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- Title
- Buckling of composite cylindrical shells with geometric, thickness and material imperfections.
- Creator
- Li, Yiwei., Florida Atlantic University, Elishakoff, Isaac, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This dissertation deals with the determination of buckling loads of composite cylindrical shell structures which involve uncertainty either in geometry, namely thickness variation, or in material properties. Systematic research has been carried out, which evolves from the simple isotropic cases to anisotropic cases. Since the initial geometric imperfection has a dominant role in the reduction of those imperfection-sensitive structures such as cylindrical shells, the combined effect of...
Show moreThis dissertation deals with the determination of buckling loads of composite cylindrical shell structures which involve uncertainty either in geometry, namely thickness variation, or in material properties. Systematic research has been carried out, which evolves from the simple isotropic cases to anisotropic cases. Since the initial geometric imperfection has a dominant role in the reduction of those imperfection-sensitive structures such as cylindrical shells, the combined effect of thickness variation and initial imperfection is also investigated in depth. Both analytic and numerical methods are used to derive the solutions to the problems and asymptotic formulas relating the buckling load to the geometric (thickness variation and/or initial imperfection) parameter are established. It is shown that the axisymmetric thickness variation has the most detrimental effect on the buckling load when the modal number of thickness variation is twice as much as that of the classical buckling mode. For the composite shells with uncertainty in material properties, the convex modelling is employed to evaluate the variability of buckling load. Based on the experimental data for the elastic moduli of the composite laminates, the upper and lower bounds of the buckling load are derived, which are numerically substantiated by the results from nonlinear programming. These bounds will be useful in practice and can provide engineers with a better view of the real load-carrying capacity of the composite structure. Finally, the elastic modulus is modeled as a function of coordinates to complete the study on variability of material property so that the result can be obtained to account for the situation where the elastic modulus is different from one place to another in the structure.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/12444
- Subject Headings
- Composite materials, Buckling (Mechanics), Shells (Engineering), Structural dynamics
- Format
- Document (PDF)
- Title
- Carbon fiber/vinylester composites in the marine environment: EIS as a means of determining an effective composite interface.
- Creator
- Vinci, Chris J., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In this research, the degradation of carbon fiber/vinylester composites in marine environments was experimentally investigated. Additionally, two types of carbon fiber surface treatments, namely Polyhedral Oligomeric Silsesquioxane (POSS) and the industrial surface treatment F0E, were evaluated to determine their effectiveness in creating a fiber/matrix (F/M) interface for use in the marine environment. Electrochemical Impedance Spectroscopy (EIS) was explored as a new application of an...
Show moreIn this research, the degradation of carbon fiber/vinylester composites in marine environments was experimentally investigated. Additionally, two types of carbon fiber surface treatments, namely Polyhedral Oligomeric Silsesquioxane (POSS) and the industrial surface treatment F0E, were evaluated to determine their effectiveness in creating a fiber/matrix (F/M) interface for use in the marine environment. Electrochemical Impedance Spectroscopy (EIS) was explored as a new application of an existing technique for use in measuring the amount of water at the F/M interface in carbon fiber/vinylester composites. EIS spectra were used to determine equivalent electric circuit models that allow for the prediction of water at the interface. The location of water within the composite was determined through Positron Annihilation Lifetime Spectroscopy (PALS). Interlaminar shear strength and transverse tensile tests were carried out for dry conditions and after hygrothermal exposure of the composites to study the influence of the integrity of the F/M interface on the macroscopic response of the composite.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/1930500
- Subject Headings
- Composite materials, Mechanical properties, Graphite fibers, Fibrous composites, Structural analysis
- Format
- Document (PDF)
- Title
- Degradation of composite materials in a marine environment.
- Creator
- Pomies, Frederic., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Degradation of composite materials in marine environments has been investigated experimentally and with analytical and numerical methods. Basic mechanical properties, fiber volume fraction, moisture absorption curves and transverse tensile properties after water absorption were determined. Transverse fracture surfaces of dry and wet composites were inspected in a scanning electron microscope (SEM). In addition, the edge replication technique was applied. Micromechanical stress analysis of a...
