The Experts below are selected from a list of 20442 Experts worldwide ranked by ideXlab platform
Claudio Ruggieri - One of the best experts on this subject based on the ideXlab platform.
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a fad based procedure for defect assessments of welded structures including effects of weld strength mismatch micromechanics approach and application to pipeline girth welds
2008 7th International Pipeline Conference Volume 2, 2008Co-Authors: Gustavo Henrique Bolognesi Donato, Claudio RuggieriAbstract:ECA procedures of crack-like defects based upon the FAD philosophy have undergone extensive developments in the past decade to form the basis for industrial codes and guidelines for structural integrity assessments. However, the application of these procedures in welded structural components with mismatch in tensile properties between the weld and base metal remains a potential open issue. Weld strength mismatch may significantly alter the crack-tip driving forces, such as J and CTOD, thereby producing crack-tip stresses quite different than the fields that arise in corresponding homogeneous material. Weld strength mismatch also affects the plastic collapse load for the structural component which further complicates the interplay between Fracture and plastic instability before gross yield section takes place. This work describes the development of a microme-chanics-based FAD methodology building upon a local Fracture Parameter, characterized by the Weibull stress (σw ), to incorporate the effects of weld strength mismatch on crack-tip driving forces. As a further refinement, the study also addresses an exploratory application of a limit load analysis including effects of weld strength mismatch to correct the loading trajectory incorporated into the FAD procedure. Fracture testing of girth welds obtained from an API X80 pipeline steel provide the data needed to validate the proposed modified FAD procedure in failure predictions. Such an application serves as a prototype for a wide class of integrity assessment problems involving the effects of weld strength mismatch.Copyright © 2008 by ASME
Jinyoung Choi - One of the best experts on this subject based on the ideXlab platform.
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overload analysis and fatigue life prediction of spot welded specimens using an effective j integral
Mechanics of Materials, 2005Co-Authors: Jinyoung ChoiAbstract:Abstract This paper proposes an integrated approach for predicting the fatigue life of spot-weld specimens. The approach is independent of specimen geometry and loading type. We establish finite element (FE) models reflecting the actual specimen behavior observed from the experimental load-deflection curves of four types of single spot-welded specimen. Using established FE models, we first evaluate J -integral as a Fracture Parameter for describing the effects of specimen geometry and loading type on the fatigue life. It is confirmed, however, that J -integral concept alone is insufficient to produce the generalized relationship between load and fatigue life of spot-welded specimens. On this ground, we introduce another effective Parameter J e composed of J I , J II , J III . The mechanism of the mixed mode Fracture, which incites the use of J e , is discussed. The Parameter J e is demonstrated to more sharply define the relation between load and fatigue life of spot-welded specimens. The crack surface displacement method is adopted for decomposition of J .
Gustavo Henrique Bolognesi Donato - One of the best experts on this subject based on the ideXlab platform.
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a fad based procedure for defect assessments of welded structures including effects of weld strength mismatch micromechanics approach and application to pipeline girth welds
2008 7th International Pipeline Conference Volume 2, 2008Co-Authors: Gustavo Henrique Bolognesi Donato, Claudio RuggieriAbstract:ECA procedures of crack-like defects based upon the FAD philosophy have undergone extensive developments in the past decade to form the basis for industrial codes and guidelines for structural integrity assessments. However, the application of these procedures in welded structural components with mismatch in tensile properties between the weld and base metal remains a potential open issue. Weld strength mismatch may significantly alter the crack-tip driving forces, such as J and CTOD, thereby producing crack-tip stresses quite different than the fields that arise in corresponding homogeneous material. Weld strength mismatch also affects the plastic collapse load for the structural component which further complicates the interplay between Fracture and plastic instability before gross yield section takes place. This work describes the development of a microme-chanics-based FAD methodology building upon a local Fracture Parameter, characterized by the Weibull stress (σw ), to incorporate the effects of weld strength mismatch on crack-tip driving forces. As a further refinement, the study also addresses an exploratory application of a limit load analysis including effects of weld strength mismatch to correct the loading trajectory incorporated into the FAD procedure. Fracture testing of girth welds obtained from an API X80 pipeline steel provide the data needed to validate the proposed modified FAD procedure in failure predictions. Such an application serves as a prototype for a wide class of integrity assessment problems involving the effects of weld strength mismatch.Copyright © 2008 by ASME
Hareesh V. Tippur - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Crack Growth Normal to an Interface in Bi-Layered Materials: An Experimental Study Using Digital Gradient Sensing Technique
Experimental Mechanics, 2015Co-Authors: Balamurugan M. Sundaram, Hareesh V. TippurAbstract:The dynamic Fracture behavior of layered architectures is experimentally studied. Specifically, crack penetration, trapping, and branching at an interface are examined. A newly introduced optical technique called Digital Gradient Sensing (DGS) that quantifies elasto-optic effects due to a non-uniform state of stress is extended to perform full-field measurements during the Fracture event using ultrahigh-speed photography. By exploiting the richness of two simultaneously measured orthogonal stress gradient fields, a modified approach for extracting stress intensity factors (SIFs) is implemented for propagating crack-tips under mixed-mode conditions. The method is first calibrated using a quasi-static experiment complemented by finite element simulations before implementing it for studying dynamic mixed-mode Fracture mechanics of layered configurations. The layered systems considered consist of two PMMA sheets bonded using an acrylic adhesive with the interface oriented normally to the initial crack propagation direction. Interfaces are characterized as ‘strong’ and ‘weak’ by their crack initiation toughness. The dynamic Fracture of monolithic PMMA sheet is also studied in the same configuration for comparison. The crack growth and Fracture Parameter histories of propagating cracks are evaluated. The interface is shown to drastically perturb crack growth behavior resulting in higher dissipation of Fracture energy by exciting crack trapping, branching, and mixed-mode growth mechanisms.
