Published: Jan 2000
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Cold forming of thin metallic plates and sheets is a common inexpensive manufacturing process for many thin lightweight components. Unfortunately, part rejection rates of cold (or warm) rolled sheet metals are high. This is especially true for materials that have a texture (i.e., cold-rolled stainless steel sheets) and are being cold-formed into geometrically complex parts. To obtain an understanding on how cold forming affects behavior and subsequent high rejection rates, a series of in-plane biaxial tests was conducted on thin 0.1-mm (0.004-in.) fully cold-rolled 304 stainless steel sheets. The sheets were tested using an in-plane biaxial test system with acoustic emission. A failure surface was mapped out for the 304 stainless steel sheet. Results from this study indicated that an angle of 72° from the transverse orientation for the peak strain direction during forming should be avoided. This was microstructurally related to the length-to-width ratio of the elongated 304 stainless steel grains. Thus on rejected parts, it is expected that a high number of cracks will be located in the plastic deformation regions of cold-formed details with the same orientation.
in-plane biaxial failure surfaces, stainless steel, texture, cold forming, equivalent stress, failure loads
St. Cloud State University, St. Cloud, MN
NASA Glenn Research Center, Cleveland, OH