Conceptual and physical disparity inherent in the modeling of multiscale fatigue crack growth: nano-micro-macro
Use specific materials have led to countless failure criteria related to strength,toughness,fatigue life,etc. They all seem to fit the data for certain situations. The search for a single criterion that can account for different service conditions relies on a knowledge of the inherent unavoidable discrepancy between the conceptual and physical aspects of modeling,in addition to the ways with which the internal structure of the material are arranged. At the nano-micro-macro size and timescale,material behavior cannot be disassociated with physical damage,say by crack growth in fatigue,a frequently encountered mode of failure.The current status of science and engineering has stymied the development of muitiscale models. The representative specimen scheme in material testing assumes that the properties of the bulk can be obtained from a portion (specimen) of the whole (structural component) although the theory does not adhere to the same rule. It dies on using a mathematically imagined element that can be summed continuously to obtained the bulk behavior. Incompatibility of the test procedure and analytical formulation becomes increasingly more seriously when the inhomogeneity of the specimen or the element differs drastically from the bulk. Such inconsistencies are revealed for the nano-micro-macro crack growth model in fa-tigue. Actual fatigue crack growth data for the 2024-T3 aluminum pre-cracked panels are used to show how damage can be assessed and connected at three different scales: the nano,micro and macro. This entails the evaluation of (anano,amicroamacro) and their corresponding crack growth rates.Two sets of relative scale parameters μ*m/m,d*m/m,σ*m/m and / μ*m/m,d*m/m,σ*m/m are used. The former refers to the micro and macro scales by the respective subscripts of m and m and the latter to the nano and micro scales by the respective subscripts of n and m. These parameters are time dependent and they express the degradation of the nano,micro and macro structure with time. It suffices to determine the bulk properties at the macroscopic scale while the local properties at the nano and micro scales are regarded as fictitious because they cannot be simulated by tests under the same conditions of material homogeneity. The objective therefore is not to simulate nature in its entity but only to model the conceptual portion that will nevertheless yield result anticipated by design. Prescription of the nano,micro,and macro structure of the material for a specific use will be used for demonstration. This entails a cracked 2024-T3 panel subjected to fatigue loading: σm=44.1MPa,σa=31.36MPa and R=0.169. Predicted is a total fatigue life of approximately 18 years out of which pre-nano and uano cracking prevailed for 8 years,microcracking for 4 years and macrocracking for 10 years. The individual time range of fatigue life can be altered by rearranging the construction of the nano,micro and macro material internal structure.
Mesomechanics Multiscaling Nano Micro Macro Interface Scale transition Segmentation Fatigue Creep Mean stress Stress amplitude Crack growth Discrete Continuum Microstructure Nanostructure Degradation Size and time effect
G.C.Sih
School of Mechanical and Power Engineering,East China University of Science and Technology,Shanghai 200237,China;Mechanical Engineering and Mechanics,Lehigh University,Bethlehem,PA 18015,USA
国际会议
Fracture Mechanics and Applications 2008(国际断裂力学2008年年会)(FM2008)
杭州
英文
1-15
2008-10-31（万方平台首次上网日期，不代表论文的发表时间）