scholarly journals Novel Approach and Interpretation for the Determination of Electromagnetic Forming Limits

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4175
Author(s):  
Koray Demir ◽  
Siddhant Goyal ◽  
Marlon Hahn ◽  
Erman Tekkaya
Keyword(s):  
Strain Rate ◽  
Biaxial Tension ◽  
Electromagnetic Forming ◽  
Shear Stresses ◽  
Plane Shear ◽  
Forming Limits ◽  
Novel Approach ◽  
Out Of Plane ◽  
Strain Paths

A new method to determine electromagnetic forming limits curves (EM-FLCs) for sheet metals is proposed. The different strain paths (between uniaxial and biaxial tension) are achieved by specific tool coil and specimen designs. It is ensured that the apex of the specimen deforms on a constant strain path, and excess bending at the apex is avoided. This is done so that the determined EM-FLCs are comparable to their quasi-static counterparts. The method determines the EM-FLCs for the aluminum alloys AA-1050a-H24 and EN AW-5083-H111 and the magnesium alloy Mg AZ31-O. Overall, it is observed that the necking limits in electromagnetic forming (EMF) are higher compared to quasi-static forming. The fracture surfaces of electromagnetically deformed specimens are examined to reveal the existence of out-of-plane shear stresses. A numerical analysis corroborates this observation and their variation with strain rate. The presence of such stresses is proposed as a possible reason for the increased necking limits in EMF. As reasons for higher forming limits, previous research has identified inertial stabilization, strain rate hardening, die impact, and change in deformation mechanism. The current study reaffirms the positive effect of inertial stabilization and makes key observations in the increase of twinning in EMF of Mg AZ31-O.

X-ray measurement of triaxial residual stress on machined surfaces by the cosα method using a two-dimensional detector

2018 ◽  
Vol 51 (5) ◽  
pp. 1329-1338 ◽  
Author(s):  
Keisuke Tanaka
Keyword(s):  
Normal Stress ◽  
New Method ◽  
Shear Stresses ◽  
Plane Shear ◽  
X Ray ◽  
Plane Normal ◽  
Out Of Plane ◽  
Cutting Direction ◽  
Machined Surfaces

In recent years, the cosα method has attracted engineers as a new method of X-ray stress measurement using the whole Debye–Scherrer (D–S) ring recorded on a two-dimensional detector. The principle of the cosα method was first proposed by Taira, Tanaka & Yamasaki [J. Soc. Mater. Sci. Jpn, (1978),27, 251–256] for in-plane biaxial stress analysis and later extended by Sasaki and co-workers [Sasaki & Hirose (1995).Trans. Jpn Soc. Mech. Eng. Part A,61, 2288–2295; Sasaki, Takahashi, Sasaki & Kobayashi (2009).Trans. Jpn Soc. Mech. Eng. Part A,75, 219–227] to the triaxial state of stress. The method proposed by Sasaki and co-workers utilizes several D–S rings taken at different incident angles of X-rays in order to determine triaxial stresses. In the present paper, the cosα method was applied to measure triaxial residual stresses of uni-directionally machined surfaces of a carbon steel made by grinding, milling and planing. A recommended procedure for experimental measurements of in-plane normal and shear stresses and out-of-plane shear stress is proposed, together with a new method for determination of the out-of-plane normal stress. The tilt angle of X-ray incidence for stress determination is recommended to be larger than 35°, where the stress constant is low and the stress sensitivity is high. Normal incidence is recommended for the determination of out-of-plane shear stresses. The out-of-plane shear stress along the cutting direction was characteristic of uni-directionally machined surfaces and increased with cutting severity in the order of grinding, milling and planing. The in-plane normal stress was compressive for ground and milled surfaces, and the magnitude of compression was larger in the direction perpendicular to the cutting direction. On the basis of the stress values measured under different tilt angles, it is suggested that the magnitude of in-plane normal residual stress increases near the surface. The out-of-plane normal stress determined by the new method indicated a small compression.

A Suitable Criterion for Precise Determination of Incipient Necking in Sheet Materials

2006 ◽  
Vol 519-521 ◽  
pp. 111-116 ◽  
Author(s):  
Q. Situ ◽  
Mukesh K. Jain ◽  
M. Bruhis
Keyword(s):  
Strain Rate ◽  
Sheet Material ◽  
Forming Limit Diagram ◽  
Precise Determination ◽  
Forming Limit ◽  
Strain History ◽  
Flow Localization ◽  
Major Strain ◽  
Strain Paths

Forming limit diagram (FLD) is a measure of the formability of a sheet material. The major-minor strain pairs that are closest to the neck on multiple specimens of various strain paths are utilized to construct a boundary between safe and unsafe zones. The challenge to obtain the FLD is the determination of incipient necking. Three approaches to determine the limit strains have been investigated and compared in this research in order to establish the optimal one for implementation: (1) commonly used Bragard criterion ( 1)e Br with periodic grids; (2) tracking the region of large local strains from strain history to locate the instance when critical major strain ( 1)e cr happens; (3) post-processing of strain history to locate the inflection in the major strain rate curve 1 max (e&&) at the onset of localization. The last criterion of inflection in strain rate 1 max (e&&) carries both a numerical and a physical meaning towards developing an understanding of flow localization, formability and fracture.

