Sheet metal formability studies at the national institute of standards and technology

Abstract

Overview Wrought and SheetSheet-metal forming is a multi-billiondollar industry in the United States, with an overwhelming portion of its use in automotive markets as formed-sheet components. With roughly one-third of the weight of an auto in this form, the Big Three automakers (Ford, General Motors, and Daimler-Chrysler) are looking for lighter, yet highstrength alternative sheet materials. Such materials would reduce the overall weight of vehicles, helping the automakers achieve gas mileage goals set down in the Partnership for a New Generation of Vehicles. Progress has been slow, however, because of a lack of knowledge and experience in forming these new materials. The National Institute of Standards and Technology, in keeping with its mission to assist industry by developing technology and standard test methods, has initiated a program to help the auto industry, as well as other industries that produce and utilize sheet metal, make the transition to these new materials.

Robustness of the sheet metal springback cup test

“…[7,8] The AISI 1010 steel blanks, with mechanical properties listed in Table I, were circular disks of 200-mm diameter and 0.88-mm nominal thickness. The diameter of the die bore was 110 mm with a rim radius of 10 mm.…”

Textural Development of AA 5754 Sheet Deformed under In-Plane Biaxial Tension

“…For plane strain (q = 0) and equibiaxial (q = 1) tension, a technique based upon the Raghavan [13] modification of the Marciniak in-plane biaxial stretching test [14] was employed; the specialized tooling is a cylindrical ram and binder. [15] Mild steel was used as a washer (driver blank) to prevent failure in the sidewall of the aluminum test sheet; lubricant was applied to those faces in contact with the tooling. The load of the hold-down ring was maintained at approximately 340 kN, so that movement of material inward over the draw bead was restricted while being deformed at a constant central ram speed of 1.0 mm/s.…”

A Method for Direct Measurement of Multiaxial Stress-Strain Curves in Sheet Metal

“…(381-mm) squares, by drilling and deburring a 3-in.-(76.2-mm-) diameter hole in the center ( Figure 2). Each sample was loaded in a manner described previously [10,11] at 0.5 mm/s between hold points, where the stress was measured with the sample under load.…”

“…[10] At each macroscopic plastic strain level, the stress is determined by measuring the change in interatomic spacing in the grains due to the applied load, from which the elastic strains and then the stress is calculated. It is important to note that this technique measures two different strains in the sample.…”