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

Size-dependent bending modulus of fibre composite laminates comprising unidirectional plies

In this work a large scale bending test, representative of conditions experienced under reeling of steel pipelines, is discussed. The pipeline material is an X65 steel and the pipe has a diameter of 273.1 mm (10.75”) wall thickness of 14.3 mm. The pipe was subject to multi-cycle reverse bending in a four-point bending rig. The crack driving force in terms of crack tip opening displacement (CTOD) was measured and compared with the results from three-dimensional finite-element analysis of the notched pipe. A number of existing estimation schemes for crack driving force, in addition to a novel estimation scheme developed by the authors, have also been evaluated. An important feature of the latter scheme is the ability to account for a yield plateau in the deformation response of the material. It has been seen that the measured CTOD-strain relationships for multi-cycle bending are closely predicted by the new estimation scheme. The first cycle, in particular, provides a robust validation of the procedure as the material response in this case is strongly affected by the existence of a yield plateau in the material tensile response.

Fracture Assessment of Elastic-Plastic Steel Pipelines Subject to Multi-cycle Bending

For safety critical applications of plant it is nec essary to ensure that conservative values of mechanical properties are used for structural integ rity assessments. Assessment procedures require fracture toughness often of the weldments as one of the input parameters. The main constituents of weldments are steel plate, weld metal and the heataffected-zone (HAZ) in the plate. This paper considers the evaluation of upper shelf fracture to ughness properties of HAZ. During fracture toughness testing using three point bend specimens th cracks tended to deviate from higher strength coarse grain HAZ into lower strength regions compri sing weld metal or fine-grained HAZ. The tests in which cracks started in the HAZ and propagated ma inly through this region yielded values of J 0.2 in the range 118MPam 1/2 to 177MPam. These experimental results are discussed with re spect to the predictions of a finite element model that consider s particularly the path followed by the crack within the weldment.

Fracture Toughness Properties of the Heat-Affected-Zone in Ferritic Steel Weldments

This paper considers the prediction of the effects of tensile and compressive residual stress in fracture mechanics specimens by the application of a mechanical pre-load. This is considered in the context of a ‘C’ shape specimen which is mechanically pre-tensioned or pre-compressed to produce, respectively, a compressive or tensile residual stress in the region where the crack is introduced. Finite-element analysis is performed to simulate the pre-loading and the subsequent fracture loading of the cracked specimens. The finite-element predictions are compared with experimental data including residual stress measurements using neutron diffraction. A discussion is presented on modelling and material issues pertaining to the use of mechanical pre-loading as a means for introducing residual stress.

Predicting the Effect of Compressive and Tensile Residual Stresses in Fracture Mechanics Specimens

Failures in engineering components operating at high temperature often initiate in welded joints, particularly in the heat-affected zone (HAZ) adjacent to a weld. This is due to the inhomogenous microstructure of the weld and adjacent material due to the different thermal histories experienced during the weld cycle. It is therefore important to accurately predict the temperature distributions arising during welding and the subsequent effect on material microstructure. The NET TG1 bead-on-plate weld geometry is examined in this work. This geometry is a single weld bead laid on the surface of an AISI 316L austenite steel plate. Experimental data from the TG1 study are available to validate different weld simulation techniques. Here, a sensitivity study to the thermal properties is carried out and the influence on the HAZ temperatures and grain size is examined. The study shows that the conductivity and the specific heat capacity significantly affect the temperature prediction in the HAZ with a similar influence on predicted grain size following welding. Results are presented for a stainless steel (316L) and a martensitic steel (P91) plate.

Noel P. O’Dowd

Papers

Size-dependent bending modulus of fibre composite laminates comprising unidirectional plies

Fracture Assessment of Elastic-Plastic Steel Pipelines Subject to Multi-cycle Bending

Fracture Toughness Properties of the Heat-Affected-Zone in Ferritic Steel Weldments

Predicting the Effect of Compressive and Tensile Residual Stresses in Fracture Mechanics Specimens

Parameter Study of a Thermal Analysis of a Bead-on-Plate Weld