Characterizing the Influence of the Textile-Sensor Interface on Stitched Sensor Performance

University of Minnesota M.S.E.E. thesis. July 2019. Major: Electrical/Computer Engineering. Advisors: Lucy Dunne, Sarah Swisher. 1 computer file (PDF); vii, 155 pages.Textile-based strain sensors are first defined with examples of various sensing mechanisms and applications, focusing on on-body smart garments for biomonitoring. A current lack of research in the textile substrate influence on sensor performance is noted, with a thesis investigation outlined to highlight key variables that may be important for successful sensor design. Two conductive thread stitch-based strain sensors are chosen for the textile-based strain sensors and two fabric substrates (2-way and 4-way stretch) are used to investigate their influence on sensor performance. Part 1 investigates if fabric strain properties change due to the attachment of sensors and how the sensor performance changes due to fabric choice and attachment angle. Part 2 uses the recommendations for textile choice, stitch geometry of the sensor, and sensor placement based on Part 1 results to create a 3-sensor, 60° strain rosette. Between the two versions of rosettes fabricated, the 4-way fabric and chainstitch geometry, the strain rosette is proven to improve the overall sensor performance in predicting force, displacement, and force direction. This rosette is characterized and using machine learning model algorithms, model-fitted for future garment based strain sensing applications

An infiltration/cure model for manufacture of fabric composites by the resin infusion process

A 1-D infiltration/cure model was developed to simulate fabrication of advanced textile composites by the resin film infusion process. The simulation model relates the applied temperature and pressure processing cycles, along with the experimentally measured compaction and permeability characteristics of the fabric preforms, to the temperature distribution, the resin degree of cure and viscosity, and the infiltration flow front position as a function of time. The model also predicts the final panel thickness, fiber volume fraction, and resin mass for full saturation as a function of compaction pressure. Composite panels were fabricated using the RTM (Resin Transfer Molding) film infusion technique from knitted, knitted/stitched, and 2-D woven carbon preforms and Hercules 3501-6 resin. Fabric composites were fabricated at different compaction pressures and temperature cycles to determine the effects of the processing on the properties. The composites were C-scanned and micrographed to determine the quality of each panel. Advanced cure cycles, developed from the RTM simulation model, were used to reduce the total cure cycle times by a factor of 3 and the total infiltration times by a factor of 2

An Overview of the Measurement of Permeability of Composite Reinforcements

Liquid composite molding (LCM) is a class of fast and cheap processes suitable for the fabrication of large parts with good geometrical and mechanical properties. One of the main steps in an LCM process is represented by the filling stage, during which a reinforcing fiber preform is impregnated with a low-viscosity resin. Darcy’s permeability is the key property for the filling stage, not usually available and depending on several factors. Permeability is also essential in computational modeling to reduce costly trial-and-error procedures during composite manufacturing. This review aims to present the most used and recent methods for permeability measurement. Several solutions, introduced to monitor resin flow within the preform and to calculate the in-plane and out-of-plane permeability, will be presented. Finally, the new trends toward reliable methods based mainly on non-invasive and possibly integrated sensors will be described

NASA Composite Materials Development: Lessons Learned and Future Challenges

Composite materials have emerged as the materials of choice for increasing the performance and reducing the weight and cost of military, general aviation, and transport aircraft and space launch vehicles. Major advancements have been made in the ability to design, fabricate, and analyze large complex aerospace structures. The recent efforts by Boeing and Airbus to incorporate composite into primary load carrying structures of large commercial transports and to certify the airworthiness of these structures is evidence of the significant advancements made in understanding and use of these materials in real world aircraft. NASA has been engaged in research on composites since the late 1960 s and has worked to address many development issues with these materials in an effort to ensure safety, improve performance, and improve affordability of air travel for the public good. This research has ranged from synthesis of advanced resin chemistries to development of mathematical analyses tools to reliably predict the response of built-up structures under combined load conditions. The lessons learned from this research are highlighted with specific examples to illustrate the problems encountered and solutions to these problems. Examples include specific technologies related to environmental effects, processing science, fabrication technologies, nondestructive inspection, damage tolerance, micromechanics, structural mechanics, and residual life prediction. The current state of the technology is reviewed and key issues requiring additional research identified. Also, grand challenges to be solved for expanded use of composites in aero structures are identified

An investigation of textile sensors and their application in wearable electronics

Using a garment as a wearable sensing device has become a reality. New methods and techniques in the field of wearable sensors are being developed and can now be incorporated into the wearer’s everyday attire. This research focuses on two types of textile based sensors – a wearable textile electrode used for ECG continuous monitoring, and a stitch sensor for monitoring body movement. These sensors were designed into a purposely engineered Smart Sports Bra (SSB) which can be regarded as a sensor itself. After a thorough investigation, two optimum textile electrodes were created; a plain electrode using cut and sew method (CSM) and a net type knitted electrode using knitting method (KM). The CSM electrode was made with conductive fabric (MedTexTM P-130) and the KM electrode was made with conductive thread (silver-plated nylon 234/34 four-ply), these materials having the lowest tested contact impedance; 450Ω and 500Ω, respectively. Both electrodes demonstrated a level of noise and baseline drift comparable with standard commercial wet-gel electrodes, which was corrected by optimising their size to 20x40 mm, holding pressure of 4 kPa (30 mmHg) and the electrode position at the 6th intercostal space on the right and left mid-clavicular, with one placed at the scapular line in the rear side (i.e. back horizontal formation) which gives clear and reliable ECG signal. These optimum electrodes were integrated directly into SSBs, in which a novel high shear, net structure, acting as a shock absorber to body movement that shows more stable electrode to skin contact by reducing the body motion artefact. During the investigation of the stitch stretch sensor the single jersey nylon fabric (4.44 tex two-ply) with 25% spandex (7.78 tex) had the highest elastic recovery (93%). Using this fabric, the work went on to show that the stitch type 304 (Zig-zag lock stitch) using the 117/17 two-ply thread demonstrated the best results i.e., maximum working range 50%, gauge factor 1.61, hysteresis 6.25% ΔR, linearity (R2 ) is 0.98, and good repeatability (drift in R2 is -0.00). The stitch stretch sensor was also incorporated into a sports bra SSB and positioned across the chest for respiration monitoring. This thesis contributes to a growing body of research in wearable E -textile solutions to support health and well-being, with fully functional sensors and easy-to-use design, for continues health monitoring

The development of a stitch-based strain sensor for woven lashing straps

In this paper the development of a stitch-based strain sensor for lashing straps is discussed. A variety of Three different commercial woven narrow fabric straps were embroidered with conductive yarns in two designed patterns to enable belt tension measurement and monitoring. The applications were tested in a cyclic elongation test and a creep elongation procedure to investigate the strain sensitivity and the influences of the narrow fabric’s properties, the stitch design, and the conductive yarn properties. It was found that the developed applications provided a good strain sensing ability but lack in cyclic recovery abilities

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 Stitched, Braided and Woven Composite Structures in the ACT Program and at Langley Research Center (1985 to 1997) Summary and Bibliography

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 NASA Langley Research in Textile Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Advanced Material Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Woven Preforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Multiaxial Knitted Preforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Braided Preforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...