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Articles 91 - 103 of 103
Full-Text Articles in Mechanics of Materials
An Investigation Of Graphite Peek Composite Under Compression With A Centrally Located Circular Discontinuity, Benjamin Wham Ii
An Investigation Of Graphite Peek Composite Under Compression With A Centrally Located Circular Discontinuity, Benjamin Wham Ii
Theses and Dissertations
The purpose of this thesis was to determine (both experimentally and analytically) the initiation and progression of failure, stress-strain response, and the failure loads of Graphite/Polyetheretherketone (Gr/PEEK) laminates, incorporating a centrally located circular discontinuity, loading in axial compression at room temperature. The laminates studied were (0°)16,(90°)16, (0°/90°)4S, (± 45°)4S, and (0°/±45°/90°)2S. The specimens were loaded within a Boeing Open Hole Compression Fixture. The micromechanical failure modes were identified using a Scanning Electron Microscope. The analytical progression of failure was predicted using a nonlinear finite element code developed by Dr. R.S. …
Computational And Experimental Investigation Into Fracture Of Brittle Fiber - Brittle Matrix Composite Systems, James P. Solti
Computational And Experimental Investigation Into Fracture Of Brittle Fiber - Brittle Matrix Composite Systems, James P. Solti
Theses and Dissertations
Experimental and computational analyses provided an improved understanding of quasi-static fracture in model composite systems. Constant displacement compression tests using borosilicate glass double cleavage drilled compression test templates provided qualitative assessments of localized toughening for crack growth near cylindrical inclusions. Large crack-tip stress fields induced interfacial slip and separation prior to arrival of the main crack. Debonding and the proliferation of secondary matrix cracks characterized the role of bridging fibers along weak interfaces. Strong residual normal compressive interfacial stresses diminished the influence of crack-tip stresses; however, slip was still observed. VHS tape and computer enhanced photos record a history of …
Investigation Of Fatigue Behavior In Notched Cross-Ply Titanium Metal Matrix Composite At Elevated Temperature, Robert P. Baker
Investigation Of Fatigue Behavior In Notched Cross-Ply Titanium Metal Matrix Composite At Elevated Temperature, Robert P. Baker
Theses and Dissertations
The objective of this research was to investigate the initiation and progression of damage which develops in notched (0/90)2S SCS-6/Ti-15-3 at elevated temperature. Testing consisted of a monotonic tensile test at 427°C followed by fatigue testing performed under load control with a stress ratio of 0.1 at a frequency of 10 Hz. A crack was defined to have initiated when it had attained a length greater than or equal to 0.124 mm. Crack initiation and progression was monitored by strain and modulus observations and visual inspection via telemicroscope. The cracks were recorded with edge and face replicas. Metallographic and …
Behavior Of A Titanium Matrix Composite Under Quasi-Static Tensile And Compressive Loading, Keith L. Bearden
Behavior Of A Titanium Matrix Composite Under Quasi-Static Tensile And Compressive Loading, Keith L. Bearden
Theses and Dissertations
Quasi-Static tensile and compressive testing was performed on a unidirectional titanium matrix composite. The specific material was SCS-9/β 21S. The initial tensile and compressive modulus for both laminates was the same. The ninety degree laminate had a tensile and compressive modulus of 115.89 GPa. The zero degree laminate had a tensile and compressive modulus of 197.51 GPa. The ninety degree laminate exhibited a three stage stress/strain response in tension. The first stage is completely linearly elastic, however, partial debonding of the fiber from the matrix was observed. This partial debased did not effect the stress/strain response. The second stage is …
Behavior Of A Centrally Notched Cross-Ply And Unidirectional Ceramic Matrix Composite In Tension-Compression Fatigue, William A. Weidenaar
Behavior Of A Centrally Notched Cross-Ply And Unidirectional Ceramic Matrix Composite In Tension-Compression Fatigue, William A. Weidenaar
Theses and Dissertations
Centrally notched (hole), cross-ply, ((0/90)2)s, and unidirectional, (0)8 laminates of Silicon Carbide fiber-reinforced Aluminosilicate glass, SiC/1723, were fatigue tested under tension-compression loading with a load ratio of -1. Damage accumulated continuously for both lay- ups, leading to eventual failure and a reduced fatigue life. Critical damage in the cross-ply consisted of longitudinal cracks in the 90° plies growing and combining with transverse cracks to effectively eliminate the 90° plies' load carrying capability and allowing the specimen to buckle. Critical damage in the unidirectional lay-up consisted of longitudinal cracks which initiated at the shear stress concentration …
Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite Under Tension-Tension And Tension-Compression Loading, Frank A. Opalski
Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite Under Tension-Tension And Tension-Compression Loading, Frank A. Opalski
Theses and Dissertations
A study was conducted which investigated the behavior of a cross-ply [0/90]2S Nicalon/Calcium-Aluminosilicate (Nicalon/CAS) ceramic matrix composite at room temperature under tension-compression fatigue loading. Material behavior and damage was recorded by stress-strain curves, elastic modulus, hysteretic energy density, and acetate replication techniques. Tension-tension fatigue tests at a load ratio R of 0.1 (R = σmin/σmax) were completed which determined that 140 MPa was the maximum stress allowable in which cycle runout (1,000,000 cycles) would occur. Above this value, transverse crack density increased with respect to cycles and failure ultimately occurred. Tension-compression tests were then performed …
Open And Filled Hole Static Tensile Strength Characterization Of Metal Matrix Composite Scs-9/Β21s, Jacob T. Roush
Open And Filled Hole Static Tensile Strength Characterization Of Metal Matrix Composite Scs-9/Β21s, Jacob T. Roush
