1,721,081 research outputs found
Self‐Healing of Internal Damage in Synthetic Vascular Materials
No full textVascular networks of microchannels (ca. 200 μm) are employed to deliver healing agents to regions of damage within an epoxy matrix material. Mechanical recovery from multiple cycles of damage is observed owing to the continuous supply of healing agents, and despite the intersection of crack damage with individual microchannels and subsequent disruption of the vascular network.</p
Structural reinforcement of microvascular networks using electrostatic layer-by-layer assembly with halloysite nanotubes
Full text linkWe demonstrate a method for tailoring local mechanical properties near channel surfaces of vascular structural polymers in order to achieve high structural performance in microvascular systems. While synthetic vascularized materials have been created by a variety of manufacturing techniques, unreinforced microchannels act as stress concentrators and lead to the initiation of premature failure. Taking inspiration from biological tissues such as dentin and bone, these mechanical deficiencies can be mitigated by complex hierarchical structural features near to channel surfaces. By employing electrostatic layer-by-layer assembly (ELbL) to deposit films containing halloysite nanotubes onto scaffold surfaces followed by matrix infiltration and scaffold removal, we are able to controllably deposit nanoscale reinforcement onto 200 micron diameter channel surface interiors in microvascular networks. High resolution strain measurements on reinforced networks under load verify that the halloysite reduces strain concentrations and improves mechanical performance
Interfacial adhesion of thin film high energy density anode materials
Full text linkFuture energy storage needs are rapidly moving beyond the capabilities of current Li-ion battery technologies. The demand for greater energy density, performance, and longevity has led to the development of numerous three-dimensional (3D) structured anodes that can leverage the incredible Li storage capacity of silicon. A common feature among many 3D structured anodes is the use of a nickel (Ni) current collector scaffold coated with amorphous silicon (a-Si) active material. Despite the importance of a-Si remaining adhered to the Ni scaffold during cycling, little work has been done to study the interface strength of Ni/a-Si systems. Here, we investigate Ni/a-Si interfacial adhesion strength through the technique of laser spallation (LS) combined with finite element analysis (FEA). It was found that the Ni/a-Si interface can withstand at least ~250 MPa in tension before failure is initiated. Tests at higher stress levels were inconclusive due to consistent failure of the sample at the substrate/a-Si interface rather than the Ni/a-Si interface. Results also showed that the adhesion strength of Ni/a-Si was much weaker when a-Si was deposited by chemical vapor deposition (CVD) rather than electron-beam (e-beam) evaporation. This study brings insight to the durability Ni/a-Si structured anodes and will prove valuable in the design of future battery technologies.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2022-12-01The student, Jacob Diamond, accepted the attached license on 2020-10-16 at 11:05.The student, Jacob Diamond, submitted this Thesis for approval on 2020-10-16 at 11:15.This Thesis was approved for publication on 2020-10-21 at 08:48.DSpace SAF Submission Ingestion Package generated from Vireo submission #15837 on 2021-03-04 at 16:19:21Made available in DSpace on 2021-03-05T21:40:40Z (GMT). No. of bitstreams: 2
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Previous issue date: 2020-10-21Embargo set by: Seth Robbins for item 117187
Lift date: 2023-03-05T21:40:52Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 117187
Lift date: 2023-03-05T21:43:00Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Onl
Healing of complex damage modes in model composites
Full text linkSelf-healing has potential to extend the usable lifetime of composite materials. Introducing self-healing systems to fiber reinforced composites has proven to be difficult due to the high temperatures and pressures of processing as well as the requirement that the delivery scheme for the healing agent must exist in the interstitial regions between fibers. Additionally, assessment of self-healing performance for composites poses a challenge as many damage modes occur during composite failure including matrix cracking and fiber-matrix debonding.
In this thesis, a tow-level model composite test is developed with a view towards simplifying characterization and improving understanding of capsule-based self-healing in fiber reinforced composites. The tow-level test is intended to allow for testing of potential healing without requiring manufacture of a complex composite panel. A modified compact tension is developed with a carbon fiber tow running orthogonally to the advancing crack plane. Initial testing of a non-healing control system reveals that the tow can survive crack propagation and that debonding of the matrix and tow occurs. Additionally, the size of the debonding damage correlates to the magnitude of energy released.
