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- Genre: Masters Thesis
Description
Woven fabric composite materials are widely used in the construction of aircraft engine fan containment systems, mostly due to their high strength to weight ratios and ease of implementation. The development of a predictive model for fan blade containment would provide great benefit to engine manufactures in shortened development cycle time, less risk in certification and fewer dollars lost to redesign/recertification cycles. A mechanistic user-defined material model subroutine has been developed at Arizona State University (ASU) that captures the behavioral response of these fabrics, namely Kevlar® 49, under ballistic loading. Previously developed finite element models used to validate the consistency of this material model neglected the effects of the physical constraints imposed on the test setup during ballistic testing performed at NASA Glenn Research Center (NASA GRC). Part of this research was to explore the effects of these boundary conditions on the results of the numerical simulations. These effects were found to be negligible in most instances. Other material models for woven fabrics are available in the LS-DYNA finite element code. One of these models, MAT234: MAT_VISCOELASTIC_LOOSE_FABRIC (Ivanov & Tabiei, 2004) was studied and implemented in the finite element simulations of ballistic testing associated with the FAA ASU research. The results from these models are compared to results obtained from the ASU UMAT as part of this research. The results indicate an underestimation in the energy absorption characteristics of the Kevlar 49 fabric containment systems. More investigation needs to be performed in the implementation of MAT234 for Kevlar 49 fabric. Static penetrator testing of Kevlar® 49 fabric was performed at ASU in conjunction with this research. These experiments are designed to mimic the type of loading experienced during fan blade out events. The resulting experimental strains were measured using a non-contact optical strain measurement system (ARAMIS).
ContributorsFein, Jonathan (Author) / Rajan, Subramaniam D. (Thesis advisor) / Mobasher, Barzin (Committee member) / Jiang, Hanqing (Committee member) / Arizona State University (Publisher)
Created2012
Description
This study focuses on implementing probabilistic nature of material properties (Kevlar® 49) to the existing deterministic finite element analysis (FEA) of fabric based engine containment system through Monte Carlo simulations (MCS) and implementation of probabilistic analysis in engineering designs through Reliability Based Design Optimization (RBDO). First, the emphasis is on experimental data analysis focusing on probabilistic distribution models which characterize the randomness associated with the experimental data. The material properties of Kevlar® 49 are modeled using experimental data analysis and implemented along with an existing spiral modeling scheme (SMS) and user defined constitutive model (UMAT) for fabric based engine containment simulations in LS-DYNA. MCS of the model are performed to observe the failure pattern and exit velocities of the models. Then the solutions are compared with NASA experimental tests and deterministic results. MCS with probabilistic material data give a good prospective on results rather than a single deterministic simulation results. The next part of research is to implement the probabilistic material properties in engineering designs. The main aim of structural design is to obtain optimal solutions. In any case, in a deterministic optimization problem even though the structures are cost effective, it becomes highly unreliable if the uncertainty that may be associated with the system (material properties, loading etc.) is not represented or considered in the solution process. Reliable and optimal solution can be obtained by performing reliability optimization along with the deterministic optimization, which is RBDO. In RBDO problem formulation, in addition to structural performance constraints, reliability constraints are also considered. This part of research starts with introduction to reliability analysis such as first order reliability analysis, second order reliability analysis followed by simulation technique that are performed to obtain probability of failure and reliability of structures. Next, decoupled RBDO procedure is proposed with a new reliability analysis formulation with sensitivity analysis, which is performed to remove the highly reliable constraints in the RBDO, thereby reducing the computational time and function evaluations. Followed by implementation of the reliability analysis concepts and RBDO in finite element 2D truss problems and a planar beam problem are presented and discussed.
