Engineering Commons^™

Energy Localization And Heat Generation In Composite Energetic Systems Under High-Frequency Mechanical Excitation, Jesus O. Mares

Open Access Dissertations

In this work, the ability to use high frequency mechanical excitation to generate significant heating within plastic bonded explosives, as well as single energetic particles embedded within a viscoelastic binder, is studied. In this work, the fundamental mechanisms associated with the conversion of high-frequency mechanical excitation to heat as applied to these composite energetic systems are thoroughly investigated.

High-frequency contact excitation has been used to generate a significant amount of heat within samples of PBX 9501 and representative inert mock materials. Surface temperature rises on the order of 10 °C were observed at certain frequencies over a range from 50 …

Biodegradable Thermoplastic Elastomers And Smart Composites, Erin Mcmullin

Dissertations - ALL

There is a need for biodegradable thermoplastic elastomers for a variety of medical applications. This dissertation aims at (i) developing and characterizing biodegradable elastomers and (ii) developing and characterizing biodegradable smart composites, both to be used as biomaterials. First, in Chapter 1, an overview was given of the literature of relevant background information on polymers, biomaterials, and previous biodegradable elastomers and responsive elastomeric systems.

The first biodegradable elastomer developed and investigated, as presented in Chapter 2, is a novel thermoplastic polyurethane that has a biodegradable soft segment and a crystalline hard segment (POSS). By varying the composition of the poly(caprolactone)-based …

Thermal Stress Analysis Of Unidirectional Composite Material By Fem Modeling, Gopal D. Gulwani

Mechanical and Aerospace Engineering Theses

Micromechanics of composite is study of complex mechanism of stress and strain transfer between fiber and matrix within a composite as well as distributions of physical fields inside heterogeneous medium. It was used successfully in predicting accurately physical properties like effective stiffness, effective linear thermal expansion of heterogeneous materials like composite. However, when it comes to strength characteristics of composite especially in transversal direction it failed to predict more accurate results. This thesis is focused on thermally induced stress analysis of unidirectional composite by finite element method. Thermal stresses which are dangerously ignored factor in mechanics of composite usually occur …

Static And Dynamic Fea Analysis Of A Composite Leaf Spring, Himanshu Arun Raut

Mechanical and Aerospace Engineering Theses

Composite materials are widely used in aeronautical, marine and automotive industries, because of their excellent mechanical properties, low density and ease of manufacture. Due to this increasing trend to utilize composite materials, it has become necessary to investigate the pros and cons of composites. This research investigated the static and dynamic behaviors for a composite leaf spring that are used in Chevrolet Corvette Grand and light tractor-trailers. The objective of this study was to find the cause of de-lamination/ failure of the unidirectional composite layers in varying cross sections of the leaf spring. Finite element method is used to calculate …

Ionic Electroactive Polymer Devices: Physics-Based Modeling With Experimental Investigation And Verification, Tyler Paul Stalbaum

UNLV Theses, Dissertations, Professional Papers, and Capstones

The primary focus of this study is to examine, understand, and model ionic electroactive polymer based systems in attempt to further develop this field of study. Physics-based modeling is utilized, as opposed to empirical modeling, to achieve a deeper insight to the underlying physics. The ionic electroactive polymer system of primary interest in this study is ionic polymer-metal composite (IPMC) devices. Other similar devices, such as anion-exchange membrane (AEM) type actuators and flow battery systems are also investigated using the developed model. The underlying physics are in the studies of transport phenomenon for describing the ionic flow within the polymer …

Development Of Metal Matrix Composite Gridlines For Space Photovoltaics, Omar K. Abudayyeh

Chemical and Biological Engineering ETDs

Space vehicles today are primarily powered by multi-junction photovoltaic cells due to their high efficiency and high radiation hardness in the space environment. While multi-junction solar cells provide high efficiency, microcracks develop in the crystalline semiconductor due to a variety of reasons, including: growth defects, film stress due to lattice constant mismatch, and external mechanical stresses introduced during shipping, installation, and operation. These microcracks have the tendency to propagate through the different layers of the semiconductor reaching the metal gridlines of the cell, resulting in electrically isolated areas from the busbar region, ultimately lowering the power output of the cell …

Physical Simulation Of Hot Plastic Deformation Of Tibw/Ti Composites, Lin Geng

The 8th International Conference on Physical and Numerical Simulation of Materials Processing

No abstract provided.

