Cel
PROJECT MTR00081 PROJECT DEFINITION The basic tests used for the quality control of rubber are in general adequately covered by national and international standards. Problems however frequently occur in relation to the results of dynamic testing because, not only are they dependent upon variables such as test machine stiffness, response time and temperature control, but some rubbers themselves display time dependent properties. The purpose of this project is to identify the relative importance of those factors which may give rise to significant variability of results. RESULTS Participants were asked to cyclically test centrally manufactured specimens of agreed designs in compression and shear at different temperatures, frequencies, pre-strains and strain amplitudes in order to show the effects of: machine stiffness and proportionality errors. materials pre-conditioning. materials sensitivity to prior strain history. variations in test conditions. The intercomparison showed that the ratio of the loss (viscous) modulus to the elastic modulus, tan d, can only be discriminated for some materials to within 0.02 which is the same order as its magnitude. Indeed, for a strain amplitudes of 1 % measurements of tan d, as required for some materials, were shown to be meaningless and should therefore be excluded from standards. The trends due to changes in temperature, frequency and strain level were shown to be consistent compared with between laboratory variations of up to 20 %.