ContributorsDeivanayagam, Arumugam (Author) / Rajan, Subramaniam D. (Thesis advisor) / Mobasher, Barzin (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2012
Description
High Voltage Direct Current (HVDC) technology is being considered for several long distance point-to-point overhead transmission lines, because of their lower losses and higher transmission capability, when compared to AC systems. Insulators are used to support and isolate the conductors mechanically and electrically. Composite insulators are gaining popularity for both AC and DC lines, for the reasons of light weight and good performance under contaminated conditions. This research illustrates the electric potential and field computation on HVDC composite insulators by using the charge simulation method. The electric field is calculated under both dry and wet conditions. Under dry conditions, the field distributions along the insulators whose voltage levels range from 500 kV to 1200 kV are calculated and compared. The results indicate that the HVDC insulator produces higher electric field, when compared to AC insulator. Under wet conditions, a 500 kV insulator is modeled with discrete water droplets on the surface. In this case, the field distribution is affected by surface resistivity and separations between droplets. The corona effects on insulators are analyzed for both dry and wet conditions. Corona discharge is created, when electric field strength exceeds the threshold value. Corona and grading rings are placed near the end-fittings of the insulators to reduce occurrence of corona. The dimensions of these rings, specifically their radius, tube thickness and projection from end fittings are optimized. This will help the utilities design proper corona and grading rings to reduce the corona phenomena.
ContributorsHe, Jiahong (Author) / Gorur, Ravi S (Committee member) / Ayyanar, Raja (Committee member) / Holbert, Keith E. (Committee member) / Arizona State University (Publisher)
Created2013
Description
The high strength to weight ratio of woven fabric offers a cost effective solution to be used in a containment system for aircraft propulsion engines. Currently, Kevlar is the only Federal Aviation Administration (FAA) approved fabric for usage in systems intended to mitigate fan blade-out events. This research builds on an earlier constitutive model of Kevlar 49 fabric developed at Arizona State University (ASU) with the addition of new and improved modeling details. Latest stress strain experiments provided new and valuable data used to modify the material model post peak behavior. These changes reveal an overall improvement of the Finite Element (FE) model's ability to predict experimental results. First, the steel projectile is modeled using Johnson-Cook material model and provides a more realistic behavior in the FE ballistic models. This is particularly noticeable when comparing FE models with laboratory tests where large deformations in projectiles are observed. Second, follow-up analysis of the results obtained through the new picture frame tests conducted at ASU provides new values for the shear moduli and corresponding strains. The new approach for analysis of data from picture frame tests combines digital image analysis and a two-level factorial optimization formulation. Finally, an additional improvement in the material model for Kevlar involves checking the convergence at variation of mesh density of fabrics. The study performed and described herein shows the converging trend, therefore validating the FE model.
ContributorsMorea, Mihai I (Author) / Rajan, Subramaniam D. (Thesis advisor) / Arizona State University (Publisher)
Created2011
Description
Composite materials are increasingly being used in aircraft, automobiles, and other applications due to their high strength to weight and stiffness to weight ratios. However, the presence of damage, such as delamination or matrix cracks, can significantly compromise the performance of these materials and result in premature failure. Structural components are often manually inspected to detect the presence of damage. This technique, known as schedule based maintenance, however, is expensive, time-consuming, and often limited to easily accessible structural elements. Therefore, there is an increased demand for robust and efficient Structural Health Monitoring (SHM) techniques that can be used for Condition Based Monitoring, which is the method in which structural components are inspected based upon damage metrics as opposed to flight hours. SHM relies on in situ frameworks for detecting early signs of damage in exposed and unexposed structural elements, offering not only reduced number of schedule based inspections, but also providing better useful life estimates. SHM frameworks require the development of different sensing technologies, algorithms, and procedures to detect, localize, quantify, characterize, as well as assess overall damage in aerospace structures so that strong estimations in the remaining useful life can be determined. The use of piezoelectric transducers along with guided Lamb waves is a method that has received considerable attention due to the weight, cost, and function of the systems based on these elements. The research in this thesis investigates the ability of Lamb waves to detect damage in feature dense anisotropic composite panels. Most current research negates the effects of experimental variability by performing tests on structurally simple isotropic plates that are used as a baseline and damaged specimen. However, in actual applications, variability cannot be negated, and therefore there is a need to research the effects of complex sample geometries, environmental operating conditions, and the effects of variability in material properties. This research is based on experiments conducted on a single blade-stiffened anisotropic composite panel that localizes delamination damage caused by impact. The overall goal was to utilize a correlative approach that used only the damage feature produced by the delamination as the damage index. This approach was adopted because it offered a simplistic way to determine the existence and location of damage without having to conduct a more complex wave propagation analysis or having to take into account the geometric complexities of the test specimen. Results showed that even in a complex structure, if the damage feature can be extracted and measured, then an appropriate damage index can be associated to it and the location of the damage can be inferred using a dense sensor array. The second experiment presented in this research studies the effects of temperature on damage detection when using one test specimen for a benchmark data set and another for damage data collection. This expands the previous experiment into exploring not only the effects of variable temperature, but also the effects of high experimental variability. Results from this work show that the damage feature in the data is not only extractable at higher temperatures, but that the data from one panel at one temperature can be directly compared to another panel at another temperature for baseline comparison due to linearity of the collected data.
