随机谱载荷中高载/小幅值载荷相互作用下铝合金裂纹扩展机理及裂纹扩展寿命模型研究

项目名称： 随机谱载荷中高载/小幅值载荷相互作用下铝合金裂纹扩展机理及裂纹扩展寿命模型研究

项目编号： No.10802003

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 轻工业、手工业

项目作者： 鲍蕊

作者单位： 北京航空航天大学

项目金额： 25万元

中文摘要： 对2324-T39铝合金在恒幅及谱载荷下的裂纹扩展行为进行了系统的研究；包括：（1）恒幅载荷下应力比、应力水平、试样形式、材料取向、试样厚度对裂纹扩展形态的影响；（2）截除载荷谱下裂纹分叉产生的原因；（3）恒幅载荷叠加高载情况下高载及其间隔对裂纹扩展行为的影响；（4）截除谱下2024-T3、2524-T3、2324-T39铝合金裂纹扩展行为的差别；（5）截除谱下2324-T39裂纹扩展寿命预测。研究表明：（1）对于Al-Cu-Mg系列的三种铝合金，高截除水平下的宏观裂纹分叉是2324-T39特有的现象，与其微观组织结构有关；（2）宏观的分叉裂纹是由于试样内部的二次裂纹扩展到了试件的表面形成的，二次裂纹的产生与载荷谱中的高载有关，但与载荷截除水平无关，是否扩展到表面与高载后的小幅值载荷的多少有关；（3）恒幅谱较高应力水平下裂纹出现明显偏折，但宏观分叉不明显，叠加高载后出现明显的分叉；（4）基于塑性的迟滞模型无法考察分叉带来的裂纹扩展速率变化。由于2324铝合金的裂纹分叉与其微观组织有直接关系，在进一步研究中可以考虑概率模型。

中文关键词： 裂纹扩展；裂纹分叉；谱载荷；2324-T39铝合金

英文摘要： Experimental investigations were carried out on the crack growth behavior of 2324-T39 aluminum alloy under constant and spectrum loading. Five aspects were involved in the study:(1) the effect of stress levels, stress ratios, specimen configurations, orientations and thickness on the crack growth morphology; (2) the reason leading to macro-level crack branching under truncated spectrum loading; (3) effects of tension overload and its intervals on crack growth behavior under simplified spectrum loading,i.e.constant amplitude loading plus tension overload; (4) comparison of the crack growth behavior in 2024-T3, 2524-T3 and 2324-T39 under truncated spectrum loading; (5) crack growth life prediction method under truncated spectrum loading. Following conclusions can be drawn: (1) macro-level crack branching was found only in the test of 2324-T39 under high load truncation level, while no such evidence was observed in the experiments on 2024-T3 and 2524-T3, which was resulted from the differences of micro-structural texture between the three alloys; (2) tension overloads result in subsurface secondary crack irrespective to load truncation level, the propagation of secondary crack to the specimen surface, which was influenced by the low stress level cycles following the overloads, result in the macro-level crack branching; (3) crack deflection was found in the tests under constant spectrum loading of high stress levels, when tension overload was added to the loading spectrum, significant crack branching was observed; (4) the available crack retardation models based on the plasticity cannot account for the crack growth rate changes due to crack branching. Probabilistic analysis methods may be a better choice to model the branching in crack propagation in the further study.

英文关键词： crack growth; crack branching; spectrum loading; 2324-T39 aluminum alloy;