SIF2004 Structural Integrity and Fracture. http://eprint.uq.edu.au/archive/00000836 Analysis Of Low Temperature Impact Fracture Data Of Thermoplastic Polymers V Pettarín 1 , R Seltzer 1 , L Fasce 1 , P Frontini 1 , K Leskovics 2 , G B Lenkey 2 , T Czigany 3 1 Institute of Materials Science and Technology, University of Mar del Plata, J B Justo 4302, B7608FDQ, Mar del Plata, Argentina. e-mail: rseltzer@fi.mdp.edu.ar 2 Bay Zoltán Foundation for Applied Research, Institute for Logistics and Production Systems Iglói u. 2., H- 3519 Miskolctapolca, Hungary 3 Department of Polymer Engineering and Textile Technology, Budapest University of Technology and Economics, H-1111, Budapest, Hungary ABSTRACT: Impact fracture toughness of polypropylene (PP) blends, high density polyethylene (HDPE) and rubber toughened polymethylmethacrylate (RTPMMA) has been studied by means of three-point bending falling weight impact testing at different temperatures ranging from –60ºC to room temperature using the cleavage fracture toughness, J C parameter [ASTM E1820-99a]. The latter Fracture Mechanics methodology was chosen due to its simplicity [Fasce et al., 2003]. Traces of the impact tests were analyzed using an inverse methodology just proposed by Pettarin et al. (2003). This methodology makes it possible to obtain from a three-point bending instrumented impact test the mechanical response of the material, discarding the dynamic effects associated with the test. The results show that the average J C values calculated with treated and untreated data are similar for a given material, while the standard deviations are larger when the calculations are made with the untreated data. It is clear that the inverse methodology used to correct the data reduces error propagation, giving place to more precise estimations, and therefore more reliable J C values. 1. INTRODUCTION The growing use of polymeric materials in engineering applications demands new methodologies in order to assess their capability to withstand load. It is well known that thermoplastics, even the toughened grades, are relatively susceptible to impact fracture. Impact testing is widely used to characterize the fracture resistance of polymers in industry because it attempts to simulate the most severe loading conditions to which a material can be subjected to and because it also diminishes the viscoelastic effects. However, the difficulty of obtaining reliable data from instrumented impact tests at high speeds is well known and pointed out in the literature [see for example Kalthoff, 1985; Williams and Adams, 1987; Pavan and Draghi, 2000]. Brittle fracture toughness, J C , is the methodology chosen to assess fracture toughness [Fasce et al., 2003]. Under three-point-bending conditions and a crack-depth to specimen-width close to 0.5, this methodology can be applied to polymers displaying either linear or non-linear unstable fracture pattern under dynamic conditions. It only consists of calculating the J-Integral at the point of unstable fracture (instability load point), which may or may not be preceded by plastic deformation or very little slow crack growth. This parameter is commonly calculated from the experimentally measured load versus time curves. However, these curves are not what theoretically should be used for this purpose, because the measured load is not equal to the load exerted on the tested specimen, the load from which the mechanical performance of the material should be evaluated. The recorded load is corrupted by other forces acting during the experimental run, which depend in part on the characteristics of the tester and in part on the properties and geometry of the tested material. A simple method which combines a model mechanically equivalent to the system specimen-impact instrument and the inverse problem concept [Pettarin et al., 2003] is used to obtain an accurate estimation of the actual flexural curve in impact testing.