In-situ characterization of microstructural changes in a carbon nanotube sheet under sustained load. (15th November 2017)

• Record Type: Journal Article
• Authors: Cobb, Gregory R.; Singh, Abhendra K.; Mall, Shankar
• Is Part Of: Materials & design. Volume 134(2017)
• Page Start: 494
• Page End: 501
• Publication Date: 2017-11-15
• Subjects: Carbon nanotube sheets -- Alignment -- Tensile -- Creep -- Pattern recognition -- Stress relaxation; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2017.09.008
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: The present study characterizes the creep behavior of carbon nanotube (CNT) sheets under externally applied sustained loads. Creep loads at levels ranging from 85% to 98% of the ultimate tensile strength of the CNT sheet were applied using a tensile tester inside a scanning electron microscope chamber. The microscope enabled in-situ characterization of the microstructural changes in the CNT sheet under the influence of the applied load. The loads were sustained for 1, 000, 000 s or failure, whichever occurred first. A computational pattern recognition technique was also developed that enabled quantitative approximation of the time dependent changes in distribution of individual CNT orientation with reference to the loading direction. It was observed that the CNTs increasingly aligned along the loading direction during the initial loading phase when the CNT sheet was ramped up to the desired load level. Further microstructural changes by way of individual CNTs continuing to gradually align along the loading direction was observed after the loads were sustained at the desired levels. The pattern recognition computational results validated the experimental findings. Slight relaxation of the CNTs was also observed upon the removal of load once 1, 000, 000 s was reached. Graphical abstract: Highlights: Carbon nanotube sheets were studied in-situ in a scanning electron microscope to characterize creep behavior. A computational pattern recognition program was created and used to characterize individual carbon nanotube alignment. The carbon nanotubes exhibited continuous alignment throughout the testing phase. The sheets did not fail after 1, 000, 000 s at high loads relative to the ultimate tensile strength.