3D Modeling and Design Optimization of Rod Shaped Ionic Polymer Metal Composite Actuator

Ionic polymer-metal composites (IPMCs) are some of the most well-known electro-active polymers. This is due to their large deformation provided a relatively low voltage source. IPMCs have been acknowledged as a potential candidate for biomedical applications such as cardiac catheters and surgical probes; however, there is still no existing mass manufacturing of IPMCs. This study intends to provide a theoretical framework which could be used to design practical purpose IPMCs depending on the end users interest. This study begins by investigating methodologies used to develop quantify the physical actuation of an IPMC in 3-dimensional space. This approach is taken in two separate means; however, both approaches utilize the finite element method. The first approach utilizes the finite element method in order to describe the dynamic response of a segmented IPMC actuator. The first approach manually constructs each element with a local coordinate system. Each system undergoes a rigid body motion along the element and deformation of the element is expressed in the local coordinate frame. The physical phenomenon in this system is simplified by utilizing a lumped RC model in order to simplify the electro-mechanical phenomena in the IPMC dynamics. The second study investigates 3D modeling of a rod shaped IPMC actuator by explicitly coupling electrostatics, transport phenomenon, and solid mechanics. This portion of the research will briefly discuss the mathematical background that more accurately quantifies the physical phenomena. Solving for the 3-dimensional actuation is explicitly carried out again by utilizing the finite element method. The numerical result is conducted in a software package known as COMSOL MULTIPHYSICS. This simulation allows for explicit geometric rendering as well as more explicit quantification of the physical quantities such as concentration, electric field, and deflection The final study will conduct design optimization on the COMSOL simulation in order to provide conceptual motivation for future designs. Utilizing a multi-physics analysis approach on a three dimensional cylinder and tube type IPMC provides physically accurate results for time dependent end effector displacement given a voltage source. Simulations are conducted with the finite element method and are also validated with empirical evidences. Having an in-depth understanding of the physical coupling provides optimal design parameters that cannot be altered from a standard electro-mechanical coupling. These parameters are altered in order to determine optimal designs for end-effector displacement, maximum force, and improved mobility with limited voltage magnitude. Design alterations are conducted on the electrode patterns in order to provide greater mobility, electrode size for efficient bending, and Nafion diameter for improved force. The results of this study will provide optimal design parameters of the IPMC for different applications

A high-throughput analysis of high-resolution X-ray CT images of stems of olive and citrus plants resistant and susceptible to Xylella fastidiosa

The bacterial plant pathogen Xylella fastidiosa causes disease in several globally important crops. However, some cultivars harbour reduced bacterial loads and express few symptoms. Evidence considering plant species in isolation suggests xylem structure influences cultivar susceptibility to X. fastidiosa. We test this theory more broadly by analysing high-resolution synchrotron X-ray computed tomography of healthy and infected plant vasculature from two taxonomic groups containing susceptible and resistant varieties: two citrus cultivars (sweet orange cv. Pera, tangor cv. Murcott) and two olive cultivars (Koroneiki, Leccino). Results found the susceptible plants had more vessels than resistant ones, which could promote within-host pathogen spread. However, features associated with resistance were not shared by citrus and olive. While xylem vessels in resistant citrus stems had comparable diameters to those in susceptible plants, resistant olives had narrower vessels that could limit biofilm spread. And while differences among olive cultivars were not detected, results suggest greater vascular connectivity in resistant compared to susceptible citrus plants. We hypothesize that this provides alternate flow paths for sustaining hydraulic functionality under infection. In summary, this work elucidates different physiological resistance mechanisms between two taxonomic groups, while supporting the existence of an intertaxonomical metric that could speed up the identification of candidate-resistant plants.</p

The impact of xylem geometry on olive cultivar resistance to Xylella fastidiosa: an image‐based study

