| Microstructural Influences on Very High Cycle Fatigue Crack Initiation in Ti-6246 (PREPRINT) |
Apr-2008 |
24 pages |
| Authors:
C J Szczepanski; S K Jha; J M Larsen; J W Jones; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS AND MANUFACTURING DIRECTORATE
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 | The fatigue behavior of an alpha + beta titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, has been characterized in the very high cycle fatigue (VHCF) regime using ultrasonic fatigue (20 kHz) techniques. Stress levels of 40 to 60% of the yield strength of this alloy have been examined. Fatigue lifetimes in the range of 10 (to the 6th) to 10 (to the 9th) cycles are observed and fatigue cracks initiate from both surface and ... |
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| Detection of Cracks in Aluminum Structure Beneath Inconel Repair Bushings |
Apr-2008 |
33 pages |
| Authors:
Richard Harrison; Yushi Sun; Kenneth J LaCivita; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH
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| Modeling Interfaces Through an Extension of Continuum Mechanics to the Nanoscale with Application to Fracture and Debonding of Composites |
31 MAR 2008 |
5 pages |
| Authors:
Jay R. Walton; Tsvetanka Sendova; TEXAS A AND M RESEARCH FOUNDATION COLLEGE STATION
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| This report summarizes the progress made in developing the theoretical underpinnings for a new theory of brittle fracture based upon an extension of continuum mechanics to the nanoscale. In contrast to classical fracture theories, the new theory predicts bounded crack tip stresses and strains by including a novel boundary condition arising from the jump momentum balance enforced on fracture surfaces which are modeled as dividing surfaces with excess physical properties ... |
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| Fiber Optic Strain Sensors (FOSS) to Monitor Strains on a Navy Vessel During Operations |
23 NOV 2007 |
12 pages |
| Authors:
Jonathan M. Nichols; Mark Seaver; Stephen T. Trickey; Kenneth C. Scandell; Liming Salvino; NAVAL RESEARCH LAB WASHINGTON DC OPTICAL TECHNIQUES BRANCH
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| This document summarizes the recent deployment of a fiber optic strain sensing (FOSS) system to monitor loads on a Navy Vessel, as requested and authorized by Commander Naval Surface Force, Atlantic. The objectives were to (1) conduct an in-service validation of the technology onboard a U.S. Navy ship and (2) determine contributing influences to recurring cracking of [new] deckplate, as described by the Southeast Regional Maintenance Center (SERMC) Port Engineer. ... |
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| Preparation of Nanoporous Silicon |
OCT 2007 |
22 pages |
| Authors:
Wayne A. Churaman; Luke Currano; ARMY RESEARCH LAB ADELPHI MD SENSORS AND ELECTRON DEVICES DIRECTORATE
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| While research has focused on the optical properties of nanoporous silicon and its use as an isolation material in integrated circuits, there is a great deal to be gained by understanding the formation process of such a versatile material. The structure itself is made up of millions of pores that are formed through an electrochemical wet etch, which results in network clusters of nanoporous material with a surface area on ... |
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| Comparison of Matrix Cracking in High Temperature and Lower Temperature PMCs from Cryogenic Exposure (Preprint) |
MAR 2007 |
11 pages |
| Authors:
Vernon T. Bechel; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH STRUCTURAL MATERIALS BRANCH/NONMETALLIC MATERIALS DIV
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| The behavior of a high temperature carbon/polyimide composite, T650/AFR-PE-4, in a cryogenic environment was studied. The results were compared to results from similar testing of a carbon/epoxy and a carbon/bismaleimide composite to begin to scale the difficulties involved with using high temperature polymer matrix composites (PMCs) in cryogen containers on launch vehicles. T650/AFR-PE-4 developed transverse cracks in all plies after fewer cycles than the carbon/bismaleimide (IM7/5250-4) when each was cycled ... |
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| Stresses and Crack Extension in Multi-Layered Ceramic Composites |
10 JUL 2006 |
18 pages |
| Authors:
