Assessing the Bendability of Ultra-High Strength Steel in Plane Strain Conditions

Inconsistent behavior and premature failure are common when bending Ultra-High strength steels (UHSS). Practicality limits laboratory testing to smaller samples, which may not replicate the conditions of production or result in plane strain loading, and larger volumes of material used in manufacturing may increase the likelihood that material inhomogeneities will cause failure. A rig was developed, capable of replicating the size and scale of production. Tests have been undertaken on a commercial grade of UHSS at 5 forming radius/thickness ratios with strains measured using digital image techniques. Results show that punch separation occurs on specimens that ultimately fail, causing bend severity to increase unexpectedly. This occurs at consistent bending punch displacements during the bending process, with initial bending strains matching until a deviation point. Clear visual separation was observed to occur more frequently when the line along which the material was bent was parallel to its rolling direction than when it was perpendicular. Upcoming investigations will focus on behavior at this deviation point to try and better understand this separation. Understanding of this phenomenon may increase suitable applications for UHSS when bend forming is required.