The Effect of Tensile Hysteresis and Contact Resistance on the Performance of Strain-Resistant Elastic-Conductive Webbing

To use e-textiles as a strain-resistance sensor they need to be both elastic and conductive. Three kinds of elastic-conductive webbings, including flat, tubular, and belt webbings, made of Lycra fiber and carbon coated polyamide fiber, were used in this study. The strain-resistance properties of the webbings were evaluated in stretch-recovery tests and measured within 30% strain. It was found that tensile hysteresis and contact resistance significantly influence the tensile elasticity and the resistance sensitivity of the webbings. The results showed that the webbing structure definitely contributes to the tensile hysteresis and contact resistance. The smaller the friction is among the yarns in the belt webbing, the smaller the tensile hysteresis loss. However the close proximity of the conductive yarns in flat and tubular webbings results in a lower contact resistance

Characterization and modification of electrospun fiber mats for use in composite proton exchange membranes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references.Electrostatic fiber formation, or electrospinning, offers a particularly simple and robust method to create polymeric nanofibers of various sizes and morphologies. In electrospinning, a viscoelastic fluid is charged so that a liquid jet is ejected from the surface of the fluid (typically in the form of a drop supplied by a needle or spinneret) and collected on a grounded plate, creating a nonwoven fiber mat. Modification of the diameter of the fibers as well as the porosity, specific surface area, and mechanical properties of the mat allows one to tailor electrospun mats for specific applications. Despite the widespread and rapidly growing use of electrospinning in the fabrication of novel nanomaterials, there are no simple, universal methods of predicting, a priori, the properties of electrospun fibers from knowledge of the polymer solution properties and electrospinning operating conditions alone. Changing a single fluid or processing parameter can affect the jet and fiber formation through several mechanisms. For example, using a different solvent can change several properties of the electrospinning fluid, such as the dielectric constant, conductivity, surface tension, and solute-solvent interaction. The work in this thesis seeks to develop a simple relation for predicting terminal jet diameter during electrospinning, which accounts for solution viscoelasticity as well as solution conductivity and operating parameters that can be easily measured and controlled. The mechanical and tribological properties of electrospun fiber mats are of paramount importance to their utility as components in a variety of applications. Although some mechanical properties of these mats have been investigated previously, reports of their tribological properties are essentially nonexistent. In this thesis, electrospun nanofiber mats of poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) and poly(hexamethylene adipamide) (PA 6,6) are characterized mechanically and tribologically. Post-spin thermal annealing was used to modify the fiber morphology, inter-fiber welding, and crystallinity within the fibers. Morphological changes, in-plane tensile response, friction coefficient, and wear rate were characterized as functions of the annealing temperature. The Young's moduli, yield stresses and toughnesses of the PA 6(3)T nonwoven mats improved by two- to ten-fold when annealed slightly above the glass transition temperature, but at the expense of mat porosity. The mechanical and tribological properties of the thermally annealed PA 6,6 fiber mats exhibited significant improvements through the Brill transition temperature, comparable to the improvements observed for amorphous PA 6(3)T electrospun mats annealed near the glass transition temperature. The wear rates for both polymer systems correlate with the yield properties of the mat, in accordance with a modified Ratner-Lancaster model. The variation in mechanical and tribological properties of the mats with increasing annealing temperature is consistent with the formation of fiber-to-fiber junctions and a mechanism of abrasive wear that involves the breakage of these junctions between fibers. A mechanically robust proton exchange membrane with high ionic conductivity and selectivity is an important component in many electrochemical energy devices such as fuel cells, batteries, and photovoltaics. The ability to control and improve independently the mechanical response, ionic conductivity, and selectivity properties of a membrane is highly desirable in the development of next generation electrochemical devices. In this thesis, the use of layer-by-layer (LbL) assembly of polyelectrolytes is used to generate three different polymer film morphologies on highly porous electrospun fiber mats: webbed, conformal coating, and pore-bridging films. Specifically, depending on whether a vacuum is applied to the backside of the mat or not, the spray-LbL assembly either fills the voids of the mat with the proton conducting material or forms a continuous fuel-blocking film. The LbL component consists of a proton-conducting, methanolimpermeable poly(diallyl dimethyl ammonium chloride)/sulfonated poly(2,6-dimethyl 1,4- phenylene oxide) (PDAC/sPPO) thin film. The electrospun fiber component consists of PA 6(3)T fibers of average diameter between 400 and 800 nm, in a nonwoven matrix of 60-90% porosity depending on the temperature of thermal annealing utilized to improve the mechanical properties. This thesis demonstrates the versatility and flexibility of this fabrication technique, since any ion conducting LbL system may be sprayed onto any electrospun fiber mat, allowing for independent control of functionality and mechanical properties. The mechanical properties of the spray coated electrospun mats are shown to be superior to the LbL-only system, and possess intrinsically greater dimensional stability and lower mechanical hysteresis than Nafion under hydration cycling. The electrochemical selectivity of the composite LbL-electrospun membrane is found to be superior to Nafion, which makes them a viable alternative proton exchange membrane for fuel cell applications. The composite proton exchange membranes fabricated in this work were tested in an operational direct methanol fuel cell, with results showing the capability for higher open circuit voltages (OCV) and comparable cell resistances when compared to Nafion.by Matthew Marchand Mannarino.Ph.D

