【作者】 许宝星；

【导师】 岳珠峰；

【作者基本信息】 西北工业大学 ， 固体力学， 2007， 硕士

【摘要】 作为一种局部的非破坏的试验方法，压痕试验技术在材料力学性能的测定中已经得到了广泛的应用。本文针对当前压痕试验还没有应用于测定材料疲劳特性方面的限制，通过对多晶铜在压痕疲劳载荷作用下的行为研究，采用理论、试验和有限元模拟相结合的方法，较为系统深入的研究了多晶铜的压痕疲劳行为以及影响因素，主要取得以下几个方面的研究成果。 推导了弹性和粘弹性半无限大体压痕疲劳载荷作用下的压痕载荷—压入位移表达式。关系式揭示出弹性和粘弹性材料的压入位移是疲劳载荷时间变化的线性函数。通过与其它压头形状下的关系式对比，说明采用平压头研究压痕疲劳更具有优势。另外，粘弹性材料在疲劳载荷作用下的压痕载荷—压入位移关系式也为确定粘弹性材料弹性模量提供了一种新途径。 通过多晶铜在恒幅和变幅疲劳载荷下的压痕疲劳试验现象发现：压痕载荷—压入位移曲线存在滞后环现象，且没有发现闭合，证实了压痕疲劳中存在压痕棘轮现象。每一个疲劳加载块作用下对应的压入位移—循环数曲线都可以划分为两个阶段：瞬态增加和稳态增加阶段，证实了稳态压痕深度率的存在。 通过考虑影响多晶铜压痕疲劳的影响因素，建立了压痕疲劳与疲劳载荷幅值、均值之间的关系式。此关系式初步建立了压痕疲劳与常规疲劳之间的关系，同时，也为利用压痕疲劳试验测定材料的疲劳特性奠定了基础。 研究了多晶铜在压痕变幅疲劳作用下压痕深度的扩展行为。研究表明单纯的疲劳过载和疲劳峰值欠载可以促进压痕深度的扩展；而单纯疲劳欠载和峰值过载却对压痕深度的扩展产生了延迟作用。结论反映出压痕疲劳深度扩展与疲劳裂纹扩展之间存在相似性。 分析了压痕疲劳作用下多晶铜的横界面微观组织结构特点。揭示出多晶铜压痕疲劳深度扩展的主要机理为压头下方和压痕周围堆积处微空洞聚集以及裂纹形核扩展。且压痕疲劳深度扩展的宏观机理可以采用塑性区残余应力模型进行有效解释。更多还原

【Abstract】 Indentation experiments have been widely used to extract the mechanical properties of materials for its fast, simple, precise and non-destructive merits. However, most of them are focused on static loading conditions. In the present study, the detailed indentation fatigue behavior of polycrystalline copper under fatigue loading has been studied experimentally using the flat cylindrical indenter. The paper aims at building the relationship between the indentation fatigue testing and conventional tension -compression fatigue testing. The main conclusion can be drawn as follows:The equations on the indentation load-indentation depth have been deduced for the elastic and visco-elastic infinite body under a fatigue loading, respectively. Those equations indicate that the indentation depth varies linearly with the fatigue loading time for the flat cylindrical indenter, while it is non-linear for other indenter geometrical shapes such as spherical indenter, sharp indenter and etc. The comparison of the indentation load - indentation depth for different indenter geometrical shapes, it can be concluded that the flat cylindrical indenter has more advantages than other indenter geometrical shapes for the indentation fatigue. In addition, those equations indicate a new method to determine the elastic modulus.The indentation fatigue behavior of polycrystalline copper under the fatigue amplitude with the flat cylindrical indenter has been carried out. The experimental results show that the indentation depth - cycle curves are analogous to the conventional strain - cycle curve of uniaxial fatigue test, which has a primary stage of decaying indentation depth per cycle followed by a secondary stage of nearly constant rate of indentation depth per cycle.It is found that the steady state indentation depth per cycle is an approximate linear function of maximum indentation load (P_max) and indentation load vary (ΔP= P_max - P_min) in the log-log grid. This relationship can be given with power-law expression as an analogy equation of steady state ratcheting rate. A comparison is made between the conventional uniaxial fatigue test and indentation fatigue test for the steady state stage. It is shown that the conventional uniaxial fatigue parameters can be obtained by the indentation fatigue method.The indentation fatigue behavior of polycrystalline copper under varied fatigue更多还原