Research On Fatigue Performance Of Riveted Structures With Different Countersink Hole Depths

Compared with ordinary fasteners in engineering practice,riveting has the characteristics of reliable connection,light weight and low cost.This technology has been widely used in aircraft structural connections.However,the aircraft will withstand alternating loads during actual operation,and a large stress concentration will occur at the rivet joints,which directly affects the reliability and operating life of the aircraft.Effective control of the depth of the countersink can improve the fatigue performance of the structural parts.From the technical point of view,the countersink depth is studied to study the fatigue performance of the riveted specimens.This has clear guiding significance and value for the study of fatigue reliability of late aircraft.The research content of this paper mainly includes:(1)Effects of three countersink depths on static tensile properties of 2024-T3 aluminum alloy specimens.Three kinds of countersink depth test pieces were taken as the research object.Scanning electron microscope(SEM)was used to observe the crack initiation and crack propagation area after fatigue fracture of the sample.The numerical simulation was performed using ANSYS software(FEM)and the stress-strain value at the countersink was analyzed.In addition,the strain gauge tool is used to measure the strain near the countersink to verify the rationality and accuracy of the finite element analysis and theoretical calculations.(2)Fatigue testing and data processing.The fatigue load was determined by the static load failure test.The fatigue test was carried out on the countersinks of different depths.The test data were fitted by the least squares method.The material constants m,Cs and the stress-life(S-N)curve of the aluminum alloy specimens were obtained according to the fitted curve.Further obtaining the confidence lower limit P-S-N curve and its functional relationship for the overall safe and reliable life.(3)The influence of the countersink depth process parameters on the fatigue life of the specimen was discussed.By comparing the fatigue life values at high and low weeks,based on the stress concentration factor and the stress intensity factor theory,the differences in the different fatigue life intervals are explained in detail.(4)The fatigue life prediction model of aluminum alloy under different countersink depth conditions was established.At the beginning of constructing the fatigue life prediction model,the theoretical method of estimating fatigue life is introduced.In the aspect of fitting fatigue test data,different countersink depth conditions are established by means of structural fracture fatigue theory and residual strength model of unnotched specimen.A predictive model of fatigue life.Based on the above analysis,it can be found that the fatigue life results of the samples with a counterbore depth of less than 1mm(0.65mm,0.90mm)are not significantly different;however,a large trend change occurred compared to the fatigue life of a sample with a counterbore depth greater than 1mm(1.20mm).The discovery of this breakthrough research has provided effective help for later practical production.