Show moreDegradation of composite materials in marine environments has been investigated experimentally and with analytical and numerical methods. Basic mechanical properties, fiber volume fraction, moisture absorption curves and transverse tensile properties after water absorption were determined. Transverse fracture surfaces of dry and wet composites were inspected in a scanning electron microscope (SEM). In addition, the edge replication technique was applied. Micromechanical stress analysis of a composite subjected to mechanical, thermal and moisture loading were performed using analytical methods and finite elements. Transverse stiffness and stress levels for interfacial debonding and matrix failure were calculated and correlated with transverse stiffness and strength obtained experimentally.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/14818
- Subject Headings
- Composite materials, Environmental monitoring, Stress corrosion
- Format
- Document (PDF)
- Title
- Degradation of mechanical properties of vinylester and carbon fiber/vinylester composites due to environmental exposure.
- Creator
- Figliolini, Alexander M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
An experimental investigation was undertaken to determine the effects of marine environmental exposure on the mechanical properties of vinylester resins (VE510A and VE8084) and carbon fiber/VE510A vinylester composites. The effect of carbon fiber sizing on the composite strengths was also examined. Neat resins were exposed to marine environments until moisture content reached a point of saturation after which they were tested in tension, compression and shear. Compared to the baseline dry...
Show moreAn experimental investigation was undertaken to determine the effects of marine environmental exposure on the mechanical properties of vinylester resins (VE510A and VE8084) and carbon fiber/VE510A vinylester composites. The effect of carbon fiber sizing on the composite strengths was also examined. Neat resins were exposed to marine environments until moisture content reached a point of saturation after which they were tested in tension, compression and shear. Compared to the baseline dry specimens, specimens subjected to moisture showed overall increased ductility and a reduction in strength. Dry and moisture saturated composite specimens were tested in tension and compression in different orientations. Longitudinal specimens were tested in in-plane shear and interlaminar shear. Composites with F-sized carbon fibers displayed overall higher strength than those with G-sized fibers at both dry and moisture saturated conditions. An analysis of moisture absorption of the composites was performed which vii shows that the moisture up-take is dominated by the fiber/matrix region which absorbs up to 90% of the moisture. The composites experienced reduced strength after moisture absorption. The results revealed that the fiber sizing has stronger effect on the fiber/matrix interface dominated strengths than moisture up-take.
Show less - Date Issued
- 2011
- PURL
- http://purl.flvc.org/FAU/3332182
- Subject Headings
- Composite materials, Mechanical properties, Polymers, Deterioration, FIbrous composites, Graphite fibers
- Format
- Document (PDF)
- Title
- Degradation of the composite fiber/matrix interface in marine environment.
- Creator
- Farooq, Muhammad Umar., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Durability of the composite materials in marine environments has been investigated experimentally and with analytical and numerical methods. The main focus of this study is on the integrity of the fiber/matrix interface under seawater exposure. A single-fiber compression test specimen called the Outwater-Murphy (OM) test has been analyzed using mechanics of materials principles and linear elastic fracture mechanics. Sizing of the OM specimen was conducted so that debonding of the fiber from...
Show moreDurability of the composite materials in marine environments has been investigated experimentally and with analytical and numerical methods. The main focus of this study is on the integrity of the fiber/matrix interface under seawater exposure. A single-fiber compression test specimen called the Outwater-Murphy (OM) test has been analyzed using mechanics of materials principles and linear elastic fracture mechanics. Sizing of the OM specimen was conducted so that debonding of the fiber from the interface should be achieved prior to yielding of the matrix and global instability failure. Stress analysis of the OM specimen has been conducted from theory of elasticity and finite element analysis. A superelement technique was developed for detailed analysis of the stress state at the fiber/matrix interface. The interface stress state at the debond site in the OM specimen, i.e. at the hole edge, was identified as biaxial tension at the fiber/matrix interface. Characterization of cure and post-cure of 8084 and 510A vinlyester resins has been performed using cure shrinkage tests based on dynamic mechanical analysis and coated beam experiments. In addition, moisture absorption, swelling and the influence of moisture on the mechanical properties of the resins were determined. Testing of OM specimens consisting of a single carbon or glass fiber embedded in vinylester resin at dry conditions and after seawater exposure revealed that the debond toughness was substantially reduced after exposure of the OM specimen to seawater. C(F) did not debond. Macroscopic carbon/vinylester woven composites where the fibers were sized with F sizing were tested in shear at dry conditions and after four weeks of seawater exposure. The shear strength was very little affected after the short immersion time.