Frederick F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| It has been demonstrated, through theory and experiments, that compressive layers arrest large surface and internal cracks to produce a stress below which the material will not fail. This enables the materials to have a Threshold Strength. The stress intensity function, K, was derived for a crack sandwiched between two compressive layers. This function suggests that the threshold strength is proportional to the magnitude of the residual, compressive stress, the ... |
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| Failure Analysis of a Cracked UH-1 Tailboom Former, P/N 205-030-807-97 |
JUN 2006 |
30 pages |
| Authors:
Scott Grendahl; Benjamin Hardisky; Russell Yocum; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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| The U.S. Army Aviation and Missile Command sent the U.S. Army Research Laboratory Weapons and Materials Research Directorate a UH-1 tailboom former (P/N 201030-807-97) from the U.S. Army Kwajalein Atoll Facility (USAKA) in the Marshall Islands for investigation. The component was being investigated due to the presence of cracks observed near bolt hole locations on the part. This component was quality deficient report exhibit number M24H90327. The material utilized to ... |
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| Large Area Instant Crack Detection and Identification Using Magnetic Carpet Probe (Briefing Charts) |
Apr-2006 |
28 pages |
| Authors:
Yushi Sun; Tianhe Ouyang; INNOVATIVE MATERIALS TESTINGS TECHNOLOGIES INC AMES IA
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| Comparative Analysis of Three Fretting Fatigue Fixtures (Preprint) |
FEB 2006 |
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| Authors:
Patrick J. Golden; Alisha L. Hutson; Bence B. Bartha; Theodore Nicholas; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS MANUFACTURING DIR/SYSTEMS SUPPORT DIV
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 | Three fixtures for conducting laboratory fretting fatigue tests are described and their respective testing methods and the results of the analysis are compared. Each of these fixtures has been used to investigate the effects of various parameters of interest in fretting fatigue. These fixtures include a unique apparatus in which all load applied to the specimen is transferred to the fretting pads, an apparatus similar to many found in the ... |
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| Synchrotron Based X-Ray Strain Mapping in Fatigued Materials Subjected to Overloading |
2006 |
11 pages |
| Authors:
Thomas Tsakalakos; Mark C. Croft; Z Zhong; R. Holtz; K. Sadananda; RUTGERS - THE STATE UNIV NEW BRUNSWICK NJ
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| The application of high-resolution strain mapping in large engineering samples with both high-spatial and strain resolution is reviewed in this report using high- energy photons between 100 and 300 KeV on beam line X17B1 of Brookhaven National Laboratory. This was achieved by using Energy Dispersive X-ray Diffraction (EDXRD) methods and synchrotron radiation for the nondestructive measurement of residual stresses in engineering components. Examples of residual stresses profiles will be presented ... |
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| Multi-Scale Approach to Investigate the Tensile and Fracture Behavior of Nano Composite Materials |
SEP 2005 |
15 pages |
| Authors:
Chi T. Liu; AIR FORCE RESEARCH LAB EDWARDS AFB CA SPACE AND MISSILE PROPULSION DIV
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| This report covers results addressing multi-scale measurements of deformation, strain, and failure behavior in particulate composites containing nano size particles. In addition, techniques are developed, based on multi-scale modeling approaches, to model particles interaction, damage initiation and evolution processes, and constitutive and crack growth behavior in particulate composites. The program's basic approach involves a blend of numerical and experimental studies. The results of these studies are evaluated and discussed. |
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| Comparison of Mechanical Suppression by Shot Peening and Low Plasticity Burnishing to Mitigate SCC and Corrosion Fatigue Failures in 300M Landing Gear Steel |
SEP 2005 |
7 pages |
| Authors:
N. Jayaraman; P. Prevey; Neal Ontko; Michael Shepard; Robert Ware; Jack Coate; LAMBDA RESEARCH CINCINNATI OH
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| 300M steel is widely used in aircraft landing gear because of its unique combination of strength and fracture toughness, but is vulnerable to foreign object damage (FOD), corrosion fatigue, and stress corrosion cracking (SCC) failures with potentially catastrophic consequences. The fatigue, corrosion fatigue in salt water, and SCC performance of LPB processed 300M steel was compared with shot peened (SP) and low stress ground (LSG) conditions. LPB, with and without ... |