In-Plane Shear Strength Determination of Composite Materials in Laminated and Sandwich Panels

1997 ◽  
Vol 50 (11S) ◽  
pp. S237-S240 ◽  
Author(s):  
J. R. Vinson
Keyword(s):  
Shear Strength ◽  
Composite Materials ◽  
Test Procedure ◽  
Sandwich Panels ◽  
Laminated Composite ◽  
Adhesive Bond ◽  
Shear Stresses ◽  
Plane Shear ◽  
Laminated Composite Materials

A simple test procedure is available to determine the in-plane shear strength of laminated composite materials, as well as other orthotropic and isotropic advanced material systems. The test apparatus is simple, inexpensive, and the flat rectangular plate test specimen is not restricted in size or aspect ratio. In addition to its use for laminated composite materials, the test can also be used for foam core sandwich panels. In sandwich panels, the tests can be used to determine the in-plane shear strength of the faces, the core and/or the adhesive bond between face and core. The shear stresses developed vary linearly in the thickness direction and are constant over the entire planform area.

A Computerized Test Setup for the Determination of the In-Plane and Out-of-Plane Shear Modulus in Orthotropic Specimens

1991 ◽  
pp. 149-155
Author(s):  
D. Van Hemelrijck ◽  
L. Schillemans ◽  
F. De Roey ◽  
I. Daerden ◽  
F. Boulpaep ◽  
...  
Keyword(s):  
Shear Modulus ◽  
Plane Shear ◽  
Test Setup ◽  
Out Of Plane

Strain Rate Effect on Out of Plane Shear Strength of Fiber Composites

2007 ◽  
Vol 345-346 ◽  
pp. 725-728
Author(s):  
Jia Lin Tsai ◽  
Jui Ching Kuo
Keyword(s):  
Shear Strength ◽  
Strain Rate ◽  
Shear Strain ◽  
Fiber Composites ◽  
Strain Rate Effect ◽  
Rate Effect ◽  
Strength Analysis ◽  
Shear Strain Rate ◽  
Plane Shear ◽  
Out Of Plane

This research aims to investigate strain rate effect on the out of plane shear strength of unidirectional fiber composites. Both glass/epoxy and graphite/epoxy composites were considered in this study. To demonstrate strain rate effect, composite brick specimens were fabricated and tested to failure in the transverse direction at strain ranges from 10-4/s to 700/s. Experimental observations reveal that the main failure mechanism of the specimens is the out of plane shear failure taking place on the plane oriented around 30 to 35 degree to the loading direction. The corresponding out-of-plane shear strength was obtained from the uniaxial failure stress through Mohr-Coulomb strength analysis. In addition, the associated shear strain rate on the failure plane was calculated through the coordinate transformation law. Results show that the out-plane shear strength increases with the increment of the shear train rates. A semi-logarithmic function expressed in terms of the normalized shear strain rate was employed to describe the rate dependence of the out-plane shear strength.

Intrinsic diagram of sheet metal forming limits for arbitrary strain paths

2008 ◽  
Vol 222 (4) ◽  
pp. 223-229 ◽  
Author(s):  
H. Fatmaoui ◽  
R. Mesrar ◽  
J. Chaoufi
Keyword(s):  
Biaxial Tension ◽  
Effective Strain ◽  
Forming Limit ◽  
Forming Limits ◽  
Stress Criterion ◽  
Localized Necking ◽  
Strain Paths ◽  
Mk Analysis ◽  
Localization Approach ◽  
Intrinsic Character

Localized necking in sheets under biaxial tension is analysed by an Marciniak—Kuczynski localization approach (MK-analysis) along with a new plane-stress criterion. Analysis is developed for a rigid viscoplastic behaviour based on flow-theory of plasticity. The model is introduced in numerical calculations to determine forming limits to ductility under linear and non-linear strain paths. However, the results are presented in a new diagram that represent the effective strain as a function of the current strain-rate ratio. A comparison with classical forming limit diagrams shows the intrinsic character of the new diagram.

scholarly journals On the Determination of Forming Limits in Polycarbonate Sheets

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 928
Author(s):  
Ana Rosa-Sainz ◽  
Gabriel Centeno ◽  
Maria Beatriz Silva ◽  
Jose Andrés López-Fernández ◽  
Andrés Jesus Martínez-Donaire ◽  
...  
Keyword(s):  
Metal Forming ◽  
Elastic Recovery ◽  
General Procedure ◽  
Incremental Sheet Forming ◽  
Forming Limits ◽  
Strain Paths ◽  
Last Stage ◽  
Strain Space ◽  
Principal Strains

By proposing an adaptation of the methodology usually used in metal forming, this paper aims to provide a general procedure for determining the forming limits, by necking and fracture, of polymeric sheet. The experimental work was performed by means of Nakajima specimens with different geometries to allow to obtain strains in the tensile, plane, biaxial and equibiaxial states for Polycarbonate sheet with 1 mm of thickness. The application of the time-dependent and flat-valley approaches used in metals has been revealed appropriate to characterize the onset of necking and obtain the forming limits of polycarbonate, despite the stable necking propagation typical of polymeric sheets. An analysis of the evolution of the strain paths along a section perpendicular to the crack allowed for a deeper understanding of the steady necking propagation behaviour and the adoption of the methodology of metals to polymers. The determination of the fracture strains was enhanced with the consideration of the principal strains of the DIC system in the last stage, just before fracture, due to the significant elastic recovery typical of polymeric sheets. As a result of this analysis, accurate formability limits by necking and fracture are obtained for polycarbonate sheet, together with the principal strain space, providing a general framework for analysing incremental sheet forming processes where the knowledge of the fracture limits is relevant.

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