The verification of strains obtained by grid measurements using digital image processing for sheet metal formability

Rasid Ahmed Yildiz*, Safak Yilmaz

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


Grid marking, which is applied before mechanical tests, is a crucial step in formability tests. In this study, four different grid marking methods, serigraphy, electro-chemical etching, photo-chemical etching, and laser marking techniques, were investigated for the stability of grids and their measurement accuracy. After examining the performance of the grid marking methods, laser marking has been selected to obtain grids on the surface of aluminum alloy parts. To evaluate the efficiency of the strains calculation using grids, tensile tests were conducted that considered different levels of elongation. A forming limit diagram of the 6061-T6 Al alloy was constructed to demonstrate the influence of possible measurement errors. Verification of grid strain evaluation revealed that the error in size measurements is dependent on overall strain values and reduced with increasing overall strain as expected. The maximum error of the implemented method does not exceed 1% when 9% of overall uniform elongation is reached. The approach used in the study provides sufficient accuracy for evaluating strains in principal axis of deformed circular grids with minimalized costs.

Original languageEnglish
Pages (from-to)506-514
Number of pages9
JournalJournal of Strain Analysis for Engineering Design
Issue number8
Publication statusPublished - 1 Nov 2017

Bibliographical note

Publisher Copyright:
© Institution of Mechanical Engineers.


The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported and funded by Istanbul Technical University, BAP Project Number 38489.

FundersFunder number
Istanbul Technical University
British Association for Psychopharmacology38489


    • 6061-T6 Al alloy
    • Grid marking
    • forming limit diagram
    • laser marking
    • strain evaluation


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