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

Abstract

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.

A Review of Sheet Metal Forming Evaluation of Advanced High-Strength Steels (AHSS)

“…Guk et al [66] utilized a diode laser marking system to generate grid patterns on multiphase steels; the scanning speed and laser power influence on the mark depth were investigated. Furthermore, Yildiz and Yilmaz [67], after applying four different grid marking methods, namely serigraphy, electro-chemical etching, photo-chemical etching, and laser, concluded that laser is best-suited due to ease of application and stability.…”

Investigation of the explosive type on the high strain forming of OFHC copper tube

“…Similarly, Dariani et al 11 experimentally determined that the higher strain rates increased the formability limits of the sheets when compared to the experiments conducted at quasi-static condition. , 52 Thus, the copper tube formed by HMX and PBX-N could have reached a higher equivalent plastic strain without damage.…”

A portable device for single point strain analysis in sheet metal forming processes

“…1 ) [2] , [3] , [4] . In the recent past, the image processing technique is gaining much popularity because of its capability to measure gridded surfaces rapidly and accurately [5] , [6] , [7] , [8] , [9] . Grid Pattern Analyser (GPA) [5] and Forming Measurement Tool Innovations (FMTI) [6] are two commercially available automatic single-point strain analysis systems based on image processing.…”