@article{EJDE_2007__2007__a63,
     author = {Ayyad,  Youssef and Sofonea,  Mircea},
     title = {Analysis of two dynamic frictionless contact problems for elastic-viscoplastic materials},
     journal = {Electronic journal of differential equations},
     year = {2007},
     volume = {2007},
     zbl = {1137.74040},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2007__2007__a63/}
}