CGA: An image processing based software for surface strain analysis in sheet metal forming

Abstract

Strain analysis is an essential step in sheet forming applications to understand the deformation behaviour of the material. The strain analysis is conventionally performed by Circle Grid Analysis (CGA). In CGA, a grid of circles with 2 mm–5 mm diameter is printed on a flat sheet and deformed into the required shape. The length of major and minor axes of the deformed ellipses are measured to estimate the strains at different locations of the formed component. The major and minor axes length of the deformed ellipses are measured either by using a manual method or automatic methods. The automated methods are faster and accurate compared to manual methods, but to perform strain measurement using commercially available automatic strain measurement system, is very expensive. Therefore, in this paper, an image processing based software has been developed with user-friendly Graphical User Interface (GUI) for strain measurement and analysis in sheet metal forming operations. The software has been tested on images obtained by printing the ellipses of known dimensions on the flat sheet by laser etching, electrochemical etching and screen printing, which are generally used for printing circular grids on flat sheets for strain analysis in sheet metal forming. It is observed that the edges of the laser engraved ellipse are very slim and easily detected by software compared to other grid printing methods. The developed software can measure the ellipse dimensions with a maximum absolute percentage error of 1.975%. Further, the results of CGA software has been compared with the commercial strain measurement system called Grid Pattern Analyzer (GPA). The mean absolute error in strain measurement using CGA and GPA was found to be 0.0106 and 0.0178, respectively. The statistical test results reveal that there is no evidence to support a claim that there is a difference in mean performance between the two methods.

Keywords

Grid marking forming limit diagram surface strain circle grid analysis ellipse detection

Get full access to this article

View all access options for this article.

References

Kalpakjian

Schmid

SR.

Sheet metal forming process. 4th ed. New York: Prentice-Hall, 2000.

Aldrich

Ayranci

Nobes

DS.

OSM-classic: an optical imaging technique for accurately determining strain. SoftwareX 2017; 6: 225–230.

Sundararaghavan

Srivastava

Microfract: an image based code for microstructural crack path prediction. SoftwareX 2017; 6: 94–97.

Benkert

Hartmann

Eder

, et al. MaterialModeler—from experimental raw data to a material model. SoftwareX 2019; 10: 100249.

Duda

Hart

PE.

Use of the Hough transformation to detect lines and curves in pictures. Commun ACM 1972; 15(1): 11–15.

Kiryati

Eldar

Bruckstein

AM.

A probabilistic Hough transform. Pattern Recognit 1991; 24(4): 303–316.

Oja

Kultanen

A new curve detection method: randomized Hough transform (RHT). Pattern Recognit Lett 1990; 11(5): 331–338.

McLaughlin

RA.

Randomized Hough transform: improved ellipse detection with comparison. Pattern Recognit Lett 1998; 19(3–4): 299–305.

Nair

Saunders

Jr . Hough transform based ellipse detection algorithm. Pattern Recognit Lett 1996; 17(7): 777–784.

10.

Plataniotis

Venetsanopoulos

AN.

Color image processing and applications. Berlin, Heidelberg: Springer Science & Business Media, 2013.

11.

Xia

Shao

, et al. Arc-support line segments revisited: an efficient high-quality ellipse detection. IEEE Trans Image Process 2019; 29: 768–781.

12.

Von Gioi

Jakubowicz

Morel

, et al. LSD: a fast line segment detector with a false detection control. IEEE Trans Pattern Anal Mach Intell 2008; 32(4): 722–732.

13.

Xia

Huang

, et al. Circle detection by arc-support line segments. In: 2017 IEEE international conference on image processing (ICIP), Chaoyang, Beijing, China, 17–20 September 2017, pp.76–80. IEEE.

14.

Gander

Golub

Strebel

Least-squares fitting of circles and ellipses. BIT Numer Math 1994; 34(4): 558–578.

15.

Bleck

Deng

Papamantellos

, et al. A comparative study of the forming-limit diagram models for sheet steels. J Mater Process Technol 1998; 83(1–3): 223–230.

16.

Swift

HW.

Plastic instability under plane stress. J Mech Phys Solids 1952; 1(1): 1–18.

17.

Hill

RT.

On discontinuous plastic states, with special reference to localized necking in thin sheets. J Mech Phys Solids 1952; 1(1): 19–30.

18.

Stören

Rice

JR.

Localized necking in thin sheets. J Mech Phys Solids 1975; 23(6): 421–441.

19.

Paul

SK.

Theoretical analysis of strain-and stress-based forming limit diagrams. J Strain Anal Eng Des 2013; 48(3): 177–188.

20.

Paul

SK.

Prediction of complete forming limit diagram from tensile properties of various steel sheets by a nonlinear regression based approach. J Manuf Processes 2016; 23: 192–200.

21.

Abdi

Coefficient of variation. In: Salkind

(ed.) Encyclopedia of research design, vol. 1. Thousand Oaks, CA: Sage, 2010, pp.169–171.

22.

Montgomery

DC.

Design and analysis of experiments. New York: John Wiley & Sons, 2017.

23.

Narayanan

Adorisio

Model studies on plate girders. J Strain Anal Eng Des 1983; 18(2): 111–117.