摘要：纳米结构材料是构成的结构单元尺度三维中有一维在纳米尺度的材料，当晶粒尺寸减小到纳米尺度时，材料硬度会显著增大，但与此同时其拉伸塑性也会变得很差。究其根本是因为纳米晶在塑性形变时缺失了传统位错滑移机制，导致应变局域化，造成断裂。经过不断尝试，人们提出了梯度纳米晶结构，通过晶粒尺寸梯度协调应变不均匀，进而展现纳米晶本身的良好的塑性。然而，至今为止学界对梯度纳米晶结构如何协调纳米晶应变局域化仍没有盖棺定论。本文采用数字图像相关这一直观、准确的非接触式测量技术，通过分析梯度纳米晶铜在不同拉伸应变下全场应变分布，得出梯度纳米晶铜表面纳米晶是通过芯部粗晶附加加工硬化产生的背应力协调其应变不均匀性的结论。

关键字 梯度纳米结构 应变不均匀协调机制 全场应变分析背应力 数字图像相关

毕业设计说明书外文摘要

Title Full Field Strain Analysis of Gradient Grain Copper

Abstract：Nano materials are defined to comprise structural units with at least one dimension of three in nanoscale. When grain Size is reduced to nanoscale, extraordinary strength will be observed in nano-grain at a cost of its tensile plasticity. Disastrous faliures in material can be ascribed to strian localization whicn is result from the absence of dislocation slip. Until recent years, Gradient Nano-grain(GNG) structure is put forward and considered universally as a favourable strategy to accommodate contradictions between strength and brittleness with its gradient grain Size. However, there is no compellent explanation about how the GNG structure coordinate different plastic strain in nanograin. So, in this particle, we resort to Digital Image Correlation Technology to analyse the Full-Field strain distribution of plastic deformation in GNG Copper. With high precision and directly sense-perceived graph, we shed valuable insight into its intrinsic mechnism and conclude that:it is back stress which plays an important role in the coordination of strain localization between nano grain layer and coarse grain layer in gradient Size grain structure. 

Keywords Gradient Nano-grain Strain Localization Strain    Coordination  Full-Field Strain Analysis  Back Stress  Digital Image Correlation

目次

1绪论 1

2二维数字图像相关(2D-DIC)系统建立 3

2.1GRID构建 3

2.2ROI选择 3

2.3单格点位移计算 4

2.3.1 INITIALGUESS 4

2.3.2 确定FACETSIZE 5

2.3.3迭代优化NCORR 5

2.4ROI格点遍历 8

2.5应变场计算 10

2.6插值显示 12

2.6.1浮点数据插值 12

2.6.2ROI跟踪 13

2.7应变场参数优化及精度验证 15

2.7.1位移场影响 15

2.7.2应变场影响 17

2.7.3实例呈现 19

3GNG-CU全场应变分析 21

3.1实验过程 21

3.1.1样品制备