40 CFR 63.1568 - What are my requirements for HAP emissions from sulfur recovery units?

Code of Federal Regulations, 2012 CFR

2012-07-01

... emissions from sulfur recovery units? 63.1568 Section 63.1568 Protection of Environment ENVIRONMENTAL... Petroleum Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Catalytic Cracking Units, Catalytic Reforming Units, Sulfur Recovery Units, and Bypass Lines § 63.1568 What...

40 CFR 63.1576 - What records must I keep, in what form, and for how long?

Code of Federal Regulations, 2010 CFR

2010-07-01

... Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Notifications, Reports, and Records... keep records required by Tables 6, 7, 13, and 14 of this subpart (for catalytic cracking units); Tables...

40 CFR 63.1576 - What records must I keep, in what form, and for how long?

Code of Federal Regulations, 2011 CFR

2011-07-01

... Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Notifications, Reports, and Records... keep records required by Tables 6, 7, 13, and 14 of this subpart (for catalytic cracking units); Tables...

Arms Against Illness: Crack Cocaine and Drug Policy in the United States.

PubMed

Watkins; Fullilove; Fullilove

1998-01-01

The emergence of crack cocaine use in the United States during the mid-1980s was one of the most significant public health problems of that era. Crack use contributed to a series of sexually transmitted disease epidemics, to epidemic increases in violent injuries and homicides, and to significant increases in the incidence and prevalence of cocaine addiction. Despite these threats to health and safety, a national public health campaign to counter crack-related morbidity and mortality was never mounted. To the contrary, the strongest response to the crack epidemic has come from the police and the courts. As a result, crack-related crimes have accounted for dramatic increases in the numbers of adolescents and adults imprisoned in the United States. Scarce attention to the public health dimensions of these policies, let alone the human rights implications, has been catastrophic for affected individuals and communities.

Petroleum Refineries (Catalytic Cracking, Catalytic Reforming and Sulfur Recovery Units): National Emission Standards for Hazardous Air Pollutants (NESHAP)

EPA Pesticide Factsheets

learn more about the NESHAP for catalytic cracking and reforming units, as well as sulfur recovery units in petroleum refineries by reading the rule history, rule summary, background information documents, and compliance information

40 CFR Table 8 to Subpart Uuu of... - Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Organic HAP Emission Limits for Catalytic Cracking Units 8 Table 8 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL..., Subpt. UUU, Table 8 Table 8 to Subpart UUU of Part 63—Organic HAP Emission Limits for Catalytic Cracking...

40 CFR Table 8 to Subpart Uuu of... - Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Organic HAP Emission Limits for Catalytic Cracking Units 8 Table 8 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL..., Subpt. UUU, Table 8 Table 8 to Subpart UUU of Part 63—Organic HAP Emission Limits for Catalytic Cracking...

40 CFR Table 8 to Subpart Uuu of... - Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Organic HAP Emission Limits for Catalytic Cracking Units 8 Table 8 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL..., Subpt. UUU, Table 8 Table 8 to Subpart UUU of Part 63—Organic HAP Emission Limits for Catalytic Cracking...

Damage properties simulations of self-healing composites.

PubMed

Chen, Cheng; Ji, Hongwei; Wang, Huaiwen

2013-10-01

Self-healing materials are inspired by biological systems in which damage triggers an autonomic healing response. The damage properties of a self-healing polymer composite were investigated by numerical simulation in this paper. Unit cell models with single-edge centered crack and single-edge off-centered crack were employed to investigate the damage initiation and crack evolution by the extended finite element method (XFEM) modeling. The effect of microcapsule's Young's modulus on composites was investigated. Result indicates the microcapsule's Young's modulus has little effect on the unit cell's carrying capacity. It was found that during the crack propagation process, its direction is attracted toward the microcapsules, which makes it helpful for the microcapsules to be ruptured by the propagating crack fronts resulting in release of the healing agent into the cracks by capillary action.

40 CFR Table 14 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 14 Table 14 to Subpart UUU of Part 63... Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 14 Table 14 to Subpart UUU of Part 63...

40 CFR Table 14 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 14 Table 14 to Subpart UUU of Part 63... Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 14 Table 14 to Subpart UUU of Part 63...