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| Numerical Simulation of Hydrogen Assisted Cracking in Supermartensitic Stainless Steel Welds |
27 JAN 2005 |
223 pages |
| Authors:
Ekkarut Viyanit; UNIVERSITAET DER BUNDESWEHR HAMBURG (GERMANY) FACHBEREICH MASCHINENBAU
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| Replacement of expensive duplex stainless steel and conventional carbon steel by a new generation of supermartensitic stainless steel has been taken into account since the last decade in order to meet the technical-economical challenge for transportation flowlines of unprocessed oil and gas products in offshore technology. Supermartensitic stainless steels can provide appropriate material properties, such as: improved strength-to-weight ratio, enhanced useful corrosion resistance, as well as application at relatively low ... |
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| Development of a Physically-Based Methodology for Predicting Material Variability in Fatigue Crack Initiation and Growth Response |
DEC 2004 |
30 pages |
| Authors:
Kwai S. Chan; SOUTHWEST RESEARCH INST SAN ANTONIO TX
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| The report summarizes the results of an interdisciplinary program aimed at developing a computational methodology for treat material variability in the fatigue crack initiation and growth responses of aerospace structural alloys. In this three-year program, physics-based fatigue crack initiation and growth models were developed and integrated into a probabilistic micromechanical code for treating fatigue life variability resulting from material variations. Dubbed MicroFaVa (Micromechanical Fatigue Variability), the code is based on ... |
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| The Influence of Surface Enhancement by Low Plasticity Burnishing on the Corrosion Fatigue Performance of AA7075-T6 |
SEP 2004 |
9 pages |
| Authors:
Paul S. Prevey; John T. Cammett; LAMBDA RESEARCH CINCINNATI OH
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| Conventional approaches to mitigate corrosion related failure mechanisms in aircraft usually involve isolation from the corrosive environment via protective coatings, alloy substitution, or modifications in design to reduce stresses. This paper describes an alternate approach employing surface enhancement by low plasticity burnishing (LPB) to eliminate or reduce the surface tensile stresses necessary for corrosion fatigue failure in AA7075-T6, without alteration of environment, material or component design. The restoration of fatigue ... |
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| Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials |
AUG 2004 |
15 pages |
| Authors:
Dongming Zhu; Dennis S. Fox; Robert A. Miller; Louis J. Ghosn; Sreeramesh Kalluri; NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH GLENN RESEARCH CENTER
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| The development of advanced high performance constant-volume- combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in ... |
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| Mitigation of SCC and Corrosion Fatigue Failures in 300M Landing Gear Steel Using Mechanical Suppression |
AUG 2004 |
13 pages |
| Authors:
Paul S. Prevey; N. Jayaraman; Neal Ontko; Michael Shepard; Robert Ware; Jack Coate; LAMBDA RESEARCH CINCINNATI OH
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| 300M steel is widely used in landing gear because of its unique combination of ultrahigh strength with high fracture toughness. However, 300M is vulnerable to both corrosion fatigue and stress corrosion cracking (SCC) failures with catastrophic consequences for aircraft landing gear. Plating and shot peening surface treatments currently used to extend life are only partly effective. A surface treatment is needed that will mitigate foreign object damage (FOD), corrosion fatigue ... |
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| A Photoelastic Study of Cracking in Motor Grain Models |
21 MAY 2004 |
11 pages |
| Authors:
C. W. Smith; J. D. Hansen; VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF ENGINEERING SCIENCE AND MECHANICS
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| By capitalizing on observed similarities between the cracked finned model and a cracked cylinder when placing the fin top at the inner edge of the cylinder, estimates were made by assuming a plane strain solution for the finned model in finite length models. Based upon the aforementioned limited results, use of a modified plane strain solution appears to yield a slightly conservative prediction for long shallow cracks to significantly conservative ... |
