Analysis of Micro/Mesoscale Sheet Forming Process by Strain Gradient Plasticity and Its Characterization of Tool Feature Size Effects

2015 ◽  
Vol 3 (1) ◽  
Author(s):  
Linfa Peng ◽  
Peiyun Yi ◽  
Peng Hu ◽  
Xinmin Lai ◽  
Jun Ni
Keyword(s):  
Strain Gradient ◽  
Size Effects ◽  
Scale Effects ◽  
Reaction Force ◽  
Equivalent Strain ◽  
Sheet Forming ◽  
Geometrical Parameters ◽  
Forming Process ◽  
Feature Size ◽  
Plastic Theory

Conventional material models cannot describe material behaviors precisely in micro/mesoscale due to the size/scale effects. In micro/mesoscale forming process, the reaction force, localized stress concentration, and formability are not only dependent on the strain distribution and strain path but also on the strain gradient and strain gradient path caused by decreased scale. This study presented an analytical model based on the conventional mechanism of strain gradient (CMSG) plasticity. Finite element (FE) simulations were performed to study the effects of the width of microchannel features. Die sets were fabricated and micro/mesoscale sheet forming experiments were conducted. The results indicated that the CMSG plastic theory achieves better agreements compared to the conventional plastic theory. It was also found that the influence of strain gradient on the forming process increases with the decrease of the geometrical parameters of tools. Furthermore, the feature size effects in the forming process were evaluated and quantitated by the similarity difference and the similarity accuracy. Various tool geometrical parameters were designed based on the Taguchi method to explore the influence of the strain gradient caused by the decrease of tool dimension. According to the scale law, the difference and accuracy of similarity were calculated. Greater equivalent strain gradient was revealed with the decrease of tool dimension, which led to the greater maximum reaction force error due to the increasing size effects. The main effect plots for equivalent strain gradient and reaction force indicated that the influence of tools clearance is greater than those of punch radius, die radius, and die width.

Analysis of the Micro/Meso Scale Sheet Forming by Strain Gradient Plasticity and its Characterization of Tool Feature Size Effects

2014 ◽  
Author(s):  
Linfa Peng ◽  
Peiyun Yi ◽  
Peng Hu ◽  
Xinmin Lai ◽  
Jun Ni
Keyword(s):  
Finite Element ◽  
Strain Gradient ◽  
Size Effects ◽  
Reaction Force ◽  
Equivalent Strain ◽  
Sheet Forming ◽  
Geometrical Parameters ◽  
Forming Process ◽  
Feature Size ◽  
Meso Scale

For conventional metal forming, finite element (FE) method becomes a powerful tool in process design. However, conventional material models cannot describe material behaviors precisely in micro/meso scale due to the size/scale effects. As a result, know-how obtained in traditional macro-forming is not suitable for the micro-forming process. In micro/meso scale forming process, the reaction force, localized stress concentration and formability are not only dependent on the strain distribution and strain path but also the strain gradient and strain gradient path caused by decreased scale. This study presented a model based on conventional mechanism based strain gradient (CMSG) plasticity. A user-defined material (UMAT) subroutine incorporating the CMSG plasticity in the ABAQUS finite element (FE) program was established. Based on the subroutine, FE simulations were performed to analyze the effects of the channel width in sheet forming process of micro-channel features. Die sets were fabricated according to the scale law and Micro/meso scale sheet forming experiments were conducted to study the effect of channel width in the die. Experimental results indicated that the CMSG plastic theory achieved better agreements compared to the conventional plastic theory. It found that the influence of the strain gradient to the forming process increased with the decrease of the geometrical parameters of the tools. Furthermore, various tool geometrical parameters were designed by Taguchi Method to explore the feature size effects caused by the decrease of tool geometrical dimensions. According the scale law, similarity difference and the similarity accuracy were calculated to evaluate the size effects. Greater equivalent strain gradient was found with the decrease of the tool geometric dimension, which lead larger maximum reaction force error due to increasing size effects. The main effect plots for equivalent strain gradient and reaction force indicated that the influence of the tools clearance was larger than punch radius, die radius and die width.

