高分子材料加工技术专业英语 Viscoelasticity of Polymers (Stress Relaxation) Lesson Viscoelasticity.ppt

* * * * * * * * * * * * * * * Testing – Impact A weighted hammer is released and swings through the test bar. ABS sample -note the hinged break Polypropylene sample -note the complete break Properties – Impact How would the impact properties change: if the temperature were increased? if the strain rate (test speed) were increased? If the molecular weight was higher? If a filler were added to the material? If there were a higher level of crystallinity in the material? If the material had a higher level of branching? Properties – Impact How would the impact properties change if the temperature were increased? Impact properties generally increase with a rise in temperature – to a point. The polymer chains being able to move more easily allows them to absorb more energy before failure, but as you approach the melting temperature the material cannot absorb the energy and fails sooner. Properties – Impact How would the impact properties change if the strain rate (test speed) were increased? An increase in the rate of impact will reduce the impact strength The chains cannot slide fast enough to absorb the energy. Properties – Impact How would the impact properties change if the molecular weight was higher? An increase in molecular weight would provide more entanglement and definitely allow the material to absorb more energy before failure? Properties – Impact How would the impact properties change if a filler were added to the material? The impact properties would change depending on the same factors that would affect a material’s tensile properties Amount of filler Type of filler Shape and size of the filler particle Fillers can either increase or decrease the impact strength, but they do always make the break more brittle Properties – Impact How would the impact properties change if there were a higher level of crystallinity in the material? A higher level of crystallinity generally lowers impact strength in polymers. The dense crystal structure does not allow