The Study On Testing Equipments Of Materials Stress Corrosion Cracking And Its Application To The 7055 Aluminum Alloy

Stress corrosion cracking has been a significant problem which has serious effect on safe working, regular maintenance and repairing of equipments. Brittle fracture at low stress caused by stress corrosion cracking is common. It is necessary to investigate the stress corrosion cracking susceptibility of the material. Based on the national standard and aviation industry standard,this thesis designs three sets of testing equipments on stress corrosion cracking. The stress corrosion cracking suscepbility of 7055-T7452 aluminum alloy in 3.5%sodium chloride solution was studied by the testing equipmentsd designed. 7055 aluminum alloy is a new type of deformed aluminum alloy, which is extensively used in the the aircraft structure due to its high strength and fracture toughness.Based on the analysis of the basic principles, this thesis had completed the design of the testing equipments which contains mechanical structure, assembly and completed the intensity checking of the main working mechanisms. And the motion control device,temperature control device and control program was designed at the same time. The strength check of the key components in this device has also carried out. The stress distribution change with the variation in loads of the specimens without environmental media had been analyzed by the finite element method. The results of the analysis provided the theoretical guidance for the stress corrosion cracking tests. Finally,the stress corrosion resistance test of the 7055-T7452 aluminum alloy was carried out on this equipment.Then a serious of experiments was carried out to test the stress corrosion resistance of the 7055-T7452 aluminum alloy by the testing equipments designed in this thesis. Stress corrosion cracking susceptibility of 7055-T7452 aluminum alloy in the 3.5% sodium chloride solution was measured with the testing equipments designed. The stress corrosion cracking threshold stress intensity (KISCC) was 19.51 MPa·m1/2 which were gained on the stress corrosion cracking of cantilever beam. The stress corrosion cracking life of 7055-T7452 aluminum alloy under 350MPa,300MPa and 260MPa tensile stress was tested by C-ring stress corrosion cracking testing equipment in 3.5% sodium chloride solution, which was more than 480 hours.