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| Dynamic Cracking and Energy Absorption in Laminates Containing Through- Thickness Reinforcement |
FEB 2004 |
177 pages |
| Authors:
Brian N. Cox; Sridhar Narayanaswamy; ROCKWELL SCIENTIFIC CO THOUSAND OAKS CA
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| Inertial effects in the mechanism of fiber pullout were examined, with emphasis on how the rate of propagation of stress waves along the fiber, and thence the pullout dynamics, are governed by friction and the propagation of companion waves excited in the matrix. The frictional sliding between the fiber and the matrix is described by a constant interfacial friction stress, the sign of which depends on the relative particle velocity ... |
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| Environmentally Assisted Cracking: Concerns for Cadmium Replacement |
DEC 2003 |
20 pages |
| Authors:
Scott M. Grendahl; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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| Recently, cadmium replacement has become the topic of an Environmental Security Technology Certification Program. As a direct result of this program, replacement coating systems will be developed and scrutinized. A fundamental starting point for corrosion-resistant coatings development work consists of a target for the overall chemical potential (galvanic series) and pH of the coating system and the substrate. This work developed the data necessary to determine the target for several ... |
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| Hydrogen Assisted Cracking of High Strength Alloys |
AUG 2003 |
195 pages |
| Authors:
Richard P. Gangloff; ALUMINUM CO OF AMERICA ALCOA CENTER PA ALCOA TECHNICAL CENTER
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| Two important advances over the past 40 years enable the optimization and management of the structural integrity of components in high performance applications. First, the solid mechanics conununity established linear elastic fracture mechanics as the premier framework for modeling the damage tolerance of fracture critical components (Irwin and Wells, 1997; Paris, 1998). Second, materials scientists developed metals with outstanding balances of high tensile strength and high fracture toughness (Garrison, 1990; ... |
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| Nondestructive Evaluation (NDE) Technology Initiatives Program (NTIP). Delivery Order 0030: Magnetoresistive Sensors for Eddy Current Imaging Nondestructive Evaluation (NDE) |
JUL 2003 |
25 pages |
| Authors:
Raymond D. Rempt; BOEING CO SEATTLE WA PHANTOM WORKS
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| Development and performance of a 64-element imaging array for use in eddy current NDE for aircraft using anisotropic magnetoresistive sensors (AMR) is described and discussed. Among the design issues are flaw field modeling, excitation current configuration, and orientation and configuration of the sensors themselves. The array can rapidly find cracks of the order of 0.2 inch under 0.3 inch or more of metal. This is a good improvement compared to ... |
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| Environmentally Assisted Cracking Properties of AA7249 Extrusions for Aerospace Applications |
02 MAY 2003 |
64 pages |
| Authors:
Kristen L. Deffenbaugh; NAVAL ACADEMY ANNAPOLIS MD
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| The Development of new military aerospace platforms is costly and time-consuming. Therefore, it is important that current platforms maximize their service lifetime. Exposure to environmental elements, particularly seawater, is especially troublesome to the Navy because it shortens required aircraft lifetime. The P-3C is an example of a versatile aircraft whose lifetime has been extended to the point that environmental attacks is now becoming a significant concern. Structural components in the ... |
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| Dwell-Time Fatigue Crack Growth in Ni-Base Superalloys |
APR 2003 |
55 pages |
| Authors:
Ashok Saxena; Kip Findley; DAYTON UNIV OH RESEARCH INST
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| The state-of-the-art dwell-time fatigue crack growth models applicable to materials systems such as Waspaloy, Rene'95, Rene'88 and IN 100 were critically assessed. The review included models based on linear elastic fracture mechanics (LEFM) and those based on time dependent fracture mechanics (TDFM). The pertinent creep deformation and time and cycle dependent crack growth rate data on these materials were also collected to enable the evaluation of these models and for ... |