Show less - Date Issued
- 2009
- PURL
- http://purl.flvc.org/FAU/228774
- Subject Headings
- Fibrous composites, Graphite fibers, Composite materials, Mechanical properties, Polymers, Deterioration
- Format
- Document (PDF)
- Title
- Durability of carbon fiber/vinylester composites subjected to marine environments and electrochemical interactions.
- Creator
- Hasnine, Md., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Degradation of the Carbon Fiber/Vinylester (CF/VE) polymer matrix composites due to different electrochemical interactions when exposed to seawater or at high temperature had been experimentally investigated. Water uptake behavior of composite specimen was examined based on weight gain measurement. Three point bending test was performed to quantify the mechanical degradation of composite immersed in seawater with different environmental and electrochemical interactions. Finally,...
Show moreDegradation of the Carbon Fiber/Vinylester (CF/VE) polymer matrix composites due to different electrochemical interactions when exposed to seawater or at high temperature had been experimentally investigated. Water uptake behavior of composite specimen was examined based on weight gain measurement. Three point bending test was performed to quantify the mechanical degradation of composite immersed in seawater with different environmental and electrochemical interactions. Finally, Electrochemical Impedance Spectroscopy (EIS) was used to better understanding of the degradation process in CF/VE composite produced by interactions between electrochemical and different environmental conditions. A detailed equivalent circuit analysis by using EIS spectra is also presented in an attempt to elucidate the degradation phenomenon in composites.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/2683124
- Subject Headings
- Composite materials, Mechanical properties, Fibrous composites, Structural analysis, Polymeric composites, Spectrum analysis
- Format
- Document (PDF)
- Title
- The effects of nitric acid and silane surface treatments on carbon fibers and carbon/vinyl ester composites before and after seawater exposure.
- Creator
- Langston, Tye A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This research focuses on carbon fiber treatment by nitric acid and 3- (trimethoxysilyl)propyl methacrylate silane, and how this affects carbon/vinyl ester composites. These composites offer great benefits, but it is difficult to bond the fiber and matrix together, and without a strong interfacial bond, composites fall short of their potential. Silanes work well with glass fiber, but do not bond directly to carbon fiber because its surface is not reactive to liquid silanes. Oxidizing surface...
Show moreThis research focuses on carbon fiber treatment by nitric acid and 3- (trimethoxysilyl)propyl methacrylate silane, and how this affects carbon/vinyl ester composites. These composites offer great benefits, but it is difficult to bond the fiber and matrix together, and without a strong interfacial bond, composites fall short of their potential. Silanes work well with glass fiber, but do not bond directly to carbon fiber because its surface is not reactive to liquid silanes. Oxidizing surface treatments are often prescribed for improved wetting and bonding to carbon, but good results are not always achieved. Furthermore, there is the unanswered question of environmental durability. This research aimed to form a better understanding of oxidizing carbon fiber treatments, determine if silanes can be bonded to oxidized surfaces, and how these treatments affect composite strength and durability before and after seawater exposure. Nitric acid treatments on carbon fibers were found to improve their tensile strength to a constant level by smoothing surface defects and chemically modifying their surfaces by increasing carbonyl and carboxylic acid concentrations. Increasing these surface group concentrations raises fiber polar energy and causes them to cohere. This impedes wetting, resulting in poor quality, high void content composites, even though there appeared to be improved adhesion between the fibers and matrix. Silane was found to bond to the oxidized carbon fiber surfaces, as evidenced by changes in both fiber and composite properties. The fibers exhibited low polarity and cohesion, while the composites displayed excellent resin wetting, low void content, and low seawater weight gain and swelling. On the contrary, the oxidized fibers that were not treated with silane exhibited high polarity and fiber cohesion., Their composites displayed poor wetting, high void content, high seawater weight gain, and low swelling. Both fiber treatment types resulted in great improvements in dry transverse tensile strength over the untreated fibers, but the oxidized fiber composites lost strength as the acid treatment time was extended, due to poor wetting. The acid/silane treated composites lost some transverse tensile strength after seawater exposure, but the nitric acid oxidized fiber composites appeared to be more seawater durable.
