| The fatigue under tension-torsion composite forces is one of the typical multi-axial fatigue models. Most of the structural parts of the civil aviation aircraft are subjected to multi axle loads such as the wing beam, wing rib and so on. 2A12 aluminum alloy is a typical aviation aluminum alloy, which is widely used in aircraft structures. So, this paper makes a comprehensive analysis of the multi axial fatigue test of 2A12 aluminum alloy, the SEM analysis of the fracture surface, modeling and simulation analysis.The 2A12 test was carried out by using SDN100/1000 type electro hydraulic servo tension-torsion fatigue test machine. By changing the main parameters, such as stress amplitude, phase angle, stress amplitude ratio and average stress, the life law of the material under different loading modes is studied. After the fatigue test, the fatigue fracture surface was analyzed, and the macro and micro analysis of the fatigue fracture surface was made. Through the displacement, load, torque and twist angle data collected during the experiment, draw the relevant cycle curve, observe the change laws in the circulation process. At last, by using the method of Patran modeling, obtain the life of different calculation method and then compare the life with experimental life, find out the best method in Patran. Study on fatigue performance of 2A12 aviation aluminum alloy from different aspects.The results show that the fatigue life of the torsion is less than tension compression fatigue life under the same Von-Mise stress 350 MPa. The fatigue life decreases with the increase of the phase difference, and it increases with the increase of tension-torsion stress amplitude ratio. Under the condition of constant normal stress amplitude 247.3MPa and shear stress amplitude 143.1MPa, one of tensile mean stress and torsion mean stress changes independently, the fatigue life can be reduced. Under the condition of 300 MPa to 350 MPa loading, the total fatigue life of the specimen increases with the increase of the primary load cycle, and exist the exercise effect.Under the condition of 350 MPa to 300 MPa loading, the total fatigue life of thespecimen decreases with the increase of the primary load cycle. Under the condition of constant normal and shear stress amplitude, the fatigue life of the sine wave is longer than triangle wave and the triangle wave lifetime is longer than square wave.The fatigue life of the combination of three waveforms is between sine wave and square wave.The angle between the sample section and the sample axis increases with the increase of the phase difference, and it decreases with the increase of tension-torsion stress amplitude ratio. On the tension compression fatigue fracture, the expansion zone has fatigue stripe. On the torsional fatigue fracture surface, the overall morphology is a vortex, a set of cracks point to the axis. Multi axial fatigue fracture surfaces have multiple crack sources. In the composite fatigue fracture, under proportional loading, can find the fatigue stripe and cellular pattern. In the non-proportional loading conditions, we can find fishbone pattern and scale pattern.Energy spectrum analysis showed that the crack source area has oxide; particle in the hole is precipitated phase.For different phase difference, the torsion property of the material has a cyclic hardening in the initial stage of fatigue test. With the decrease of the stress amplitude ratio, the cyclic hardening in the initial stage is more obvious. Compared with the sine wave and triangular wave, square wave has more obvious hysteresis phenomenon,and the sample reflects better structural consumption energy.For this material and sample size, comparing the forecast life of different methods in Patran: Fatemi-Socie method is more accurate in predicting the proportional mode. The Wang-Brown+Mean method is better in predicting the non-proportional mode. The two are all in 2 times of the dispersion. |
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