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.

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.

On the Hall–Petch relation between flow stress and grain size

2006 ◽  
Vol 97 (12) ◽  
pp. 1661-1666 ◽  
Author(s):  
W. Blum ◽  
Y. J. Li ◽  
J. Chen ◽  
X. H. Zeng ◽  
K. Lu
Keyword(s):  
Grain Size ◽  
Flow Stress ◽  
Petch Relation

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.

Progressive and Compound Forming for Producing Plunger-Typed Microparts by Using Sheet Metal

2020 ◽  
Vol 8 (2) ◽  
Author(s):  
Jun-Yuan Zheng ◽  
Ming-Wang Fu
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Sheet Metal ◽  
Mass Production ◽  
Grain Size Effect ◽  
Sheet Metals ◽  
Forming Process ◽  
Deformation Behaviors ◽  
Progressive Forming ◽  
Insight Into

Abstract The plunger part in temporary electronic connectors is traditionally fabricated by micromachining. Progressive forming of microparts by directly using sheet metals is developed and proven to be an efficient microforming process to overcome some intrinsic drawback in realization of mass production of microparts. By employing this unique micromanufacturing process, an efficient approach with progressive microforming is developed to fabricate plunger-shaped microparts. In this endeavor, a progressive forming system for making microplungers using extrusion and blanking operations is developed, and the grain size effect affected deformation behaviors and of surface qualities of the microformed parts are studied. The knowledge for fabrication of plunger-shaped microparts via progressive microforming is developed, and the in-depth understanding and insight into the deformation behaviors and tailoring the product quality and properties will facilitate the design and development of the forming process by using this unique microforming approach.

SIZE EFFECT OF FLOW STRESS IN ISOTHERMAL UPSETTING DEFORMATION

2009 ◽  
Vol 23 (06n07) ◽  
pp. 1745-1750
Author(s):  
BIN GUO ◽  
CHUNJU WANG ◽  
DEBIN SHAN ◽  
LINING SUN
Keyword(s):  
Grain Size ◽  
Flow Stress ◽  
Size Effect ◽  
Room Temperature ◽  
Size Dependence ◽  
Treatment Process ◽  
Different Dimensions ◽  
Single Grain ◽  
The Difference ◽  
Different Grain Size

With the miniaturization of parts, size effect occurs. The isothermal forming processes are performed to obtain homogenizing deformation. In the paper, a serial of isothermal upsetting tests are carried out with billets of different dimensions. Difference of flow stress is accepted as the parameter to evaluate the size dependence of flow stress on billets dimensions. The experimental results show that size effect occurs clearly. With the increasing of temperature, the difference of flow stress becomes smaller, which means that the degree of size dependence is reduced. Scatter of flow stress is observed in the tests at room temperature. When the deformation temperature is raised, the fluctuation of flow stress tends towards decreasing. In order to investigate the effect of grain size, different grain size is obtained with the heat treatment process. At the same temperature, the difference of flow stress increases with the increasing of grain size. These phenomena can be explained from the viewpoint of polycrystalline structure of material. The anisotropy of individual grain is appeared obviously, which leads the fluctuation of flow stress. In the isothermal deformation, the effect of single grain is smaller than that at room temperature.

scholarly journals Indentation Size Effect and the Hall-Petch ‘Law’

2010 ◽  
Vol 662 ◽  
pp. 13-26 ◽  
Author(s):  
L.M. Brown
Keyword(s):  
Grain Size ◽  
Flow Stress ◽  
Size Effect ◽  
Indentation Size Effect ◽  
Rotational Flow ◽  
Slip Systems ◽  
Square Root ◽  
Grain Size Effect ◽  
Indentation Size ◽  
The Relationship

The flow of material out from under regions in compression must occur by the operation of many slip systems, which together produce rotational flow. Such flow requires the accumulation of geometrically necessary dislocations, and leads to the indentation size effect: smaller indents produce higher hardness, a component of the hardness being inversely proportional to the square-root of the indenter size. A pattern of flow in polycrystals which satisfies both continuity of normal stress and continuity of matter at boundaries can be achieved by rotational flow, and it leads to a grain-size effect. Under most circumstances, the flow stress has a component which is inversely proportional to the square-root of the grain size, the Hall-Petch law. The flow is accompanied by the build-up of internal stress which can be relieved by intercrystalline cracking, thereby limiting the cohesive strength of polycrystals. The relationship between these ideas and traditional views is briefly explained, and an analysis is given of recent experimental results.

Grain Size Effect in Sheet Metal Microforming Simulation Adopting Strain Gradient Concept

2007 ◽  
Vol 364-366 ◽  
pp. 1285-1291
Author(s):  
Wing Bun Lee ◽  
Yi Ping Chen ◽  
Suet To
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Sheet Metal ◽  
Crystal Plasticity ◽  
Strain Gradient ◽  
Grain Size Effect ◽  
Active System ◽  
Rate Dependent ◽  
Slip Resistance ◽  
Non Local

A strain gradient dependent crystal plasticity approach is adopted to model the size effect in the microforming process of sheet metal. To take into account the grain size effect in the simulation, the total slip resistance in each active system was assumed to be due to a mixed population of forest obstacles arising from both statistically stored and geometrically necessary dislocations. The non-local crystal plasticity has been established by directly incorporating the above slip resistance into the conventional rate-dependent crystal plasticity and implemented into the Abaqus/Standard FE platform by developing the user subroutine UMAT. The formulation has been recapitulated and followed by presentation of the numerical examples employing both the local and non-local formulation. The comparison of the counterpart simulation results reveals the grain size effect in the microforming process and demonstrates the availability of the code developed.

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