Show less - Date Issued
- 2008
- PURL
- http://purl.flvc.org/FAU/172669
- Subject Headings
- Silane compounds, Testing, Surface chemistry, Composite materials, Biodegradation, Carbon compounds, Testing
- Format
- Document (PDF)
- Title
- Enhancement of spike and stab resistance of flexible armor using nanoparticles and a cross-linking fixative.
- Creator
- Lambert, Vincent., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A novel approach has been introduced in making flexible armor composites. Armor composites are usually made by reinforcing Kevlar fabric into the mixture of a polymer and nanoscale particles. The current procedure deviates from the traditional shear thickening fluid (STF) route and instead uses silane (amino-propyl-trimethoxy silane) as the base polymer. In addition, a cross-linking fixative such as Glutaraldehyde (Gluta) is added to the polymer to create bridges between distant pairs of...
Show moreA novel approach has been introduced in making flexible armor composites. Armor composites are usually made by reinforcing Kevlar fabric into the mixture of a polymer and nanoscale particles. The current procedure deviates from the traditional shear thickening fluid (STF) route and instead uses silane (amino-propyl-trimethoxy silane) as the base polymer. In addition, a cross-linking fixative such as Glutaraldehyde (Gluta) is added to the polymer to create bridges between distant pairs of amine groups present in Kevlar and silated nanoparticles. Water, silane, nanoparticles and Gluta are mixed using a homogenizer and an ultra-sonochemical technique. Subsequently, the admixture is impregnated with Kevlar - bypassing the heating and evaporating processes involved with STF. The resulting composites have shown remarkable improvement in spike resistance; at least one order higher than that of STF/Kevlar composites. The source of improvement has been traced to the formation of secondary amine C-N stretch due to the presence of Gluta.
Show less - Date Issued
- 2009
- PURL
- http://purl.flvc.org/FAU/186769
- Subject Headings
- Armor, Design and construction, Composite materials, Testing, Nanoparticles, Testing, Viscoelasticity
- Format
- Document (PDF)
- Title
- Fabrication and characterization of copper/molybdenum coatings on carbon fibers by electrodeposition.
- Creator
- Maucione, Luke J., Florida Atlantic University, Lipka, Stephen M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The codeposition of a smooth and uniform coating of copper and molybdenum was successfully achieved on T-650 carbon fiber. The effect of various plating parameters on the electrodeposition of copper and molybdenum such as plating bath chemistry, current density, and pulse frequency were studied. By adjusting the aforementioned variables, qualitative and quantitative analysis was conducted to evaluate the deposit smoothness, uniformity, and wetting characteristics. Qualitative analysis of the...
Show moreThe codeposition of a smooth and uniform coating of copper and molybdenum was successfully achieved on T-650 carbon fiber. The effect of various plating parameters on the electrodeposition of copper and molybdenum such as plating bath chemistry, current density, and pulse frequency were studied. By adjusting the aforementioned variables, qualitative and quantitative analysis was conducted to evaluate the deposit smoothness, uniformity, and wetting characteristics. Qualitative analysis of the deposits were made using scanning electron microscopy and energy dispersive spectroscopy. Quantitative analysis of the deposit coating was conducted using inductively coupled plasma chemical analysis, dewetting tests, X-ray diffraction, transmission electron microscopy, and auger electron spectroscopy. Based on the results, a plating line was designed and constructed for the continuous deposition of copper and molybdenum onto carbon fiber tows.
Show less - Date Issued
- 1995
- PURL
- http://purl.flvc.org/fcla/dt/15124
- Subject Headings
- Composite materials, Alloy plating, Metallic composites, Molybdenum alloys
- Format
- Document (PDF)
- Title
- Fatigue and fracture of foam cores used in sandwich composites.
- Creator
- Saenz, Elio., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This study focused on the fracture and fatigue crack growth behavior in polyvinylchloride (PVC) and polyethersulfone (PES) foams. A new sandwich double cantilever beam (DCB) test specimen was implemented. Elastic foundation and finite element analysis and experimental testing confirmed that the DCB specimen is appropriate for static and cyclic crack propagation testing of soft polymer foams. A comprehensive experimental mechanical analysis was conducted on PVC foams of densities ranging from...
