Over the past century, polymeric materials have become ubiquitous within technology and daily life. Often plastic products must be able to survive impacts over a large range of temperatures such as those used in electrical enclosures (e.g. battery casings in phones and cars) and physical barriers (e.g. windows and goggles). In the past, impact failure was evaluated with destructive tests, but this is expensive and time-consuming. Past research and advances in computing have led to computer aided design and finite element analysis methods which can be used to simulate a number of mechanical properties of polymeric structures. However, the impact properties of many polymers have not been successfully modeled.Polymeric materials are composed of long chains of individual molecules known as monomers which are held together by secondary bonds. Amorphous and semi-crystalline polymers have a glass transition temperature above which some secondary bonds weaken allowing its macromolecular chains greater ability to rotate and shift relative to each other. Thus, an increase in temperature results in an increase in viscosity.The WLF equation can be used for materials above their glass transition temperature to predict mechanical properties related to viscoelasticity. It shows that the change in mechanical properties resulting from a temperature shift is equivalent to the change in properties caused by a shift in the time scale. This phenomenon is perfectly demonstrated by Silly Putty; at room temperature a piece of Silly Putty will flow far slower than it does at an elevated temperature. Under the same loading conditions, a shift in either temperature or time will give you the same set of properties. The WLF equation is commonly applied to materials undergoing low rates of strain and experiencing either creep or stress relaxation but it can be used to predict any property that is the result of viscoelastic behavior.This paper examines modeling the temperature-dependent impact behavior of polymers based on the WLF equation. Although polymers experience viscoelastic behavior for an incredibly short amount of time prior to fracture under impact testing, the lessons of the WLF equation can be utilized to make similar predictions within that time frame. By comparing the rate of change of impact energy versus time at different temperatures in a standard ASTM D3763 multiaxial impact test, the researchers hope to create a generalized rule for modelling impact properties that can be applied to crystalline and semi-crystalline polymers. In this paper, data from high-speed puncture tests for semicrystalline polymer polypropylene (PP) are the basis for creating such a rule for modelling its own impact properties and applying it to other polymers such as semi-crystalline polymer high-density polyethylene (HDPE), and the glassy polymer polymethyl methacrylate (acrylic, PMMA).

Temperature Dependent Impact Properties of ABS Polymer

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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