40 CFR Table 7 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Continuous Compliance With Operating Limits for Metal HAP Emissions From Catalytic Cracking Units 7 Table 7 to Subpart UUU of Part 63... Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 7 Table 7 to Subpart UUU of Part 63...

40 CFR Table 7 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Continuous Compliance With Operating Limits for Metal HAP Emissions From Catalytic Cracking Units 7 Table 7 to Subpart UUU of Part 63... Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 7 Table 7 to Subpart UUU of Part 63...

40 CFR Table 11 to Subpart Uuu of... - Requirements for Performance Tests for Organic HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2010 CFR

2010-07-01

...) for Carbon Monoxide (CO) 11 Table 11 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 11 Table 11 to Subpart UUU of Part 63—Requirements for Performance Tests for Organic HAP Emissions...

40 CFR Table 7 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Continuous Compliance With Operating Limits for Metal HAP Emissions From Catalytic Cracking Units 7 Table 7 to Subpart UUU of Part 63... Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 7 Table 7 to Subpart UUU of Part 63...

40 CFR Table 11 to Subpart Uuu of... - Requirements for Performance Tests for Organic HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2011 CFR

2011-07-01

...) for Carbon Monoxide (CO) 11 Table 11 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 11 Table 11 to Subpart UUU of Part 63—Requirements for Performance Tests for Organic HAP Emissions...

40 CFR Table 14 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 14 Table 14 to Subpart UUU of Part 63... Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 14 Table 14 to Subpart UUU of Part 63...

Prevalence and correlates of crack-cocaine injection among young injection drug users in the United States, 1997-1999.

PubMed

Santibanez, Scott S; Garfein, Richard S; Swartzendruber, Andrea; Kerndt, Peter R; Morse, Edward; Ompad, Danielle; Strathdee, Steffanie; Williams, Ian T; Friedman, Samuel R; Ouellet, Lawrence J

2005-03-07

We estimated prevalence and identified correlates of crack-cocaine injection among young injection drug users in the United States. We analyzed data from the second Collaborative Injection Drug Users Study (CIDUS II), a 1997-1999 cohort study of 18-30-year-old, street-recruited injection drug users from six US cities. Crack-cocaine injection was reported by 329 (15%) of 2198 participants. Prevalence varied considerably by site (range, 1.5-28.0%). No participants injected only crack-cocaine. At four sites where crack-cocaine injection prevalence was greater than 10%, recent (past 6 months) crack-cocaine injection was correlated with recent daily injection and sharing of syringes, equipment, and drug solution. Lifetime crack-cocaine injection was correlated with using shooting galleries, initiating others into drug injection, and having serologic evidence of hepatitis B virus and hepatitis C virus infection. Crack-cocaine injection may be a marker for high-risk behaviors that can be used to direct efforts to prevent HIV and other blood-borne viral infections.

40 CFR 60.100 - Applicability, designation of affected facility, and reconstruction.

Code of Federal Regulations, 2013 CFR

2013-07-01

... petroleum refineries: fluid catalytic cracking unit catalyst regenerators, fuel gas combustion devices, and... petroleum refinery. (b) Any fluid catalytic cracking unit catalyst regenerator or fuel gas combustion device... regenerator under paragraph (b) of this section which commences construction, reconstruction, or modification...

40 CFR 60.100 - Applicability, designation of affected facility, and reconstruction.

Code of Federal Regulations, 2014 CFR

2014-07-01

... petroleum refineries: fluid catalytic cracking unit catalyst regenerators, fuel gas combustion devices, and... petroleum refinery. (b) Any fluid catalytic cracking unit catalyst regenerator or fuel gas combustion device... regenerator under paragraph (b) of this section which commences construction, reconstruction, or modification...

40 CFR 63.1082 - What definitions do I need to know?

Code of Federal Regulations, 2010 CFR

2010-07-01

...) National Emission Standards for Ethylene Manufacturing Process Units: Heat Exchange Systems and Waste... resulting from the quench and compression of cracked gas (the cracking furnace effluent) at an ethylene... within an ethylene production unit. Process wastewater is not organic wastes, process fluids, product...