ContributorsVizzini, Anthony James, II (Author) / Chattopadhyay, Aditi (Thesis advisor) / Fard, Masoud (Committee member) / Papandreou-Suppappola, Antonia (Committee member) / Arizona State University (Publisher)
Created2012
Description
Composite materials are finally providing uses hitherto reserved for metals in structural systems applications – airframes and engine containment systems, wraps for repair and rehabilitation, and ballistic/blast mitigation systems. They have high strength-to-weight ratios, are durable and resistant to environmental effects, have high impact strength, and can be manufactured in a variety of shapes. Generalized constitutive models are being developed to accurately model composite systems so they can be used in implicit and explicit finite element analysis. These models require extensive characterization of the composite material as input. The particular constitutive model of interest for this research is a three-dimensional orthotropic elasto-plastic composite material model that requires a total of 12 experimental stress-strain curves, yield stresses, and Young’s Modulus and Poisson’s ratio in the material directions as input. Sometimes it is not possible to carry out reliable experimental tests needed to characterize the composite material. One solution is using virtual testing to fill the gaps in available experimental data. A Virtual Testing Software System (VTSS) has been developed to address the need for a less restrictive method to characterize a three-dimensional orthotropic composite material. The system takes in the material properties of the constituents and completes all 12 of the necessary characterization tests using finite element (FE) models. Verification and validation test cases demonstrate the capabilities of the VTSS.
ContributorsHarrington, Joseph (Author) / Rajan, Subramaniam D. (Thesis advisor) / Neithalath, Narayanan (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2015
Description
Composite materials are widely used in various structural applications, including within the automotive and aerospace industries. Unidirectional composite layups have replaced other materials such as metals due to composites’ high strength-to-weight ratio and durability. Finite-element (FE) models are actively being developed to model response of composite systems subjected to a variety of loads including impact loads. These FE models rely on an array of measured material properties as input for accuracy. This work focuses on an orthotropic plasticity constitutive model that has three components – deformation, damage and failure. The model relies on the material properties of the composite such as Young’s modulus, Poisson’s ratio, stress-strain curves in the principal and off-axis material directions, etc. This thesis focuses on two areas important to the development of the FE model – tabbing of the test specimens and data processing of the tests used to generate the required stress-strain curves. A comparative study has been performed on three candidate adhesives using double lap-shear testing to determine their effectiveness in composite specimen tabbing. These tests determined the 3M DP460 epoxy performs best in shear. The Loctite Superglue with 80% the ultimate stress of the 3M DP460 epoxy is acceptable when test specimens have to be ready for testing within a few hours. JB KwikWeld is not suitable for tabbing. In addition, the Experimental Data Processing (EDP) program has been improved for use in post-processing raw data from composites test. EDP has improved to allow for complete processing with the implementation of new weighted least squares smoothing options, curve averaging techniques, and new functionality for data manipulation.
