Comparsion of forming and fracture limits of an aluminum alloy and austenitic stainless steel

Abstract

Forming and fracture limits of AA 3104 aluminum alloy and AISI 304 type stainless steel were studied. Hydraulic bulge testing was employed in the stretch forming experiments. Marciniak-type in-plane tests and tensile testing were carried out to study the limit strains in the deep drawing region. Both screen-printed and laser-marked grids were used to measure the surface strains. Although the forming limits of the AA 3104 were generally much lower than the AISI 304 stainless steel, they both failed in stretch forming by ductile shearing in the through thickness direction without any visible local necking. The preferred failure direction for AA 3104 alloy was transverse to the rolling direction, as could be observed in the bulge tests with a circular die. In the Marciniak-type in-plane tests the AA 3104 alloy showed multiple necking similar to what has previously been reported for low-carbon steel. In the tensile testing, central cracking and subsequent local necking as well as local necking without previous central crack formation were observed both for the AA 3104 aluminum alloy and the AISI 304 stainless steel.

Forming and fracture limits of aluminium alloy

“…However, since the exact fracture site was not known, several measurements at various locations were made. Also, the accuracy of the original grid affects the results, as discussed previously by Korhonen et al 23 The calculated limit strains in Fig. 9 correspond to diffuse and local necking limits.…”

“…Scanning electron microscopy measurements may give smaller thickness values, since it is well known that the strain values tend to increase towards the fracture site. 23 The forming limit strains shown in Fig. 9 show considerable scatter.…”

“…As far as the authors know, Takuda et al used a micrometre for the thickness measurements. Scanning electron microscopy measurements may give smaller thickness values, since it is well known that the strain values tend to increase towards the fracture site 23…”

On the application of the forming limit diagrams for quality control of blanks for wheelbarrow of ASTM A1008 carbon steel

“…The results consisted of the FLC for each alloy sheet thickness giving an improvement in formability as the sheet thickness increased. Another research by Korhonen et al (2009) studied the forming and fracture limits of AISI 304 stainless steel and AA3104 aluminum alloy. The yield and ultimate tensile strengths for AA3104 alloy were 277 and 298 MPa respectively, while they were 241 and 610 MPa for 304 stainless steel.…”

Characterisation of Diffuse and Local Necking of Aluminium Alloy Sheets using DIC Technique

“…The hardening exponent (n) is defined by the uniform elongation (Ag%) with formula n=ln(1+Ag/100). The location of diffuse instability according to Hill [2] and other authors [3,4] is εD=n. Similarly, according to equation (2) the true uniaxial strain in tensile direction is εL=2n at the beginning of local necking.…”