ECCM15 - 15 TH EUROPEAN CONFERENCE ON COMPOSITE MATERIALS, Venice, Italy, 24-28 June 2012 1 MODELING THE INFLUENCE OF SPEED OF TESTING AND TEMPERATURE ON THE BEHAVIOR OF POLYURETHANE FOAMS D.A. Apostol 1 , D.M. Constantinescu 1* , M.O. Stoica 1 1 Department of Strength of Materials, University POLITEHNICA of Bucharest, Splaiul Independentei nr. 313, 060042 Bucharest, Romania *dan.constantinescu@upb.ro Keywords: polyurethane foams, temperature and speed of testing, analytical model, specific strain energy. Abstract Polyurethane foams with densities of 35, 93, and 200 kg/m3 were tested in tension and compression at three levels of temperatures as: -60 °C, 23 °C, and 80 °C. The influence of speed of testing from 2 mm/min up to 6 m/s (0.0014 to 545/s) on the response of the foams is analyzed. Testing is done separately on the rise direction and on the in-plane direction of the foams and differences in their behavior are commented. The variations of the modulus of elasticity, maximum stress at yielding, behavior in the yielding region are analyzed showing that they are density, speed of testing, direction of testing, and temperature dependent. An analytical model, based on the one established by Nagy, is proposed to generate the characteristic curves for different speeds of testing and densities, starting from a reference curve established experimentally at 2 mm/min. 1 Introduction Foam materials have a cellular structure and hence behave in a complex manner, especially under conditions of progressive crush. This crush behavior is dependent on the geometry of the microstructure and on the characteristics of the parent material. Foam materials are often used as cores in sandwich construction, and in this application the material can be subjected to multi-axial stresses prior to and during crush. Well-known advantages of cellular metals are their excellent ability for energy adsorption, good damping behavior, sound absorption, excellent heat insulation and a high specific stiffness combined with a low weight. The combination of these properties opens a wide field of potential applications, i.e. as core materials in sandwich panels. A good knowledge of the behavior of different grades of foams is important for being able to design high performance sandwich composites adapted to the special needs of a particular application, [1], [2]. Polyurethane (PU) foam is an engineering material for energy absorption and has been widely used in many applications such as packaging and cushioning. The mechanical testing of rigid PU foams under compression in the rise and transverse direction gives different deformation responses in each direction which are attributed to the anisotropy in the internal cellular structure. Strain rate and temperature effects on the crush behavior of foams were studied in [3]. Following, Mines [4] studies strain rate effects on Divinycell PVC foam, Rohacell PMI