弯曲载荷下薄壁结构疲劳裂纹扩展性能

对某飞机座舱盖侧型材与锁环连接部位的疲劳裂纹扩展性能进行了研究。该结构区别于常见薄壁结构的特征是承受较大的弯曲载荷，使得利用薄板I型裂纹扩展的常用方法进行寿命分析会产生较大的误差。为了研究弯曲载荷下薄壁结构的疲劳裂纹扩展性能，开展了带孔板和侧型材结构模拟件的疲劳裂纹扩展试验。通过有限元仿真分析，研究了弯曲载荷对裂尖应力强度因子的影响，提出了一种当量应力强度因子变程公式；对本文所涉及的2种类型受弯曲载荷作用的试件，裂纹扩展寿命预测结果与试验吻合较好。研究表明，在相同的名义应力和裂纹长度下，薄板受弯时裂纹应力强度因子、裂纹扩展速率远低于受拉的情况；结构受到弯曲载荷时，锁环对连接部位的应力有显著的抑制作用，可以减缓疲劳裂纹的扩展；此外，合理的结构设计能够增加关键部位受弯时的疲劳裂纹扩展寿命。

Fatigue crack growth performance of thin-walled structure under bending load

The fatigue crack growth performance at the joint sites between the lockring and the side profile of the canopy in a certain aircraft is studied. The main difference of such structure from other common thin-walled structures lies in its large bending load, resulting in large errors in fatigue life analysis conducted with the common method for thin-walled mode I crack growth. To study the fatigue crack growth performance of thin-walled structures under the bending load, we first conducted fatigue crack growth tests of hole plates and side profile structural simulator specimens. Effects of the bending load on the Stress Intensity Factor (SIF) were then studied by finite element simulations, and a modified formula with the equivalent SIF range was further proposed. The predicted results of the crack growth life in the two types of specimens under bending involved in this paper agree well with the test results. It is shown that SIF and thus fatigue crack growth rates are much lower than those under tension with the same nominal stress and crack length; when the structure is subjected to the bending load, the lockring has a significant inhibiting effect on the stress at the joint sites, thus reducing corresponding fatigue crack growth rates; moreover, reasonable structure design can enhance the fatigue crack growth life of critical parts under bending.