111。8 mm。 To ensure repeatability of experimental data, two spe- cimens with nominal thickness of 1 mm and 2 mm respectively were manufactured。 This would provide two experimental data values for cylinder with nominally the same geometry。 Specimens were designated as: CY1_t0。5。 The number following ‘t’ indicates the  thickness  of  the  cylinder。  For  example,  CY1_t0。5 implies

Fig。 1。  Geometry of analyzed cylinder (a), a close look of the top edge after spring-back/unloading during experimentation    (b)。

Fig。 2。  Photograph of five mild steel cylinder manufactured via MIG welding process。

Table 2

Measured data of the wall thickness for all tested cylinders。

tnom tmin tmax tave tstd

mm

CY1_t0。5 0。5 0。48 0。52 0。5 0。0105

CY1_t1。0 1。0 1。01 1。03 1。02 0。0121

CY2_t1。0 1。0 1。03 1。13 1。08 0。0289

CY1_t2。0 2。0 1。98 2。08 2。02 0。0278

CY2_t2。0 2。0 1。98 2。08 2。02 0。0225

cylinder 1 with 0。5 mm thickness。

Material properties of the mild steel plate from which the cy- linders are made from were obtained by testing a number of flat tensile specimen。 The flat tensile specimen were designed ac- cording to British Standard (BS EN 10002-1: 2001), Ref。 [16]。 Three specimens each were cut from the flat plate for the three different thicknesses。 The specimens were cut out in the same orientation as the cylindrical specimens。 All nine specimens were subjected to uniaxial tensile tests。 Only flat tensile specimen with 0。5 mm thickness were strain-gauged (two KR-120-5P-11-1L strain gauges, one in transverse direction and one in longitudinal direction)  in

order to verify the extensometer's readings and to obtain the value of Poisson's ratio, ѵ。

Table 1 shows the material properties which were obtained in the tests。 The summary of the average Young's modulus and average upper yield are given in columns 3 and 4 of Table 4 re-

spectively。 Poisson's ratio for specimen with 0。5 mm thickness was found to be, ѵ¼ 0。348。

3。2。Cylindrical specimen manufacturing and  testing

Cylindrical specimens were cut and rolled from flat mild steel plate with nominal thickness (t ¼ 0。5, 1。0, 2。0 mm)。 The ends of the rolled specimens were joined together using Metal Inert Gas (MIG) welding process。 The flat tensile specimens and the cylinders were not stress relieved at any point during and after the manufacturing process。 Prior to testing, wall thickness, axial length and diameter measurements were taken for all cylinders。 First, the wall thick- ness   for  0。5 mm   and  1 mm  cylinders  were  carried   out    using