다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

http://web.mit.edu/durint/PDF/Dao_et_alFR.pdf

Computational modeling of the forward and reverse problems in instrumented sharp indentation

A class of phenomenological strain gradient plasticity theories is formulated to accommodate more than one material length parameter. The objective is a generalization of the classical J2 3ow theory of plasticity to account for strain gradient e4ects that emerge in deformation phenomena at the micron scale. A special case involves a single length parameter and is of similar form to that proposed by Aifantis and co-workers. Distinct computational advantages are associated with this class of theories that make them attractive for applications requiring the generation of numerical solutions. The higher-order nature of the theories is emphasized, involving both higher-order stresses and additional boundary conditions. Competing members in the class of theories will be examined in light of experimental data on wire torsion, sheet bending, indentation and other micron scale plasticity phenomena. The data strongly suggest that at least two distinct material length parameters must be introduced in any phenomenological gradient plasticity theory, one parameter characterizing problems for which stretch gradients are dominant and the other relevant to problems when rotation gradients (or shearing gradients) are controlling. Flow and deformation theory versions of the theory are highlighted that can accommodate multiple length parameters. Examination of several basic problems reveals that the new formulations predict quantitatively similar plastic behavior to the theory proposed earlier by the present authors. The new formulations improve on the earlier theory in the manner in which elastic and plastic strains are decomposed and in the representation of behavior in the elastic range. ? 2001 Elsevier Science Ltd. All rights reserved.

http://www-mech.eng.cam.ac.uk/profiles/fleck/papers/143.pdf

A reformulation of strain gradient plasticity

The presence of casting defects within Ni-base single crystal superalloy components in gas turbine engines is known to lead to the nucleation of microcracks during service. In this work, a micromechanics-based formulation is proposed to describe the growth of initially spherical defects within single crystals under different multiaxial stress states. The framework provides an explicit link between the mesoscopic (at the level of the voids) and the macroscopic (at the component level) length scales. A recently proposed finite strain rate-dependent crystallographic theory is used to describe the constitutive behaviour of the single crystal. The effects of material anisotropy, stress state, temperature and interaction with a free surface on the growth rate of a single void are quantified from detailed finite element analyses of a representative material volume containing a void. Based on these results, a meso-mechanics formulation of void growth for single crystal materials is presented.

A Rate Dependent Formulation for Void Growth in Single Crystal Materials

Fracture mechanics analysis of heterogeneous welds: numerical case studies involving experimental heterogeneity patterns

Quality prediction of ultrasonically welded joints using a hybrid machine learning model

Modern installation techniques for marine pipelines and subsea risers are often based on the reel-lay method, which introduces significant (plastic) strains on the pipe during reeling and un-reeling. The safe assessment of crack-like flaws under such conditions requires accurate estimations of the elastic-plastic crack driving forces, ideally expressed in a strain-based formulation to better account for the displacement controlled nature of the reeling method. This paper aims to facilitate such assessments by presenting a strain-based expression of the well-known EPRI estimation scheme for the J integral, which is directly based upon fully plastic descriptions of fracture behaviour under significant plasticity. Parametric finite element simulations of bending of circumferentially cracked pipes have been conducted for a set of crack geometries, pipe dimensions and material hardening properties representative of current applications. These provide the numerical assessment of the crack driving force upon which the non-dimensional factors of the EPRI methodology, which scale J with applied strain, are derived. Finally, these factors are presented in convenient graphical and tabular forms, thus allowing the direct and accurate assessment of the J integral for circumferentially cracked pipes subjected to reeling.Copyright © 2013 by ASME

Noel P. O’Dowd

Papers

A Rate Dependent Formulation for Void Growth in Single Crystal Materials

Fracture mechanics analysis of heterogeneous welds: numerical case studies involving experimental heterogeneity patterns

Quality prediction of ultrasonically welded joints using a hybrid machine learning model

Fully-Plastic Strain-Based J Estimation Scheme for Circumferential Surface Cracks in Pipes Subjected to Reeling

Optimisation of ultrasonically welded joints through machine learning