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| Fracture Mechanics and Service Life Prediction Research |
AUG 2002 |
27 pages |
| Authors:
C. T. Liu; AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIRECTORATE WEST
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| The goal of this program is to develop a basis for developing advanced crack growth and service life prediction technologies for predicting the service life of solid rocket motors. The objectives of this program are to: (1) gain a fundamental understanding of fracture and crack growth behavior in solid rocket motors; (2) investigate the effects of damage, material nonlinearity, pressure, and loading rate on crack growth behavior in a solid ... |
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| Crack Detection for Aerospace Quality Spur Gears |
APR 2002 |
15 pages |
| Authors:
Harry J. Decker; ARMY RESEARCH LAB CLEVELAND OH*
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| Health and Usage Monitoring System research and development involves analysis of the vibration signals produced by a gearbox throughout its life. There are two major advantages of knowing the actual lifetime of a gearbox component: safety and cost. In this report, a technique is proposed to help extract the critical data and present it in a manner that can be easy to understand. The key feature of the technique is ... |
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| Gear Crack Detection Using Tooth Analysis |
APR 2002 |
15 pages |
| Authors:
Harry J. Decker; ARMY RESEARCH LAB CLEVELAND OH*
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| Gear cracks are typically difficult to diagnose with sufficient warning time. Significant damage must he present before algorithms detect the damage. A new feature extraction and two new detection techniques are proposed. The time synchronous averaging concept was extended from revolution-based to tooth engagement-based. The detection techniques are based on statistical comparisons among the averages for the individual teeth. These techniques were applied to a series of three seeded fault ... |
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| Brittle to Ductile Transition in Cleavage Fracture of Alpha-Iron: Experiments and Modeling of Mechanisms |
15 FEB 2002 |
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| Authors:
Ali S. Argon; MASSACHUSETTS INST OF TECH CAMBRIDGE
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| In this research the mechanisms of the brittle to dud tile transition of fracture initiated primarily by crack tip processes under both quasi-static as well as dynamic conditions was studied experimentally, and mechanistically modeled. Additional experiments and modeling included the role of grain boundaries in resisting cleavage cracking among grains in Fe-3%Si alloy, also associated with modeling. |
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| Determination of Strain Fields at the Nanometer Scale with Applications to MEMS Design and Micromechanics |
FEB 2002 |
11 pages |
| Authors:
Wolfgang G. Knauss; Ioannis Chasiotis; CALIFORNIA INST OF TECH PASADENA GRADUATE AERONAUTICAL LABS
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| This project focused on the determination of mechanical properties of thin films manufactured by polycrystalline silicon using the surface micromachining method. In addition to the measurement of mechanical properties by using an Atomic Force Microscope (AFM) or a Scanning Tunneling Microscope (STM) with the aid of the Digital Image Correlation Method (DIC), several other aspects of fracture behavior were addressed, including the effects of surface roughness and of notches to ... |
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| Smart Patches for Monitoring Fatigue Crack Growth in Aircraft Structures |
30 NOV 2001 |
30 pages |
| Authors:
Jeong-Beom Ihn; Fu-Kuo Chang; STANFORD UNIV CA DEPT OF AERONAUTICS AND ASTRONAUTICS
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| A built-in cost-effective diagnostic system for monitoring crack growth in aircraft structures was developed, particularly for riveted fuselage joints and cracked aircraft parts with composite bonded patches. Different smart patch designs for crack growth monitoring at fuselage lab joints and cracked parts with composite bonded patches were developed and integrated with the corresponding aircraft parts. Using the diagnostic software, pre-selected diagnostic signals are propagated from a designated piezoelectric actuator to ... |
