Strain Rate and Orientation Effects on Fracture Strain Limits in Advanced High Strength Steel

There is increasing interest in establishing fracture limits for advanced high strength steels where there is significant likelihood of fracture intervening during crash of structural components. Fracture strain data obtained from quasi-static tensile tests conducted at 10⁻³/s are commonly extended to predict crash events in design. In this study, true fracture strain measurements based on DIC as well as microscopy are presented for several high strength steels with ultimate tensile strength ranging from 1000-1200 MPa under uniaxial tension conditions over a range of strain rates from 10⁻³/s to 10⁻¹/s and in different sheet orientations. Implications of orientation and strain rate effects on fracture strain will be discussed in the context of local versus global formability considerations used in material selection as well as usage of fracture strain data in crash simulation. (paper)