Xylella fastidiosa is a xylem-limited plant pathogen infecting many crops globally and is the cause of the recent olive disease epidemic in Italy. One strategy proposed to mitigate losses is to replant susceptible crops with resistant varieties. Several genetic, biochemical and biophysical traits are associated to X. fastidiosa disease resistance. However, mechanisms underpinning resistance are poorly understood. We hypothesize that the susceptibility of olive cultivars to infection will correlate to xylem vessel diameters, with narrower vessels being resistant to air embolisms and having slower flow rates limiting pathogen spread. To test this, we scanned stems from four olive cultivars of varying susceptibility to X. fastidiosa using X-ray computed tomography. Scans were processed by a bespoke methodology that segmented vessels, facilitating diameter measurements. Though significant differences were not found comparing stem-average vessel section diameters among cultivars, they were found when comparing diameter distributions. Moreover, the measurements indicated that although vessel diameter distributions may play a role regarding the resistance of Leccino, it is unlikely they do for FS17. Considering Young–Laplace and Hagen–Poiseuille equations, we inferred differences in embolism susceptibility and hydraulic conductivity of the vasculature. Our results suggest susceptible cultivars, having a greater proportion of larger vessels, are more vulnerable to air embolisms. In addition, results suggest that under certain pressure conditions, functional vasculature in susceptible cultivars could be subject to greater stresses than in resistant cultivars. These results support investigation into xylem morphological screening to help inform olive replanting. Furthermore, our framework could test the relevance of xylem geometry to disease resistance in other crops

Biomechanical limits to soil penetration by earthworms: direct measurements of hydroskeletal pressures and peristaltic motions

Burrows resulting from earthworm activity are important for supporting various physical and ecological soil processes. Earthworm burrowing activity is quantified using models for earthworm penetration and cavity expansion that consider soil moisture and mechanical properties. Key parameters in these models are the maximal pressures exerted by the earthworm's hydroskeleton (estimated at 200 kPa). We designed a special pressure chamber that directly measures the pressures exerted by moving earthworms under different confining pressures to delineate the limits of earthworm activity in soils at different mechanical and hydration states. The chamber consists of a Plexiglas prism fitted with inner flexible tubing that hosts the earthworm. The gap around the tubing is pressurized using water, and the earthworm's peristaltic motion and concurrent pressure fluctuations were recorded by a camera and pressure transducer. A model that links the earthworm's kinematics with measured pressure fluctuations was developed. Resulting maximal values of radial pressures for anecic and endogeic earthworms were 130 kPa and 195 kPa, respectively. Mean earthworm peristaltic frequencies were used to quantify burrowing rates that were in agreement with previous results. The study delineates mechanical constraints to soil bioturbation by earthworms by mapping the elastic behaviour in the measurement chamber onto the expected elasto-viscoplastic environment of natural soils.</p

Supplementary material 3: Pressure measurements placed in the context of natural soil conditions from Biomechanical limits to soil penetration by earthworms: direct measurements of hydroskeleton pressures and peristaltic motions

Burrows resulting from earthworm activity are important for supporting various physical and ecological soil processes. Earthworm burrowing activity is quantified using models for earthworm penetration and cavity expansion that consider soil moisture and mechanical properties. Key parameters in these models are the maximal pressures exerted by earthworm's hydroskeleton (estimated at 200 kPa). We designed a special pressure chamber that directly measures the pressures exerted by moving earthworms under different confining pressures to delineate the limits of earthworm activity in soils at different mechanical and hydration states. The chamber consists of a Plexiglas prism fitted with inner flexible tubing that hosts the earthworm. The gap around the tubing is pressurized using water, and the earthworm peristaltic motion and concurrent pressure fluctuations were recorded by camera and a pressure transducer. A model that links the earthworm's kinematics with measured pressure fluctuations was developed. Resulting maximal values of radial pressures for anecic and endogeic earthworms were 130 kPa and 195 kPa, respectively. Mean earthworm peristaltic frequencies were used to quantify burrowing rates that were in agreement with previous results. The study delineates mechanical constraints to soil bioturbation by earthworms by mapping the elastic behaviour in the measurement chamber onto the expected elasto-viscoplastic environment of natural soils

Supplementary material 4: Modeling peristaltic kinematics under extreme compression from Biomechanical limits to soil penetration by earthworms: direct measurements of hydroskeleton pressures and peristaltic motions

