车及建筑等行业。由于颗粒增强金属基复合材料最大的缺点是其延伸率和断裂韧性较低,目前先进复合材料设计研究致力于揭示微观组织对复合材料变形和破坏机制的影响规律。但是微观结构如颗粒形貌、大小、分布、含量及界面性能对复合材料整体性能影响至今还没有得到充分的了解。关于微观结构对复合材料力学性能的影响数值研究,以前三维(Three-dimensional,3D)多颗粒有限元模型分别分析了颗粒形貌、分布及界面损伤的单一或共同作用,但是都没有考虑基体中应变梯度的作用,不能考察微米尺度下复合材料中颗粒大小变化对整体性能的影响。针对上述问题,本文建立了颗粒增强复合材料3D周期性有限元分析模型,采用扩展应变梯度理论研究颗粒大小对基体中应变梯度强化影响;采用粘聚力模型模拟界面损伤对复合材料的弱化作用。首先推导了扩展应变梯度理论在有限元中的应力、应变增量更新公式,而后采用基于节点平均塑性应变计算塑性应变梯度的方法,开发编写了有限元软件Abaqus的用户子程序UMAT和URDFIL,将扩展应变梯度理论嵌入有限元中进行计算。通过和实验结果的对比证明了本文模型的正确性。然后本文建立了颗粒大小、形貌、界面强度及分布各不相同的有限元模型,以SiC颗粒增强Al基体复合材料为例,分析了微观结构变化对复合材料单轴拉伸弹塑性力学行为、颗粒/基体载荷分配、局部应力应变场分布、界面损伤起始和发展的影响规律。并且分析了颗粒大小、形貌对复合材料中热残余应力大小及分布以及热残余应力对材料在后续加载过程中的力学性能的影响。本文的数值分析表明:(1)在颗粒形貌和大小相同的情况下,界面越强,复合材料的流动应力、拉伸强度、均匀应变越高。在界面强度和颗粒形貌相同的情况下,颗粒越小复合材料的流动应力、拉伸强度和均匀应变越高。在界面强度和颗粒大小相同的情况下,颗粒形貌对均匀应变影响比较一致,都是球形颗粒材料的均匀应变较高。颗粒形貌对流动应力的影响受界面强度的影响:在弱界面的条件下,两类材料的流动应力基本一致;但在强界面条件下,立方颗粒材料中的流动应力高于球形颗粒材料。综合来讲,强界面条件下立方小颗粒增强材料的流动应力最高,强度最好;而强界面条件下球形小颗粒材料均匀应变最大,韧性最好。(2)对3D单个颗粒和多个颗粒随机分布的模型对比分析表明:对于球形颗粒增强材料,单个颗粒模型和多个颗粒模型计算得到的流动应力曲线和均匀应变的差异几乎可以忽略,因此可以用单个颗粒模型分析复合材料的性能以节省计算资源。对于立方颗粒增强材料,单个颗粒模型计算得到的流动应力低于多个颗粒模型的流动应力,主要由于单个颗粒模型假设所有颗粒界面损伤同步发生,在加载早期会高估界面中的平均损伤,导致颗粒中的平均应力水平从加载早期就明显低于多颗粒模型中的值。因此应采用多颗粒模型对立方颗粒增强复合材料性能进行评估。(3)其它情况相同时,颗粒团聚分布、层状分布和随机分布下的流动应力基本一致。但是颗粒分布状态对均匀应变的影响较大。当颗粒层状分布时,材料的均匀应变在所有分布中最小,主要是由于拉伸方向垂直于层面,界面损伤容易快速发展。与一般的实验结果不同,颗粒的团聚分布并没有对材料性能造成损伤,材料的均匀应变反而高于颗粒均匀分布时候的值。这主要是由于本文的模型没有考虑颗粒团聚分布可能带来的缺陷,如团簇内部的空隙的影响。本章的计算结果表明,相对于其他颗粒分布状态,颗粒团聚现象本身不会对复合材料性能造成损伤。(4)当复合材料从高温冷却到室温时,平均热残余应力(绝对值)的大小随颗粒尺寸的增加而增加;立方颗粒材料中的热残余应力明显高于球形颗粒材料中的值。热残余应力(应变)对复合材料弹性模量和微屈服行为影响比较大,对流动应力有微弱的影响。整体来讲,热残余应力使得材料微屈服强度降低,流动应力稍微增加,热残余塑性应变使得材料弹性模量下降。热残余应力对复合材料中的界面损伤影响很小,有或者没有热残余应力的复合材料的均匀应变非常接近。以上这些结论,对复合材料的优化设计具有重要的理论依据的意义。
[Abstract]:Particle reinforced metal matrix composite material with high strength, high elastic modulus, wear-resistant characteristics and good thermal conductivity properties, widely used in aerospace, electronics, automobile and construction industries. Because of particle reinforced metal matrix composites, the biggest drawback is its elongation and fracture toughness is low, the current research of advanced composite materials the design aims to reveal the microstructure of the composite deformation and failure mechanism of the influence law. But the microstructure such as particle morphology, size, distribution, content and interface properties of the overall performance of the composite materials still have not been fully understood. The influence of microstructure on the mechanical properties of the composites were investigated, the previous 3D (Three-dimensional 3D), the finite element model of multi particles were analyzed by particle morphology, distribution and function of single or joint interface damage, but did not consider the strain matrix Gradient, change the size of particles in the composite can not be investigated at micron scale on the overall performance. Aiming at the above problems, this paper established the particle reinforced composites 3D periodic finite element analysis model, using extended strain gradient theory of particle size on the matrix strain gradient strengthening effect; the cohesion model simulation interface weakening effect the composite material damage. Firstly, extension strain gradient theory in finite element stress, strain increment update formula, then the node average plastic strain calculation method of plastic strain gradient based on the developed finite element software Abaqus user subroutine UMAT and URDFIL, will be extended to calculate the strain gradient theory embedded finite element. By comparing with the experimental results to demonstrate the correctness of this model. Then this paper established the particle size, morphology, interface The intensity and distribution of different finite element model with SiC particle reinforced Al matrix composite materials as an example, analyzed the microstructure change of composite uniaxial tensile elastic-plastic behavior of load distribution of the particle / matrix, local stress and strain field distribution, interface damage initiation and development. The influence and analysis the particle size and morphology of the composite material thermal residual should influence the size and distribution of residual stress and thermal stress on the mechanical properties