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| Development of Innovative Nondestructive Evaluation Technologies for the Inspection of Cracking and Corrosion Under Coatings |
NOV 2001 |
116 pages |
| Authors:
Kirsten G. Lipetzky; Michele R. Novack; Ignacio Perez; William R. Davis; NAVAL SURFACE WARFARE CENTER CARDEROCK DIV BETHESDA MD
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| Three different innovative nondestructive evaluation technologies were developed and evaluated for the ability to detect fatigue cracks and corrosion hidden under painted aluminum panels. The three technologies included real-time ultrasound imaging, thermal imaging, and near-field microwave imaging. With each of these nondestructive inspection methods, subtasks were performed in order to optimize each methodology. |
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| Failure Beneath Cannon Thermal Barrier Coatings by Hydrogen Cracking; Mechanisms and Modeling |
SEP 2001 |
23 pages |
| Authors:
John H. Underwood; Gregory N. Viglante; Edward Troiano; ARMY ARMAMENT RESEARCH DEVELOPMENT AND ENGINEERING CENTER WATERVLIET NY BENET LABS
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| Army experience with hydrogen cracking failures of cannons is described, including extensive testing of high-strength steel and nickel-iron base alloys to address the failures. Cracking of cannon pressure vessel steels just under bore thermal barrier coatings is now common, and can be explained by the combined action of hydrogen-bearing combustion gases and thermally induced tensile residual stresses. Above-yield transient thermal compression and resultant residual tension stresses beneath the coating are ... |
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| High-Temperature Fatigue Cracking Mechanisms |
31 AUG 2001 |
100 pages |
| Authors:
Keh-Minn Chang; Bernard Cooper; Bruce Kang; WEST VIRGINIA UNIV MORGANTOWN
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| The objective of this research is to develop a comprehensive understanding of high-temperature fatigue cracking mechanisms in various high- strength superalloys. The alloying effects on fatigue cracking resistance will be studied through a multi-disciplinary effort, which combines metallurgy, micro-mechanics, finite element analysis, and material physics. |
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| Experiences and Modeling of Hydrogen Cracking in a Thick-Walled Pressure Vessel |
AUG 2001 |
21 pages |
| Authors:
Edward Troiano; G. N. Vigilante; John H. Underwood; ARMY ARMAMENT RESEARCH DEVELOPMENT AND ENGINEERING CENTER WATERVLIET NY BENET LABS
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| Hydrogen cracking associated with armament structures has become more prevalent in recent times. Recent work by Troiano et al. has clearly shown that the utilization of specific barrier coatings, such as nickel, can impede the absorption of hydrogen and retard hydrogen-induced cracking. In this work, a thick-walled, autofrettaged pressure vessel was manufactured from ASTM A723 Grade 2 steel and heat treated to a yield strength of 1170 MPa. An outside ... |
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| Thermographic Assessment of the Heat Dissipation Associated with Fatigue Crack Growth in Mild Steel |
AUG 2001 |
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| Authors:
N. Rajic; DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION VICTORIA (AUSTRALIA) AERONAUTICAL AND MARITIME RESEARCH LAB
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| This report examines the feasibility of predicting rates of crack growth in mild steel based on an evaluation of the crack tip dissipated energy A numerical scheme is developed to provide a basis for the computation of dissipated power from measurements of temperature acquired using remote infrared detection. An experimental study is then described where measurements of crack- growth rate in mild-steel coupons exposed to constant amplitude cyclic loading are ... |
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| Reliable Ceramic Structural Composites Designed with Threshold Strength |
30 APR 2001 |
10 pages |
| Authors:
M. P. Rao; J. Roedel; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| A stress intensity (K) function describing the extension of a crack through bounding compressive layers has been experimentally verified using two methods. For one method the crack length was measured using a replicating technique; in the other, the crack length was continuously measured in-situ with an optical microscope during loading. In both, cracks were observed to propagate in a stable, nearly straight path across the compressive layer with increasing applied ... |