Show moreThis study focused on the fracture and fatigue crack growth behavior in polyvinylchloride (PVC) and polyethersulfone (PES) foams. A new sandwich double cantilever beam (DCB) test specimen was implemented. Elastic foundation and finite element analysis and experimental testing confirmed that the DCB specimen is appropriate for static and cyclic crack propagation testing of soft polymer foams. A comprehensive experimental mechanical analysis was conducted on PVC foams of densities ranging from 45 to 100 kg/m3 and PES foams of densities ranging from 60 to 130 kg/m3. An in-situ scanning electron microscope study on miniature foam fracture specimens showed that crack propagation in the PVC foam was inter-cellular and in the PES foam, failure occurred predominately by extensional failure of vertical cell edges. Sandwich DCB specimens were loaded cyclically as well. For the PVC foams, the crack growth rates were substantially influenced by the density. For the PES foams, there was no clear indication about the influence of foam density on the crack growth rate.
Show less - Date Issued
- 2012
- PURL
- http://purl.flvc.org/FAU/3352829
- Subject Headings
- Sandwich construction, Composite materials, Fibrous composites, Strains and stresses, Management, Laminated materials, Plastics, Fatigue
- Format
- Document (PDF)
- Title
- Fatigue modeling of composite ocean current turbine blade.
- Creator
- Akram, Mohammad Wasim, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The success of harnessing energy from ocean current will require a reliable structural design of turbine blade that is used for energy extraction. In this study we are particularly focusing on the fatigue life of a 3m length ocean current turbine blade. The blade consists of sandwich construction having polymeric foam as core, and carbon/epoxy as face sheet. Repetitive loads (Fatigue) on the blade have been formulated from the randomness of the ocean current associated with turbulence and...
Show moreThe success of harnessing energy from ocean current will require a reliable structural design of turbine blade that is used for energy extraction. In this study we are particularly focusing on the fatigue life of a 3m length ocean current turbine blade. The blade consists of sandwich construction having polymeric foam as core, and carbon/epoxy as face sheet. Repetitive loads (Fatigue) on the blade have been formulated from the randomness of the ocean current associated with turbulence and also from velocity shear. These varying forces will cause a cyclic variation of bending and shear stresses subjecting to the blade to fatigue. Rainflow Counting algorithm has been used to count the number of cycles within a specific mean and amplitude that will act on the blade from random loading data. Finite Element code ANSYS has been used to develop an S-N diagram with a frequency of 1 Hz and loading ratio 0.1 Number of specific load cycles from Rainflow Counting in conjunction with S-N diagram from ANSYS has been utilized to calculate fatigue damage up to 30 years by Palmgren-Miner's linear hypothesis.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/2867332
- Subject Headings
- Turbines, Blades, Materials, Fatigue, Marine turbines, Mathematical models, Structural dynamics, Composite materials, Mathematical models, Sandwich construction, Fatigue
- Format
- Document (PDF)
- Title
- Feasibility studies on carbon fiber composite cables in reinforced/prestressed concrete structures.
- Creator
- Kanneganti, Srikanth., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The feasibility studies on the use of non-metallic continuous fiber reinforcement in reinforced and prestressed concrete structures are presented herein. Experimental results from studies on relaxation, bond and transfer length of Carbon Fiber Composite Cables (CFCC) are presented followed by results of flexural load tests on concrete beams reinforced and prestressed with CFCC. Durability of the CFCC is another prime concern, and hence part of the study also focuses on establishing the...
Show moreThe feasibility studies on the use of non-metallic continuous fiber reinforcement in reinforced and prestressed concrete structures are presented herein. Experimental results from studies on relaxation, bond and transfer length of Carbon Fiber Composite Cables (CFCC) are presented followed by results of flexural load tests on concrete beams reinforced and prestressed with CFCC. Durability of the CFCC is another prime concern, and hence part of the study also focuses on establishing the durability of the CFCC exposed to aggressive environments like alkali solution and sea water. The basic mechanics that govern the structural behavior of the beams, provide important insight into the potential that CFCC has to offer.
Show less - Date Issued
- 1994
- PURL
- http://purl.flvc.org/fcla/dt/15080
- Subject Headings
- Fiber reinforced plastics, Reinforced concrete, Fiber, Composite materials, Prestressed concrete construction--Deterioration, Carbon fibers
- Format
- Document (PDF)
- Title
- Interlaminar crack propagation in thick composite shells.
