【作者】 韩春光；

【导师】 黄小清；

【作者基本信息】 华南理工大学 ， 固体力学， 2011， 博士

【摘要】 泡沫金属材料作为一种新型的工程材料,具有质轻、比强度和比刚度高、比表面积大、隔音、吸能性能优异、高效散热与隔热等多种优异的物理特性,已经广泛应用于航空航天、汽车、建筑等领域。本文对开孔泡沫铝材料的拉伸性能进行了实验研究,重点研究了开孔泡沫金属材料细观结构与宏观力学性能之间的关系,深入分析了开孔泡沫金属材料变形的细观力学机制,探讨了材料非均匀性质和单元细观结构特征对材料宏观力学性能的影响,并在此基础上研究材料性能参数与本构关系,其结果及相关方法不仅能加深了解泡沫金属材料的细观破坏机理,而且还有助于促进细观力学的发展。本文的主要研究内容有:基于开孔泡沫铝试件的准静态拉伸试验,分析了开孔泡沫铝材料的准静态拉伸力学性能,探讨了泡沫金属材料的初始非均匀特性,重点研究了初始相对密度对材料在准静态拉伸过程的破坏特征的影响,观察了材料拉伸破坏的非均匀特征。通过分析各阶段材料等效弹性模量与应变的实验曲线,提出一种较简洁的开孔泡沫铝准静态拉伸经验本构关系。为了研究泡沫金属材料的非均匀特性对其拉伸力学性能的影响,本文建立了泡沫金属材料的一维拉伸等应变格子单元模型,假设格子单元的弹性模量、屈服应变与破坏应变等独立地满足Weibull分布,结合统计理论分析了单元处于不同拉伸状态下的概率大小,进而导出了准静态拉伸下开孔泡沫金属材料的多参数本构方程,可对材料拉伸破坏曲线进行合理的解释。对Gibson-Ashby空心立方体模型进行推广,通过综合考虑单元横梁挠曲与立柱拉伸变形的作用,对开孔泡沫金属材料的立方体单元模型进行了变形机制的分析,定义了空心立方体单元模型的拉伸名义屈服应变,使材料单元具有弹性-理想塑性性质,并通过引入塑性铰长度概念,确定了单元的破坏模式,建立了开孔泡沫金属材料单元的拉伸破坏应变公式,使得该模型首次能用于描述泡沫金属的拉伸破坏。通过假定Gibson-Ashby空心立方体单元模型的单元结构尺寸满足一定概率分布的方式,以表征材料的非均匀性质。进而推导了单元弹性模量、屈服应变和破坏应变的概率分布,运用细观损伤力学的方法成功地推导出适合中高孔隙率开孔泡沫金属材料在准静态拉伸条件下的本构关系。此本构关系能较好地模拟了材料从弹性到破坏的全过程。对中高孔隙率的开孔泡沫金属材料参数的概率分布函数进行了分析,分析结果表明:只有在高孔隙率下,泡沫金属材料单元的弹性模量、屈服应变、破坏应变等才满足Weibull分布。对于中孔隙率泡沫金属,它们不严格满足Weibull分布,但它们均可以找到比较理想的等效Weibull分布,并首次揭示了这些Weibull分布不是独立的。根据由细观统计模型导出的泡沫金属本构关系和单元参数的概率分布函数,推导了泡沫金属在拉伸过程中弹性单元、塑性单元和破坏单元的概率及其随泡沫金属拉伸应变的变化规律,该规律支持了我们创新性地提出用应力-应变曲线的极大曲率来定义材料宏观的屈服和破坏点的观点。更多还原

【Abstract】 As a new kind of engineering materials, metallic foam possesses various excellent physical and mechanical properties including light-weight, high specific strength and stiffness, large surface, well sound insulation, high energy-absorbing capability, and novel thermal properties etc. It has been extensively used in engineering fields such as aircraft, spacecraft, automobile, and architecture and so on. In this dissertation experimental research to investigate the tensile performances of open-celled metal form was carried out , which focusing on the relation between the meso-structures and the macro mechanical performances; The meso-mechanical mechanism of deformations was analyzed; The effects of the material heterogeneous features and the structural characteristics of meso elements on the macro mechanical performances was also researched. Based on the above studies, the relationship between material property parameters and the constitutive relation is exploited. The research results and developed methods can not only realize failure mechanism of metallic foam but also do great help on meso mechanics. The details of the research include:Based on the quasi-static tensile test, the tensile mechanical performance of open-celled aluminum foams has been analyzed, and heterogeneity of the metal foam material was also studied with a focus on the impact of initial relative density upon the failure characteristics in the process of quasi-static tensile, non-uniformity of the failure in the metal foam was observed. By analyzing the experimental curves of tensile open-celled aluminum foam, this dissertation yielded a concise relation function of the open-celled foam aluminum materials under quasi-static tension.In order to investigate the heterogeneous characteristics of foam metal materials on their tensile mechanical performances, this dissertation built a one-dimension equivalent-strain grid element model to simulate metal foam, in which assuming that the elastic modulus, the yield strain, and the failure strain all meets the Weibull distribution independently. The probabilities of the elements in each tensile state were analyzed by using the statistical theory. Consequently, the multi-parameter constitutive equation of open-celled metal foam under quasi-static tension was deduced, which can rationally explain the failure curves of the tensile metal foam.By modifying Gibson-Ashby’s hollow-cubic model and synthetically considering the deformations of deflection of the beam and the tension of the column, an analysis was presented for the deformation mechanism of the cubic element model, and a tensile yield strain of the hollow-cubic element model was defined, which makes the material element possessing an elastic–perfect plastic characteristic. Further by introduced the concept of plastic hinge length, the element failure model and the failure strain were determined, which let the Gibson-Ashby be used for depict the tensile of metal foam firstly.The internal heterogeneity of the metal foam was charactered by using the element structural dimension in Gibson-Ashby model as a specific statistical distribution. Further, the probability distributions of elastic modulus, yield strain and failure strain were derived. By employing the method of statistical meso-damage mechanics, the appropriate constitute relation of medium and high porosity open-celled metal foams under quasi-static tension was successfully deduced. This constitutive relation can effectively model the whole process from elasticity to material failure.Analysis is presented for the probability distribution function of medium and high porosity open-celled foam metal materials’parameters. Results showed that, only under a higher porosity do the elastic modulus, yield strain, and the failure strain of metal foam element satisfy the Weibull distribution. For metal foams of medium porosity, though the Weibull distribution did not strictly satisfy, a perfectly equivalent Weibull distribution can always be found, which firstly indicated that and these Weibull distributions are not dependent.According to the derived constitutive relation and the probability distributions of elementparameters, the probability and its variation against tensile strain of elemet in elasticity, yielding and failure were derived, The variation supports a new view, we recommended firstly, that the yield and failure state can be defined by the maximum curevatures in the stress-strain curve.? ?更多还原