Apparent Porosity And Compressive Strength Of Heat-Treated Clay/Iron Sand/Rice Husk Ash Composites Over A Range Of Sintering Temperatures, M. Nizar Machmud, Zulkarnain Jalil, Mochammad Afifuddin

Makara Journal of Technology

Novel composites of clay/iron sand/rice husk ash (RHA) have been developed. Electric furnace was used to perform heat treatment on the composites to study the effect of sintering temperature on their apparent porosity and compressive strength. Two types of RHA with different bulk density were prepared to gain an understanding of the influence of apparent porosity on compressive strength of the heat-treated composites over a range of sintering temperatures. Heattreated composites, made of clay/iron sand and clay/RHA, were also prepared as a referenced material. X-ray diffraction (XRD) analysis was further performed to comprehensively discuss the role of iron sand on …

Additive Manufacturing Of Carbon Fiber-Reinforced Thermoplastic Composites, Nicholas M. Denardo

Open Access Theses

Additive manufacturing, or 3D printing, encompasses manufacturing processes that construct a geometry by depositing or solidifying material only where it is needed in the absence of a mold. The ability to manufacture complex geometries on demand directly from a digital file, as well as the decreasing equipment costs due to increased competition in the market, have resulted in the AM industry experiencing rapid growth in the past decade. Many companies have emerged with novel technologies well suited to improve products and/or save costs in various industries.

Until recently, the applications of polymer additive manufacturing have been mainly limited to prototyping. …

Representation Of Permittivity For Multiphase Dielectric Mixtures In Fdtd Modeling, Marina Koledintseva, J. Wu, H. Zhang, James L. Drewniak, Konstantin Rozanov

James K. Wu, M.D.

A simple method of approximating frequency characteristics of composites in a form convenient for time-domain numerical modeling is proposed. The frequency characteristics can be obtained from experiment or calculations based on the Maxwell Garnett mixing formalism. The resultant frequency characteristic might be of a complex shape corresponding to a combination of a number of absorption peaks. The approximation is made by a series of Debye-like terms using a genetic algorithm (GA). This leads to the necessity of taking a number of terms in the approximating series. Every term corresponds to its pole, i.e., the frequency where the maximum loss occurs. …

Studies On The Electrical Transport Properties Of Carbon Nanotube Composites, Taylor Warren Tarlton

Doctoral Dissertations

This work presents a probabilistic approach to model the electrical transport properties of carbon nanotube composite materials. A pseudo-random generation method is presented with the ability to generate 3-D samples with a variety of different configurations. Periodic boundary conditions are employed in the directions perpendicular to transport to minimize edge effects. Simulations produce values for drift velocity, carrier mobility, and conductivity in samples that account for geometrical features resembling those found in the lab. All results show an excellent agreement to the well-known power law characteristic of percolation processes, which is used to compare across simulations. The effect of sample …

Fiber Length Attrition In Additive Manufacturing, Michael Chapiro

Materials Engineering

Chopped carbon fibers are used as reinforcements in thermoplastics, but the viscous shear forces that arise in melt-processing reduces the fiber length well below its critical length resulting in only moderate strength and stiffness gains compared to the neat resin. This research project aimed to experimentally determine the effect of the melt–flow portion of a single-screw- extrusion process on carbon fiber length attrition in isolation from the immediately preceding screw–plastication step that is responsible for most of the heat needed for melting. Carbon fibers with an initial length of 2 mm were stirred into 5,000 centipoise and 10,000 centipoise silicone …

Design Of Magnesium Phosphate Cement Based Composite For High Performance Bipolar Plate Of Fuel Cells, Wenbin Hao, Hongyan Ma, Zeyu Lu, Guoxing Sun, Zongjin Li

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

In this work, we report a comprehensive study on a magnesium phosphate cement (MPC) based composite as the construction material for high performance bipolar plates of fuel cells. MPC with partial replacement of fly ash was employed as the binding matrix. Some carbon-based materials, such as graphite, carbon black, carbon fiber, and multi-walled carbon nanotubes were used to construct the conductive phase. A simple hot-press process was applied to produce the composite. The formula and the structure of the composite was modified and adjusted to optimize the properties of the composite to meet the US DOE 2015 technical targets, including …

Finite Element Modeling Of Delamination Damage In Carbon Fiber Laminates Subject To Low-Velocity Impact And Comparison With Experimental Impact Tests Using Nondestructive Vibrothermography Evaluation, George Rodriguez Iv

Master's Theses

Carbon fiber reinforced composites are utilized in many design applications where high strength, low weight, and/or high stiffness are required. While composite materials can provide high strength and stiffness-to-weight ratios, they are also more complicated to analyze due to their inhomogeneous nature. One important failure mode of composite structures is delamination. This failure mode is common when composite laminates are subject to impact loading.

