Instability and fracture in sheet metal

Abstract

The regime of sheet metal deformation extends from pure shear, ϵ1= - ϵ2, through plane strain, ϵ2=0, to balanced biaxial tension, under which ϵ1=ϵ2. During deformation a material passes into different states, termed (1) uniform straining, (2) diffuse straining, and (3) localized straining, respectively. Depending on the strain ratio, (1) alone, (1) & (2) & (3), (1) & (3) or (1) & (2) can be experienced by a sheet between zero strain and fracture. In this work the deformation behaviour, in tensile and hydraulic bulge testing, of steel, aluminium and 70-30 brass has been studied. The onset of state (3) has been correlated with strain measurements, taken from a cine film of the deformation, indicated by a grid electrochemically marked on the sheet surface. Various theories predict the major and minor strains at the initiation of these states, and the theoretical and experimental results are compared for the various materials; also the implications with respect to forming-limit diagrams are discussed.

Numerical and experimental investigations of forming limit diagrams in metal sheets

“…According to this theory, localized will not occur in a sheet metal subjected to positive biaxial stretching. Practical experience FLD introduced by Keeler [30], Goodwin [31], Hecker [32] and experimental tests by Azrin and Backofen [33], Ghosh and Hecker [34], Painter and Pearce [35] have demonstrated that thin sheets subjected to positive biaxial tension can fail by localized necking criterion [36].…”

Effects of Tramp Elements on Formability of Low-carbon TRIP-aided Multiphase Cold-rolled Steel Sheets

“…In general, the higher FLC is evaluated as the better formability, and the value of the limit plane strain, FLC o , corresponding to the lowest point in a plane strain mode of Ϫ0.1Ͻe 2 Ͻ0.2 typically indicates a typical barometer used to evaluate the formability. 24,25) The ECO-6 steel having the highest FLC o and the ECO-8 steel showing similar value as the ECO-6 steel are considered to have excellent formability. The ECO-7 and ECO-9 steels whose FLC o values are much lower than those of the ECO-6 and ECO-8 steels have poor formability.…”

Effect of heat treatment on formability in 0.15C−1.5Si−1.5Mn multiphase cold-rolled steel sheet

“…The FLCo value, which is the limit plane strain corresponding to the lowest point in a plane Table 3. Chemical compositions and mechanical properties of steel sheets for purpose of comparison with ECO-A and ECO-B specimens [7,18] strain mode (−0.1<ε 2 <0.2), indicates the level of forming performance [22][23][24]. Although the FLCo values of both steels are a little lower than that of aluminum-killed coldrolled steels [25], the pattern of the curves is similar.…”