- Creator
- Ozdil, Feridun., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Delamination growth has been investigated as a potential failure mechanism for filament-wound composite cylinders used for offshore and underwater structures. Analysis and experiments on DCB, ENF, and MMB beam fracture specimens machined from angle-ply laminate panels and filament-wound composite cylinders are presented. Bending analysis of beam fracture specimens machined from flat panels and composite cylinders was derived from first order shear deformation theory and one-dimensional...
Show moreDelamination growth has been investigated as a potential failure mechanism for filament-wound composite cylinders used for offshore and underwater structures. Analysis and experiments on DCB, ENF, and MMB beam fracture specimens machined from angle-ply laminate panels and filament-wound composite cylinders are presented. Bending analysis of beam fracture specimens machined from flat panels and composite cylinders was derived from first order shear deformation theory and one-dimensional expressions obtained from laminated plate and shell theories. For the DCB specimens, elastic foundation effects were modeled. Experiments on flat, glass/polyester laminate beam specimens considered [0]6, [+/-30]5 and [+/-45] 5 lay-ups with mid-plane delaminations. Experiments on beam specimens machined from composite cylinders were conducted on [+/- q ]6 and [+/- q ]12 lay-ups with mid-surface delaminations where q = 30 degrees, 55 degrees and 85 degrees. For all lay-ups and specimen configurations, beam model predictions of compliance were in good agreement with experimental data over the range of laminate thicknesses, ply angles, and crack lengths examined. Fracture toughness for delamination propagation was examined for flat glass/polyester panels and glass/epoxy cylinders. The initiation value of mode II fracture toughness, GIIc, was much larger than the initiation value of mode I fracture toughness GIc. The initiation value of mixed mode fracture toughness, Gc, increased with decreased ratio GI/GII and increased ply angle q . Debonding of transversely oriented fiber bundles was observed as a major crack arrest and fracture resistance mechanism for the flat, glass/polyester angle-ply laminates. Bridging by interlaced fiber bundles and crack jumping to another interface contributed to crack arrest and limited the growth in the curved, glass/epoxy angle-ply laminates. For all lay-ups, the crack propagated in a non-uniform manner across the width of the specimen as explained by elastic coupling effects in the laminate beams of the cracked region.
Show less - Date Issued
- 1999
- PURL
- http://purl.flvc.org/fcla/dt/12588
- Subject Headings
- Laminated materials, Shells (Engineering), Composite materials
- Format
- Document (PDF)
- Title
- Interlaminar mode III fracture ECT method - testing and analysis.
- Creator
- Browning, Grant., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In an effort to obtain an improved mode III fracture toughness test suitable for a testing standard, mechanics analysis, experimental testing, and finite element analysis (FEA) have been conducted. Of particular concern are the merits of one-point and two-point edge crack torsion (ECT) test methods, the influence of specimen geometry that overhangs beyond load/support points, and the influence of crack length on the compliance and energy release rate. Shear stress distributions at the crack...
Show moreIn an effort to obtain an improved mode III fracture toughness test suitable for a testing standard, mechanics analysis, experimental testing, and finite element analysis (FEA) have been conducted. Of particular concern are the merits of one-point and two-point edge crack torsion (ECT) test methods, the influence of specimen geometry that overhangs beyond load/support points, and the influence of crack length on the compliance and energy release rate. Shear stress distributions at the crack front are determined to examine the uniformity of mode III loading and mode II influence. The shear stress distributions in the one-point and two-point tests are virtually identical, indicating that either of the two tests could be used interchangeably. Based on the uniformity of the mode III shear stress distribution along the crack front, it was found that the ECT specimen should have minimum overhang. Longer crack lengths tend to produce nonuniform shear stress distributions. A modified two-point ECT test fixture was developed to allow testing of specimens with a range of dimensions. This development enabled experimental verification of the results from the FEA overhang series. The specimens with a minimum overhang produced consistant mode III toughness data. The most reliable way to reduce data is through the original compliance calibration method. A modified ECT specimen was developed with a staggered crack front to produce uniform mode III crack growth. Finite element analysis of the modified ECT specimen shows a uniform mode III stress distribution along the crack front with little mode II interaction.
