Multifunctional and multiscale characteristics of PEEK and CF/PEEK composite structures processed via FFF additive manufacturing

  • Hasan Alhashmi

Student thesis: Doctoral Thesis

Abstract

Polyetheretherketone (PEEK) is a high temperature thermoplastic possessing excellent mechanical properties and chemical stability. The use of PEEK has been demonstrated in biomedical, automotive, aerospace, and oil and gas applications. Incorporation of carbon-based fillers into PEEK matrix imparts electro- and thermo-conductive characteristics to PEEK composites in addition to enhancing their mechanical attributes. Advances in additive manufacturing (AM) have enabled processing of PEEK and other semi-crystalline thermoplastics through fused filament fabrication (FFF). This study is focused on the multiscale and multifunctional characteristics of PEEK and PEEK composites reinforced with chopped carbon fibers (enabled by FFF AM). Initially, filament feedstocks were characterized via XRD, TGA, and DSC. The mechanical response of PEEK samples was evaluated under tensile, compressive and flexural loadings. FFF CF/PEEK composites show improved modulus (170%) and strength (25.9%), but lower strain-tolerance (-98.2%) compared to FFF PEEK. The piezoresistive characteristics of CF/PEEK samples under tensile, compressive and flexural loadings were studied (gauge factor varies from 0.36 to 5.6). Fatigue performance of PEEK under repetitive cyclic loading was evaluated by varying the maximum applied stress, frequency and the temperature. Scanning electron microscopy (SEM) and micro-computed tomography (╬╝CT) techniques were used to further understand the fatigue behavior. Leveraging the architectural freedom offered by AM, mechanical and piezoresistive response of PEEK and CF/PEEK honeycomb cellular structures respectively under quasi-static and low-velocity impact loadings were investigated. Hexagonal, re-entrant and chiral cell topologies were considered. Under in-plane compression, PEEK hexagonal honeycombs exhibit about 45% and 40% improved energy absorption capacity over chiral and re-entrant honeycombs, respectively. CF/PEEK re-entrant honeycombs evince about 80% improved energy absorption capacity over hexagonal honeycombs. Under low-velocity impact energy of 150 J, PEEK honeycombs exhibit failure after absorbing about 40% energy while CF/PEEK honeycombs absorbed more than 90%. Under out-of-plane compression both PEEK and CF/PEEK honeycombs exhibit an energy absorption efficiency of more than 60% with gauge factor ranging from 2.8-3.7. AM of high performance PEEK and electro-conductive PEEK composites in particular, holds tremendous promise for biomedical applications, such as for design of self-sensing knee replacement implants that more closely mimic native physiology.
Date of AwardJan 2020
Original languageAmerican English

Keywords

  • PEEK CF/PEEK Characterization Fatigue Piezoresistive response Honeycombs Auxetic structures Impact performance Energy absorption.

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