3D Printed Smart Materials of Continuous Wire Polymer Composites for Sensing Applications

Smart material with sensing capability is an exciting new technology that will impact many applications, including structural health monitoring, biomedical implants, wearable sensors, and actuators. Internal damage in polymer composites is usually hard to predict, and they need to be continuously monitored for any sign of internal damage for safety issues and to increase the life cycle. In this study, continuous wire polymer composites (CWPCs) were 3D-printed using the fused filament fabrication (FFF) technique to produce functional smart materials with different sensing capabilities like strain and thermal sensing. Here, the integrated wire within the conductive polymer composite structure acts as a sensing element. For strain sensing characterization, different design parameters such as matrix type, wire type, and loading condition were investigated to study the effect of these parameters on the efficacy of the CWPC sensor. The different matrices used have different mechanical properties representing rigid (polylactic acid) and flexible (thermoplastic polyurethane) structures to widen the range of applications of CWPCs as strain sensors. The change of the electrical resistance of the integrated wire within the CWPCs was measured under tensile loading and plotted against the applied strain. The results of this electromechanical testing demonstrate the ability of CWPCs to be used as strain sensor for either rigid or flexible structures. To check the reliability and reversibility of CWPCs structure as strain sensor, the electromechanical behaviour was investigated under fatigue/cyclic loading. The results of this work demonstrate the reverse piezoresistance behaviour of the CWPC sensor. From thermal sensing standpoint, different design parameters like wire type, matrix type, and sensor thickness were studied to investigate the application of CWPCs as temperature and heat flux sensors which can be readily designed and adapted to suit unique and bespoke thermal applications. The change of the electrical resistance of the integrated wires was correlated to the applied temperature to measure the heat conducted through a surface. A prototype of a real-world application was designed for the heat flux measurements using CWPC sensor. Generally, this study demonstrates the applicability of FFF technique to print sensors with continuous integrated wire with tuneable properties for different sensing applications

Analysis and Characterization of Embroidered Textile Strain Sensors for Use in Wearable Mechatronic Devices

