整体机身结构纵向裂纹转折与止裂特性分析

Exploring Engineering Significance of Turning of Longitudinal Crack in Integral Airframe Structure

对某试验型整体机身壁板纵向裂纹损伤容限试验件的止裂特性和裂纹转折现象进行了计算和分析。借助有限元软件ABAQU S,计算了不同蒙皮纵向裂纹长度下的应力强度因子KⅠ、KⅡ和T-应力等,在此数据基础上,应用线弹性断裂力学准则和线弹性断裂力学加塑性修正准则,计算了剩余强度特征曲线,对2种准则做了对比分析,对两跨裂纹时的止裂特性进行了分析。最后,应用裂纹转折的二阶线弹性理论,对两跨内纵向裂纹在扩展过程中的裂纹转折现象进行了计算和分析。

Aim. In the past decade or so,researchers abroad have done considerable work on the turning of longitudinal crack.But in China,this research of engineering significance for properly designing large aircraft has just begun. We now report some preliminary results of our exploration into it.Assuming that the longitudinal crack propagates at first along a straight line,we calculate the stress intensity factors（KⅠ,KⅡ）,given in Figs.5 and 6 in the full paper,and T-stresses,given in Fig.7,associated with different crack lengths by using finite element software ABAQUS V6.5;then,based upon these data,we calculate the residual strength curves,given in Fig.9,according to the two fracture criteria：（1） linear elastic fracture criterion and（2） linear elastic fracture criterion modified by yield correction.Using the second order linear elastic crack turning theory,we study furthermore the crack turning phenomenon as the straight crack is approaching adjacent arresting frames.Although the crack growing along a straight line is not arrested at two bays,the crack is turning when it is approaching adjacent arresting frames and therefore the two-bay residual strength criterion is also satisfied.;thus crack turning as a potential crack arrest mechanism is worthy of consideration for designing pressurized integral fuselage structure.