of materials in the subsequent loading process. The numerical analysis shows that: (1) in the same shape and particle size under the condition that the interface is strong, flow stress of composites the tensile strength, strain, even higher. The morphology of interfacial strength and particle under the same, the smaller the particle flow stress of composites, the tensile strength and uniform strain is high. In the interface strength and particle size under the same circumstances, a Effect of particle morphology on uniform strain is consistent, is even higher strain spherical particles. The influence of particle shape on the flow stress is affected by the interfacial strength in weak interface under the condition of two kinds of material flow stress are basically the same; but in strong interface conditions, cube in granular material flow the stress is higher than that of spherical particles. In general, the material flow stress intensity is highest, the best under the condition of strong interface cubic particles reinforced; small spherical particles and strong interface under the condition of uniform material strain is the largest, best toughness. (2) the model comparison between 3D particles and a plurality of single particle random distribution analysis showed that: for the spherical particle reinforced material, calculated by single particle model and multiple model particle flow difference of stress curve and uniform strain is almost negligible, so you can analyze properties of composite materials with single particle model To save computational resources. The cubic particle reinforced material, calculated by single particle model of flow stress is lower than a particle model of flow stress, mainly because of the single particle model assumes that all particles interface damage occur simultaneously, in the early stage of loading will overestimate the average damage in the interface, resulting in an average particle stress level from loading early is obviously lower than that of the values of the model. So the particles should adopt multi particle model of cubic particle reinforced composites to evaluate the performance. (3) other conditions are the same, the particle agglomeration distribution, layered distribution and random distribution of the flow stress are basically the same. But the effect of particle distribution on the uniform strain greatly. When when the particle layer distribution, the minimum in all materials uniform strain distribution, mainly due to the tensile direction perpendicular to the interface level, easy to damage with a like rapid development. The experimental results of different particle distribution and agglomeration caused no damage to the material properties, uniform strain material is higher than that of the particle distribution time value. This is mainly because this model does not consider the particle agglomeration distribution may be caused by defects, such as air gap clusters. The effect of this chapter the calculation results show that, compared with the other particle distribution, particle agglomeration itself does not cause damage to the properties of the composite materials. (4) when the composite cooling from high temperature to room temperature, the average thermal residual stress (absolute value) of the size increase with the increase of the particle size; thermal residual stress in the cubic granular material was significantly higher than that of spherical particles in the material the value of thermal residual stress (strain) is relatively large on the elastic modulus of composites and micro yield behavior influence on flow stress have little effect. Overall, the thermal residual stress of the material micro The yield strength is reduced, the flow stress increases slightly, the thermal residual plastic strain makes the elastic modulus decreased. The thermal residual stress is very small on the influence of interfacial damage in composite materials, with or without the thermal residual stress of the composite uniform strain is very close. These conclusions have important theoretical basis for the optimization design composite meaning.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB33

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