Healing studies utilized a phase-separated thermoplastic-epoxy matrix with solvent filled microcapsules. Initial reference tests with the matrix but no microcapsules showed high healing efficiency of over 100% when the solvent was injected manually. However, no mechanical healing response could be observed when microcapsules were incorporated to deliver healing agent to the crack. Attempts were made at altering the healing agent delivery scheme as well as the healing conditions to increase healing response, but no combination of conditions was shown to be suitable for self-healing to occur.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2018-03-13 without embargo termsThe student, Andrew Lauer, accepted the attached license on 2017-12-15 at 10:16.The student, Andrew Lauer, submitted this Thesis for approval on 2017-12-15 at 10:25.This Thesis was approved for publication on 2017-12-15 at 13:11.DSpace SAF Submission Ingestion Package generated from Vireo submission #11994 on 2018-03-13 at 10:12:55Made available in DSpace on 2018-03-13T15:49:22Z (GMT). No. of bitstreams: 2
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Previous issue date: 2017-12-1
Micromechanics of piezocomposites
No full textOver the past two decades, materials engineers have developed piezoelectric-polymer composite materials that enable effective electromechanical properties to be tailored for a specific application. These materials are made by combining conventional piezoelectric ceramics with piezoelectrically passive polymers in a variety of geometrical configurations. As with any composite material, the properties and behavior of piezocomposites are highly dependent on the properties of the constituent materials and the local arrangement of the different phases. In particular, the ceramic-polymer interface plays an important role in determining the electromechanical coupling in the piezocomposite. In this dissertation, the electromechanical behavior of 1-3 piezocomposites is investigated from both theoretical and experimental standpoints.Theoretical investigations centered on the development of a micromechanics model for predicting the local fields and effective behavior in piezocomposites with 1-3 connectivity. Since the presence of a thin interlayer or polymer coating around the ceramic rods can influence the local interaction between the piezoceramic and polymer matrix and change the overall performance of the composite, a finite composite cylinder model was developed to incorporate an interlayer with varying properties. Experimental studies focused on probing the surface displacements of 1-3 piezocomposites using a scanning heterodyne laser interferometer. Static surface displacements of 1-3 PZT rod-epoxy samples with different interphase regions were measured and correlated with the effective low-frequency performance of the composite. Several types of interphase region were considered. Coatings with elastic moduli lower than that of the epoxy matrix were applied to the rods. The influence of a silane coupling agent was also investigated. Experimental displacement profiles were compared with micromechanical predictions using the finite composite cylinder model. The results demonstrate that the presence of an interphase between the piezoceramic and the polymer matrix influences the local deformations and changes the overall performance of the composite. Thus, the interphase plays an important role in determining the electromechanical coupling in the piezocomposite.The study of electromechanical coupling in piezocomposites was further developed by investigating the hydrostatic performance of 1-3 piezocomposites, an important issue in design of piezocomposites for low-frequency applications. Emphasis was placed on determining the stress transferred between the passive matrix and the active piezoceramic rods and using this data to indicate the level of electromechanical coupling. The stress field in the piezoelectric ceramic under hydrostatic loading was predicted using the analytical micromechanical model developed and a finite-element model as well. Optimal electromechanical coupling was achieved when a certain favorable stress field was induced in the piezoceramic. The influence of such design parameters as the matrix stiffness, the interphase stiffness, the interphase thickness, the Poisson's ratio of the polymers, and piezoceramic rod aspect ratio on the hydrostatic performance of 1-3 piezocomposites was also investigated. Although the current work is focused on the electromechanical behavior of 1-3 piezocomposites at low frequency, the research results and conceptual understanding obtained have importance for optimizing the design of piezocomposites in other applications as well.Made available in DSpace on 2011-05-07T14:05:29Z (GMT). No. of bitstreams: 2
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Previous issue date: 1995Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T15:02:49Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:29:54-05:00
Original Data
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Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
Autonomous indication of damage in epoxy coatings
Full text linkDSpace SAF Submission Ingestion Package generated from Vireo submission #8579 on 2015-09-29 at 15:06:42Industrial coatings are applied for their aesthetic appeal and ability to protect the underlying substrate material from the environment. The indication of coating flaws for correction becomes more important for coatings operating in extreme environments. Visual indication coating damage can aid in quickly locating and repairing damage before the underlying substrate degrades or fails. In this work, fluorescent damage indication was achieved with a dual capsule system embedded in an epoxy coating. Fluorescamine, a turn-on fluorescent indicator chosen for selectivity towards primary amines, and an amine based epoxy curing agent were separately encapsulated and incorporated into an epoxy coating. When mechanical damage ruptures both capsules, fluorescamine instantly reacts with primary amines to develop a bright blue fluorescence. This dual capsule system holds the promise of creating a smart coating with damage sensing and autonomous self-healing.
