弯曲载荷下薄壁结构疲劳裂纹扩展性能

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.