scholarly journals Fatigue Crack Initiation of Metals Fabricated by Additive Manufacturing—A Crystal Plasticity Energy-Based Approach to IN718 Life Prediction

Crystals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 905
Author(s):  
Chun-Yu Ou ◽  
Rohit Voothaluru ◽  
C. Richard Liu
Keyword(s):  
Shear Stress ◽  
Additive Manufacturing ◽  
Crack Initiation ◽  
Strain Hardening ◽  
Elastic Constants ◽  
Crystal Plasticity ◽  
Stress Strain ◽  
Hardening Modulus ◽  
Critical Resolved Shear Stress ◽  
Effect Of Microstructure

There has been a long-standing need in the marketplace for the economic production of small lots of components that have complex geometry. A potential solution is additive manufacturing (AM). AM is a manufacturing process that adds material from the bottom up. It has the distinct advantages of low preparation costs and a high geometric creation capability. However, the wide range of industrial processing conditions results in large variations in the fatigue lives of metal components fabricated using AM. One of the main reasons for this variation of fatigue lives is differences in microstructure. Our methodology incorporated a crystal plasticity finite element model (CPFEM) that was able to simulate a stress–strain response based on a set of randomly generated representative volume elements. The main advantage of this approach was that the model determined the elastic constants (C11, C12, and C44), the critical resolved shear stress (g0), and the strain hardening modulus (h0) as a function of microstructure. These coefficients were determined based on the stress–strain relationships derived from the tensile test results. By incorporating the effect of microstructure on the elastic constants (C), the shear stress amplitude (Δτ2) can be computed more accurately. In addition, by considering the effect of microstructure on the critical resolved shear stress (g0) and the strain hardening modulus (h0), the localized dislocation slip and plastic slip per cycle (Δγp2) can be precisely calculated by CPFEM. This study represents a major advance in fatigue research by modeling the crack initiation life of materials fabricated by AM with different microstructures. It is also a tool for designing laser AM processes that can fabricate components that meet the fatigue requirements of specific applications.

Evaluation of Anisotropic Pipe Steel Stress-Strain Relationships Influence on Strain Demand

2012 ◽  
Author(s):  
James D. Hart ◽  
Nasir Zulfiqar ◽  
Joe Zhou
Keyword(s):  
Strain Hardening ◽  
Pipe Steel ◽  
High Strain ◽  
Strain Curve ◽  
High Strength ◽  
Strain Response ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Hardening Modulus ◽  
Strain Relationship

Buried pipelines can be exposed to displacement-controlled environmental loadings (such as landslides, earthquake fault movements, etc.) which impose deformation demands on the pipeline. When analyzing pipelines for these load scenarios, the deformation demands are typically characterized based on the curvature and/or the longitudinal tension and compression strain response of the pipe. The term “strain demand” is used herein to characterize the calculated longitudinal strain response of a pipeline subject to environmentally-induced deformation demands. The shape of the pipe steel stress-strain relationship can have a significant effect on the pipe strain demands computed using pipeline deformation analyses for displacement-controlled loading conditions. In general, with sufficient levels of imposed deformation demand, a pipe steel stress-strain curve with a relatively abrupt or “sharp” elastic-to-plastic transition will tend to lead to larger strain demands than a stress-strain curve with a relatively rounded elastic-to-plastic transition. Similarly, a stress-strain curve with relatively low strain hardening modulus characteristics will tend to lead to larger strain demands than a stress-strain curve with relatively high strain hardening modulus characteristics. High strength UOE pipe can exhibit significant levels of anisotropy (i.e., the shapes of the stress-strain relationships in the longitudinal tension/compression and hoop tension/compression directions can be significantly different). To the extent that the stress-strain curves in the different directions can have unfavorable shape characteristics, it follows that anisotropy can also play an important role in pipeline strain demand evaluations. This paper summarizes a pipeline industry research project aimed at evaluation of the effects of anisotropy and the shape of pipe steel stress-strain relationships on pipeline strain demand for X80 and X100 UOE pipe. The research included: a review of pipeline industry literature on the subject matter; a discussion of pipe steel plasticity concepts for UOE pipe; characterization of the anisotropy and stress-strain curve shapes for both conventional and high strain pipe steels; development of representative analytical X80 and X100 stress-strain relationships; and evaluation of a large matrix of ground-movement induced pipeline deformation scenarios to evaluate key pipe stress-strain relationship shape and anisotropy parameters. The main conclusion from this work is that pipe steel specifications for high strength UOE pipe for strain-based design applications should be supplemented to consider shape-characterizing parameters such as the plastic complementary energy.

