机身壁板LBW结构DFR值试验测定及理论计算

DFR value testing and theoretical calculation on laser beam welded structures of fuselage panel

飞机机身壁板是疲劳的关键位置,空客公司首先在飞机机身壁板采用激光焊接(LBW)结构代替传统铆接结构.为评价该激光焊接结构的疲劳性能,结合试验测定和统计学理论计算两种方法,对两组新型铝锂合金2060-T3激光焊接焊后热处理(PWHT,即焊后固溶+时效热处理和焊后时效热处理)结构进行疲劳试验、断口分析及细节疲劳额定强度(DFR值)分析,分别计算了试验测定DFR值和理论DFR值.分析结果表明,试验测定焊后固溶+时效热处理激光焊接结构的DFR值为118.0 MPa,焊后时效热处理的DFR值为113. 7 MPa,理论DFR值分别为115. 8 MPa (误差为1. 86%)和112. 2 MPa (误差为1.32%);两组结构均在焊趾处产生裂纹源,裂纹沿板材厚度方向进行扩展,裂纹扩展区均表现为脆性解理河流花样,不同的是前者瞬断区为微孔聚集型断裂,断口存在大量微小韧窝,后者瞬断区为沿晶断裂,断口存在大量晶粒;采用统计学理论计算,可以较好地还原威布尔分布的形状参数,验证了统计学理论分析方法的工程适用性,为机身壁板LBW结构的DFR值测定提供了参考依据.

The aircraft fuselage panel is the key position of fatigue.To evaluate the fatigue performance of the laser beam welded(LBW)structures which are first applied in aircraft fuselage panel by Airbus Company instead of traditional riveted structure,two methods of experimental determination and statistical theoretical calculation were used.The fatigue tests,fracture analyses and detail fatigue rating(DFR)analyses were carried out on two groups of laser beam welded structures which were obtained by different post weld heat treatment(PWHT)processes(solid solution+aging treatment,and aging treatment)with the new type of aluminum lithium alloy 2060-T3,and the test DFR value was acquired as well as the theoretical DFR value.The analysis results show that the test DFR value of the solid solution+aging treatment is 118.0 MPa and the one of aging treatment is 113.7 MPa.The theoretical DFR values for them are 115.8 MPa(the relative error is 1.86%)and 112.2 MPa(the relative error is 1.32%),respectively.The source of cracks in the two structures is produced both at the weld toe.The crack propagates along the thickness of the plate and the crack propagation area is characterized by brittle cleavage river pattern.The difference is that final fracture region of the former is characterized by micropore aggregation fracture with many small dimples in the fracture,and the one of the latter is intergranular fracture with many grains in the fracture.The theoretical analysis can be used to restore the Weibull shape parameter,to verify the applicability of the theory of statistical analysis method,and to provide the reference for the DFR value of laser beam welded structures of fuselage panel.