Stress State Dependence of Impact Strengths for Engineering Plastics

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Charpy impact (Mode I) and puncture impact (Mode+I+II+III) tests were adopted to study stress state dependence of impact strengths for engineering plastics. For specimen materials, HIPS,PPE,PBT,PBT/PPE (blend), PA6, PA6/EPR,PA6/PPE/SBS,PA6/PPE/SBS/EPR were employed. Instrumented impact apparatus was used to evaluate impact load, displacement and energy in fracture of the specimens.Impact energy values in both tests, E_<3pb> (Charpy) and E_<pun> (puncture), were defined as follows : E_<3pb>=E/(B・a_l), E_<pun>=E/B, where E is total energy measured by the apparatus, B specimen thickness and a_l length of ligament region.It has been found from the result that the engineering plastics above mentioned can be classified into three categories : (I) PBT and PA6, (II) PBT/PPE,PPE/SBS and PA6/PPE/SBS,(III) PA6/EPR and PE6/PPE/SBS/EPR depending on the stress state dependency. Plastics of class I are quite weak under one dimensional stress concentration, and those of III are tough under both one and mixed three mode stress states. Plastics of class II exhibit toughness in betwen.It is concluded from the study that the method proposed here is available for studying the stress state dependency on impact strength of engineering plastics.A fundamental study was also performed on instrumented impact testing. Oscillation signals from a strain gauge of a dart impacting PC Charpy specimens were experimentally analyzed. A method to place a thin rubber sheet on an impact surface of a specimen is proposed to minimize dynamic effects contained in the dart sugnals.