Theses and Dissertations
SCS-9/β21s has a reduced gauge thickness, in comparison with other metal matrix composites, due to a smaller diameter fiber. This reduced gauge thickness makes it an attractive candidate for the skin of hypersonic vehicles. Tensile testing of (0/90)2s and (O/±45/90)s laminates was performed at room temperature, 482°C, and 650°C. Both notched and unnotched specimens were tested. Notched specimens, open and filled hole, had a width-to-diameter ratio of six. Materials 7075-T6 and Mar-m-246 were used as pins in the filled hole tensile testing. Analytical work was completed to predict material properties, elastic and plastic stress concentration factors, residual stresses, …
Crack Growth Rate Modeling Of A Titanium-Aluminide Alloy Under Thermal-Mechanical Cycling, John J. Pernot
Crack Growth Rate Modeling Of A Titanium-Aluminide Alloy Under Thermal-Mechanical Cycling, John J. Pernot
Theses and Dissertations
In this study, a model is developed to predict crack growth rates in a titanium-aluminide alloy under thermal-mechanical fatigue (TMF). This TMF crack growth rate prediction model, which requires only isothermal data to define its parameters, is distinguished from earlier models in two ways. First, it accounts for mechanical-fatigue and environmental crack growth rate contributions while it also considers a retardation mechanism thought to be caused by creep blunting of the crack tip. This is the first study to account for such a retardation mechanism during TMF. The second uniqueness of the model is that its general form can account …
Failure Characteristics Of Scs-6/Ti-24al-11nb Composite With A Circular Hole At Room And Elevated Temperatures, Joseph E. Overbeck
Failure Characteristics Of Scs-6/Ti-24al-11nb Composite With A Circular Hole At Room And Elevated Temperatures, Joseph E. Overbeck
Theses and Dissertations
Off-axis loading of eight ply, unidirectional specimens with and without a circular hole determined the ultimate tensile strength of SCS-6/Ti- 24A1-11Nb composite at temperatures of 25°C and 650°C and fiber orientations of 0 degrees, 15 degrees, 45 degrees. Longitudinal moduli of the tested orientations compared closely to the rule of mixtures calculated values, and strengths compared closely to those predicted by the Tsai-Wu failure theory. The small diameter hole does not act as a stress concentrator, but merely reduces the material's strength in proportion to area loss. This result differs from those predicted by linear finite element analysis and orthotropic …
Failure Characterization Of A Fiber Reinforced Ceramic Matrix Composite With Circular Holes, Daniel E. Bullock
Failure Characterization Of A Fiber Reinforced Ceramic Matrix Composite With Circular Holes, Daniel E. Bullock
Theses and Dissertations
The purpose of this study was to investigate the performance of a fiber reinforced ceramic matrix composite with circular holes. The specific objectives were to (1) determine the relationship between tensile failure stress and the ratio of hole diameter to specimen width, and (2) to examine the initiation and progression of damage. The ceramic matrix composite used was SiC/ 1723, composed of continuous silicon titanium carbide fibers in an aluminosilicate glass ceramic matrix. Uniaxial tensile tests were performed at room temperature on two different layups; unidirectional [0]8, and [0/90]2s symmetric. Each layup was tested at three diameter-to-width …
Investigation Of Fatigue Damage Mechanisms In A Metal Matrix Composite Under Elevated Temperature, Barry D. Portner
Investigation Of Fatigue Damage Mechanisms In A Metal Matrix Composite Under Elevated Temperature, Barry D. Portner
Theses and Dissertations
This study investigated the fatigue damage initiation and progression in SCS-6/Ti-15-3 under an environment of fatigue loading at isothermal temperature. This program included two parts. First, an 808 Ultimate Tensile Strength system was set up to accommodate testing at two frequencies of 2.0 and 0.0208 cps at a constant temperature of 427° C. Second, at intervals during the load cycle process, the test specimens were characterized by establishing damage parameters based on changing modulus of elasticity, average strain, strain range, and ultimate tensile strength. Damage progression was documented in the form of failure of the fiber-matrix interface, matrix cracking, fiber …
Failure Mechanisms In A Quasi-Isotropic Ceramic Composite Laminate Under Tensile Fatigue Loading, Gregory D. Tracy
Failure Mechanisms In A Quasi-Isotropic Ceramic Composite Laminate Under Tensile Fatigue Loading, Gregory D. Tracy
Theses and Dissertations
A study was conducted to experimentally investigate the tensile fatigue damage mechanisms in a quasi-isotropic ceramic matrix composite (Corning's Nicalon/CASIII). The goals of this study were to (1) develop a grip fixture for a servo-hydraulic MTS test machine and (2) conduct a series of tests with (0/±45/90)s specimens subjected to tensile fatigue loading to study their fatigue damage growth mechanisms. Results showed that when the material was subjected to stresses below 90 MPa, it lasted over 1000000 cycles but when stressed at or above 90 MPa, it failed in less than 1000 cycles.
Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe
Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe
Theses and Dissertations
Metal matrix composites (MMCs) are rapidly becoming strong candidates for high temperature and high stiffness structural applications such as the Advanced Tactical Fighter (ATF). This study systematically investigated the failure modes and associated damage in a cross-ply, [0/90]2s SCS6/Ti-15-3 metal matrix composite under in-phase and out-of-phase thermomechanic fatigue. Initiation and progression of fatigue damage were recorded and correlated to changes in Young's Modulus of the composite material. Experimental results show an internal stabilization of reaction zone size but degradation and separation from constituent materials under extended cyclic thermal loading. Critical to damage were transverse cracks initiating in the 90° …