Small-Scale Effects on the Buckling of Skew Nanoplates Based on Non-Local Elasticity and Second-Order Strain Gradient Theory

2017 ◽  
Vol 34 (4) ◽  
pp. 443-452 ◽  
Author(s):  
B. Shahriari ◽  
S. Shirvani
Keyword(s):  
Strain Gradient ◽  
Scale Effects ◽  
Buckling Load ◽  
Strain Gradient Theory ◽  
Small Scale ◽  
Geometrical Parameters ◽  
Gradient Theory ◽  
Vast Number ◽  
Non Local ◽  
The Galerkin Method

AbstractIn recent years, nanostructures have been used in a vast number of applications, making the study of the mechanical behaviour of such structures important. In this paper, two different constitutive equations including first-order strain gradient and simplified differential non-local are employed to model the buckling behaviour of skew nanoplates. The Galerkin method is used for solving the equations in order to obtain buckling load. Using this method, the influence of different parameters consisting of non-classical properties, boundary conditions, and geometrical parameters such as length and angle on the buckling load, are studied. The results showed that small-scale effects are very important in skew graphene sheets and their inclusion results in smaller buckling loads.

Micro/Meso Scale Metallic Sheet Forming Process Analysis Based on the Strain Gradient Plasticity Theory

2011 ◽  
Vol 675-677 ◽  
pp. 991-994
Author(s):  
Peng Hu ◽  
Lin Fa Peng ◽  
Xin Min Lai ◽  
Wei Gang Zhang
Keyword(s):  
Strain Gradient ◽  
Process Analysis ◽  
Simulation Method ◽  
Sheet Forming ◽  
Plasticity Theory ◽  
Gradient Plasticity ◽  
Forming Process ◽  
Metallic Parts ◽  
Metallic Sheet ◽  
Meso Scale

Increasing demands for miniature metallic parts have driven the application of micro/meso forming process in various industries. The present study focuses on the size effect which appears in the micro/meso scale sheet forming process. Micro/meso scale stamping experiments and finite element simulations incorporating the CMSG plasticity theory are conducted, respectively. It is found that the numerical simulation results, with strain gradient and strain gradient path taken into account, match the experimental results better than those of conventional simulation method.

Study of the process of forming a hole for a thread at manufacturing a high nut

2020 ◽  
Vol 76 (8) ◽  
pp. 841-846
Author(s):  
I. G. Shubin ◽  
A. A. Kurkin
Keyword(s):  
Metal Flow ◽  
Nonlinear Dependence ◽  
Geometrical Parameters ◽  
Relative Height ◽  
Forming Process ◽  
Normal Height ◽  
Accuracy Class ◽  
Limit Values ◽  
Program Complex ◽  
Class B

During manufacturing nuts of increased height, a problem of obtaining correct cylindrical form of the hole for thread and overall geometrical parameters arises. To solve the problem it is necessary to know regularity of the blank forming process. Results of the study of a technological process of high hexahedral nuts forming presented. The nuts were M18 of 22 mm height, M16 of 19 mm height and M12 of normal height 10 mm according to GOST 5915–70, accuracy class B, steel grade 10 according to GOST 10702–78. The volumetric stamping was accomplished at the five-position automatic presses of АА1822 type. It was determined, that unevenness of the metal flow in the process of plastic deformation of blanks of increased height nuts was caused by different stress conditions by their sections. To simulate the mode of deformation, the program complex QForm-3D was chosen. The complex ensured to forecast with necessary accuracy the metal flow in a blank, as well as to define the deformation force and arising stress in the working instrument. The simulation showed the presence of regularity between preliminary formed buffle and deviation of dimensions and form of a blank wall after its finishing piercing, which can be expressed by a nonlinear dependence. The limit values of the relative height of the buffle С/D = 0.56–0.588 defined, exceeding which will result in rejection of the finished product. Accounting the limit values of the relative height of the buffle will enable to correct a mode of technological operations and technological instruments at stamping of high hexahedral nuts.

