One of the more important mechanical properties related to stretch forming is the work-hardening exponent or n value. As readers of this column already know, n value is a key influence on the severity of strain gradients and the height of forming-limit curves. The n value becomes very important for understanding stretchability of higher-strength steels and especially the new generation of advanced high-strength steels. Understanding n value also is important to users of aluminum, copper and other nonferrous metal alloys. However, procedures to measure n value are not commonly available or explained. The n value is measured during the same tensile test used to acquire yield strength, tensile strength and total elongation. Most data-acquisition programs used to automatically obtain the other tensile properties also will compute and print out n value. However, many persons still must compute n value by hand.
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