腐蚀条件下基于Gerber模型的DFR推导及实测

DFR method based on Gerber model under corrosion conditions

为了研究等寿命曲线模型的选取对细节疲劳额定值计算结果的影响,针对六种典型航空材料对比了Gerber模型和Goodman模型对于高周疲劳数据的拟合精度;推导基于Gerber模型的DFR计算公式、腐蚀折算系数CC的表达式;针对2024-T3铝合金(表面阳极化)进行了预腐蚀0 h、6 h、12 h、24 h、36 h和72 h的疲劳实验并分析预腐蚀72 h的疲劳断口。结果表明:Gerber模型适用于LY12CZ等铝合金,并且在N_(95/95)>10~5次时,基于Gerber模型的DFR法才能发挥延性材料的潜能;随着预腐蚀时间增长,2024-T3铝合金DFR值下降,基于Gerber模型计算的DFR分别为84.251 MPa、84.721 MPa、79.683 MPa、80.745 MPa、77.026 MPa和74.996 MPa,腐蚀折算系数CC为1.006、0.946、0.958、0.914、0.890,拟合得到DFR随预腐蚀时长的变化曲线是DFR=84.251[lg(t+10)]^(-0.15578);断口分析发现预腐蚀产生的蚀坑和材料中的夹杂物会加速疲劳裂纹的形成和扩展,导致结构的疲劳性能降低,但与裸材相比,阳极化过的试件的DFR在腐蚀环境中下降趋势减缓。

In order to study the influence of the equal-life curve models on DFR,the fitting accuracies of Gerber model and Goodman model for high-cycle fatigue data were compared with six typical aviation materials.The formula of DFR based on Gerber model and the expression of corrosion conversion coefficient CC were derived,pre-corrosion fatigue tests for 0 h,6 h,12 h,24h,36 h,and 72h of 2024-T3 aluminum alloy(surface anodizing)were carried out,and the fatigue fracture of pre-corrosion for 72 hours was analyzed.The results show that Goodman model is suitable for brittle materials while Gerber model is suitable for ductile materials.As the pre-corrosion time increases,the DFR of 2024-T3 aluminum alloy decreases.The DFR based on Gerber model are 84.251 MPa,84.721 MPa,79.683 MPa,80.745 MPa,77.026 MPa and 74.996 MPa respectively,and the CC is 1.006,0.946,0.958,0.914 and 0.890,the fitting curve of the DFR with the pre-corrosion time is DFR=84251[lg(t+10)]^-0.15578.It is found that when N95/95>10^5,the DFR method based on Gerber model can give full play to the fatigue performance of ductile materials.Corrosion pits produced by pre-corrosion and inclusions in materials can accelerate the formation and expansion of fatigue cracks,but DFR of the anodized specimens is decreased in a corrosive environment compared with the bare materials.