Stroke and musculoskeletal disorders affect hundreds of millions of people around the world. To aid in the recovery process of people affected by these conditions, the use of wearable mechatronic devices has been proposed during traditional rehabilitation therapies. However, factor such as rigidity, increased weight, and overall bulkiness have hindered the adoption of these devices in a clinical setting. Therefore, alternative solutions in the form of soft wearable mechatronic devices have been proposed recently. This is due to these devices being lightweight and comfortable, and compliant, which makes them easier to conform to the human body. To achieve such compliance, high emphasis has been placed on the development of soft sensing mechanisms, as they are in charge of collecting information from the device, the environment and user. Among these sensing mechanisms, force and motion sensors have been extensively studied, as they are the simplest to integrate in wearable mechatronic devices. However, the majority of these sensors have been developed using soft materials that are not breathable and can cause skin irritations due to the materials used to fabricate them. For these reasons, textile sensors have been proposed as an alternative. Among these textile solutions, embroidered sensors have shown great potential, as they are relatively simple to manufacture and have high scalability characteristics. Unfortunately, embroidered sensors have the disadvantage of not being stretchable, which is one of the many characteristics of motion and force sensors. To address these issues, this thesis focuses on the design, development, characterization, and performance assessment of embroidered textile strain sensors. To this end, a framework for the development of embroidered textile strain sensors was proposed. This framework included all the necessary steps to design and fabricate these sensors. To achieve the required stretchability of embroidered sensors, a set of customizable parameters were included within this framework. Then, following the guidelines of the proposed framework, a novel embroidered strain sensor was created using a honeycomb pattern. This pattern had two main purposes: a distribution of the axial forces across the walls of the honeycomb design to protect the conductive thread; and the addition of stretchiness to the embroidered sensor. Sensors created using this pattern were embroidered onto an elastic band and then attached to a strain compensation system to increase the stretchability of the sensor further. After 50 stretching cycles, sensors showed good linearity, an average gauge factor of 0.24, an average hysteresis of 36.85% and up to 55.56% working range. This demonstrated the ability of the embroidered sensor to work as a strain sensor, without showing signs of damage and without showing signs of deformation. Lastly, a series of embroidered sensors were fabricated using a Kirigami design. These sensors were created to measure forces under dynamic conditions. Before testing, these sensors were attached to a strain compensation mechanism, which in turn was attached to a force sensing device that served as ground truth for the data collected by the embroidered sensors. The embroidered sensors were tested under three different speed profiles: slow speed, medium speed, and high speed. On each speed profile, each sensor showed high linearity, a low hysteretic behaviour, and relatively good repeatability. These results established the capabilities of the embroidered strain sensors as force sensors that could be used inside soft wearable mechatronic devices

Development of the core technology for the creation of electronically-active, smart yarn

The general use of textiles began twenty-seven thousand years ago. However, today, textiles are used, not only in the production of clothing but are also found in numerous applications in medicine, the military, transport, construction sectors and in many industrial applications. Normally textiles are passive, however active textiles have been developed that exhibit the capability of adapting their functionality according to changes in their surroundings, i.e. environment. Such textiles are known as Smart and Interactive Textiles (SMIT) and are capable of sensing and being active. The integration of semiconductor devices into textiles has enormous potential in the creation of SMIT. Such SMIT structures will pave the way for the creation of truly-wearable electronic systems in the near future. The aim of this research is the development of a core technology for embedding functional semiconductor devices within the fibres of a yarn, in order to create electronically-active yarns (e-yarn). Such electronically-active yarns will be the building blocks of the next generation of wearable electronics. Moreover, this will facilitate the creation of innovative solutions able to overcome current problems and difficulties which the manufacturers of wearable textiles are experiencing and open the doors for designers to develop the next generation of truly-wearable computers which are comfortable to wear, flexible and washable. The e-yarns could be used in medical applications such as monitoring of ECG, respiratory patterns, blood pressure and skin temperature. They could be adopted by industries such as automotive, retail, manufacturing, military, the internet of soft things, consumer products, sports, fashion and entertainment. The development of the core technology required raw materials analysis in terms of physical, mechanical and electrical properties; creation of interconnections of electronic semi-conductor chips with copper filaments; encapsulation of the interconnections to improve washability and provide extra mechanical strength to the core filaments prior to making the final yarn. The final step was the process of manufacturing yarns using the knit braiding technique. A number of prototypes of e-textiles were produced including illuminated yarns, thermistor yarns, RFID yarns, magnetic yarns, vibration sensor yarns, illuminated garment, illuminated car seat, RFID-intergraded garments, a temperature-monitoring fabric mat and temperature-monitoring socks in order to investigate the manufacturing viability, identify practical issues, and to promote the technology to attract further funds and potential commercial partners

