整体加筋壁板的破损安全特性与断裂控制分析

用有限元和断裂力学方法分析大型整体机翼下壁板的破损安全特性。对一个九桁条铝合金整体加筋板,裂纹从断裂筋条下向两侧均匀扩展的开裂形式,进行了应力强度因子和剩余强度计算,并和另一个具有相同构形的铆接加筋板的结果进行对比。当裂纹长度在两倍桁条间距以内时两种加筋板的剩余强度水平相当。但是当整体壁板中的裂纹穿过外侧相邻桁条时,整体桁条的止裂能力逐渐减弱。研究对整体壁板蒙皮胶接止裂条的断裂控制措施及有限元建模分析方法,描述止裂条胶层局部脱粘的处理方法和迭代过程。止裂条材料分别选用了钛合金和单向层压复合材料。计算结果说明胶接止裂措施能显著提高整体加筋板的破损安全性能。

An Analysis of Fail-Safety and Fracture Control of Integrally Stiffened Panels

The fail safety of large integrally stiffened panel is investigated based on the linear elastic fracture mechanics and finite element analysis.A nine-stringer integral aluminum alloy panel is analyzed for a skin crack under central broken stringer propagating toward the adjacent stringers.Comparison is made between the stress intensity and residual strength results of the panel and those of a rivet stiffened panel with the same configurations.The fail safe capability of the integral panel is not satisfactory when the crack is beyond two bay length,due to the crack growth and breaking on stringer web.To improve the fail safety of the integral stringer panel,the adhesively bonded strap is chosen as crack stopper.The material of the strap is either titanium(alloy) or fiber-reinforced unidirectional composite laminate.The method to simulate crack propagation and local strap debonding is designed and the computer code is made for the iterative use of NASTRAN package.The simulation shows that the bonding straps are very effective in reducing the stress intensity of integral panel cracks and thereby improve the fail safety of the panel remarkably.