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| Reliable Ceramic Structural Composites Designed with a Threshold Strength |
30 APR 2001 |
19 pages |
| Authors:
Fred F. Lange; M. P. Rao; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Compressive layers, placed within a laminate, can arrest cracks. With an increasing applied stress, the arrested crack can propagate through the compressive layer. These phenomena produce a material with a threshold strength, i.e., failure can not occur below a critical stress. A previously reported stress intensity function describes different variables, e.g., magnitude of compressive stress, thickness of compressive layer, distance between compressive layers, that govern the threshold strength. Laminar composites ... |
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| Reliable Ceramic Structural Composites Designed with a Threshold Strength |
30 APR 2001 |
22 pages |
| Authors:
Fred F. Lange; Kais Hbaieb; Robert M. McMeeking; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Finite element analysis was carried out to predict the threshold strength of a laminar ceramics loaded parallel to the layers. These materials are composed of alternate layers of two different ceramics in which residual stress is generated. Strength limiting cracks are trapped by the compressive layers and require a minimum (threshold) applied stress to cause them to fail the laminated ceramic. The calculations were utilized to study the influence of ... |
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| Dynamic Cracking and Energy Absorption in Laminates Containing Through- Thickness Reinforcement |
18 APR 2001 |
102 pages |
| Authors:
B. N. Cox; S. Narayanaswamy; ROCKWELL INTERNATIONAL CORP THOUSAND OAKS CA SCIENCE CENTER
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| We report several fundamental results in the delamination resistance of through-thickness reinforced structures under dynamic load conditions. The main results are: (1) An elaborate micromechanical model shows how a bridging tow should behave if it is initially inclined to the fracture plane and subject to mixed mode quasistatic loading (2) A bridging law for fiber reinforced composites under dynamic crack propagation conditions has been derived. INertial effects in the mechanism ... |
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| Crack Growth Data Collection and Reduction Methodology Survey |
18 APR 2001 |
8 pages |
| Authors:
T. C. Miller; AIR FORCE RESEARCH LAB EDWARDS AFB CA SPACE AND MISSILE PROPULSION DIV
|
| Engineers responsible for predicting solid rocket motor performance and ensuring reliability know that during manufacture, transport, and storage of motors, cracks may appear in the propellant that threaten this reliability. when they discover cracks, engineers use fracture mechanics principles to assess the crack stability. Structural analysis shows the critical loads for the cracked motor, and testing of specimens determines the tendency of the material toward crack growth initiation, as well ... |
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| Nondestructive Three-Dimensional Microtexture/Strain Quantification in Al-Li 2090 |
APR 2001 |
4 pages |
| Authors:
Stuart R. Stock; GEORGIA INST OF TECH ATLANTA SCHOOL OFMATERIALS ENGINEERING
|
| Micro- and meso-textures" roles in defining fatigue crack path in Al- Li 2090 T8E41 compact tension samples was the central focus of the research. Near-single crystal volumes up to 0.4 mm x 1 mm x 2 mm, i. e. stacks of five or more adajacent, pancake-shaped grains, comprise over 40 vols of the center portions of 2090 plates; two other Al alloys showed little to near-single crystal volumes. The synchrotron ... |
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| Crack Growth Rates in a Propellant Under Various Conditions |
16 MAR 2001 |
10 pages |
| Authors:
T. C. Miller; AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIRECTORATE WEST
|
| Cracks may form in a solid rocket propellant during the manufacture, handling, storage, or use of the solid rocket motor. However, even after the formation of these cracks, the motor may still be usable, because the cracks may not grow under anticipated loads or may grow slowly enough to avoid catastrophic consequences before service life ends. This study attempts to answer two key questions about cracks in solid propellant: (1) ... |
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| Cracking of a Homogeneous Half Plane Due to Sliding Contact |
MAR 2001 |
85 pages |
| Authors:
Fazil Erdogan; Serkan Dag; LEHIGH UNIV BETHLEHEM PA
|