Eight-Year Summary of Fort Irwin, CA, Family Housing Comparison Test: Operation and Maintenance Costs of Manufactured vs. Conventionally Built Units

DTIC Science & Technology

1993-07-01

Ruptured polybutylene pipe from Building 3858, Unit C 77 F20 Longitudinal hair line crack in PB pipe from Building 3802, Unit B 78 F21 Microscopic...of the 200 housing units used national standards in the unit construction which included the use of polybutylene ( PB ) piping. The piping was...in PB Pipe from Building 3802, Unit B Figure F 21: Microscopic View of Longitudinal Hair Line Crack 78 Figure F22: White Coating on Acetld Fitting

40 CFR Table 3 to Subpart Uuu of... - Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units 3 Table 3 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 3 Table 3 to Subpart UUU of Part 63—Continous Monitoring...

40 CFR Table 13 to Subpart Uuu of... - Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 13 Table 13 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 13 Table 13 to Subpart UUU of Part 63—Continuous...

40 CFR Table 13 to Subpart Uuu of... - Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 12 2011-07-01 2009-07-01 true Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 13 Table 13 to Subpart UUU of Part 63 Protection of... Units Pt. 63, Subpt. UUU, Table 13 Table 13 to Subpart UUU of Part 63—Continuous Compliance With Organic...

40 CFR Table 12 to Subpart Uuu of... - Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 12 Table 12 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 12 Table 12 to Subpart UUU of Part 63—Initial Compliance...

40 CFR Table 12 to Subpart Uuu of... - Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 12 2011-07-01 2009-07-01 true Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 12 Table 12 to Subpart UUU of Part 63 Protection of... Units Pt. 63, Subpt. UUU, Table 12 Table 12 to Subpart UUU of Part 63—Initial Compliance With Organic...

40 CFR Table 12 to Subpart Uuu of... - Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 12 2010-07-01 2010-07-01 true Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 12 Table 12 to Subpart UUU of Part 63 Protection of... Units Pt. 63, Subpt. UUU, Table 12 Table 12 to Subpart UUU of Part 63—Initial Compliance With Organic...

40 CFR Table 2 to Subpart Uuu of... - Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Operating Limits for Metal HAP Emissions From Catalytic Cracking Units 2 Table 2 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 2 Table 2 to Subpart UUU of Part 63—Operating Limits for Metal HAP...

40 CFR Table 13 to Subpart Uuu of... - Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 12 2010-07-01 2010-07-01 true Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 13 Table 13 to Subpart UUU of Part 63 Protection of... Units Pt. 63, Subpt. UUU, Table 13 Table 13 to Subpart UUU of Part 63—Continuous Compliance With Organic...

40 CFR Table 14 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 12 2011-07-01 2009-07-01 true Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 14 Table 14 to Subpart UUU of Part 63... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 14 Table 14 to Subpart UUU of Part 63—Continuous...

40 CFR Table 9 to Subpart Uuu of... - Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 9 Table 9 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 9 Table 9 to Subpart UUU of Part 63—Operating Limits for Organic HAP...

40 CFR Table 13 to Subpart Uuu of... - Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 13 Table 13 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 13 Table 13 to Subpart UUU of Part 63—Continuous...

40 CFR Table 2 to Subpart Uuu of... - Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Operating Limits for Metal HAP Emissions From Catalytic Cracking Units 2 Table 2 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 2 Table 2 to Subpart UUU of Part 63—Operating Limits for Metal HAP...

40 CFR Table 3 to Subpart Uuu of... - Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units 3 Table 3 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 3 Table 3 to Subpart UUU of Part 63—Continous Monitoring...

40 CFR Table 13 to Subpart Uuu of... - Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Continuous Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 13 Table 13 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 13 Table 13 to Subpart UUU of Part 63—Continuous...

40 CFR Table 2 to Subpart Uuu of... - Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Operating Limits for Metal HAP Emissions From Catalytic Cracking Units 2 Table 2 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 2 Table 2 to Subpart UUU of Part 63—Operating Limits for Metal HAP...

40 CFR Table 12 to Subpart Uuu of... - Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 12 Table 12 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 12 Table 12 to Subpart UUU of Part 63—Initial Compliance...

