scholarly journals Investigation of Strain Gradients and Magnitudes During Microbending

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Lijie Wang ◽  
Yannis Korkolis ◽  
Brad L. Kinsey
Keyword(s):  
Grain Size ◽  
Metal Forming ◽  
Polycrystalline Material ◽  
Current Trend ◽  
Electronics Industry ◽  
Image Correlation ◽  
Feature Size ◽  
Strain Gradients ◽  
Data Scatter ◽  
Individual Grains

Sheet metal forming of parts with microscale dimensions is gaining importance due to the current trend toward miniaturization, especially in the electronics industry. In microforming, although the process dimensions are scaled down, the polycrystalline material stays the same (e.g., the grain size remains constant). When the specimen feature size approaches the grain size, the properties of individual grains begin to affect the overall deformation behavior. This results in inhomogeneous deformation and increased data scatter of the process parameters. In this research, the influence of the specimen size and the grain size on the distribution of plastic deformation through the thickness during a three-point microbending process is investigated via digital image correlation (DIC). Results showed that with miniaturization, a decrease in the strain gradient existed which matched previous research with respect to microhardness measurement.

scholarly journals Investigation of Strain Gradients and Magnitudes During Microbending

2011 ◽  
Author(s):  
Lijie Wang ◽  
Brad L. Kinsey ◽  
Yannis Korkolis
Keyword(s):  
Grain Size ◽  
Metal Forming ◽  
Polycrystalline Material ◽  
Current Trend ◽  
Hardness Measurement ◽  
Image Correlation ◽  
Micro Hardness ◽  
Feature Size ◽  
Data Scatter ◽  
Individual Grains

Sheet metal forming of parts with microscale dimensions is gaining importance due to the current trend towards miniaturization, especially in the electronics industry. In microforming, although the process dimensions are scaled down, the polycrystalline material stays the same (e.g., the grain size remains constant). When the specimen feature size approaches the grain size, the properties of individual grains begin to affect the overall deformation behavior. This results in inhomogeneous deformation and increased data scatter of the process parameters. In this research, the influence of the specimen size and the grain size on the distribution of plastic deformation through the thickness during a 3-point microbending process is investigated via digital image correlation. Results showed that with miniaturization, a decrease in the strain gradient existed which matched previous research with respect to micro-hardness measurement.

Slip traces caused by plastic deformation during recrystallization of thin metal sheets

1994 ◽  
Vol 52 ◽  
pp. 620-621
Author(s):  
H. Lin ◽  
D. P. Pope
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Sample Thickness ◽  
List Type ◽  
Metal Sheets ◽  
Second Phases ◽  
Slip Traces ◽  
Series Of Experiments ◽  
Cold Rolled ◽  
Individual Grains

During a study of mechanical properties of recrystallized B-free Ni3Al single crystals, regularly spaced parallel traces within individual grains were discovered on the surfaces of thin recrystallized sheets, see Fig. 1. They appeared to be slip traces, but since we could not find similar observations in the literature, a series of experiments was performed to identify them. We will refer to them “traces”, because they contain some, if not all, of the properties of slip traces. A variety of techniques, including the Electron Backscattering Pattern (EBSP) method, was used to ascertain the composition, geometry, and crystallography of these traces. The effect of sample thickness on their formation was also investigated.In summary, these traces on the surface of recrystallized Ni3Al have the following properties:1.The chemistry and crystallographic orientation of the traces are the same as the bulk. No oxides or other second phases were observed.2.The traces are not grooves caused by thermal etching at previous locations of grain boundaries.3.The traces form after recrystallization (because the starting Ni3Al is a single crystal).4.For thicknesses between 50 μm and 720 μm, the density of the traces increases as the sample thickness decreases. Only one set of “protrusion-like” traces is visible in a given grain on the thicker samples, but multiple sets of “cliff-like” traces are visible on the thinner ones (See Fig. 1 and Fig. 2).5.They are linear and parallel to the traces of {111} planes on the surface, see Fig. 3.6.Some of the traces terminate within the interior of the grains, and the rest of them either terminate at or are continuous across grain boundaries. The portion of latter increases with decreasing thickness.7.The grain size decreases with decreasing thickness, the decrease is more pronounced when the grain size is comparable with the thickness, Fig. 4.8.Traces also formed during the recrystallization of cold-rolled polycrystalline Cu thin sheets, Fig. 5.

