Local Mechanical Properties of a Magnesium Hood Inner Component Formed at Elevated Temperature

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Vesna Savic ◽  
Louis G. Hector ◽  
Sooho Kim ◽  
Ravi Verma
Keyword(s):  
Grain Size ◽  
Finite Element ◽  
True Strain ◽  
Local Strain ◽  
Tensile Specimen ◽  
Finite Element Simulations ◽  
Image Correlation ◽  
Specimen Thickness ◽  
Average Grain Size ◽  
Tensile Data

There is considerable worldwide interest in magnesium (Mg) sheet as a replacement for heavier steel and aluminum alloys in vehicle closure components. As Mg gains acceptance in the automotive industry, there will be an increasing demand for accurate material properties for finite element simulations of Mg structures. In this paper, we investigate the extent to which average grain size and postformed tensile properties vary across a Mg AZ31B hood inner component formed at 485°C for 20 min under a constant gas pressure. Tensile specimens were extracted from six regions of the hood inner, which underwent varying degrees of thinning. A state-of-the-art digital image correlation (DIC) algorithm and custom image acquisition software provided true stress-true strain data for each specimen. Tensile data acquired during room temperature testing was compared with that from baseline (undeformed) Mg AZ31B in a fully recrystallized condition (O-temper). Due to its importance in finite element simulations, particular emphasis was placed on the variation of postformed yield strength with specimen thickness and average grain size. Finally, we compute local strain fields during fracture in a tensile specimen with DIC grids positioned in the failure region.

Study on Dynamic Recrystallization Behavior in Deformed Austenite of 52100 Steel by Using JMAK-Model

2013 ◽  
Vol 275-277 ◽  
pp. 1833-1837
Author(s):  
Ke Lu Wang ◽  
Shi Qiang Lu ◽  
Xin Li ◽  
Xian Juan Dong
Keyword(s):  
Grain Size ◽  
Dynamic Recrystallization ◽  
Hot Deformation ◽  
Volume Fraction ◽  
True Strain ◽  
Strain And Strain Rate ◽  
Average Grain Size ◽  
Dynamic Recrystallization Behavior ◽  
Simulation And Experiment ◽  
Good Agreement

A Johnson-Mehl-Avrami-Kolmogorov (JMAK)-model was established for dynamic recrystallization in hot deformation process of 52100 steel. The effects of hot deformation temperature, true strain and strain rate on the microstructural evolution of the steel were physically studied by using Gleeble-1500 thermo-mechanical simulator and the experimental results were used for validation of the JMAK-model. Through simulation and experiment, it is found that the predicted results of DRX volume fraction, DRX grain size and average grain size are in good agreement with the experimental ones.

scholarly journals Prediction of Epitaxial Grain Growth in Single-Track Laser Melting of IN718 Using Integrated Finite Element and Cellular Automaton Approach

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5202
Author(s):  
Amir Reza Ansari Dezfoli ◽  
Yu-Lung Lo ◽  
M. Mohsin Raza
Keyword(s):  
Grain Size ◽  
Finite Element ◽  
Grain Growth ◽  
Heat Input ◽  
Single Track ◽  
Laser Melting ◽  
Melt Pool ◽  
Initial Substrate ◽  
Average Grain Size ◽  
Epitaxial Grain Growth

The mechanical properties of selective laser melting (SLM) components are fundamentally dependent on their microstructure. Accordingly, the present study proposes an integrated simulation framework consisting of a three-dimensional (3D) finite element model and a cellular automaton model for predicting the epitaxial grain growth mode in the single-track SLM processing of IN718. The laser beam scattering effect, melt surface evolution, powder volume shrinkage, bulk heterogeneous nucleation, epitaxial growth, and initial microstructure of the substrate are considered. The simulation results show that during single-track SLM processing, coarse epitaxial grains are formed at the melt–substrate interface, while fine grains grow at the melt–powder interface with a density determined by the intensity of the heat input. During the solidification stage, the epitaxial grains and bulk nucleated grains grow toward the top surface of the melt pool along the temperature gradient vectors. The rate of the epitaxial grain growth varies as a function of the orientation and size of the partially melted grains at the melt–substrate boundary, the melt pool size, and the temperature gradient. This is observed that by increasing heat input from 250 J/m to 500 J/m, the average grain size increases by ~20%. In addition, the average grain size reduces by 17% when the initial substrate grain size decreases by 50%. In general, the results show that the microstructure of the processed IN718 alloy can be controlled by adjusting the heat input, preheating conditions, and initial substrate grain size.

