Modeling Near-Crack-Tip Plasticity from Nano- to Micro-Scales

Several efforts that are aimed at understanding the plastic deformation mechanisms related to crack propagation at the nano-, meso- and micro-length scales including atomistic simulation, discrete dislocation plasticity, strain gradient plasticity and crystal plasticity are discussed. The paper focuses on discussion of newly developed methodologies and their application to understanding damage processes in aluminum and its alloys. Examination of plastic mechanisms as a function of increasing length scale illustrates increasingly complex phenomena governing plasticit

A Geometric Approach to Modeling Microstructurally Small Fatigue Crack Formation

The objective of this paper is to develop further a framework for computationally modeling microstructurally small fatigue crack growth in AA 7075-T651 [1]. The focus is on the nucleation event, when a crack extends from within a second-phase particle into a surrounding grain, since this has been observed to be an initiating mechanism for fatigue crack growth in this alloy. It is hypothesized that nucleation can be predicted by computing a non-local nucleation metric near the crack front. The hypothesis is tested by employing a combination of experimentation and nite element modeling in which various slip-based and energy-based nucleation metrics are tested for validity, where each metric is derived from a continuum crystal plasticity formulation. To investigate each metric, a non-local procedure is developed for the calculation of nucleation metrics in the neighborhood of a crack front. Initially, an idealized baseline model consisting of a single grain containing a semi-ellipsoidal surface particle is studied to investigate the dependence of each nucleation metric on lattice orientation, number of load cycles, and non-local regularization method. This is followed by a comparison of experimental observations and computational results for microstructural models constructed by replicating the observed microstructural geometry near second-phase particles in fatigue specimens. It is found that orientation strongly influences the direction of slip localization and, as a result, in uences the nucleation mechanism. Also, the baseline models, replication models, and past experimental observation consistently suggest that a set of particular grain orientations is most likely to nucleate fatigue cracks. It is found that a continuum crystal plasticity model and a non-local nucleation metric can be used to predict the nucleation event in AA 7075-T651. However, nucleation metric threshold values that correspond to various nucleation governing mechanisms must be calibrated

Fracture in Natural and Engineered Systems

IASS-IACM 2008 Session: Fracture in Natural and Engineered Systems -- Session Organizers: Robert HABER (UIUC), Anthony INGRAFFEA (Cornell Univ.) -- Keynote Lecture: "Assessment of stiffened shell structures using advanced fracture and damage mechanics methods" by Karl-Heinz SCHWALBE , Wolfgang BROCKS, Alfred CORNEC, Wernfried Schonfeld, Ingo SCHEIDER, Uwe ZERBST (GKSS Research Centre) -- "Residual strength characterization of integrally-stiffened structures utilizing novel manufacturing technologies" by B. R. SESHADRI, S. W. SMITH , W. M. JOHNSTON, JR. (NASA Langley Research Center) -- "Towards modeling of fragmentation and dynamic delamination interactions in CFRP composites" by Jean-Mathieu GUIMARD , Oliver ALLIX (ENS Cachan), Nicolas PECHNIK (AIRBUS France), Pascal THEVENET (EADS France) -- "A damage-based cohesive model in an adaptive spacetime discontinuous Galerkin method" by Reza ABEDI, Robert B. HABER (University of Illinois at Urbana-Champaign) -- "A unified potential-based cohesive model of mixed-mode fracture" by Glaucio H. PAULINO , Kyoungsoo PARK, Jeffrey ROESLER (The University of Illinois at Urbana-Champaign) -- "Surface and embedded cracks in offshore pipelines subjected to plastic strains" by Espen BERG , Bjorn SKALLERUD, Kjell HOLTHE (Norwegian University of Science and Technology) -- "Automated finite element based predictions of simultaneous crack growth and delamination growth in multi-layers in advanced metallic hybrid stiffened panels using the Alcoa ASPAN-FP tool" by Henry SKLYUT , Michael KULAK, Marcus HEINIMANN, Mark JAMES (Alcoa Technical Center), Olexander V. GONDLIAKH, Roman PASHINSKIJ (KPI, Kiev, Ukraine) -- "Crack trajectory prediction in thin shells using finite element analysis" by Jake D. HOCHHALTER , Ashley D. SPEAR, Anthony R. INGRAFFEA (Cornell University) -- "Analysis of localized failure in metal beams and plates" by Jaka DUJC, Bostjan BRANK (University of Ljubljana), Adnan IBRAHIMBEGOVIC (ENS Cachan