Clear epoxy coatings with various concentrations of indicator and amine capsules were deposited onto glass slides and scratched with a razor blade. A coating containing an even distribution of 5 wt% indicator capsules and 5 wt% amine capsules achieved the most consistent indication performance. Using the same capsule concentration, an epoxy coating with carbon black as a pigment was used to dye the epoxy matrix. Damage indication in the pigmented coating performed similarly to the clear epoxy coating. Another coating consisted of two distinct layers, where clear epoxy with embedded microcapsules was covered with an acrylic spray paint. When scratched, fluorescent indication response was considerably muted when compared to a clear epoxy coating.
Indication of low velocity impact damage to glass fiber composite coupons was also achieved with this system. Fluorescence was present where the impact tup contacted the smart coating on the specimen top surface. The back surface suffered micro-cracks and delamination but did not fluoresce due to poor mixing of indicator and amine in the damage region.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2017-08-01The student, Christopher Matthews, accepted the attached license on 2015-07-20 at 22:00.The student, Christopher Matthews, submitted this Thesis for approval on 2015-07-20 at 22:08.This Thesis was approved for publication on 2015-07-21 at 13:17.Made available in DSpace on 2015-09-29T21:08:21Z (GMT). No. of bitstreams: 2
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Previous issue date: 2015-07-21Embargo set by: Seth Robbins for item 89588
Lift date: 2017-09-29T21:08:35Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 89588 on 2017-09-30T09:15:38Z
Embedded microvascular networks for electronically reconfigurable materials
Full text linkMicrovascular networks in biological systems carry out various functions, such as damage repair, temperature regulation, and nutrient transport. Biological vasculature has inspired the use of microfluidic networks in various synthetic materials to achieve similar functionality such as vascular-based healing and cooling in structural composites.
A recent use of microvascular structures in synthetic materials is for the selective alteration of electromagnetic properties of materials using conductive fluids. Specifically a Gallium-Indium alloy which is liquid at room temperature is used to reconfigure radio frequency wireless signal devices. Previous work has focused on the use of microelectromechanical systems, solid state diodes, or physical actuation to reconfigure such devices, but various problems limit the applicability of these solutions to high power applications.
This thesis first describes a new set of fabrication techniques used to overcome various issues with previous applications of conductive fluids in microvascular networks for electromagnetic configurability. Vascular networks are formed in a structural epoxy which is bonded to the active device. The channels selectively contact electronic components, forming conductive pathways between components when filled with liquid metal.