Burrows resulting from earthworm activity are important for supporting various physical and ecological soil processes. Earthworm burrowing activity is quantified using models for earthworm penetration and cavity expansion that consider soil moisture and mechanical properties. Key parameters in these models are the maximal pressures exerted by earthworm's hydroskeleton (estimated at 200 kPa). We designed a special pressure chamber that directly measures the pressures exerted by moving earthworms under different confining pressures to delineate the limits of earthworm activity in soils at different mechanical and hydration states. The chamber consists of a Plexiglas prism fitted with inner flexible tubing that hosts the earthworm. The gap around the tubing is pressurized using water, and the earthworm peristaltic motion and concurrent pressure fluctuations were recorded by camera and a pressure transducer. A model that links the earthworm's kinematics with measured pressure fluctuations was developed. Resulting maximal values of radial pressures for anecic and endogeic earthworms were 130 kPa and 195 kPa, respectively. Mean earthworm peristaltic frequencies were used to quantify burrowing rates that were in agreement with previous results. The study delineates mechanical constraints to soil bioturbation by earthworms by mapping the elastic behaviour in the measurement chamber onto the expected elasto-viscoplastic environment of natural soils

Supplementary material 2: Quantifying system compressibility from Biomechanical limits to soil penetration by earthworms: direct measurements of hydroskeleton pressures and peristaltic motions

Burrows resulting from earthworm activity are important for supporting various physical and ecological soil processes. Earthworm burrowing activity is quantified using models for earthworm penetration and cavity expansion that consider soil moisture and mechanical properties. Key parameters in these models are the maximal pressures exerted by earthworm's hydroskeleton (estimated at 200 kPa). We designed a special pressure chamber that directly measures the pressures exerted by moving earthworms under different confining pressures to delineate the limits of earthworm activity in soils at different mechanical and hydration states. The chamber consists of a Plexiglas prism fitted with inner flexible tubing that hosts the earthworm. The gap around the tubing is pressurized using water, and the earthworm peristaltic motion and concurrent pressure fluctuations were recorded by camera and a pressure transducer. A model that links the earthworm's kinematics with measured pressure fluctuations was developed. Resulting maximal values of radial pressures for anecic and endogeic earthworms were 130 kPa and 195 kPa, respectively. Mean earthworm peristaltic frequencies were used to quantify burrowing rates that were in agreement with previous results. The study delineates mechanical constraints to soil bioturbation by earthworms by mapping the elastic behaviour in the measurement chamber onto the expected elasto-viscoplastic environment of natural soils

Quantifying coupled deformation and water flow in the rhizosphere using X-ray microtomography and numerical simulations

Background and aimsThe rhizosphere, the soil immediately surrounding roots, provides a critical bridge for water and nutrient uptake. The rhizosphere is influenced by various forms of root–soil interactions of which mechanical deformation due to root growth and its effects on the hydraulics of the rhizosphere are the least studied. In this work, we focus on developing new experimental and numerical tools to assess these changes.MethodsThis study combines X-ray micro-tomography (XMT) with coupled numerical simulation of fluid and soil deformation in the rhizosphere. The study provides a new set of tools to mechanistically investigate root-induced rhizosphere compaction and its effect on root water uptake. The numerical simulator was tested on highly deformable soil to document its ability to handle a large degree of strain.ResultsOur experimental results indicate that measured rhizosphere compaction by roots via localized soil compaction increased the simulated water flow to the roots by 27 % as compared to an uncompacted fine-textured soil of low bulk density characteristic of seed beds or forest topsoils. This increased water flow primarily occurred due to local deformation of the soil aggregates as seen in the XMT images, which increased hydraulic conductivity of the soil. Further simulated root growth and deformation beyond that observed in the XMT images led to water uptake enhancement of ~50 % beyond that due to root diameter increase alone and demonstrated the positive benefits of root compaction in low density soils.ConclusionsThe development of numerical models to quantify the coupling of root driven compaction and fluid flow provides new tools to improve the understanding of plant water uptake, nutrient availability and agricultural efficiency. This study demonstrated that plants, particularly during early growth in highly deformable low density soils, are involved in active mechanical management of their surroundings. These modeling approaches may now be used to quantify compaction and root growth impacts in a wide range of soils