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American Society for Testing and Materials

A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

An extended model for void growth and coalescence - application to anisotropic ductile fracture

Today, a large number of different steels are being processed by Additive Manufacturing (AM) methods. The different matrix microstructure components and phases (austenite, ferrite, martensite) and the various precipitation phases (intermetallic precipitates, carbides) lend a huge variability in microstructure and properties to this class of alloys. This is true for AM-produced steels just as it is for conventionally-produced steels. However, steels are subjected during AM processing to time-temperature profiles which are very different from the ones encountered in conventional process routes, and hence the resulting microstructures differ strongly as well. This includes a very fine and highly morphologically and crystallographically textured microstructure as a result of high solidification rates as well as non-equilibrium phases in the as-processed state. Such a microstructure, in turn, necessitates additional or adapted post-AM heat treatments and alloy design adjustments. In this review, we give an overview over the different kinds of steels in use in fusion-based AM processes and present their microstructures, their mechanical and corrosion properties, their heat treatments and their intended applications. This includes austenitic, duplex, martensitic and precipitation-hardening stainless steels, TRIP/TWIP steels, maraging and carbon-bearing tool steels and ODS steels. We identify areas with missing information in the literature and assess which properties of AM steels exceed those of conventionally-produced ones, or, conversely, which properties fall behind. We close our review with a short summary of iron-base alloys with functional properties and their application perspectives in Additive Manufacturing.

Steels in additive manufacturing: A review of their microstructure and properties

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processing heat treatments to improve the mechanical properties of the parts. An important aspect that still hinders this technology is certification and nondestructive testing of the parts, and this is discussed. Finally, a general perspective of future advancements is presented.

Current Status and Perspectives on Wire and Arc Additive Manufacturing (WAAM)

Additive manufacturing using WAAM with AA5183 wire

Efficient fracture assessment of pipelines. A constraint-corrected SENT specimen approach

During installation operations offshore pipes are often strained beyond yielding. Due to the high loading condition and the high costs of these operations it is important with accurate defect assessment analysis to avoid delays caused by unnecessary repairs or failure because of flaws that should have been detected and repaired. There is therefore a need for an accurate assessment procedure that can be a tool for defect assessment analysis for this application. It is commonly accepted that the fracture toughness is dependent on the geometry constraint at the crack tip. The traditional single edge notch bend (SENB) specimens have a high geometry constraint, and give lower bound fracture toughness for all geometries. For reeling operations these fracture toughness values are often too low to be used in defect assessment of reeling operations. The same is the assumption of plastic collapse when the net section stress is equal to the average between the yield strength and tensile strength. In this paper, the single edge notch tension specimen (SENT) is presented as an alternative fracture mechanics specimen. This specimen has a geometry constraint that is much closer to flaws in pipes than SENB specimens, which will give more realistic fracture properties of the pipe. In the procedure for defect assessments we present, both the fracture toughness and plastic collapse properties are taken from testing of SENT specimens. FE simulations and full scale testing verify the procedure.Copyright © 2003 by ASME

SENT Specimens an Alternative to SENB Specimens for Fracture Mechanics Testing of Pipelines

Effects of crack depth and specimen size on ductile crack growth of SENT and SENB specimens for fracture mechanics evaluation of pipeline steels

https://folk.ntnu.no/zhiliang/Zhiliangs-Papers-in-PDF-format/ZZ-J050-2009-IJSS-XR-ZZ-BN.pdf

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Papers

Additive manufacturing using WAAM with AA5183 wire

Efficient fracture assessment of pipelines. A constraint-corrected SENT specimen approach

SENT Specimens an Alternative to SENB Specimens for Fracture Mechanics Testing of Pipelines

Effects of crack depth and specimen size on ductile crack growth of SENT and SENB specimens for fracture mechanics evaluation of pipeline steels

Effect of residual stresses on the crack-tip constraint in a modified boundary layer model