scholarly journals A Physical-Based Plane Stress Constitutive Model for High Strength AA7075 under Hot Forming Conditions

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 314
Author(s):  
Fulong Chen ◽  
Haitao Qu ◽  
Wei Wu ◽  
Jing-Hua Zheng ◽  
Shuguang Qu ◽  
...  
Keyword(s):  
Grain Size ◽  
Aluminum Alloy ◽  
Plane Stress ◽  
Metal Forming ◽  
Electron Backscatter Diffraction ◽  
High Strength ◽  
Material Model ◽  
Hot Forming ◽  
Industrial Processing ◽  
Average Grain Size

Physicallybased constitutive equations are increasingly used for finite element simulations of metal forming processes due to the robust capability of modelling of underlying microstructure evolutions. However, one of thelimitations of current models is the lack of practical validation using real microstructure data due to the difficulties in achieving statistically meaningful data at a sufficiently large microstructure scale. Particularly, dislocation density and grain size governing the hardening in sheet deformation are of vital importance and need to be precisely quantified. In this paper, a set of dislocation mechanics-based plane stress material model is constructed for hot forming aluminum alloy. This material model is applied to high strength 7075 aluminum alloy for the prediction of the flow behaviorsconditioned at 300–400 °C with various strain rates. Additionally, an electron backscatter diffraction (EBSD) technique was applied to examine the average grain size and geometrical necessary dislocation (GND) density evolutions, enabling both macro- and micro- characteristics to be successfully predicted. In addition, to simulate the experienced plane stress states in sheet metal forming, the calibrated model is further extended to a plane stress stateto accuratelypredict the forming limits under hot conditions.The comprehensively calibrated material model could be used for guidinga better selection of industrial processing parameters and designing process windows, taking into account both the formed shape as well as post formed microstructure and, hence, properties.

Expressions for the effective diffusivity in materials with interphase boundaries

2004 ◽  
Vol 819 ◽  
Author(s):  
Irina V. Belova ◽  
Graeme E. Murch
Keyword(s):  
Polycrystalline Material ◽  
Effective Diffusivity ◽  
Poor Agreement ◽  
Two Phase ◽  
Interphase Boundaries ◽  
Long Time ◽  
Simulation Results ◽  
The Individual ◽  
Individual Grains ◽  
Good Agreement

AbstractWe address the problem of calculating the long-time-limit effective diffusivity in stable two- phase polycrystalline material. A phenomenological model is used where the high diffusivity interphase boundaries are treated as connected “coatings” of the individual grains. Derivation of expressions for the effective diffusivity with segregation is made along Maxwell lines. Monte Carlo simulation using lattice-based random walks is used to test the validity of the expressions. It is shown that for the case analysed the derived expressions for the effective diffusivity are in very good agreement with simulation results. The equivalent of the Hart equation is also derived. It is shown to be in poor agreement with simulation results.

Severe Plastic Deformation-Key Features, Methods and Application

2020 ◽  
Vol 1003 ◽  
pp. 31-36
Author(s):  
Marko Vilotic ◽  
Li Hui Lang ◽  
Sergei Alexandrov ◽  
Dragisa Vilotic
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Grain Size ◽  
Tensile Strength ◽  
Severe Plastic Deformation ◽  
Metal Forming ◽  
Good Corrosion Resistance ◽  
Processed Material ◽  
Key Features ◽  
Forming Methods

Compared to conventional metal forming methods, processing by severe plastic deformation is mostly used to improve the mechanical properties and not for the shaping of a product. Processed material usually has an average crystal grain size of less than a micron and as a result, the material exhibits improvements in most of the mechanical properties, such as yield and ultimate tensile strength, microhardness, sufficiently high workability, good corrosion resistance, and implant biocompatibility and others. In this paper, a brief review of the processing by severe plastic deformation was presented, including the benefits, major methods, and the application. Additionally, a brief review of two methods made by authors was made.

