宋彦琦, 李向上, 李名. A7085铝合金Ⅰ-Ⅱ复合型疲劳裂纹扩展及其数值模拟[J]. 工程科学学报, 2018, 40(12): 1510-1517. DOI: 10.13374/j.issn2095-9389.2018.12.009
引用本文: 宋彦琦, 李向上, 李名. A7085铝合金Ⅰ-Ⅱ复合型疲劳裂纹扩展及其数值模拟[J]. 工程科学学报, 2018, 40(12): 1510-1517. DOI: 10.13374/j.issn2095-9389.2018.12.009
SONG Yan-qi, LI Xiang-shang, LI Ming. Ⅰ-Ⅱ mixed-mode fatigue crack propagation of A7085 aluminum alloy and its numerical simulation[J]. Chinese Journal of Engineering, 2018, 40(12): 1510-1517. DOI: 10.13374/j.issn2095-9389.2018.12.009
Citation: SONG Yan-qi, LI Xiang-shang, LI Ming. Ⅰ-Ⅱ mixed-mode fatigue crack propagation of A7085 aluminum alloy and its numerical simulation[J]. Chinese Journal of Engineering, 2018, 40(12): 1510-1517. DOI: 10.13374/j.issn2095-9389.2018.12.009

A7085铝合金Ⅰ-Ⅱ复合型疲劳裂纹扩展及其数值模拟

Ⅰ-Ⅱ mixed-mode fatigue crack propagation of A7085 aluminum alloy and its numerical simulation

  • 摘要: 为探究不同加载角度下A7085铝合金Ⅰ-Ⅱ复合型疲劳裂纹扩展机理,在MTS疲劳试验机上采用紧凑拉伸剪切试件(CTS)对A7085铝合金进行不同加载角度的疲劳实验;用有限元分析计算不同裂纹扩展长度的裂纹尖端应力强度因子,通过七点递增多项式法对数据进行处理,计算出A7085铝合金Paris公式中的参数Cm.结果表明不同加载角度的裂纹基本沿着与外载荷垂直的方向扩展,裂纹扩展路径近似为一条直线,裂纹扩展角测量结果基本符合最大环向拉应力理论;Ⅰ-Ⅱ复合型裂纹一旦发生扩展,Ⅱ型应力强度因子K所占比例急剧减小,Ⅰ型应力强度因子K不断增大,此后K远远小于K,有效应力强度因子(KK的组合)基本等于K,相当于裂纹扩展主要受Ⅰ型应力强度因子控制,研究结果有助于对Ⅰ-Ⅱ复合型疲劳裂纹扩展机理的理解.

     

    Abstract: Compared with other types of aluminum alloys, A7085 aluminum alloy has a series of excellent properties such as high strength, high toughness, and high fatigue resistance. These advantages meet the requirements of aircraft performance; thus, A7085 aluminum alloy is widely used for fabricating aircraft components. The shell cracks in aeronautical structures are often mixed-mode cracks, i. e., comprising open type and sliding type, and they are also known as the Ⅰ-Ⅱ compound crack. It has been found that fatigue fracture is the main reason for the failure of most specimens. At present, most studies on fatigue crack are focused on mode Ⅰ crack, but the load on the specimen is usually not a single pure type Ⅰ, Ⅱ, or Ⅲ mode. It is usually a combination of these three kinds of loads. When the crack is subjected to Ⅰ-Ⅱ mixed-mode loads, its crack growth rate and crack growth path are affected by the loading conditions. To investigate the mechanism of Ⅰ-Ⅱ mixed-mode fatigue crack growth of A7085 under different loading angles, mixed-mode (Ⅰ-Ⅱ) fatigue crack growth tests were performed on compact tension shear (CTS) specimens using a servo-hydraulic fatigue testing machine. The stress intensity factor of the crack tip was calculated by finite element analysis. Furthermore, C and m in the Paris law were calculated using seven-point incremental polynomial methods. The results show that when under different loading angles, cracks will extend along the vertical direction of the external load. Moreover, the path seems to be a straight line. The results of experiments agree with the maximum tensile stress theory. Once the crack expands, type Ⅱ stress intensity factor K basical-ly remains at 0, while type Ⅰ stress intensity factor K increases gradually. The stress intensity factor amplitude is almost equal to K Ⅰ, and crack propagation is mainly controlled by K. The result is helpful to understand the mechanism of the Ⅰ-Ⅱ fatigue crack propagation.

     

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