Research On High Temperature Fatigue And Creep-Fatigue Crack Growth Behavior Of An Aerospace Material

With the development of modern aerospace technology,performance of high temperature structures requires be improved.Structures in service at high temperature are subject to not only constant loads but also cyclic loads.The fatigue and fracture mechanical behavior of structures at high temperature has become a very complex and important issue in the field of materials.Systematic research will play an important role in ensuring structural security of component in high temperature service.In this paper experiments are performed on the high temperature fatigue and creep-fatigue crack growth behavior of 2A12 aluminum alloy and 7075 aluminum alloy.The effects of temperature and dwell time on fatigue crack growth behavior of two materials were studied,and description was established.The test data of a variety of materials with significant creep-fatigue interaction effects reported in the literature were studied,and a universal description was studied.The following aspects are studied in this dissertation to achieve innovative results for engineering application.(1)Fatigue crack growth test of 7075 aluminum alloy were performed on room temperature(RT)and 175?.It was found that the minimum grain size of the material has effect on crack growth rate.The critical?K of crack growth rate curve was calculated,and a segmented model was established.(2)Fatigue crack growth test of 2A12 aluminum alloy were conducted under various temperature,it was found that there is a critical temperature.When the temperature is lower than the critical temperature,the fatigue crack growth rate of material increases as the temperature rises.When the temperature is higher than the critical temperature,it decreases with increasing temperature.A fatigue crack growth rate model including temperature parameter was established based on test data.(3)The crack growth behavior of two materials at 175?and 280?with various dwell times were studied.It was found that 300s dwell time at 175?had a limited effect on 2A12 aluminum alloy.When the temperature is 280?,the dwell time has a significant effect on 2A12 aluminum alloy.Based on the test data of 2A12 aluminum alloy at 280?,a description model including dwell time was established.(4)The creep-fatigue interaction crack growth behavior of materials in literature were studied.At a given temperature,?K and t_haffect the crack growth rate.By summarizing and deriving the existing model,a binomial model was established that includes?K and t_h.The characteristic dwell time t_inc in the model which correspond to the dwell time of the most significant interaction effect.The applicability of the model is verified by test data of alloy 718,2650 aluminum alloy,P91 and Astroloy.