The fabrication techniques described are then used to fabricate two novel reconfigurable radio frequency wireless devices, a coplanar waveguide and a cross-polarization patch antenna. The coplanar waveguide achieves phase reconfiguration with a single serpentine channel design, while the cross-polarization antenna achieves polarization reconfiguration using dual 3D network architectures.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2017-08-01The student, Anthony Griffin, accepted the attached license on 2015-07-22 at 11:31.The student, Anthony Griffin, submitted this Thesis for approval on 2015-07-22 at 11:39.This Thesis was approved for publication on 2015-07-22 at 12:53.DSpace SAF Submission Ingestion Package generated from Vireo submission #8608 on 2015-09-29 at 15:06:49Made available in DSpace on 2015-09-29T21:08:24Z (GMT). No. of bitstreams: 3
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Previous issue date: 2015-07-22Embargo set by: Seth Robbins for item 89594
Lift date: 2017-09-29T21:08:35Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 89594 on 2017-09-30T09:15:24Z
Local Displacements and Load Transfer of Shape Memory Alloys in Polymeric Matrices
No full textAverage interfacial bond strength between an embedded SMA and an epoxy matrix were measured using pullout tests. The effects of various mechanical and chemical surface treatments on the bond strengths were examined. In-situ out-of-plane displacements of two-way trained SMA wires in epoxy were measured using heterodyne microinterferometry. The interfacial bond strengths from the pullout tests were correlated with the maximum wire displacements. The transient load transfer behavior of a one-way SMA ribbon in a room temperature cured polymer matrix was quantified using two-dimensional photoelasticity. The effects of residual stress were examined using high temperature cured matrices. In-plane displacements of room temperature cured SMA ribbon composites were obtained using moire interferometry. Displacements due to thermal expansion were separated from displacements due to SMA actuation. An experimental value for the velocity of propagation of the SMA actuation front was calculated. A finite element model based on one-dimensional constitutive equations was developed for ribbon composites. Displacements and stresses in the ribbon were compared with experimental values.Made available in DSpace on 2015-09-28T16:23:55Z (GMT). No. of bitstreams: 2
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Previous issue date: 1997Embargo set by: Seth Robbins for item 89048
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only162 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997
Stress and Orientation Effects in Ferroelectric Thin Films
No full textU of I Only139 p.The effects of stress on the response of ferroelectric thin films are measured directly by a beam bending experiment in a unique double-beam laser interferometer. Application of a compressive bending stress to relieve the tensile residual stress in PZT (52/48) film increases the field-induced strains. The opposite effect is observed for application of a tensile stress. To gain further insight into these observations, a previously developed micro-electro-mechanical model is applied to numerically simulate the response of ferroelectrics under a general state of stress and electric field. Material parameters obtained by fitting simulation results with available experimental data are used to predict effects of the preferred crystallographic orientation and biaxial tensile stress applied transverse to the poling direction. The simulation results are consistent with experimental observations of the preferred orientation and stress effects in PZT (52/48) thin films.Made available in DSpace on 2015-09-28T16:23:30Z (GMT). No. of bitstreams: 2
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Previous issue date: 2001Embargo set by: Seth Robbins for item 88977
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsThesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2001
Microvascular Networks for Continuous Self -Healing Materials
No full textMicrocapsule-based and hollow glass fiber-based self-healing composites enable a single repair of crack damage in a given location. Re-mendable polymers have demonstrated crack mending for multiple cycles, but only with heat treatment and applied pressure. We demonstrate, for the first time, the autonomic characteristics of microencapsulated systems with the ability to heal repeated damage events in a continuous self-healing coating on a microvascular substrate. A three-dimensional, interconnected microvascular network in the substrate serves as a delivery system for healing materials to heal damage in a polymer coating. Two approaches to microvascular delivery are explored: one using a fluid monomer in the network with solidphase catalyst particles in the coating, and one using two or more separate networks with two fluid healing components. In both systems, the fluid(s) flow from the microchannels into the crack plane through capillary action, and polymerization occurs to heal the crack. In the single-fluid system, a single crack in a brittle epoxy coating is healed as many as seven times, and the ability to heal continuously is limited only by the availability of catalyst. The two-part healing system contained in separate networks in a specimen has significant potential to extend the repeatability of the healing process due to the microvascular supply of both healing components. Preliminary tests of this two-part system demonstrate that multiple healing cycles are possible.Made available in DSpace on 2015-09-28T16:23:46Z (GMT). No. of bitstreams: 2
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Previous issue date: 2007Embargo set by: Seth Robbins for item 89023
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only122 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007
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