Show less - Date Issued
- 2009
- PURL
- http://purl.flvc.org/FAU/187206
- Subject Headings
- Laminated materials, Testing, Fracture mechanics, Strength of materials, Testing, Composite materials, Testing
- Format
- Document (PDF)
- Title
- Investigation of nanoscale reinforcement into textile polymers.
- Creator
- Khan, Mujibur Rahman., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A dual inclusion strategy for textile polymers has been investigated to increase elastic energy storage capacity of fibers used in high velocity impact applications. Commercial fibers such as Spectra and Dyneema are made from ultra high molecular weight polyethylene (UHMWPE). Dynamic elastic energy of these fibers is still low therefore limiting their wholesale application without a secondary metallic or ceramic component. The idea in this investigation is to develop methodologies so that the...
Show moreA dual inclusion strategy for textile polymers has been investigated to increase elastic energy storage capacity of fibers used in high velocity impact applications. Commercial fibers such as Spectra and Dyneema are made from ultra high molecular weight polyethylene (UHMWPE). Dynamic elastic energy of these fibers is still low therefore limiting their wholesale application without a secondary metallic or ceramic component. The idea in this investigation is to develop methodologies so that the elastic energy of polyethylene based fibers can be increased by several folds. This would allow manufacturing of an all-fabric system for high impact applications. The dual inclusion consists of a polymer phase and a nanoscale inorganic phase to polyethylene. The polymer phase was nylon-6 and the inorganic phase was carbon nanotubes (CNTs). Nylon-6 was blended as a minor phase into UHMWPE and was chosen because of its large fracture strain - almost one order higher than that of UHMWPE. On the other hand, CNTs with their very high strength, modulus, and aspect ratio, contributed to sharing of load and sliding of polymer interfaces as they aligned during extrusion and strain hardening processes. A solution spinning process was developed to produce UHMWPE filaments reinforced with CNTs and nylon-6. The procedure involved dispersing of CNTs into paraffin oil through sonication followed by dissolving polymers into paraffin-CNT solution using a homogenizer. The admixture was fed into a single screw extruder for melt mixing and extrusion through an orifice. The extrudate was rinsed via a hexane bath, stabilized through a heater, and then drawn into a filament winder with controlled stretching. In the next step, the as produced filaments were strain-hardened through repeated loading unloading cycles under tension., Neat and reinforced filaments were characterized through DSC (Differential Scanning Calorimetry), XRD (X-ray Diffraction), Raman Spectroscopy, SEM (Scanning Electron Microscope), and mechanical tests. Phenomenal improvement in properties was found; modulus, strength, fracture strain, and elastic energy increased by 219%, 100%, 107% and 88%, respectively before strain hardening. Once strain hardened the strength, modulus and elastic energy increased by almost one order of magnitude. Source of these improvements were traced to increase in crystallinity and rate of crystallization, formation of microdroplets as a minor phase, sliding between minor and major phases, coating of nanotubes with polymer and alignment of nanotubes.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/2976443
- Subject Headings
- Nanostructured materials, Composite materials, Textile fibers, Synthetic, Polymers, Electric properties
- Format
- Document (PDF)
- Title
- Reinforcement of syntactic foam with SiC nanoparticles.
- Creator
- Das, Debdutta., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In this investigation, polymer precursor of syntactic foam has been reinforced with SiC nanoparticles to enhance mechanical and fracture properties. Derakane 8084 vinyl ester resin was first dispersed with 1.0 wt% of SiC particles using a sonic cavitation technique. In the next step, 30.0 wt% of microspheres (3M hollow glass borosilicate, S-series) were mechanically mixed with the nanophased vinyl ester resin, and cast into rectangular molds. A small amount of styrene was used as dilutant to...
Show moreIn this investigation, polymer precursor of syntactic foam has been reinforced with SiC nanoparticles to enhance mechanical and fracture properties. Derakane 8084 vinyl ester resin was first dispersed with 1.0 wt% of SiC particles using a sonic cavitation technique. In the next step, 30.0 wt% of microspheres (3M hollow glass borosilicate, S-series) were mechanically mixed with the nanophased vinyl ester resin, and cast into rectangular molds. A small amount of styrene was used as dilutant to facilitate mixing of microspheres. The size of microspheres and SiC nanoparticles were 20-30 um and 30-50 nm, respectively. Tension, compression, and flexure tests were conducted following ASTM standards and a consistent improvement in strength and modulus within 20-35% range was observed. Fracture toughness parameters such as KIC and GIC were also determined using ASTM E-399. An improvement of about 11-15% was observed. Samples were also subjected to various environmental conditions and degradation in material properties is reported.
