scholarly journals Modeling of the Size Effects on the Behavior of Metals in Microscale Deformation Processes

2006 ◽  
Vol 129 (3) ◽  
pp. 470-476 ◽  
Author(s):  
Gap-Yong Kim ◽  
Jun Ni ◽  
Muammer Koç
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Size Effects ◽  
Specimen Size ◽  
Material Behavior ◽  
Accurate Analysis ◽  
Analysis And Design ◽  
Scaling Model ◽  
Simple Tension ◽  
Two Parameters

For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/mesoscale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the feature/specimen size effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with three separate experiments obtained from previous research: a simple compression with a round specimen, a simple tension with a round specimen, and a simple tension in sheet metal. The predicted results had a very good agreement with the experiments. Quantification of the miniaturization effect has been achieved by introducing two parameters, α and β, which can be determined by the scaling parameter n, to the Hall–Petch equation. The scaling model offers a simple way to model the size effect down to length scales of a couple of grains and to extend the use of continuum plasticity theories to micro/mesolength scales.

Modeling of Size Effects on the Flow Stress of Type 304 Stainless Steel and Application in Coining Process

2007 ◽  
Author(s):  
Gap-Yong Kim ◽  
Muammer Koc ◽  
Jun Ni
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Flow Stress ◽  
Size Effect ◽  
Size Effects ◽  
Specimen Size ◽  
304 Stainless Steel ◽  
Length Scales ◽  
Type 304 ◽  
Type 304 Stainless Steel

Application of microforming in various research areas has received much attention due to the increased demand for miniature metallic parts that require mass production. For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/meso-scale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the “feature/specimen size” effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with experiments obtained from previous research and showed a very good agreement. The model was also applied to forming of micro-features by coining. A flow stress model for Type 304 stainless steel taking into consideration the effect of the grain and feature size was developed and implemented into a finite element simulation tool for an accurate numerical analysis. The scaling model offered a simple way to model the size effect down to length scales of a couple of grains and extended the use of continuum plasticity theories to micro/meso-length scales.

FE Analysis of Size Effect on Deformation Behavior of Metal Microtube Considering Surface Roughness in Flaring Test

2009 ◽  
Vol 623 ◽  
pp. 79-87 ◽  
Author(s):  
Mohammad Ali Mirzai ◽  
Kenichi Manabe
Keyword(s):  
Surface Roughness ◽  
Size Effect ◽  
Wall Thickness ◽  
Size Effects ◽  
Fe Analysis ◽  
Material Behavior ◽  
Test Results ◽  
Feature Size ◽  
Analysis And Design ◽  
Smoothing Process

Reliable test results that show the material characteristics of a micromaterial are necessary for the accurate analysis and design of microforming processes. The size effects in the microforming are predicted to have a significant impact on the material behavior. Two size effects are explored in metallic materials. One is the grain size effect, and the other is the feature/specimen size effect. In this study, the feature size effect on the smoothing process with the consideration of tool surface roughness is investigated numerically for metal microtubes by the flaring test. Stainless-steel (SUS 316L) microtubes with the same outer diameter of 500 μm and different wall thicknesses of 50, 25 and 10 μm were used in the FE analysis to study the feature size effect on the microscale by the flaring test. The surface roughnesses of the inner and outer surfaces of the microtube, as well as the surface asperity of the conical tool, were modeled in the cyclic concave-convex configuration. It is found, in the flaring test with using rough and fine tools, that the smoothing process on the inner surface of the microtube (ISM), as well as the plastic strain in the wall thickness of microtube, is affected owing to the rigidity of the microtube, which decreases as the wall thickness of the microtube decreases. These results suggest that the feature size affects the flaring test results for the metal microtube.

Study of the Size Effects and Friction Conditions in Microextrusion—Part II: Size Effect in Dynamic Friction for Brass-Steel Pairs

2007 ◽  
Vol 129 (4) ◽  
pp. 677-689 ◽  
Author(s):  
Lapo F. Mori ◽  
Neil Krishnan ◽  
Jian Cao ◽  
Horacio D. Espinosa
Keyword(s):  
Grain Size ◽  
Friction Coefficient ◽  
Size Effect ◽  
Contact Pressure ◽  
Size Effects ◽  
Numerical Models ◽  
Kolsky Bar ◽  
Experimental Results ◽  
Material Response ◽  
Dynamic Coefficients