The Correlation Length: A Measure of Inhomogeneities in Polycrystalline Materials

2004 ◽  
Author(s):  
Igor Simonovski ◽  
Marko Kovacˇ ◽  
Leon Cizelj
Keyword(s):  
Grain Size ◽  
Finite Element ◽  
Stress Field ◽  
Yield Strength ◽  
Correlation Length ◽  
Shear Bands ◽  
Polycrystalline Materials ◽  
Internal Length ◽  
Correlation Lengths ◽  
Average Grain Size

This paper deals with the correlation length estimated from a mesoscopic model of a polycrystalline material. The correlation length can be used in some macroscopic material models as a material parameter that describes the internal length. It can be estimated directly from the strain and stress fields calculated from a finite-element model, which explicitly accounts for the selected mesoscopic features such as the random orientation, shape and size of the grains. The crystal plasticity material model was applied during the finite-element analysis. Different correlation lengths were obtained depending on whether the strain or the stress field was used. The correlation lengths also changed with the macroscopic load. While the load is below the yield strength the correlation lengths are constant, and of the order of the average grain size. Increasing the load above the yield strength creates shear bands that temporarily increase the values of the correlation lengths calculated from the strain fields. With a further load increase the correlation lengths decrease slightly below the average grain size. The correlation lengths calculated from the stress field are smaller than the ones calculated from the strain field. However, with the exception of the load region where significant shear bands appear, both seem to follow the same qualitative rules.

scholarly journals Effect of True Strains in Isothermal abc Pressing on Mechanical Properties of Ti49.8Ni50.2 Alloy

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1313
Author(s):  
Oleg Kashin ◽  
Konstantin Krukovskii ◽  
Aleksandr Lotkov ◽  
Victor Grishkov
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
True Strain ◽  
Main Idea ◽  
Strain Curve ◽  
Subgrain Structure ◽  
Average Grain Size ◽  
Abc Pressing

The paper analyzes the microstructure and mechanical properties of Ti49.8Ni50.2 alloy (at.%) under uniaxial tension at room temperature after isothermal abc pressing to true strains e = 0.29 − 8.44 at T = 723 K. The analysis shows that as the true strain e is increased, the grain–subgrain structure of the alloy is gradually refined. This leads to an increase in its yield stress σy and strain hardening coefficient θ = dσ/dε at linear stage III of its tensile stress–strain curve according to the Hall–Petch relation. However, the ultimate tensile strength remains invariant to such refinement. The possible mechanism is proposed to explain why the ultimate tensile strength can remain invariant to the average grains size (dav). It is assumed that the sharp increase of the ultimate tensile strength σUTS begins when (dav) is less than the critical average grain size (dav)cr. In our opinion, for the investigated alloy (dav)cr ≈ 0.5 µm. In our study, the attained average grain size is larger the critical one. The main idea of the mechanism is next. In alloys with an average grain size (dav) less than the critical one, a higher external stress is required for the nucleation and propagation of the main crack.

Validation of a Conventional Finite Element Model for Simulation of a Micropunching Process

2014 ◽  
Author(s):  
Amrit Sagar ◽  
Christopher R. Nehme ◽  
Anil Saigal ◽  
Thomas P. James
Keyword(s):  
Grain Size ◽  
Finite Element ◽  
Bulk Material ◽  
Foil Thickness ◽  
Homogeneous Material ◽  
Element Analysis ◽  
Hardening Material ◽  
Material Inhomogeneity ◽  
Finite Element Software ◽  
Average Grain Size

Finite element analysis (FEA) of metal microforming processes may require Crystal Plasticity Finite Element (CPFE) formulations to incorporate material inhomogeneity as feature size approaches grain size. Presently, it is unknown if the micropunching process, where holes are formed by shearing thin metal foils with a thickness on the same scale as grain size, can be accurately simulated by using the material’s bulk material properties or if CPFE is required. In the current research, validity of conventional FEA in simulating micropunching is investigated as CPFE formulations have yet to be integrated with most commercially available programs. Using DEFORM finite element software, strain hardening and strain rate hardening material models were employed to approximate flow stress when punching 200 μm diameter holes in 25 μm thick annealed copper foil. For validation of peak punching force, micro holes were fabricated with a nominal diameter of 200 μm for die clearances ranging from 7.6% to 48% of material thickness. The average grain size of the foil was determined to be approximately 47 μm. Therefore, micropunching was predominantly through a single grain across foil thickness and less than a grain in the direction of radial die clearance. Results indicate that the homogeneous material model in DEFORM is capable of predicting the maximum punching forces with reasonable accuracy, concluding that a CPFE model is not necessary for this category of micropunching. Regardless of die clearance, the maximum punching force was approximately 3 N.

