· Grain size gradient length scale in ballistic properties optimization of functionally graded nanocrystalline steel plates Antoine Je´rusalem,a,⇑ William Dickson,b Maria Jesu´sPe´rez-Martı´n,c Ming Dao,b Jian Lud and Francisco Ga´lvezc aDepartment of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK bDepartment of Materials …