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Dynamic Crack Propagation in Layered Transparent Materials Studied Using Digital Gradient Sensing Method
Dynamic Behavior of Materials, Volume 1, 2015Co-Authors: Balamurugan M. Sundaram, Hareesh V. TippurAbstract:In this work, dynamic Fracture behavior of layered PMMA sheets is studied. Specifically, crack penetration, branching and deflection across an interface are examined. Two PMMA sheets are bonded together using a commercially available transparent acrylic adhesive to form the layered material system. The bond layer is characterized by its static Fracture toughness. Different bond thicknesses, 25 μm to 1.3 mm, are used to vary interfacial Fracture toughness. The interface angles of 90° and 45° relative to initial crack propagation direction are used between the two PMMA sheets. Dynamic crack growth experiments on these layered materials are carried out using a long-bar impactor setup in conjunction with a novel optical technique called Digital Gradient Sensing (DGS). DGS exploits elasto-optic effects exhibited by transparent solids subjected to non-uniform state of stress causing deflection of light rays propagating through the material. This on-going research includes extraction of Fracture Parameter histories in the monolithic and layered configurations and identification of underlying crack growth behaviors based on optical measurements.
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dynamic Fracture of compositionally graded materials with cracks along the elastic gradient experiments and analysis
Mechanics of Materials, 2001Co-Authors: Carlernst Rousseau, Hareesh V. TippurAbstract:Abstract Crack tip deformation and Fracture Parameter histories in compositionally graded glass-filled epoxy are evaluated for low velocity impact loading. The situations when the elastic gradient is unidirectional with crack orientation along the gradient are examined. The Fracture behavior of graded compositions is studied relative to homogeneous counterparts made of identical constituents. Optical method of CGS and high-speed photography are used to measure crack tip deformations prior to crack initiation and during dynamic crack growth. The apparent stress intensity factors prior to crack initiation are determined using dynamic equivalent of the stationary fields for FGMs while crack tip fields for steadily growing cracks in FGMs are used for post-initiation situations. Results from finite element simulations up to crack initiation are in excellent agreement with the experimental evaluations. Post crack initiation stress intensity factor histories and crack growth resistance behaviors for FGMs with monotonically increasing and decreasing elastic gradient are strikingly different. When the crack growth occurs into material with progressively increasing filler volume fraction, continuously increasing KID(t) is seen while a decreasing trend is observed when the gradient is of the opposite sense. The Fracture behaviors are explained by independent Fracture tests and Fractured surface micrographs.
M Langseth - One of the best experts on this subject based on the ideXlab platform.
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assessment of yield and Fracture criteria using shear and bending tests
Materials & Design, 2009Co-Authors: Aase Gavina Roberg Reyes, Odd Sture Hopperstad, O.-g. Lademo, Magnus Eriksson, M LangsethAbstract:This article deals with the calibration of a Fracture criterion that has been implemented in a material model in LS-DYNA. The failure process in thin-walled metallic materials is complex and often due to interaction between plastic instability phenomena and ductile Fracture. The material failure often occurs due to highly localized plastic deformation originating from plastic instability. The present work aims at establishing an in-plane shear test, which gives direct information about the phenomenon of ductile Fracture, and a numerical scheme for identification of the Fracture Parameter. Shear tests of extruded plates in AA7108 temper T6 were carried out, and the Fracture Parameter was found through inverse modeling. AA7108 has previously been characterized and an anisotropic yield criterion has been calibrated with simple material tests including standard uniaxial tensile tests and through-thickness compression tests. It is discussed how the yield criterion calibration can be improved through in-plane shear tests and related numerical analyses. In order to evaluate the model and calibration, simple three-point bending tests of the same material were carried out. In these tests, the nose shape of the indenter was varied. Numerical analyses of the tests were then carried out with the implemented model and identified model Parameters.