Show less - Date Issued
- 2009
- PURL
- http://purl.flvc.org/FAU/359923
- Subject Headings
- Composite materials, Design, Polyurethanes, Mechanical properties, Epoxy resins, Nanostructured materials
- Format
- Document (PDF)
- Title
- Study of edge effects in laminated sandwich specimens.
- Creator
- Mankuzhy, Pradeep Prabhakaran., Florida Atlantic University, Merry, Stephanie L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Different methods have been employed to calculate the interlaminar stresses and to study the edge effect in a laminated sandwich specimens under uniaxial tension. However, Finite Element Analysis and Force Balance Method produced stress values which disagreed in both magnitude and sign, a controversy which exists in the case of composite laminates also. Experimental methods, photoelastic coating method and strain gaging, were attempted to obtain the strain distribution on the top surface of a...
Show moreDifferent methods have been employed to calculate the interlaminar stresses and to study the edge effect in a laminated sandwich specimens under uniaxial tension. However, Finite Element Analysis and Force Balance Method produced stress values which disagreed in both magnitude and sign, a controversy which exists in the case of composite laminates also. Experimental methods, photoelastic coating method and strain gaging, were attempted to obtain the strain distribution on the top surface of a sandwich specimen in three point bending. However, these conventional methods failed to show the sharp strain gradient that exists near the free edge. The Force Balance Method was simplified for sandwich specimens by considering the face laminate as a homogeneous and orthotropic material with averaged properties. Simplified expressions were also obtained for calculating the boundary layer thickness. The boundary layer thickness was found to vary linearly with core thickness for the cases considered.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14523
- Subject Headings
- Sandwich construction--Fatigue, Composite materials, Strains and stresses, Structural analysis (Engineering)
- Format
- Document (PDF)
- Title
- A study of the effects of nanoparticle modification on the thermal, mechanical and hygrothermal performance of carbon/vinyl ester compounds.
- Creator
- Powell, Felicia M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Enhancement of mechanical, thermal and hygrothermal properties of carbon fiber/vinyl ester (CFVE) composites through nanoparticle reinforcement has been investigated. CFVE composites are becoming more and more attractive for marine applications due to two reasons : high specific strength and modulus of carbon fiber and low vulnerability of vinyl ester resin to sea water. However, the problem with this composite system is that the fiber matrix (F/M) interface is inherently weak. This leads to...
Show moreEnhancement of mechanical, thermal and hygrothermal properties of carbon fiber/vinyl ester (CFVE) composites through nanoparticle reinforcement has been investigated. CFVE composites are becoming more and more attractive for marine applications due to two reasons : high specific strength and modulus of carbon fiber and low vulnerability of vinyl ester resin to sea water. However, the problem with this composite system is that the fiber matrix (F/M) interface is inherently weak. This leads to poor mechanical properties and fast ingress of water at the interface further deteriorating the properties. This investigation attempts to address these deficiencies by inclusion of nanoparticles in CFVE composites. Three routes of nanoparticle reinforcement have been considered : nanoparticle coating of the carbon fiber, dispersion of nanoparticles in the vinyl ester matrix, and nanoparticle modification of both the fiber and the matrix. Flexural, short beam shear and tensile testing was conducted after exposure to dry and wet environments. Differential scanning calorimetry and dynamic mechanical analysis were conducted as well. Mechanical and thermal tests show that single inclusion of nanoparticles on the fiber or in the matrix increases carbon/vinyl ester composite properties by 11-35%. However, when both fiber and matrix were modified with nanoparticles, there was a loss of properties.
Show less - Date Issued
- 2012
- PURL
- http://purl.flvc.org/FAU/3352286
- Subject Headings
- Composite materials, Mechanical properties, Nanostructured materials, Testing, Carbon compounds, Testing, Fibrous composites, Testing, Surface chemistry
- Format
- Document (PDF)
