摘要本实验采用 8 道次等径角挤压法来制备超细晶纯铜样品。通过测量应力应变曲线来对比 超细晶铜与粗晶铜的力学性能差异。本实验采用弹塑性断裂力学的方法解决断裂韧性问题， 并采用 DSCM 测量小样品加载线位移。通过对超细晶纯铜紧凑拉伸试样加载卸载的方法测量 柔度，从而测量裂纹扩展阻力曲线并定量的计算试样的断裂韧性。对紧凑拉伸试样断口以 及拉伸试样断口进行观察并分析。实验结果显示由于等径角挤压法产生晶粒细化使超细晶 铜的屈服强度和抗拉强度提高但是塑性变差。通过 DIC 装置测量裂纹口张开位移从而测量 材料的断裂韧性，这种方法测量误差小结果准确可靠。紧凑拉伸试样断口分为四个区域是 由应力状态造成的。74253

毕业论文关键词 断裂韧性 断裂机理 超细晶铜

毕 业 设 计 说 明 书 外 文 摘 要

Title a  study  on  the  fracture  mechanics  and  the  fracture  toughness of nanocrystalline materials

Abstract Pure copper (99。98%) was processed by Equal channel angular pressing with route Bc up to 8 passes for the synthesis of the material。 The mechanical properties of ultrafine-grained copper and coarse grained copper were compared by measuring the stress-strain curves。 In this study the fracture toughness of ultrafine-grained copper was assessed by means of elasto-plastic。The exact load-line displacement of compact test specimen was measured by using the method of DSCM。 The fracture toughness was quantitatively measured by JIC and the fracture resistance curve of UFG copper in terms of the J-Integral versus the crack extension Δa is plotted。 by measuring the experimental compliance,which is measured by the mean of load/reload sequence。The fracture surfaces of compact test specimen and tensile test specimen were observed and analysed。The results show that there is a strong increase in strength(yield and ultimate tensile strength), whereas the ductility related measures deteriorate ,due to the ECAP-processing and the connected grain-refinement。The result is accurate and reliable,which is acquired by using DIC to measure the displacement of CT specimen。 The fracture surface of the compact  tension specimen is pided into four classes,which are final fracture,stretched zone,fatigue pre-crack and lateral contraction。

Key words  fracture thoughness    fracture fracture mechanics    ultrafine-grained  copper

本科毕业设计说明书 第 I 页

目 次

1  引言 1

1。1  研究背景 1

1。2  纳米晶材料的制备 2

1。2。1 机械合金化 2

1。2。2 大塑性变形 2

1。2。3 惰性气体冷凝 2

1。2。4 电沉积 2

1。3  纳米晶材料的断裂机理 3

1。4  断裂韧性的测量方法 5

1。4。1 三点弯曲法 5

1。4。2 紧凑拉伸法 5

1。4。3 圆形紧凑拉伸法 6

1。5  断裂韧性研究现状 7

1。6  本次毕业设计探索的目标、内容和创新性