The derivation of a strain hardening modulus from true stress-strain curves for thermoplastics

Polymer ◽  
1994 ◽  
Vol 35 (18) ◽  
pp. 3858-3862 ◽  
Author(s):  
R.N Haward
Keyword(s):  
Strain Hardening ◽  
True Stress ◽  
Stress Strain ◽  
Hardening Modulus

Effect of Crystal Plasticity Parameters on Microscopic Stress Distribution in Polycrystalline Aggregate Model

2013 ◽  
Vol 05 (01) ◽  
pp. 1350003 ◽  
Author(s):  
Yoshiki Mikami ◽  
Kazuo Oda ◽  
Masahito Mochizuki
Keyword(s):  
Stress Distribution ◽  
Crystal Plasticity ◽  
Strain Curve ◽  
Polycrystalline Aggregate ◽  
Aggregate Model ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Microscopic Scale ◽  
Macroscopic Stress ◽  
Hardening Modulus

Crystal plasticity parameters for numerical simulations are difficult to experimentally measure on the microscopic scale. One possible approach to avoid the difficulty is to determine the parameters that can be used to reproduce the stress–strain curve by employing a polycrystalline aggregate model. In this study, the effect of crystal plasticity parameters on stress–strain curves on a macroscopic scale and on stress distribution on a microscopic scale was investigated by using polycrystalline aggregate simulation. The parameters investigated were initial slip strength (τ0), initial hardening modulus (h0) and saturation slip strength (τs). The effect of these parameters on macroscopic stress–strain curves was found to be the followings: τ0 controls the yield stress or proof stress, and both h0 and τs control the strain-hardening behavior. The effect of these parameters on microscopic stress distribution was also investigated because similar stress–strain curve can be obtained by using different sets of crystal plasticity parameters. Consequently, even if these parameters are slightly different, a similar microscopic stress distribution can be obtained by properly reproducing the macroscopic stress–strain curve.

Effect of Lattice Rotation on Hardening Behavior of HCP Metals

2016 ◽  
Vol 725 ◽  
pp. 502-507
Author(s):  
Takaaki Kurisu ◽  
Yuichi Tadano ◽  
Seiya Hagihara
Keyword(s):  
Shear Stress ◽  
Slip System ◽  
Strain Hardening ◽  
Lattice Rotation ◽  
Plasticity Model ◽  
Hexagonal Close Packed ◽  
Hardening Behavior ◽  
Crystal Plasticity Model ◽  
Strain Hardening Behavior ◽  
Critical Resolved Shear Stress

Strain hardening behavior is known to strongly affect the formability of metallic sheets. The effect of lattice rotation on the hardening behavior of hexagonal close-packed (HCP) metals is numerically investigated using a homogenization-based crystal plasticity model to represent the polycrystalline behavior. The effect of lattice rotation on strain hardening behavior evaluated using different initial textures, and the geometrical hardening effect of HCP metals is investigated. In addition, the critical resolved shear stress of each slip system is varied and is shown to affects the strain hardening in HCP metals. In this study, we further discuss the possibility to improve the formability of HCP metals.

A Multi-Scale Approach for Prediction of Irradiation Effect on RPV Steel Toughness

2005 ◽  
Author(s):  
O. Diard
Keyword(s):  
Shear Stress ◽  
Nuclear Reactor ◽  
Homogenization Method ◽  
Plastic Behavior ◽  
Irradiation Effect ◽  
Slip Systems ◽  
Local Approach ◽  
Stress Strain ◽  
Crystallographic Slip ◽  
Critical Resolved Shear Stress

Nuclear reactor pressure vessel steels are subjected to an irradiation-induced embrittlement in service and this may lead to a shift of the ductile-to-brittle transition temperature. The prediction of irradiation effect on toughness requires an accurate description of the elasto-visco-plastic behavior of irradiated steels. Recent progresses have been done to describe microstructural evolutions induced by irradiation. Ab-initio computations, molecular dynamics and discrete dislocations dynamics can predict the defects formation and the hardening induced by the dislocations – defects interactions. At this level, the irradiation effect is essentially reported as an increase of the critical resolved shear stress on the crystallographic slip systems. A numerical homogenization method is proposed to predict stress-strain curves of irradiated steels from the computed critical resolved shear stress evolution. Computations of realistic 3D aggregates and classical homogenization are performed with a Finite Element code [1]. Each grain is described as a single crystal with a crystal plasticity law, which naturally introduces the irradiation effect on the slip systems activity. The resulting average response over the whole aggregate corresponds to classical stress-strain curves. A Beremin type local approach is then applied to compute the fracture toughness of irradiated CT specimens. Assuming that the local approach parameters do not depend on the irradiation level, this methodology is able to take benefits of MD and DDD results to predict the irradiation effect on RPV steels toughness.

Evaluating a Critical Resolved Shear Stress Criterion for Domain Nucleation in Ferroelastic Ceramics

2020 ◽  
Author(s):  
Charles S. Smith ◽  
Quentin Rizzardi ◽  
Robert Maaß ◽  
Jessica A. Krogstad
Keyword(s):  
Shear Stress ◽  
Stress Criterion ◽  
Critical Resolved Shear Stress

scholarly journals Enhanced lattice distortion, yield strength, critical resolved shear stress, and improving mechanical properties of transition-metals doped CrCoNi medium entropy alloy

RSC Advances ◽  
2021 ◽  
Vol 11 (38) ◽  
pp. 23719-23724
Author(s):  
Md. Lokman Ali
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Transition Metals ◽  
Yield Strength ◽  
Lattice Distortion ◽  
Critical Resolved Shear Stress

The effect of transition-metals (TM) addition on the mechanical properties of CrCoNi medium entropy alloys (MEAs) was investigated.

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