Pergamon Int. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR J. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ Impact Engng Vol. 19, No. 2, pp. 135-146, 1997 Copyright 0 1996 ElsevierScienceLtd Printed in Great Britain. All rights reserved PII:SO734-743X(96)OOBl7-6 0734-743x/97$17.00 + 0.00 DYNAMIC TENSILE TESTING OF ARAMID AND POLYETHYLENE FIBER COMPOSITES IS. CHOCRON BENLOULO, J. RODRIGUEZ, M.A. MARTINEZ and V. SANCHEZ GALVEZ Departamento de Ciencia de Materiales, E.T.S.1 Caminos Canales y Puertos, Universidad Polittcnica de Madrid, Madrid 28040, Spain (Received 11 M ay 1995; in revised form 25 April 1996) Summary-Dynamic properties of materials such as aramid and polyethylene fiber reinforced composites are rarely found in the literature, in spite of their significance in ballistic design. It is also difficult to find detailed descriptions of the testing techniques and procedures to characterize these materials. This paper describes a dynamic tensile testing technique for these composite materials, and discusses problems such as the specimen size and the clamping system. A full numerical simulation is performed in Autodyn-2D to elucidate what is happening during the experiment. Finally this testing technique is applied to show that reliable data can be obtained from the Hopkinson bar for aramid and polyethylene fiber reinforced composites. Stress-strain, stress versus rate of strain and strain versus rate of strain curves are included. The results indicate that for these materials the tensile strength rises with the strain rate while the maximum strain diminishes in the range studied. Copyright 0 1996 Elsevier Science Ltd. Keywords: aramid, polyethylene, dynamic, Hopkinson bar, characterisation. NOTATION CFRP GFRP PET PP E : S carbon fiber reinforced composites glass fiber reinforced composites polyethylenterefthalate polypropylene sound velocity Young’s modulus bulk modulus shear modulus standard deviation INTRODUCTION The tensile dynamic characterization of composite materials is a difficult, but interesting work. It is difficult because the failure process (tension, shear failure or pull-out) is usually out of control and not repetitive, and because the specimen has to be small enough to ensure the equilibrium state before failure. Additionally, when high fiber content composites for ballistic applications are investigated, a large clamping or gluing surface is needed to avoid slip and stress concentrations. It is interesting because little work has been done in this field and the data may be essential for numerical or analytical modeling. Some results in CFRP and a description of the testing technique can be found in Harding [ 11.Additional high strain rate data of another composite material (GFRP) can be consulted, for instance, in Harding [2,3], Newill [4] or Staab [S]. In spite of these studies, the difficulty in finding high strain rate properties increases when aramid or polyethylene fiber reinforced plastics are the objective. The reader can compare aramid composite characterization in Morrison [6] or in the DuPont Company Guide [7] with the results of this paper. Extensive information on composite materials at high strain rate is available in Abrate [S] and Cantwell [9]. In this work, an experimental technique based on the Hopkinson bar for testing materials such as aramid and polyethylene composites is described. Static, intermediate and high strain rate tensile tests are performed. The study is completed with a full numerical simulation in order to show the reliability of the Hopkinson bar as a tool for the dynamic characterization 135