【作者】 张勇；

【导师】 张瑞金；

【作者基本信息】 东北大学 ， 机械工程（专业学位）， 2015， 硕士

【摘要】 铝合金是纯铝加入一些合金元素制成的,如铝-锰合金,铝-铜合金,铝-铜-镁系列合金,铝合金材料容易加工,具有高度的散热性,轻质但是机械性能很出色。由于上述这些优点,铝合金被广泛应用到工程结构中。但是铝合金材料结构往往承受复杂的载荷条件,其中就包括:不同应力比下裂纹扩展速率的不同,裂纹尖端塑性区对裂纹扩展的影响。不考虑其影响预测结构的寿命是危险的,所以研究裂尖塑性区对裂纹扩展的影响有着很大的实际意义。本文以7N01S-T5铝合金材料为研究对象完成了该种材料的断裂力学性能试验,并且研究了塑性区对其断裂力学性能的影响。本文的主要工作内容如下:(1)针对具体工程问题,本文采用了 SE(B)试样和M(T)试样进行了疲劳裂纹扩展试验设计,完成了不同应力比下的恒幅疲劳裂纹扩展试验,基于Pairs公式得到了不同应力比下疲劳裂纹扩展速率模型。(2)分别建立了两种试样的有限元分析模型,采用了多线性随动强化模型近似模拟实际的铝合金材料的应力应变曲线,采用弹塑性有限元分析得到了不同应力比下裂尖点的应力应变场分布,研究了裂纹尖端应力应变场和正反向塑性区的分布,分析并且讨论了变化规律。(3)通过弹塑性有限元分析,结合Irwin提出的正向塑性区和反向塑性区理论,解释了在负应力比下的压载荷部分对裂纹扩展的促进作用机理,以及应力比对裂纹扩展速率的影响。(4)在小范围屈服条件下,以应力强度因子为断裂力学参量,依据弹塑性有限元分析出的拉-压循环下的裂纹尖端应力随时间变化曲线,确定了有效应力强度因子幅值,通过修正后的Pairs公式拟合试验数据获得了负应力比下统一的裂纹扩展速率模型。(5)对于拉-拉循环载荷,讨论了小范围屈服条件范围,分别采用了 Walker公式和Elber公式对试验数据进行拟合,并对比分析,建立了正应力比下的裂纹扩展速率模型。更多还原

【Abstract】 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.更多还原