| Aluminium alloy is made by adding some alloy elements into pure aluminum,such as aluminum-magnesium alloy,aluminum-copper alloy,aluminium-copper-magnesium series of alloy.Aluminium alloy materials are easy for processing,as they have the traits of high heat resistance,lightweight and excellent mechanical properties.Due to above these advantages,aluminum alloy is widely used in engineering structure,bearing complex loading conditions that includes the differences under different stress ratios in terms of the values of different crack propagation rate,the effects of crack propagation rate with considering plastic zones.at crack tip The behavior of predicting the lifespan of engineering structure is dangerous without considering the influence of plastic zones for promoting or inhibiting crack propagation rate,so researching and analyzing the effects of plastic zones at crack tip is of particular significance.This paper and has completed fatigue fracture test focused on 7N01S-T5 aluminium alloy material The main contents in this paper include:(1)According to specific engineering problems,this paper has selected SE(B)specimen and M(T)specimen to design the process of fatigue crack propagation test and has got the model of fatigue crack propagation rate.(2)Based on ANSYS software,this paper has established two kinds of samples of finite element model,and it has not only adopted multiple linear servo reinforcement to simulate the actual stress-strain curve of aluminium alloy material but it also selected elastic-plastic element to analyze the distribution of the stress-strain at crack tip,this paper has already studied the distribution of positive and negative plastic zones(3)This paper has explained the inner mechanism of pressure load promoting crack propagation at negative stress ratios by both elastic-plastic element analyze and the theory of plastic zones proposed by Irwin,it has also explained the effects of stress ratios on crack propagation rate.(4)This paper has analyzed the curves of stress changing with time of M(T)specimen model at negative ratios under the condition of small scale yielding and finally determined the value of the effective stress intensity factor,this paper has used the revised Pairs formula fitting the experiment data and established the model of crack model under positive ratios.(5)For finite element analyzing results of SE(B)specimen at positive stress ratios,this paper has already discussed the scope of the condition of small scale yielding and used both Walker formula and Elber formula to fit the experiment data,and eventually established the model of crack propagation rate by contrastive analysis. |
PDF Full Text Request