Volume 19, Issue 5 (September 1991)
A Cantilever-Type Bend Test Technique for Formability Analysis of Strip/Plate Metals
The minimum bend radius-to-thickness ratio (R/t), determined by the conventional 90° bend test for strip materials, has been found insensitive to changes in formability of Cu-Be-Co alloys with thermo-mechanical treatment. In an attempt to improve the 90° bend tests, an alternating-current potential drop (ACPD) measurement technique was incorporated. The ACPD modification was successful in monitoring the onset of crack formation under laboratory conditions, but it is considered unsuitable for more widespread use such as in quality control.
A new cantilever-type bend test apparatus has been designed and used to measure the maximum bend angle, θM, at which the sample cracks during bending in angular rotation up to 135°. The reproducibility of the apparatus was good and the sensitivity such that changes in θM as small as 3 to 4° could be detected. The θM value was found to be dependent on sample thickness. However, a thickness correction procedure, which was developed from an analytical model, allowed a corrected maximum bending angle, θCM, to be easily calculated. The θCM data have been successfully used to investigate the effect on bendability of thermo-mechanical treatment of Cu-Be-Co alloys and of both testing orientation and thermo-mechanical treatment on Al-Mg-Mn alloys. Results from Al-Mg-Mn alloys have shown that the apparatus is capable of testing samples with thicknesses up to 5 mm.