Cumulative index to NASA Tech Briefs, 1963-1967

Cumulative index to NASA survey on technology utilization of aerospace research outpu

Cumulative Index to NASA Tech Briefs, 1963 - 1966

Cumulative index of NASA Tech Briefs dealing with electrical and electronic, physical science and energy sources, materials and chemistry, life science, and mechanical innovation

Development of carbon fibre reinforced carbon-silicon carbide composites for advanced friction brake applications

In the present study, different origins of recycled carbon fibre and carbon are evaluated against virgin-based alternatives as cost-effective constituents inside carbon fibre/carbon-silicon carbide (Cf/C-SiC) composites. These include: recycled, end-of-life or reclaimed carbon fibre and pyrolytic carbon (pyC), which are investigated inside these composites for potential friction materials to replace or extend the life of current high-end automotive, industrial and aircraft brake discs. The literature review begins by investigating the differences and implications of the applications on the requirements of the carbon fibre inside the composite and documents past and current progress made. The constituents that comprise these composites were investigated and the manufacture routes were reported in terms of their advantages and disadvantages. A three-step process was identified as the most costeffective and promising route to manufacture these new Cf/C-SiC composites with suitably high mechanical properties: 1). Polymer infiltration (PI) and hot pressing (HP) to create a carbon fibre reinforced plastic (CFRP), 2). Pyrolysis to convert the CFRP into a porous Cf/C composite, 3). Liquid silicon infiltration (LSI) to introduce the silicon carbide (SiC) matrix. Beyond this, the aims, feasibility and current progress of recycling carbon fibres were documented. It was found that current recycling technologies are in their infancy, in both academia and industry, although great commercial potential is recognised. Investigations herein revealed the capability to mechanically recycle carbon fibres from waste carbon fibre pre-pregs and CFRP spars, re-use end-of-life carbon fibre pre-pregs and reclaim carbon fibre from existing CFRP spars using pyrolysis. Testing and analysis were split into two stages: firstly, how the pre-preg architecture changes during pyrolysis and secondly, the resulting Cf/C-SiC composites: microstructural evolution after LSI; physical, mechanical and micro-mechanical properties; frictional performance. Pyrolysis of end-of-life pre-pregs revealed no significant difference in comparison to virgin carbon fibre pre-pregs. Instead, any differences were attributed to the: fibre orientation, preform architecture and resin carbon yield. Testing revealed that end-of-life pre-pregs and reclaimed CFRP’s were suitable for pyrolysis and further processing toward Cf/C-SiC composites. In addition, the architecture could be either customised or inherited from the original. Physical and mechanical property testing revealed that Cf/C-SiC composites incorporating recycled, end-of-life and re-claimed carbon fibre could achieve comparable densities, open porosities and flexural strengths compared to similarly processed virgin Cf/C-SiC composites. Microstructural examination by optical and electron microscopy revealed that the hierarchy order of the developed microstructure inside these composites by LSI was the same irrespective of the carbon fibre or carbon format. Combined TEM and XRD investigations indicated that the generated SiC and silicon belonged to the same polytypes regardless of the carbon format and that the most likely type was facecentered cubic (FCC) β 3C-SiC and cubic silicon respectively. Small-scale dyno in a disc-on-pad configuration revealed that a Cf/C-SiC composite comprising end-of-life fibre could achieve the required mechanical strength to perform dyno testing and that the surface topography had a significant influence on the coefficient of friction (COF), COF stability and wear rate

NASA Thesaurus. Volume 1: Hierarchical listing

There are 16,713 postable terms and 3,716 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary