Engineering Science and Materials Commons^™

Viscoplastic Characterization And Fatigue Modeling Of Titanium Based Metal Matrix Composites, Mark A. Foringer

Theses and Dissertations

Viscoplastic characterization and fatigue modeling of titanium-based metal matrix composites was accomplished by combining a unified viscoplastic theory, a nonlinear micromechanics model, and a linear damage accumulation model. First. Ti 15-3 was characterized using the Bodner-Partom viscoplastic theory. A micromechanics model was then employed in a linear damage accumulation fatigue model to predict the fatigue behavior of titanium based composites. The viscoplastic behavior predictions of the micromechanics model were used to eliminate separately defined time dependent terms in the fatigue model. Also, a new linear damage accumulation model was developed from the fatigue behavior of the composite constituents. Finally, it …

Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite At Elevated Temperature Under Tension-Tension Loading, Craig D. Steiner

Theses and Dissertations

This study investigated the fatigue behavior and damage mechanisms of a [0-90]_4s SiC-MAS ceramic matrix composite under tension-tension loading at two elevated temperatures and two frequencies. Stress and strain hystereses, maximum and minimum strain, and modulus of elasticity were evaluated to characterize the material behavior. Microscopy and fractography were used to evaluate damage progression and mechanisms. Fatigue life was independent of frequency at both temperatures.

Investigation Of Tension-Compression Fatigue Behavior Of A Notched Cross-Ply Metal Matrix Composite At Elevated Temperature, Matthew W. Yocum

Theses and Dissertations

This research extends the existing knowledge of MMC fatigue damage mechanisms by studying the tension-compression fatigue behavior of a notched cross-ply laminate MMC at elevated temperature. A [0-90]_2S SCS-6-Ti-15-3 laminate with a center hole was subjected to tension-compression fatigue at 427 °C (800 °F). Stress and strain data was taken to evaluate macro-mechanic behavior of the material. Microscopy and fractography were performed to characterize the damage on a micro-mechanical level. Crack initiation and progression was monitored using acetate face replicas. Four cracks were found to develop around the periphery of the hole, two of which became dominant and proceeded …

Investigation Into The Behavior Of Geometrically Nonlinear Composite Arches, John C. Bailey

Theses and Dissertations

This research modifies the existing finite element formulation of a potential energy based large deformation and moderate rotation theory. Hermitian shape functions replace the existing linear bending angle interpolations. Negligible differences between the two formulations indicate the underlying kinematics limit the accuracy, not the finite element interpolations. Using the new program, numerous nonlinear arch geometries are modeled to investigate the effects of arc length and thickness variations. Local and global snapping phenomena are captured as well as through the thickness shear driven nonlinearities.

Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite Subjected To Tension-Tension Cycling With Hold Time, Scott A. Grant

Theses and Dissertations

This study was carried out to investigate the elevated temperature behavior of the SiC-MAS5 cross- ply [0-90]_4S ceramic matrix composite manufactured by Corning Inc. to fatigue with loading waveforms that combine the characteristics of stress rupture and high cycle fatigue. The test results were compiled in the form of S-N (cycles to failure), S-T (exposure time versus cycles to failure), S-S (energy exposure versus cycles to failure), normalized modulus degradation, strain progression, and hysteresis loop progression. From the mechanical behavior demonstrated by these curves, relationships between the effect of the environment and loading waveform were developed. In addition, a …

Characterization Of Fatigue Behavior Of 2-D Woven Fabric Reinforced Ceramic Matrix Composite At Elevated Temperature, Daniel J. Groner

Theses and Dissertations

This study investigated the fatigue behavior and associated damage mechanisms in notched and unnotched enhanced Sic-SiC ceramic matrix composite specimens at 1100°C. Stiffness degradation, strain variation, and hysteresis were evaluated to characterize material behavior. Microscopic examination was performed to characterize damage mechanisms. During high cycle-low stress fatigue tests, far less fiber-matrix interface debond was evident than in low cycle-high stress fatigue tests. Notched specimens exhibited minimal stress concentration during monotonic tensile testing and minimal notch sensitivity during fatigue testing. Damage mechanisms were also similar to unnotched.

Investigation Of Tension-Compression Fatigue Behavior Of A Unidirectional Metal Matrix Composite At Elevated Temperature, Darren L. Kraabel

Theses and Dissertations

This study investigated the fatigue behavior in a unidirectional metal matrix composite under tension-compression loading conditions. Stress-strain responses, modulus and strain trends were monitored to characterize damage. Fractography and microscopy were used to characterize failure modes. Fatigue life curves were plotted base on different parameters such as stress and strain. Tension-compression fatigue life was shorter than the obtained under tension-tension fatigue cycling. Creep, observed in tension-tension. fatigue cycling, and the effects of the compressive load on the plastic zone around the crack tip explain shorter life under tension-compression fatigue loading.

