6156-T4铝合金焊接加筋薄壁结构剩余强度评估的CTOD方法

为保证飞机设计满足损伤容限性能要求,有必要对其进行剩余强度评估。针对6156-T4铝合金焊接连接薄壁结构进行了R曲线和剩余强度试验,判断了裂纹扩展经过筋条时的裂纹扩展路径,测量了母板和筋条两个方向的裂纹扩展速率,并采用不同的断裂准则和分析方法对单及双跨度多个初始裂纹长度焊接加筋薄板的剩余强度进行了预测。结果表明:裂纹扩展在经过筋条时,同时沿着母板和筋条继续扩展,筋条上的裂纹扩展方向垂直于母板且两个方向的裂纹扩展速率基本相同;采用净截面屈服准则进行剩余强度预测时会低估这种韧性较好的焊接连接薄壁结构的剩余强度;基于SINTAP-FITNET评价体系,以裂纹尖端张开位移(CTOD-δ5)作为裂纹尖端弹塑性表征参量进行剩余强度预测时,预测结果比采用K曲线预测方法精度高。

Residual strength prediction of welded stiffened thin-walled structures made of Al 6156-T4 alloy based on CTOD method

In order to ensure that aircraft performance satisfies the damage tolerance design requirements, it is necessary to assess its residual strength. This paper deals with the R-curve and residual strength analysis of welded thin-walled structures for aircraft fuselage applications made of Al 6156-T4 alloy. The experimental results have been used to verify the proposed analysis route for the residual strength prediction. In addition, the crack propagation paths are detected when the crack through the stringer and the crack growth rates are measured in two directions. The residual strength is predicted for one-bay and two-bay thin-walled structure with variety initial crack length using different criteria. The results show that crack branching (into skin and stringer) when crack growing approached to the stringer in a perpendicular form. It is found that the residual strength is underestimated using the net section yield criteria for the residual strength prediction. In particular, the prediction based on SINTAP-FITNET evaluation system using parameters CTOD-δ₅ is more accurate than using K curve method.