Deformation dependent electrical resistance of MWCNT layer and MWCNT/PEO composite films

It has been well documented that the electrical properties of a carbon nanotube (CNT) can be either metallic or semiconducting depending upon the tube\u27s chirality. Theoretical aspects of the unique electrical properties of CNTs are reviewed. Based upon the fundamental understanding of this special feature, the deformation-dependent electrical resistance of multiwalled carbon nanotube (MWCNT) layer and MWCNT/polyethylene oxide (PEO) composite in the macroscopic scale are investigated considering both experimental and theoretical aspects. In the first set of experiments, a MWCNT layer was grown by plasma enhanced chemical vapor deposition (PECVD) process on a surface of copper substrate and a copper probe was applied to this surface inducing compressive deformation onto the MWCNT layer. It was found that the electrical resistance of the MWCNT layer under compression was reduced by 80 percent. The possible mechanisms for electrical resistance reduction were analyzed and suggested. Also, the MWCNT-enhanced surface showed a finite slope of electrical resistance as a function of contact force, thereby making possible the use of this arrangement as a small-scale force or pressure sensor. However, there is limitation on the direct use of MWCNT grown directly onto copper substrates for real applications due to the easy separation of the MWCNTs from the copper surface and the low yield of MWCNTs by the given metal deposition and PECVD system. The processing method developed for the second set of experiments uses intentional coagulation of dispersed MWCNT in polymer solution. This process is simple and effective to fabricate MWCNT-filled polymer films. MWCNT/PEO composite was selected after comparative resistivity measurement and microstructure analysis. The percolation threshold of MWCNT/PEO was determined experimentally to be between 0.14 to 0.28 vol% of MWCNT. Films having MWCNT content above the percolation threshold were conductive and exhibited repeatable values of electrical conductivity. Unique and repeatable relationships of resistance versus strain were obtained for multiple samples with different volume fractions of MWCNT. The overall pattern of electrical resistance change versus strain for the samples of each volume fraction of MWCNT consists of linear and non-linear regions. A model to describe the combination of linear and non-linear modes of electrical resistance change as a function of strain is suggested. The unique characteristics in electrical resistance change for different volume fractions implies that nanotube-based composites can be used as tunable strain sensors for application into embedded sensor systems in structures

Strain-dependent electrical resistance of multi-walled carbon nanotube/polymer composite films

"The strain-dependent electrical resistance characteristics of multi-walled carbon nanotube (MWCNT)/polymer composite films were investigated. In this research, polyethylene oxide (PEO) is used as the polymer matrix. Two representative volume fractions of MWCNT/PEO composite films were selected: 0.56 vol% (near the percolation threshold) and 1.44 vol% (away from the percolation threshold) of MWCNT. An experimental setup which can measure electrical resistance and strain simultaneously and continuously has been developed. Unique and repeatable relationships in resistance versus strain were obtained for multiple specimens with different volume fractions of MWCNT. The overall pattern of electrical resistance change versus strain for the specimens tested consists of linear and nonlinear regions. A resistance change model to describe the combination of linear and nonlinear modes of electrical resistance change as a function of strain is suggested. The unique characteristics in electrical resistance change for different volume fractions imply that MWCNT/PEO composite films can be used as tunable strain sensors and for application into embedded sensor systems in structures."http://deepblue.lib.umich.edu/bitstream/2027.42/64159/1/nano8_5_055705.pd

Analysis of a J69-T-25 engine turbine blade fracture

International audienceThe fracture of a turbojet engine turbine blade was investigated. Visual and surface examination showed that the turbine blade had initially cracked by a fatigue mechanism over a period of time and then failed by overload at the last moment. The fatigue crack initiated on a surface damaged by rubbing. Also the cracked turbine blade was severly damaged by hot gas flow and discolored. This heat damage made the gamma prime phase in the matrix (Ni-base superalloy) coarsen and lowered the fatigue strength of the base material assisting to the premature fatigue fracture. The decrease of the strength of the material due to degradation of gamma prime phase was verified by hardness measurements. The possible relevance of other parts attached to the engine shaft to the fracture was reviewed. From this reviewit is inferred that the root cause of cracking and excessive heat damage might be attributed to eccentricity of the shaft resulting from various reasons—shaft misalignment, uneven wear of bearing elements and mismatch in clearance, etc. However this is an assumption that should be verified by positive supporting evidence from condition monitoring of engines

Excellent dispersion of MWCNTs in PEO polymer achieved through a simple and potentially cost-effective evaporation casting

A simple, reliable and potentially cost-effective composite film casting procedure is presented using the evaporation of solvent (water) from a dilute mixture of multiwalled carbon nanotubes (MWCNTs) and polyethylene oxide (PEO) polymer. It is found that the fabrication method develops excellent dispersion of MWCNTs in PEO confirmed by morphology observations, final crystallinity of polymer (amorphous) and a lower percolation threshold (closer to theoretical value) as well as higher electrical conductivity. A film thickness prediction model is derived based upon the fact that final film thickness is mainly dependent upon the dimensions of the casting mold and the loading of the MWCNTs and polymer. This simple model provides important insight that the material loss and the actual density of the base polymer are critical factors making the current casting method truly cost effective and controlling final thickness

COVID-19 impact on city and region: what's next after lockdown?

