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.

scholarly journals Recent Approaches for the Determination of Forming Limits by Necking and Fracture in Sheet Metal Forming

2015 ◽  
Vol 132 ◽  
pp. 342-349 ◽  
Author(s):  
M.B. Silva ◽  
A.J. Martínez-Donaire ◽  
G. Centeno ◽  
D. Morales-Palma ◽  
C. Vallellano ◽  
...  
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Forming Limits

Sheet Metal Forming Limits Under Complex Strain Paths Using Void Growth and Coalescence Model

1986 ◽  
Vol 108 (3) ◽  
pp. 240-244 ◽  
Author(s):  
U. S. Rao ◽  
R. C. Chaturvedi
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Void Growth ◽  
Metal Forming ◽  
Strain Ratio ◽  
Forming Limits ◽  
Coalescence Model ◽  
Strain Paths ◽  
Complex Strain ◽  
Void Growth And Coalescence

It is well established that ductile fracture occurs by nucleation, growth and coalescence of voids. Several models have been developed to predict limits under constant strain ratio paths considering void inhomogeneity and void growth. In this paper the void growth and coalescence model developed by Rao and Chaturvedi for predicting forming limits under constant strain ratio paths, has been extended for predicting forming limits under two stage strain paths. The predicted results have been compared with experimental results of Ishigaki and analyzed.

New methodology for the characterization of failure by fracture in bulk forming

2018 ◽  
Vol 53 (4) ◽  
pp. 242-247 ◽  
Author(s):  
Joao P Magrinho ◽  
Maria Beatriz Silva ◽  
Luis M Alves ◽  
AG Atkins ◽  
Paulo AF Martins
Keyword(s):  
Metal Forming ◽  
Stress Triaxiality ◽  
Image Correlation ◽  
Principal Strain ◽  
Bulk Metal ◽  
Bulk Metal Forming ◽  
Aisi 1045 ◽  
Steel Aisi ◽  
Strain Paths ◽  
Strain Space

This article is focused on the formability limits by fracture obtained from standard bulk metal forming tests performed with cylindrical, tapered and flanged specimens. A total of two novel features are presented: the use of digital image correlation to determine strain paths and immersion of steel specimens in liquid nitrogen after the onset of crack formation to reveal the mode of fracture. A new methodology to determine the fracture loci in principal strain space is proposed based on the combination of experimental force–displacement evolutions with in-plane strain measurements. The experimental work is performed in cold-drawn steel AISI 1045 and two new formability tests with different values of stress triaxiality are proposed for obtaining strains at fracture in regions of principal strain space that are not sufficiently well covered by standard bulk metal forming tests.

Forming Limits Prediction of the Sheet Metal Forming Process by the Energy-Based Damage Model

2006 ◽  
Vol 22 (1) ◽  
pp. 43-50 ◽  
Author(s):  
H.-Y. Yeh ◽  
J.-H. Cheng
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Damage Model ◽  
Uniaxial Tensile ◽  
Strain History ◽  
Forming Process ◽  
Forming Limits ◽  
Metal Forming Process ◽  
Strain Paths

AbstractAn energy-based damage model is proposed and applied to predict the fracture initiation of the sheet metal forming process. The fracture mechanism is investigated through the plastic energy dissipation. The concepts of the damaging work and the fracture energy are proposed for the quantitative description of damage evolution and crack initiation. The developed formulations are implemented into the finite element program ABAQUS to simulate the biaxial stretching of sheet metals and to predict the fracture strains. The material parameter needed in the damage model for fracture prediction is determined by the stress-strain history of the uniaxial tensile test. The forming limits for aluminum alloy sheets under various strain paths are predicted by the present approach and then compared to the measured data quoted from the literatures [1,2]. Good agreements are found between this study and the previous results.

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.

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