Hardness of thin Films of Nanocrystalline Silver and Nickel Composites Studied by Nanoindentation and Finite Element Analysis

1995 ◽  
Vol 400 ◽  
Author(s):  
Boqin Qiu ◽  
Yang-Tse Cheng ◽  
James P. Blanchard
Keyword(s):  
Thin Films ◽  
Grain Size ◽  
Finite Element ◽  
Two Phase ◽  
Element Analysis ◽  
Gas Condensation ◽  
Nano Crystalline ◽  
Average Grain Size ◽  
Nickel Composites ◽  
Xrd And Tem

AbstractWhile gas condensation and mechanical alloying have been used to produce nano-phase powders, an effective method of applying these powders as coatings is still lacking. Furthermore, fundamental studies of the mechanical properties of nano-phase powders may be complicated by the porosity associated with consolidation processes. Recently, we have made nano-crystalline composite thin films of Ag-Mo and Ag-Ni by depositing two immiscible elements simultaneous onto substrates. We found, using XRD and TEM, that the average grain size varies from 10 to 100 nm by choosing an appropriate substrate temperature. Nanoindentation measurements showed the hardness of the composite is increased four times by reducing the grain-size of both phases from 100 to 10 nm. The load vs. displacement curves were simulated using a finite element method (ABAQUS). A relationship between the hardness of the two-phase composite and the yield strength of each phase is obtained.

Procedure for the Determination of True Stress-Strain Curves From Tensile Tests With Rectangular Cross-Section Specimens

2004 ◽  
Vol 126 (1) ◽  
pp. 70-76 ◽  
Author(s):  
I. Scheider ◽  
W. Brocks ◽  
A. Cornec
Keyword(s):  
Finite Element ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Strain Curve ◽  
Tensile Tests ◽  
Tensile Specimen ◽  
True Stress ◽  
Image Correlation ◽  
Stress Strain ◽  
Three Dimensional Finite Element

The problem of determining true stress-strain curves from flat tensile specimens beyond the onset of necking has been investigated based on finite element analyses under consideration of experimental accessible data using digital image correlation (DIC). The displacement field on the specimen surface is determined by in-situ deformation field measurement. A three-dimensional finite element study with different stress-strain-curves has been carried out to develop a formula, with which it is possible to calculate the true stress subject to the strain in the necking region. The method has been used to evaluate the true stress-strain curve with a so-called micro flat tensile specimen, which is normally used to determine the material properties in the material gradient around thin weldments.

scholarly journals Modelling Microstructure Evolution in ATI 718Plus® Alloy

2016 ◽  
Vol 716 ◽  
pp. 352-359
Author(s):  
Aleksey Reshetov ◽  
Olga Bylya ◽  
Michal Gzyl ◽  
Malgorzata Rosochowska ◽  
Paul Blackwell
Keyword(s):  
Finite Element Analysis ◽  
Grain Size ◽  
Finite Element ◽  
Grain Growth ◽  
Microstructure Evolution ◽  
Deformation Process ◽  
Main Trend ◽  
Main Body ◽  
Element Analysis ◽  
Average Grain Size

The present study details the results of finite element analysis (FEA) based predictions for microstructure evolution in ATI 718Plus® alloy during the hot deformation process. A detailed description of models for static grain growth and recrystallisation is provided. The simulated average grain size is compared with those experimentally measured in aerofoil parts after forging trials. The proposed modified JMAK model has proved to be valid in the main body of the forging. The results predicted for the surface are less accurate. The recrystallised grain size on the surface is smaller than in the centre of the part which corresponds to the experimental results and reflects the main trend.

Young’s Modulus of Polysilicon Thin Film Evaluated by Finite Element Analysis

2007 ◽  
Vol 353-358 ◽  
pp. 2227-2230
Author(s):  
Kazuto Tanaka ◽  
Kohji Minoshima ◽  
Takehiro Imoto
Keyword(s):  
Thin Film ◽  
Grain Size ◽  
Finite Element ◽  
Young’S Modulus ◽  
Crystal Orientation ◽  
Young's Modulus ◽  
Fem Analysis ◽  
Front Surface ◽  
Element Analysis ◽  
Average Grain Size

To analyze the effect of the crystal orientations and the grain size on the Young's modulus of thin polysilicon microelements, two-dimensional finite element models in plain strain condition were developed using a Voronoi structure. The number of grains in a model of a 10 μm square area was changed from 23 to 1200. The grain size and the crystal orientation of the film were analyzed by means of an electron back-scattering diffraction pattern (EBSP) method. The average grain size of the front surface of the thin film was about 0.69 μm, which is almost equal to the grain size of the Voronoi model having 300 grains. From the results of EBSP analysis, the specimen had no oriented structure. Therefore, random crystal orientation was given to each grain of the FEM models. When the number of grains increased, the Young's modulus converged on about 171 GPa and its scatter caused by the different sets of the random orientation was reduced. The Young's modulus obtained by the FEM analysis was larger than the value obtained by the tensile tests.

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