ContributorsSchmidt, Nathan William (Author) / Rajan, Subramaniam D. (Thesis advisor) / Neithalath, Narayanan (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2016
Description
Composite insulators on overhead lines are frequently subjected to corona discharges due to increased electric field intensities under various conditions. These discharges can cause localized heating on the surface and affect the hydrophobicity of the insulator. A study has been undertaken to quantify and evaluate the thermal degradation that composite insulation is subjected to from corona discharges. This has been conducted primarily at the power frequency (60 Hz) and at the low frequency range (37 kHz). Point to plane corona discharge experiments have been performed in the laboratory at both the frequencies and varying levels of thermal degradation has been observed. The amplitude and the frequency of current spikes have been recorded at different voltage levels. A temperature model based on the amplitude and the frequency of current data has been formulated to calculate the maximum temperature attained due to these discharges. Visual thermal degradation has been found to set in at a low frequency range while there is no visual degradation observed at power frequency even when exposed to discharges for relatively much longer periods of time. However, microscopic experiments have been conducted which revealed degradation on the surface at 60 Hz. It has also been found that temperatures in excess of 300 Celsius have been obtained at 37 kHz. This corroborates the thermo gravimetric analysis data that proves thermal degradation in silicone rubber samples at temperatures greater than 300 Celsius. Using the above model, the maximum temperature rise can be evaluated due to discharges occurring on high voltage insulation. This model has also been used to calculate the temperature rise on medium voltage distribution equipment such as composite bushings and stand-off plugs. The samples were subjected to standard partial discharge tests and the corresponding discharge magnitudes have been recorded. The samples passed the tests and the corresponding temperatures plotted have been found to be within thermal limits of the respective insulation used on the samples. The experimental results concur with the theoretical model. A knowledge of the maximum temperatures attained due to these discharges can help in design of insulation with better thermal properties.
ContributorsSangaraju Venkateshwara, Pradeep Varma (Author) / Gorur, Ravi S (Thesis advisor) / Farmer, Richard (Committee member) / Vittal, Vijay (Committee member) / Arizona State University (Publisher)
Created2010
Description
This research work illustrates the use of software packages based on the concept of nu-merical analysis technique to evaluate the electric field and voltage distribution along composite insulators for system voltages ranging from 138 kV up to 1200 kV ac. A part of the calculations was made using the 3D software package, COULOMB 8.0, based on the concept of Boundary Element Method (BEM). The electric field was calculated under dry and wet conditions. Compo-site insulators experience more electrical stress when compared to porcelain and are also more prone to damage caused by corona activity. The work presented here investigates the effect of corona rings of specific dimensions and bundled conductors on the electric field along composite insulators. Inappropriate placement or dimensions of corona rings could enhance the electric field instead of mitigating it. Corona ring optimization for a 1000 kV composite insulator was per-formed by changing parameters of the ring, such as the diameter of the ring, thickness of the ring tube and the projection of the ring from the high voltage energized end fitting. Grading rings were designed for Ultra High Voltage (UHV) systems that use two units of composite insulators in pa-rallel. The insulation distance, which bears 50% of the total applied voltage, is raised by 61% with the grading ring installed, when compared to the distance without the grading ring. In other words, the electric field and voltage distribution was found to be more linear with the application of grad-ing rings. The second part of this project was carried out using the EPRI designed software EPIC. This is based on the concept of Charge Simulation method (CSM). Comparisons were made be-tween electric field magnitude along composite insulators used for suspension and dead end configuration for system voltages ranging from 138 kV to 500 kV. It was found that the dead end composite insulators experience significantly higher electrical stress when compared to their suspension counterpart. It was also concluded that this difference gets more prominent as the system voltage increases. A comparison made between electric field distribution along composite insulators used in single and double dead end structures suggested that the electric stress experienced by the single dead end composite insulators is relatively higher when compared to double dead end composite insulators.
ContributorsDoshi, Tanushri (Author) / Gorur, Ravi S (Thesis advisor) / Vittal, Vijay (Committee member) / Farmer, Richard (Committee member) / Arizona State University (Publisher)
Created2010