June 26, 2011
June 26, 2011
June 29, 2011
22.1569.1 - 22.1569.9
Undergraduate Research on High Temperature Creep Behavior of PolymersAbstract Creep is very slow deformation of materials and is one of several mechanisms of failurein materials under various loading conditions. It is a diffusion phenomenon prompted andaccelerated by higher temperatures at stress level below yield strengths. Due to diffusivedriving force creep is a slow process of permanent deformation over a long period of time.Physical mechanisms of creep in metals and polymers are very different because the atomicand crystal structures are so different. Creep in metals and alloys are well established by notso for polymers and composites. Under stress polymer chains slip over each other resulting inradical reorganization of the crystal structure during creep. Temperature and stress are themost effective factors in creep rate and rupture time in a creep test. Specific knowledge ofcreep deformation is necessary for designing and application of polymer based products underelevated temperatures at given stress. A senior design group, motivated by creep studiesduring previous semester, decided to design and build a high temperature creep tester forexperimental creep study of small polymer specimens. The group had already acquiredsufficient skills in CAD, Manufacturing as well as Materials Science and some machine design tounderstand the creep as a failure process and develop a tester that will meet certain testingand usage requirements. The tester was designed to test small dog bone specimens undertensile load inside a heated chamber. It was equipped with automated temperature controland instrumented for computerized monitoring and logging of both temperature andelongation over time. Tests performed by the design group demonstrated the functionality ofthe tester as well as creep behavior of a limited set of polymers selected for their commercialimportance and availability. Past summer two undergraduate students were selected toperform experimental creep research. A set of common engineering polymers such as Nylon6/6, Delrin, and PVC were selected for creep testing at various elevated temperatures. Thepurpose of the research was to determine how these specific materials respond to tensilestresses under a steady temperature over long time. Dog bone specimens were prepared fromflat polymer stocks using a CNC machine and a custom program. The polymer specimens weretested at various stress levels and set temperatures. Experimental results revealed thethreshold temperatures for creep and demonstrated the dependence of creep rate ontemperature under a given stress level and vice versa. The research is not complete by anymeans but an overview of the creep behavior of these limited set of polymers are revealed.Some experimental results and creep curves along with creep threshold temperatures atspecific stresses for given polymers are included. Testing should be continued for common highstrength polymers and composites such as Kevlar Filled Nylon, Glass-Filled PTFE, Aramid W/SBRBinder and others such engineered materials to get a better overall picture of creep behaviorfor this extended set of polymers and composites. The experience with this researchhighlighted much about polymer characteristics and shed light on importance of consideringhigh temperature creep characteristics while designing and operating machines with polymercomponents at elevated temperatures. However the best outcome was the learningexperience of the undergraduate research students in the field of materials science and failuremodes. These two undergraduate students won the 1st prize in oral presentation for thisguided research at the PSLSAMP student conference under engineering and technologycategory.
Atiqullah, M. M. (2011, June), Undergraduate Research on High Temperature Creep Behavior of Polymers Paper presented at 2011 ASEE Annual Conference & Exposition, Vancouver, BC. 10.18260/1-2--18657
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