40 CFR Table 9 to Subpart Uuu of... - Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 9 Table 9 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 9 Table 9 to Subpart UUU of Part 63—Operating Limits for Organic HAP...

40 CFR Table 12 to Subpart Uuu of... - Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 12 Table 12 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 12 Table 12 to Subpart UUU of Part 63—Initial Compliance...

40 CFR Table 14 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 12 2010-07-01 2010-07-01 true Continuous Compliance With Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 14 Table 14 to Subpart UUU of Part 63... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 14 Table 14 to Subpart UUU of Part 63—Continuous...

40 CFR Table 3 to Subpart Uuu of... - Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units 3 Table 3 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 3 Table 3 to Subpart UUU of Part 63—Continous Monitoring...

40 CFR Table 9 to Subpart Uuu of... - Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 9 Table 9 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 9 Table 9 to Subpart UUU of Part 63—Operating Limits for Organic HAP...

Strength Behaviour of Fatigue Cracked Lugs (Festigkeitsverhalten von Rissbehafteten Augenstaeben),

DTIC Science & Technology

1981-01-01

either surface cracks or corner cracks at holes. NASA TN 1)-8244 64 A.F. Grandt Stress intensity factors for some through fracked fastener holes...with Hydropuise L~ngszylinder longitudinal cylinder Druckblversorgung =pressure oil Supply Hydraulikaggregat = hydraulic control unit Fig 7.5 Plan of

Quantification of cracks in concrete bridge decks in Ohio District 3.

DOT National Transportation Integrated Search

2012-02-01

The development of cracks in reinforced bridge decks is a critical problem, not only in Ohio state, but the whole of United States. Many bridge decks constructed within the last 10 years in Ohio have already shown varying levels and patterns of crack...

Quantification of cracks in concrete bridge decks in Ohio district 3.

DOT National Transportation Integrated Search

2012-02-01

The development of cracks in reinforced bridge decks is a critical problem, not only in Ohio state, but the whole of United States. Many bridge decks constructed within the last 10 years in Ohio have already shown varying levels and patterns of crack...

TRAC-BF1 thermal-hydraulic, ANSYS stress analysis for core shroud cracking phenomena

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shoop, U.; Feltus, M.A.; Baratta, A.J.

1996-12-31

The U.S. Nuclear Regulatory Commission sent Generic Letter 94-03 informing all licensees about the intergranular stress corrosion cracking (IGSCC) of core shrouds found in both Dresden unit I and Quad Cities unit 1. The letter directed all licensees to perform safety analysis of their boiling water reactor (BWR) units. Two transients of special concern for the core shroud safety analysis include the main steam line break (MSLB) and recirculation line break transient.

40 CFR 63.1561 - Am I subject to this subpart?

Code of Federal Regulations, 2011 CFR

2011-07-01

... Standards for Hazardous Air Pollutants for Petroleum Refineries: Catalytic Cracking Units, Catalytic..., and fuel oils), or lubricants; (ii) Separating petroleum; or (iii) Separating, cracking, reacting, or...

40 CFR 63.1561 - Am I subject to this subpart?

Code of Federal Regulations, 2010 CFR

2010-07-01

... Standards for Hazardous Air Pollutants for Petroleum Refineries: Catalytic Cracking Units, Catalytic..., and fuel oils), or lubricants; (ii) Separating petroleum; or (iii) Separating, cracking, reacting, or...

7 CFR 51.1583 - Damage.

Code of Federal Regulations, 2010 CFR

2010-01-01

... FRESH FRUITS, VEGETABLES AND OTHER PRODUCTS 1,2 (INSPECTION, CERTIFICATION, AND STANDARDS) United States... container. (b) Air cracks which are deep, or shallow air cracks which materially injure the appearance of...

76 FR 21822 - Airworthiness Directives; Empresa Brasileira de Aeronautica S.A. (EMBRAER) Model EMB-135ER...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-04-19

... [Brazilian] AD results from reports of cracking in the firewall of the auxiliary power unit (APU). This AD is... the APU. * * * * * The proposed AD would require actions that are intended to address the unsafe... reports of cracking in the firewall of the auxiliary power unit (APU). This AD is being issued to detect...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 12 2010-07-01 2010-07-01 true Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 12 2011-07-01 2009-07-01 true Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

Continuous AE crack monitoring of a dissimilar metal weldment at Limerick Unit 1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hutton, P.H.; Friesel, M.A.; Dawson, J.F.

