J. Phys. IY France 10 (2000) O EDP Sciences, Les Ulis Experimental and numerical simulation of impact of thin plates with loss of contact between plates and impactor V. Grolleau, G. Rio, H. Laurent, N. Couty* and Y. Fanch le Merdi** LG2M, Universite de Bretagne Sud, rue de Saint Maude, 56325 Lorient cedex, France * IRCN, Nantes, France ** GERBAM, Lorient, France Abstract. The present investigation is concerned with the impact of thin plates used in chip building. The problem is studied both numerically with a particular finite element resolution and experimentally with an apparatus propelling the projectile with a crossbow. The initial speed of the projectile is about 30mJs. Loss of contact has been detected between the plate and the projectile during the impact. Presumably, the loss of contact is due to waves propagating in the plate and in the projectile. Strain gages are used to study the flexural waves propagating along the plate. 1. EXPERIMENTS 1.1 Experimental set-up The experimental apparatus is showed Fig. 1. It was conceived at the laboratory and is composed of a crossbow, two steering bars and two lockout cylinders. The clamping force is 20 tons. The crossbow is capable of propelling the 200g, 20mm diameter hard steel hemispherically- ended cylindrical projectile at velocities up to 30mIs. The clamped sample of sheet metal is rectangular. The sheet is 250 mm wide ; 20 mm long and 4 mm thick, in common chip building material with a 360MPa elastic limit. Impact takes place at the center of the sample. Two data acquisition boards have been used to record the data from several sensors : the accelerometer placed in the head of the projectile, the speed sensor, the LASER shift sensor of the center of the plate, the strain gages bonded to the plate and the electric difference of potential between the plate and the projectile. Figure 1. Experimental apparatus. 1.2 Results of the experiments 1.2.1 Shift WThe Plate The data from experiments will be compared with the numerical results. First we need to check the coherence between the data given by the sensor accelerometer, the speed of the projectile and the shift sensor. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:2000983