In this paper, the results of experiments conducted to investigate the friction coefficient existing at a brass-steel interface are presented. The research discussed here is the second of a two-part study on the size effects in friction conditions that exist during microextrusion. In the regime of dimensions of the order of a few hundred microns, these size effects tend to play a significant role in affecting the characteristics of microforming processes. Experimental results presented in the previous companion paper have already shown that the friction conditions obtained from comparisons of experimental results and numerical models show a size effect related to the overall dimensions of the extruded part, assuming material response is homogeneous. Another interesting observation was made when extrusion experiments were performed to produce submillimeter sized pins. It was noted that pins fabricated from large grain-size material (211μm) showed a tendency to curve, whereas those fabricated from billets having a small grain size (32μm), did not show this tendency. In order to further investigate these phenomena, it was necessary to segregate the individual influences of material response and interfacial behavior on the microextrusion process, and therefore, a series of frictional experiments was conducted using a stored-energy Kolsky bar. The advantage of the Kolsky bar method is that it provides a direct measurement of the existing interfacial conditions and does not depend on material deformation behavior like other methods to measure friction. The method also provides both static and dynamic coefficients of friction, and these values could prove relevant for microextrusion tests performed at high strain rates. Tests were conducted using brass samples of a small grain size (32μm) and a large grain size (211μm) at low contact pressure (22MPa) and high contact pressure (250MPa) to see whether there was any change in the friction conditions due to these parameters. Another parameter that was varied was the area of contact. Static and dynamic coefficients of friction are reported for all the cases. The main conclusion of these experiments was that the friction coefficient did not show any significant dependence on the material grain size, interface pressure, or area of contact.

Modeling of Size Effect on Tensile Flow Stress of Sheet Metal in Microforming

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Daw-Kwei Leu
Keyword(s):  
Grain Size ◽  
Flow Stress ◽  
Size Effect ◽  
Sheet Metal ◽  
Sheet Thickness ◽  
Hyperbolic Function ◽  
Zone Model ◽  
Petch Relation ◽  
Simple Tension ◽  
Dependent Factor

This investigation considers the size effect on the deformation behavior of simple tension in microforming and thus proposes a simple model of the tensile flow stress of sheet metal. Experimental results reveal that the measure of the flow stress can be represented as a hyperbolic function tanh(T/D), which is a function of T/D (sheet thickness/grain size). The predicted flow stress agrees very well with the published experiment. Notably, a specimen with smaller grains has lower normalized flow stress for a given T/D. Since the material properties of the macroscale specimen do not pertain to the microscale, a critical condition (T/D)c that distinguishes the macroscale from the microscale in the tensile flow stress is subsequently proposed, based on the “affected zone” model, the pile-up theory of dislocations, and the Hall–Petch relation. The distribution of the predicted (T/D)c is similar to the experimental finding that the (T/D)c decreases as the grain size increases. However, the orientation-dependent factor β is sensitive to (T/D)c. Hence, further study of the orientation-dependent factor β is necessary to obtain a more accurate (T/D)c and, thus, to evaluate and understand better the tensile flow stress of sheet metal in microforming.

Main Problems of Nanostructured Materials Science

2005 ◽  
Vol 494 ◽  
pp. 113-120 ◽  
Author(s):  
R.A. Andrievski
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Nanostructured Materials ◽  
Size Effects ◽  
Materials Science ◽  
Nanocomposite Materials ◽  
New Approaches ◽  
Structures And Properties ◽  
Complex Influence

Size effects in nanostructured (nanocrystalline, nanophase or nanocomposite) materials (NMs) and their stability are of great importance for fundamental considerations and modern practice. The size effect peculiarities in NMs are analyzed and the complex influence of grain size and other factors on NM properties is emphasized. New approaches in the development of thermostable NMs are considered with a special attention to the importance of the reproducibility of NM structures and properties.

scholarly journals Size Effect on Recycled Concrete Strength and Its Prediction Model Using Standard Neutrosophic Number

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
X. Peng ◽  
Q. W. Yang ◽  
F. J. Qin
Keyword(s):  
Size Effect ◽  
Size Effects ◽  
Concrete Strength ◽  
Engineering Application ◽  
Specimen Size ◽  
Recycled Concrete ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Aggregate Concrete ◽  
Neutrosophic Number

In recent years, research on recycled aggregate concrete has become a hot issue in the field of civil engineering. This paper mainly studies the size effects on compressive and tensile strengths of the recycled aggregate concrete. Firstly, four sets of recycled concrete cube specimens with different sizes are produced in the laboratory. Secondly, the experiments on compressive and tensile strengths are carried out to obtain the rules of the strength value with the change of the specimen size. Thirdly, a standard neutrosophic number is proposed and used in modelling the size effect law more reasonably. According to the experimental results, it was found that the compressive and tensile strengths of recycled concrete both have obvious size effects. In general, the strength value decreases gradually with the increase of specimen size. Using the standard neutrosophic number, the proposed new formula on size effect law is more suitable for tackling the indeterminacy in the experimental data. It has been shown that the size effect law based on the standard neutrosophic number is more realistic than the existing size effect law. The results may be useful for the engineering application of the recycled concrete and can be extended to other types of size effect laws in the future.

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