Various finite element methods for analyzing delamination exist. In this research, a modeling strategy based on contact tiebreak definitions in LS-DYNA^®was used. A finite element model of a low-velocity impact event was created to …

Effect Of Structural Variations On Thermal Deformation Of Single Curvature Composite Sandwich Panels, Brady C. Lotz

Mechanical and Aerospace Engineering Theses

Composite structures cured at a high temperature in a contoured female mold have a tendency to deform or spring-in when brought down to room temperature from cure temperature. This thesis investigates the effects of various structural parameters on the spring-in of the curved shape of a composite sandwich panel due to thermal deformation. A finite element model of a single curved composite sandwich panel is developed using 3D shell elements and validated against other published articles and classical lamination theory. Using a control structure of AS4/3501-6 carbon/epoxy with half inch Nomex honeycomb core with a layup of [0°/90°/0°/90°/Core/90°/0°/90°/0°]T, structural parameters …

Mens Doped Adhesive And Influence On Fracture Toughness, Kao Z. Yang

FIU Electronic Theses and Dissertations

Composites are in high demand; however, fasteners are often required for joining process and can reduce their advantages. One solution is adhesive bonding, but uncertainty exists regarding long term durability and the ability to interrogate bonds noninvasively. One potential solution to qualify bond integrity over its service life is to dope an adhesive with magneto-electric nanoparticles (MENs). MENs can yield output magnetic signatures that are influenced by bond quality and damage state. In this study, adhesives have been doped with MENs prior to bonding at 1% volume concentration. For optimum implementation, this health monitoring system should be evaluated for effects …

Modified Yttrium Hydroxide/Mc Nylon Nanocomposites And Scaling Effects In Multilayer Polyethylene Films, Jia Chen

USF Tampa Graduate Theses and Dissertations

In this thesis, monomer casting (MC) nylon was synthesized. MC nylon could replace nonferrous metals in certain applications, including gears, wheels, and other moving parts. However, compared with metals, MC nylon products have poor strength and stiffness, and crack easily, especially at low temperatures. In addition, the dimensional stability of MC nylon is poor, especially in the large casting nylon products, causing significant internal stresses due to shrinkage. Thus, MC nylon cracks easily when cast and molded. The yttrium hydroxide particles were modified by stearic acid and dispersed in the caprolactam. The polymerization time was short due to fast anionic …

Effect Of Low Velocity Impact On The Vibrational Behavior Of A Composite Wing, Richard M. De Luna

Master's Theses

Impact strength is one of the most important structural properties for a designer to consider, but it is often the most difficult to quantify or measure. A major concern for composite structures in the field is the effect of foreign objects striking composites because the damage is often undetectable by visual inspection. The objective for this study was to determine the effectiveness of using dynamic testing to identify the existence of damage in a small scale composite wing design. Four different impact locations were tested with three specimens per location for a total of 12 wings manufactured. The different impact …

Dynamic Transverse Debondong Of A Single S-2 Fiber, Stephen E. Levine

Open Access Theses

Fiber reinforced composites are becoming increasingly common due to their high strength to weight ratios as compared to more conventional materials. Along with this increased used comes the need to have a higher level of understanding of the material characteristics. Specifically, the interface between the fiber and matrix is of particular interest. Loss of adhesion at this interface, known as debonding, can greatly decrease material strength. There has been significant research into debdonding phenomena at low strain rates. However, there is still a need for further insight at higher strain rates. In addition, given the opacity of many epoxy resins, …

Oxygen-Free Layer-By-Layer Assembly Of Lithiated Composites On Graphene For Advanced Hydrogen Storage, Guanglin Xia, Yingbin Tan, Xiaowei Chen, Fang Fang, Dalin Sun, Xingguo Li, Zaiping Guo, Xuebin Yu

Australian Institute for Innovative Materials - Papers

A facile hydrogenation-induced self-assembly strategy to synthesize lithium hydride (LiH) nanosheets with a thickness of 2 nm that are uniformly distributed on graphene is reported and designed. Taking advantage of LiH nanosheets with high reactivity and a homogeneous distribution on graphene support as a nanoreactor, the confined chemical synthesis of oxygen-free lithiated composites is effectively and efficiently realized.