COVID-19 is unique in that it is spread through everyday contact with other people. Therefore, social protective measures, beyond medical protective measures, such as social distancing, lockdowns, border closures, and human tracing are initiated to control the spread of COVID-19. Such responses have produced secondary issues such as drastic changes in people's way of life and work, housing instability, economic shock, and privacy issues. This paper examines the four domains of urban and regional issues related to the secondary impact of COVID-19, including (1) social distancing, urban structure, community, and density; (2) housing affordability; (3) lockdowns, border closures, reshoring, and regional economic recovery; and (4) smart city technology, contact tracing, and privacy. The following six recommendations have been proposed. First, institutional and cultural factors are more important than urban features, such as population density. To handle infectious diseases such as COVID-19, it is important to build systems, technology, infrastructure, and urban structures that can strengthen resilience instead of implementing a directionless policy of dispersion. Second, it is necessary to improve accessibility to essential services at the community level, including medical facilities and food supply. Third, continuous effort should be made to boost housing affordability, as it is directly related to people's basic life. Fourth, measures are needed to protect those people who are socioeconomically disadvantaged. There is also the need to restore global trade and economic relations. Fifth, since data technology-based COVID-19 control raises the human tracing and privacy issue, we must ensure the principles of privacy management, such as transparency and voluntary consent, are being met. Finally, since COVID-19 is spread through people, individuals may become anxious and fearful of others without grounds; this may increase prejudice and hatred, including xenophobia. Significant social effort is needed to overcome such ill-defined anxiety and fear and maintain a healthy civil society

Rate-dependent deformation of amorphous sulfide glass electrolytes for solid-state batteries

Sulfide glasses are emerging as potential electrolytes for solid-state batteries. The mechanical behavior of these materials can significantly impact cell performance, and it is thus imperative to understand their deformation and fracture mechanisms. Previous work mainly reports properties obtained under quasi-static loading conditions, but very little is known about deformation under dynamic conditions. The current investigation shows that the sulfide glass mechanical behavior is dominated by viscoplasticity, differing substantially from polycrystalline oxide and sulfide solid electrolytes. Finite element modeling indicates that the sulfide glass stiffness is high enough to maintain good contact with softer lithium metal electrodes under moderate stack pressures. The observed viscoplasticity also implies that battery operating conditions will play an important role in electro-chemo-mechanical processes that are associated with dendritic lithium penetration. In general, the rate-dependent mechanical behavior of the sulfide glass electrolytes documented here offers a new dimension for designing next-generation all-solid-state batteries.Published versionThe authors acknowledge financial support from SK Innovation and the National Science Foundation (DMR-2124775)

Green solvent approach for printable large deformation thermoplastic elastomer based piezoresistive sensors and their suitability for biomedical applications

Composites based on biocompatible thermoplastic elastomer styrene-ethylene/butylene-styrene (SEBS) as matrix and multi-walled carbon nanotubes (MWCNT) as nanofillers show excellent mechanical and piezoresistive properties from low to large deformations. The MWCNT/SEBS composites have been prepared following a green solvent approach, to extend their range of applicability to biomedical applications. The obtained composites with 2, 4 and 5 wt% MWCNT content provide suitable piezoresistive response up to 80% deformation with a piezoresistive sensibility near 2.7, depending on the applied strain and MWCNT content. Composite sensors were also developed by spray and screen printing and integrated with an electronic data acquisition system with RF communication. The possibility to accurately control the composites properties and performance by varying MWCNT content, viscosity and mechanical properties of the polymer matrix, shows the large potential of the system for the development of large deformation printable piezoresistive sensors.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013. Financial support also provided by ERDF funds through the Portuguese Operational Programme for Competitiveness and Internationalization – COMPETE 2020, and national funds through FCT, under projects PTDC/EEI-SII/5582/2014 and PTDC/CTMENE/ 5387/2014. J.O., S.R. and V. C. thank the FCT for the SFRH/BPD/98219/2013, SFRH/BD/111478/2015 and SFRH/BPD/97739/2013 grants, respectively. SLM thanks financial support from the Basque Government Industry Department under the ELKARTEK Program and the Diputación Foral de Bizkaia for finantial support under the Bizkaia Talent program; European Union’s Seventh Framework Programme; Marie Curie Actions – People; Grant agreement nº 267230. The authors thank Dynasol for providing the high quality materials