| In this report the initiation and subcritical growth of surface cracks in homogeneous materials due to sliding contact are considered The load is applied through a rigid stamp with an arbitrary profile. The problem is formulated and solved under the assumptions of plane elasticity and Coulomb friction. The stress state on the surface of the half plane is analyzed in the absence of any cracks in order to determine the ... |
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| The Collinear Crack Problem in a Graded Medium |
MAR 2001 |
48 pages |
| Authors:
Murat Ozturk; Fazil Erdogan; LEHIGH UNIV BETHLEHEM PA
|
| The collinear crack problem in an inhomogeneous orthotropic medium is considered under Mode I plane strain or plane stress loading conditions. It is shown that by introducing certain averaged orthotropy parameters, aside from a scaling parameter the results become only weakly dependent on the orthotropy constants. The main results of the study consist of the stress intensity factors at various crack tips as influenced by the material inhomogeneity parameter and ... |
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| Crack Problems in Graded Coatings |
MAR 2001 |
52 pages |
| Authors:
Bora Yildirim; Fazil Erdogan; LEHIGH UNIV BETHLEHEM PA
|
| In this report a two-dimensional finite element technique is developed to study various mechanical, thermal and fracture mechanics problems encountered in the failure analysis of thermal barrier coatings. The system considered consists of the substrate, bond coat, thermally grown oxide and the top coat. The fracture problems studied include edge debonding, surface cracking, T-shaped cracks and periodic debond cracks along the bond coat / thermally grown oxide interface. The results ... |
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| Cracking of a Graded Half Plane Due to Sliding Contact |
MAR 2001 |
95 pages |
| Authors:
Frazil Erdogan; Serkan Dag; LEHIGH UNIV BETHLEHEM PA
|
| In this report the initiation and subcritical growth of surface cracks in graded materials due to sliding contact are considered. After a brief introduction the general coupled crack/contact problem for a semi-infinite graded medium subjected to a sliding rigid stamp of arbitrary profile is formulated. Solving the problem in the absence of any cracks, the complete stress state on the surface of the medium is evaluated and critical stress that ... |
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| Micro-Raman Scattering From Hexagonal GaN, AlN, and AlxGa1-xN Grown on (111) Oriented Silicon: Stress Mapping of Cracks |
2001 |
7 pages |
| Authors:
C. Ramkumar; T. Prokofyeva; M. Seon; M. Holtz; K. Choi; J. Yun; S. A. Nikishin; H. Temkin; TEXAS TECH UNIV LUBBOCK DEPT OF ELECTRICAL ENGINEERING
|
| We report post-growth micro-Raman stress mapping of cracks in GaN, AlN, and AlxGa1-xN grown on (111) oriented silicon. Cracks with an average spacing of ~ 100 mum are observed. These cracks are categorized into two types. The first type of crack propagates through the epilayer, and several microns deep into the substrate and is observed in all the samples investigated. The second type cracks epilayer only and is observed only ... |
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| The Surface Crack Problem for a Functionally Graded Coating Bonded to a Homogeneous Layer |
OCT 2000 |
267 pages |
| Authors:
Fazil Erdogan; Matheendra Kasmaklar; LEHIGH UNIV BETHLEHEM PA
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| In the continuing search for materials which can withstand the grueling requirements of modem day applications, Functionally Graded Materials (FGMs) seem to be a promising alternative to conventional materials. These nonhomogeneous materials offer better interfacial properties by improving bond strength and reducing thermal mismatch. Before putting these materials into application, an important step in the design of FGMs is the stress analysis and fracture characterization. The fracture performance of FGM ... |
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| Damage Analysis for Mixed Mode Crack Initiation |
JUN 2000 |
17 pages |
| Authors:
Y. Wei; C. L. Chow; C. T. Liu; AIR FORCE RESEARCH LAB EDWARDS AFB CA SPACE AND MISSILE PROPULSION DIV
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| The paper presents a numerical simulation for mixed mode crack initiation based on the concepts of damage mechanics. A model with two scalar damage variables is introduced for characterization of damage in a material element. Then a tangent modulus tensor is derived for damage-coupled constitutive equations. A failure criterion is developed with the concept of damage accumulation not only to identify the location of damaged element with the crack initiation ... |
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Reports by Keyword(s)
*CRACKING_FRACTURING_
