On the Impact Energy Absorption of an Advanced High‐Strength Bilayer Steel Composite Consisting of Carbide‐Free Bainitic Steel and High‐Mn Twinning‐Induced Plasticity Steel

The relationship between strength and impact energy is analyzed for a bilayer composite consisting of carbide‐free bainitic (CFB) steel and high‐Mn twinning‐induced plasticity (TWIP) steel. The mechanical behavior is evaluated by uniaxial tensile testing, Charpy V‐notch (CVN) impact testing, and three‐point bending. The thickness of each layer varies between 40% and 60% of the total thickness. The yield stress of the bilayer material follows the rule of mixtures. The fracture strain is essentially independent of the volume fraction of the soft and hard layers in the above range. For the bilayer materials, the energy absorbed during CVN tests shows a strong dependence on the volume fractions of the soft and hard layers. The results also depend on whether the notch is machined into the TWIP or CFB side. In general, the samples show an increase in energy absorption as the percent thickness of the unnotched layer increases. When the notch is positioned in the CFB layer, interface delamination leads to the arrest of the crack. As a result, the TWIP layer can experience very large deformation. When the notch is positioned in the TWIP layer, the crack propagates slowly through the TWIP steel, allowing for codeformation of both layers.