Multiscale approach to micro/macro fatigue crack growth in 2024-T3 aluminum panel

摘要：

　　When two contacting solid surfaces are tightly closed and invisible to the naked eye,the discontinuity is said to be microscopic regardless of whether its length is short or long.By this definition,it is not sufficient to distinguish the difference between a micro-and macro-crack by using the length parameter.Microcracks in high strength metal alloys have been known to be several centimeters or longer.Considered in this work is a dual scale fatigue crack growth model where the main crack can be micro or macro but there prevails an inherent microscopic tip region that is damaged depending on the irregularities of the microstructure.This region is referred to as the micro-tip and can be simulated by a sharp wedge with different angles in addition to mixed boundary conditions.The combination is sufficient to model microscopic entities in the form of voids,inclusions,precipitations,interfaces,in addition to subgrain imperfections,or cluster of dislocations.This is accomplished by using the method of singularity representation such that closed form asymptotic solutions can be obtained for the development of fatigue crack growth rate relations with three parameters.They include:(1) the crack surface tightness σ* represented by σo/σ∞ =0.3-0.5 for short cracks in region Ⅰ,and 0.1-0.2 for long cracks in region Ⅱ,(2) the micro/macro material properties reflected by the shear modulus ratioμ* (=μmicro/μmacro varying between 2 and 5) and (3) the most sensitive parameter d* being the micro-tip characteristic length d* (=d/do) whose magnitude decreases in the direction of region Ⅰ →Ⅱ.The existing fatigue crack growth data for 2024-T3 and 7075-T6 aluminum sheets are used to reinterpret the two-parameter da/dN=C(△K)n relation where △K has now been re-derived for a mierocrack with surfaces tightly in contact.The contact force will depend on the mean stress σm or mean stress ratio R as the primary parameter and on the stress amplitude σa as the secondary parameter.

关键词： microcrack macrocraack microstructure singularity multiscaling scale shift micro/macro crack growth 7075-T6 and 2024-T3

作者: G.C.Sih

作者单位: International Center for Sustainability,Accountability and Eco-Affordability of the Large and Small(ICSAELS)Lehigh University,Bethlehem,PA 18015,USA;Key Laboratory of Pressure Systems and Safety,Ministry of Education,School of Mechanical Engineering,East China University of Science and Technology,Shanghai 200237,China

会议类型: 国际会议

会议名称: International Conference on Airworthiness & Fatigue -7th ICSAELS Series Conference(大飞机安全性能与疲劳国际会议)

会议地点: 北京

会议语种:英文

页码: 31-42

在线出版日期: 2013-03-24（万方平台首次上网日期，不代表论文的发表时间）