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Undergraduate Materials Research: Tensile Impact Toughness of Polymers

Abstract

Materials science and engineering knowledge is vital for a solid foundation in mechanical engineering. However, often students lose interest in this subject under the pressure of other mainstream subjects such as mechanics, design, manufacturing etc. Strong foundation in materials leads to improved student interest and success in follow up courses such as design. A group of 4 senior machine design students was assigned to design and build a prototype of a bench top portable impact tester for polymers. The tester was designed to use standard ASTM D18221 procedure and specimens. The readout of the impact fracture energy is intentionally designed to require the user to do some fundamental calculations, thereby refreshing some physics of work, energy and velocity. Various polymeric materials are tested at various strain rates in a Universal Testing Machine and the impact tester. With the limited set of data acquired so far correlation was observed between strain rate and the fracture energy. It is expected that continued experimentation will provide clear correlations for various polymers. Two aspects of materials education is emphasized in this endeavor. First the engineering design and second the materials research. Both have been achieved to reasonable extents. Furthermore the interest developed among students has been an added benefit. This paper provides a detail account of the background, the design, application outline and the results of the research. The tester has been included in the materials laboratory syllabus for current semester. As many as 5 sections of 12 students can use the tester per semester. Usage of the tester is described in a format suitable for use in a materials laboratory. Extended set of experimentation and collection of student feedback are planned.

Key Words

Materials research Impact test Strain rate Strain hardening Ductile-to-brittle transition Glass transition temperature

Introduction

Polymers are as common these days as steel was during the industrial revolution. More and more industrial, commercial and domestic products are manufactured from plastics. Thus it is of vital importance that students understand the structure, mechanical properties as well as failure modes of plastics in general. Most materials tensile properties vary with temperature, higher values drive the strength down and ductility up. At certain lower temperature (range) many otherwise ductile materials, including metals and polymers, behave more like brittle materials. And thus their responses to loads also change. For metals this temperature range is known as ductile-to-brittle temperature (range). Similar characteristic of polymers is known as glass

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Atiqullah, M. (2008, June), Undergraduate Materials Research: Tensile Impact Toughness Of Polymers Paper presented at 2008 Annual Conference & Exposition, Pittsburgh, Pennsylvania. 10.18260/1-2--3867