Fatigue Behavior Of A Cross-Ply Metal Matrix Composite At Elevated Temperature Under Strain Controlled Mode, Leon B. Dennis

Theses and Dissertations

This research extends the existing knowledge of cross-ply metal matrix composites (MMC) to include fatigue behavior under strain-controlled fully reversed loading. This study investigated fatigue life, failure modes and damage mechanisms of the SCS-6-Ti-15-3, [O-9O]_2s, MMC. The laminate was subjected to fully reversed fatigue at elevated temperature (427° C) at various strain levels. Stress, strain and modulus data were analyzed to characterize the macro-mechanical behavior of the composite. Microscopy and fractography were accomplished to identify and characterize the damage mechanisms at the microscopic level. Failure modes varied according to the maximum applied strain level showing either mixed mode …

Rapid Relaxation Of An Axisymmetric Vortex, Andrew J. Bernoff, Joseph F. Lingevitch

All HMC Faculty Publications and Research

In this paper it is argued that a two‐dimensional axisymmetric large Reynolds number (Re) monopole when perturbed will return to an axisymmetric state on a time scale (Re^1/3) that is much faster than the viscous evolution time scale (Re). It is shown that an arbitrary perturbation can be broken into three pieces; first, an axisymmetric piece corresponding to a slight radial redistribution of vorticity; second, a translational piece which corresponds to a small displacement of the center of the original vortex; and finally, a nonaxisymmetric perturbation which decays on the Re^1/3 time scale due to a shear/diffusion …

Artificial Dielectric Materials : Synthesis And Optical Characterization Of Small Metal Clusters Embedded In Polymeric Matrix, Nazneen Karim Shilpee

Theses

This study is concerned with the fabrication of films made of gold, nickel, and silicon clusters dispersed in a polymeric matrix. The films were fabricated by use of metal or semiconductor sputtering and plasma polymerization of Methyl Methacrylate monomer in a capacitively coupled RF (13.56 MHz) sputtering system. Optical transmittance and optical reflectance were measured as a function of wavelength. The optical absorption of metal or silicon clusters was studied as a function of cluster size. Cluster size and content were determined from Transmission Electron Micrographs (TEM). The absorption band resulting from a plasma resonance in the clusters was found …

Design And Analysis Of Constrained Layer Damping Treatments For Bending And Torsion, Kimberly J. Balkema

Theses and Dissertations

In this dissertation, different aspects of constrained layer damping treatments on beams of various geometries are studied. First, the optimal length of a constrained layer damping treatment mounted on a surface in linear strain is identified as a function of the relative stiffnesses of the damping layers and the non-uniformity of the surface stain. The analysis extends previous work that considered the case of uniform surface strain. Sixth order sandwich beam theory is then modified for use with a rectangular beam covered with a segmented constrained layer damping treatment. Non-dimensional variables are used to simplify the form of the problem. …

An Experimental And Analytical Investigation Of The Iosipescu Shear Test For Composite Materials, Barry Stuart Spigel

Mechanical & Aerospace Engineering Theses & Dissertations

Mechanical properties of composite materials under shear loading are difficult to determine. The Iosipescu Shear test, originally proposed for metals, has in recent years been applied to composites. It has the advantages of small specimen size, simple loading and a reasonably uniform shear stress in the test section.

The purpose of this work is to study the validity of the Iosipescu test method for measuring the shear modulus and shear strength of composites. Finite element analyses indicate that optimum specimen geometry and load locations depend upon the degree of orthotropy of the composite. Test results for a quasi-isotropic graphite/epoxy laminate …

Development Of Vibration And Sensitivity Analysis Capability Using The Theory Of Structural Variations, Ting-Yu Rong

Mechanical & Aerospace Engineering Theses & Dissertations

In the author's previous work entitled "General Theorems of Topological Variations of Elastic Structures and the Method of Topological Variation," 1985, some interesting properties of skeletal structures have been discovered. These properties have been described as five theorems and synthesized as a theory, called the theory of structural variations (TSV). Based upon this theory, an innovative analysis tool, called the structural variation method (SVM), has been derived for static analysis of skeletal structures (one-dimensional finite element systems).

The objective of this dissertation research is to extend TSV and SVM from one-dimensional finite element systems to multi-dimensional ones and from statics …

A Memorable Meeting, February 1994, Fathi Habashi

Fathi Habashi

Decision taken at the Steering Committee Meeting of the International Mineral Processing Congress in San Francisco February 1994 to name the IMPC Award.

Permeability Control Using Polymer Impregnation In Sandy Soil, Mohamed Salah Mohamed Ahmed

Archived Theses and Dissertations

No abstract provided.

Application Of Machine Learning Principles To Modeling Of Nonlinear Dynamic Systems, Murray R. Clark

Journal of the Arkansas Academy of Science

A method for the development of mathematical models for dynamic systems with arbitrary nonlinearities from measured data is described. The method involves the use of neural networks as embedded processors in dynamic system simulation models. The technique is demonstrated through generation of models for anharmonic oscillators described by the Duffing Equation and the Van der Pol Equation from measured input/output data. It is shown that high quality models of these systems can be developed using this technique which are efficient in terms of model size. Using neural networks as embedded processors, accurate models of the Duffing Oscillator and the Van …