On Micro-Buckling Of Unidirectional Fiber-Reinforced Composites By Means Of Computational Micromechanics, Nestor D. Barulich, Luis A. Godoy, Ever J. Barbero

Faculty & Staff Scholarship

Micro-buckling of unidirectional fiber-reinforced composites is investigated in this paper by means of an explicit representation of a geometrically imperfect fiber within the context of kinematical and material non-linear behavior. Two types of fiber imperfections are considered: a helicoidal shape, identified as 3D imperfection; and a sinusoidal plane shape (2D imperfection). Both imperfection models are characterized by a maximum misalignment angle of the fiber with respect to the ideal or perfect configuration, as is usually considered in this field. A total of 816 cases were computed in terms of imperfection type (either 2D or 3D), fiber volume fraction, fiber arrangement …

Finite Element Simulation Of Single-Lap Shear Tests Utilizing The Cohesive Zone Approach, Wilson A. Perez

Honors Undergraduate Theses

Many applications require adhesives with high strength to withstand the exhaustive loads encountered in regular operation. In aerospace applications, advanced adhesives are needed to bond metals, ceramics, and composites under shear loading. The lap shear test is the experiment of choice for evaluating shear strength capabilities of adhesives. Specifically during single-lap shear testing, two overlapping rectangular tabs bonded by a thin adhesive layer are subject to tension. Shear is imposed as a result. Debonding occurs when the shear strength of the adhesive is surpassed by the load applied by the testing mechanism. This research develops a finite element model (FEM) …

Damage Tolerance And Assessment Of Unidirectional Carbon Fiber Composites, Mark David Flores

Open Access Theses & Dissertations

Composites are beginning to be used in a variety of different applications throughout industry. However, certification and damage tolerance is a growing concern in many aerospace and marine applications. Although compression-after-impact have been studied thoroughly, determining a damage tolerance methodology that accurately characterizes the failure of composites has not been established. An experimental investigation was performed to study the effect of stacking sequence, low-velocity impact response, and residual strength due to compression and fatigue. Digital Image Correlation (DIC) captured the strains and deformation of the plate due to compression. Computational investigations integrated non-destructive techniques (C-Scan, X-Ray) to determine the extent …

Mechanical Properties And Tribological Behavior Of Aluminum Matrix Composites Reinforced With In-Situ Alb2 Particles, Linlin Yuan, Jingtao Han, Jing Liu, Zhengyi Jiang

Faculty of Engineering and Information Sciences - Papers: Part A

Aluminum matrix composites (AMCs) reinforced with in-situ AlB₂ particles have been fabricated using a combination of powder metallurgy, hot rolling and solution treatment. The effects of boron content (7 and 12 wt%), hot rolling and heat treatment parameters on the microstructures and mechanical properties of the composites were investigated by means of scanning electron microscopy (SEM), tensile test and micro-hardness measurements. The friction coefficient, wear behavior and scratch morphology of the AMCs and pure aluminum were also studied using scratch tests. The hardness and wear properties are higher in a case of composites when compared to unreinforced matrix material.

Fibre Bragg Grating Sensing Technology For The Evaluation Of Physical Properties Of Dental Resin Composites, Ginu Rajan, Paul Shouha, Ayman Ellakwa, Jiangtao Xi, Gangadhara B. Prusty

Faculty of Engineering and Information Sciences - Papers: Part A

The characterization of the physical properties of dental resin composites is fraught with difficulties relating to significant intra and inter test parameter variabilities and is relatively time consuming and expensive. The main aim of this study was to evaluate whether optical fibre Brag grating (FBG) sensing system may become a viable tool to study dental material characteristics. Of particular focus was the potential for the system to demonstrate a multi parameter all-in-one feature. A miniature FBG was embedded in six different dental resin composites and employed as a sensor to evaluate linear polymerization shrinkage, thermal expansion and water sorption. This …

Fabrication And Testing Of Cfrp Composites With Embedded Piezoelectric Particles For Temperature Sensing And Energy Harvesting, Emilio Tarango Valles

Open Access Theses & Dissertations

As a part of this world's continuous evolution and technological advancements, smart materials and functional composites have become an attractive topic. In many cases, these new functional composites are replacing the traditional engineering material due to their customizable mechanical properties. This Thesis analyzes and demonstrates the signal response, sensing capabilities and structural properties from Carbon/Glass Fiber Reinforced Plastic Composites (CFRP) with embedded Lead Zirconate Titanate Particles (PZT). The added PZT particles function as actuators, giving the composites a functionality. The PZT quantity inside each composite was variated to study better and characterize the mechanical and electrical properties; the variations were …