Effects of stress ratio on fatigue crack propagation properties of submicron-thick free-standing copper films
Effects of stress ratio on fatigue crack propagation properties of submicron-thick free-standing copper films
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DOI：
10.1016/j.actamat.2013.07.017
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发表时间：
2013-09
期刊：
影响因子：
9.4
通讯作者：
T. Kondo;Takahiro Imaoka;H. Hirakata;Masayuki Sakihara;K. Minoshima
中科院分区：
文献类型：
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作者：
T. Kondo;Takahiro Imaoka;H. Hirakata;Masayuki Sakihara;K. Minoshima
约中疲劳裂纹扩展的主要力学和机制。使用疲劳裂纹扩展实验在三个应力比 R= 0.1、0.5 和 0.8 下对 500 nm 厚的独立式铜膜进行亚微米级评估。疲劳裂纹从缺口根部开始，并在循环载荷作用下稳定扩展。疲劳裂纹扩展速率 (da/dN) 与应力强度因子范围 (ΔK) 的关系取决于应力比 R；da/dN 随着 R 的增加而增加。 da/dNvs 绘图。无论R如何，最大应力强度因子（Kmax）在高Kmax区域（Kmax⩾ 4.5 MPa m1/2）表现出一致的特征，表明Kmax是疲劳裂纹扩展的主导因素。在此区域中，疲劳裂纹以拉伸断裂模式扩展，与 R 值无关。疲劳裂纹尖端前方的区域因拉伸变形而塑性拉伸，导致厚度方向的颈缩变形，从而导致凿点断裂。相反，在低 Kmax 区域（Kmax< 4.5 MPa m1/2），da/dNvs.Kmax 函数随着 R 的减小而呈现较高的值；在这个区域，断裂机制取决于R。在较高的 R 值 (R= 0.8) 下，疲劳裂纹以类似于高 Kmax 区域的拉伸断裂模式扩展。另一方面，在较低的R值（R=0.1和0.5）下，出现了疲劳裂纹扩展的特征机制：在几个晶粒内，沿着Σ3孪晶边界在裂纹尖端之前形成侵入/挤压，并且疲劳裂纹优先通过侵入/挤压扩展。
The dominant mechanics and mechanisms of fatigue crack propagation in ca. 500 nm thick free-standing copper films were evaluated at the submicron level using fatigue crack propagation experiments at three stress ratios,R= 0.1, 0.5 and 0.8. Fatigue cracking initiated at the notch root and propagated stably under cyclic loading. The fatigue crack propagation rate (da/dN) vs. stress intensity factor range (ΔK) relation was dependent on the stress ratioR;da/dN, increases with increasingR. Plots of da/dNvs. the maximum stress intensity factor (Kmax) exhibited coincident features in the high-Kmaxregion (Kmax⩾ 4.5 MPa m1/2) irrespective ofR, indicating thatKmaxis the dominant factor in fatigue crack propagation. In this region, the fatigue crack propagated in tensile fracture mode irrespective of theRvalue. The region ahead of the fatigue crack tip is plastically stretched by tensile deformation, causing necking deformation in the thickness direction and consequent chisel-point fracture. In contrast, in the low-Kmaxregion (Kmax< 4.5 MPa m1/2), the da/dNvs.Kmaxfunction assumes higher values with decreasingR; in this region, the fracture mechanism depends onR. At the higherRvalue (R= 0.8), the fatigue crack propagates in the tensile fracture mode similar to that in the high-Kmaxregion. On the other hand, at the lowerRvalues (R= 0.1 and 0.5), a characteristic mechanism of fatigue crack propagation appears: within several grains, intrusions/extrusions form ahead of the crack tip along the Σ3 twin boundaries, and the fatigue crack propagates preferentially through the intrusions/extrusions.