scholarly journals Critical Temperatures for Vibrations and Buckling of Magneto-Electro-Elastic Nonlocal Strain Gradient Plates

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 87
Author(s):  
Giovanni Tocci Monaco ◽  
Nicholas Fantuzzi ◽  
Francesco Fabbrocino ◽  
Raimondo Luciano
Keyword(s):  
Strain Gradient ◽  
Thermal Environment ◽  
Scale Effects ◽  
Nonlocal Theory ◽  
Elastic Plates ◽  
Critical Temperatures ◽  
Buckling Behavior ◽  
Linear Vibrations ◽  
Nonlocal Strain Gradient ◽  
Plate Kinematics

An analytical method is presented in this work for the linear vibrations and buckling of nano-plates in a hygro-thermal environment. Nonlinear von Kármán terms are included in the plate kinematics in order to consider the instability phenomena. Strain gradient nonlocal theory is considered for its simplicity and applicability with respect to other nonlocal formulations which require more parameters in their analysis. Present nano-plates have a coupled magneto-electro-elastic constitutive equation in a hygro-thermal environment. Nano-scale effects on the vibrations and buckling behavior of magneto-electro-elastic plates is presented and hygro-thermal load outcomes are considered as well. In addition, critical temperatures for vibrations and buckling problems are analyzed and given for several nano-plate configurations.

Scale-Dependent Crack Modeling for Investigation the Effect of Geometrically Necessary Dislocations in Micro/Nano Grain Size of Copper

2016 ◽  
Vol 15 ◽  
pp. 1-16 ◽  
Author(s):  
Amin Zaami ◽  
Ali Shokuhfar
Keyword(s):  
Grain Size ◽  
Stress Concentration ◽  
Strain Gradient ◽  
Stress Concentration Factor ◽  
Size Effects ◽  
Crack Tip ◽  
Length Scale ◽  
State Variables ◽  
Dependent Model ◽  
Homogeneous Strain

In this study, a scale-dependent model is employed to investigate the size effects of copper on the behavior of the crack-tip. This model includes the homogeneous and non-homogeneous strain hardening based on the wavelet interpretation of size effect. Introducing additional micro/nano structural considerations together with decreasing grain size, different size effects can be obtained. As the size dependency is not taken into account in conventional plasticity, an enhanced theory which is related to the strain gradient introduces a length scale will give more realistic representations of state variables near the crack-tip. Accordingly, the contribution of geometrically necessary dislocations (GNDs) activity on strengthening and stress concentration factor is identified in the crack-tip. Finally, the affected zone which is dominated by presence of GNDs is identified

Development of a prototype for modelling soil–pipe interaction and its application for predicting uplift resistance to buried pipe movements in sand

2018 ◽  
Vol 55 (10) ◽  
pp. 1451-1474 ◽  
Author(s):  
Yousef Ansari ◽  
George Kouretzis ◽  
Scott W. Sloan
Keyword(s):  
Scale Effects ◽  
Reaction Force ◽  
Failure Surface ◽  
Relative Displacement ◽  
Published Data ◽  
Buried Pipe ◽  
Image Velocimetry ◽  
Close Range ◽  
Uplift Resistance

This paper presents a testing rig for measuring the reactions on rigid pipes buried in sand during episodes of relative displacement. Following a detailed presentation of the 1g prototype, the test preparation procedure, and the characterization of the test sand’s shear strength and dilation potential under the low confining stresses pertinent to the problem, the paper focuses on the workflow devised to obtain accurate measurements of friction and arching effects, and accordingly normalize them to account for scale (stress level) effects. Emphasis is put on demonstrating the effectiveness of the sand deposition method for accurately controlling the density of the sample, and on quantitatively assessing its uniformity. Measurements obtained during a series of uplift tests, including reaction force – pipe displacement curves and images of the developing failure surface, facilitated by particle image velocimetry and close-range photogrammetry techniques, are compared against published data and analytical methods. The results lead to the development of a new simplified formula for calculating the uplift resistance to buried pipe movements in sand: capable of accounting for scale effects, yet simple enough to be used for the analysis of pipes in practice.

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