Dynamical crack propagation in a 2D elastic body The out-of plane state Serge Nicaise Universit´ e de Valenciennes et du Hainaut Cambr´ esis MACS Institut des Sciences et Techniques de Valenciennes F-59313 Valenciennes Cedex 9 (France) Anna–Margarete S¨ andig Universit¨ at Stuttgart Mathematisches Institut A Pfaffenwaldring 57 D-70569 Stuttgart (Germany) 1