| The understanding of strain history during a metal forming operation is important as the continuous plastic deformation may alter yield stress of the finished product via work hardening. A non-invasive digital imaging procedure has been developed to quantify the local strain behavior during metal forming. From digital images, obtained during the forming process, discrete spatial data of the object profile was acquired. A B-spline approximation method with an optimal number of control points was then applied to obtain a continuous profile. The weights of the B-spline function were calculated using linear least square regression. The deformation strains were calculated from the curvature of the continuous profile, and a local averaging approach was used to smooth the fluctuations of the calculated curvature. The proposed procedure was applied to an electric resistance welded (ERW) pipe forming process, and validated using measured strain gauge data. |