Tem Study of Yielding in Polycrystalline Gold Thin Films

1997 ◽  
Vol 505 ◽  
Author(s):  
Kwame Owusu-Boahen ◽  
Alexander H. King
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Size ◽  
Rock Salt ◽  
Gold Films ◽  
Plastic Yielding ◽  
Transmission Electron ◽  
Mean Grain Size ◽  
Polycrystalline Gold ◽  
Individual Grains

ABSTRACTWe have used transmission electron microscopy (TEM) to study the microstructure of thin gold films which were grown on 〈100〉 rock salt. The samples were annealed on the rock salt substrate or on a gold TEM specimen grid. Films annealed on rock salt had a larger mean grain size than those annealed on TEM grids. All of the annealed films have a 〈111〉 preferred orientation. Several cracks are observed in the film annealed on rock salt. Plastic yielding of the film was identified by the presence of dislocations, and is caused by tensile stress derived from grain growth. In spite of the uniform texture of the films, the observed dislocations were concentrated only in some individual grains, while their surrounding grains remained dislocation-free. Yielded grains showed no difference of orientation that would lead to higher Schmid factors, so other predictors of yielding must be considered.

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.

Reliability Studies for Package-on-Package Components in Drop and Shock Environments

2011 ◽  
Author(s):  
Pradeep Lall ◽  
Arjun Angral ◽  
Jeff Suhling
Keyword(s):  
Life Prediction ◽  
Prediction Models ◽  
Electronics Industry ◽  
Consumer Electronics ◽  
Production Costs ◽  
Image Correlation ◽  
Optimum Process ◽  
Testing Procedures ◽  
Portable Electronics ◽  
Fe Simulations

The consumer electronics industry stands at a critical juncture where manufacturers strive to incorporate more functionality in smaller packages. In the highly competitive consumer electronics market, a continued demand for products with smallest possible form-factor yet high functionality has led to the proliferation of 3D packaging technologies. Package-on-Package (PoP) architectures, in particular have attracted a lot of interest, especially in portable electronics industry. The advantages of these stacked 3D architectures include simplified and compact design, savings of board space allowing for more package landings, reduced pin counts and optimized production costs. While a lot of recent research, in the field of PoP architectures has been focused on development of optimum process flows and warpage control during reflow, the effects of reflow parameters on the quality of PoP build and the associated reflow defects including warpage have not been extensively researched. Additionally, studies on reliability issues associated with PoP assemblies in drop and shock environments are scarce. Since PoP architectures find their applications mainly in portable electronics, which are susceptible to frequent drops and careless handling at the hand of the consumer, the reliability of PoP architectures in environments representative of the real world is critical to their success in the industry. In this study, Single component PoP test vehicles have been fabricated as per JEDEC standards for quantifying the reliability of PoP packages in drop and shock. Daisy chained double-stack PoP components have been used to identify failure for subsequent drop/shock performance analysis. Experimental strain data acquired using Digital Image Correlation and high speed continuity data- for identifying failure has been used in conjunction with validated FE simulations of drop test events; for development of life prediction models for PoP architectures. Validated node based global-local FE simulations are used to predict strains in critical solder balls in both layers of the PoP stack. The drop/shock reliability studies and life prediction models presented in this work, present an insight into PoP failures and eliminate the need for exhaustive testing procedures.

Analytical Prediction of Geometrically Necessary Dislocation Density during Plane Strain Microbending

2016 ◽  
Vol 693 ◽  
pp. 734-739 ◽  
Author(s):  
Li Jie Wang ◽  
Brad L. Kinsey ◽  
Sunal Parasiz
Keyword(s):  
Dislocation Density ◽  
Plane Strain ◽  
Analytical Model ◽  
Cross Section ◽  
Strain Gradient ◽  
Analytical Prediction ◽  
Feature Size ◽  
Strain Gradients ◽  
Geometrically Necessary Dislocation ◽  
The Cross

As components with proportional feature and tooling sizes are miniaturized, strain gradients through the cross-section increase. This causes strain gradient hardening as the density of geometrically necessary dislocations increases. This will lead to higher required forces in the process than expected. In this paper, an analytical model to predict the dislocation density increases, and thus strain gradient hardening, during microbending is presented. These results match previous research in terms of the feature size where modest and significant strain gradient hardening was observed.

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