1993-12-01

Acoustic emission (AE) technology for continuous surveillance of a reactor component(s) to detect crack initiation and/or crack growth has been developed at Pacific Northwest Laboratory (PNL). The technology was validated off-reactor in several major tests, but it had not been validated by monitoring crack growth on an operating reactor system. A flaw indication was identified during normal inservice inspection of piping at Philadelphia Electric Company (PECO) Limerick Unit 1 reactor during the 1989 refueling outage. Evaluation of the flaw indication showed that it could remain in place during the subsequent fuel cycle without compromising safety. The existence of this flawmore » indication offered a long sought opportunity to validate AE surveillance to detect and evaluate crack growth during reactor operation. AE instrumentation was installed by PNL and PECO to monitor the flaw indication during two complete fuel cycles. This report discusses the results obtained from the AE monitoring over the period May 1989 to March 1992 (two fuel cycles).« less

NSTS Orbiter auxiliary power unit turbine wheel cracking risk assessment

NASA Technical Reports Server (NTRS)

Cruse, T. A.; Mcclung, R. C.; Torng, T. Y.

1992-01-01

The present investigation of turbine-wheel cracking problems in the hydrazine-fueled APU turbine wheel of the Space Shuttle Orbiter's Main Engines has indicated the efficacy of systematic probabilistic risk assessment in flight certification and safety resolution. Nevertheless, real crack-initiation and propagation problems do not lend themselves to purely analytical studies. The high-cycle fatigue problem is noted to generally be unsuited to probabilistic modeling, due to its extremely high degree of intrinsic scatter. In the case treated, the cracks appear to trend toward crack arrest in a low cycle fatigue mode, due to a detuning of the resonance model.

40 CFR Table 9 to Subpart Uuu of... - Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 12 2010-07-01 2010-07-01 true Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 9 Table 9 to Subpart UUU of Part 63 Protection of Environment..., Subpt. UUU, Table 9 Table 9 to Subpart UUU of Part 63—Operating Limits for Organic HAP Emissions From...

40 CFR Table 9 to Subpart Uuu of... - Operating Limits for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 12 2011-07-01 2009-07-01 true Operating Limits for Organic HAP Emissions From Catalytic Cracking Units 9 Table 9 to Subpart UUU of Part 63 Protection of Environment..., Subpt. UUU, Table 9 Table 9 to Subpart UUU of Part 63—Operating Limits for Organic HAP Emissions From...

Implementation of a Smeared Crack Band Model in a Micromechanics Framework

NASA Technical Reports Server (NTRS)

Pineda, Evan J.; Bednarcyk, Brett A.; Waas, Anthony M.; Arnold, Steven M.

2012-01-01

The smeared crack band theory is implemented within the generalized method of cells and high-fidelity generalized method of cells micromechanics models to capture progressive failure within the constituents of a composite material while retaining objectivity with respect to the size of the discretization elements used in the model. An repeating unit cell containing 13 randomly arranged fibers is modeled and subjected to a combination of transverse tension/compression and transverse shear loading. The implementation is verified against experimental data (where available), and an equivalent finite element model utilizing the same implementation of the crack band theory. To evaluate the performance of the crack band theory within a repeating unit cell that is more amenable to a multiscale implementation, a single fiber is modeled with generalized method of cells and high-fidelity generalized method of cells using a relatively coarse subcell mesh which is subjected to the same loading scenarios as the multiple fiber repeating unit cell. The generalized method of cells and high-fidelity generalized method of cells models are validated against a very refined finite element model.

Steam generator feedwater nozzle transition piece replacement experience at Salem Unit 1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patten, D.B.; Perrin, J.S.; Roberts, A.T.

Cracking of steam generator feedwater piping adjacent to the feedwater nozzles has been a recurring problem since 1979 at Salem Unit 1 owned and operated by Public Service Electric and Gas Company. In addition to the cracking problem, erosion-corrosion at the leading edge of the feedwater nozzle thermal sleeve was also observed in 1992. To provide a long-term solution for the pipe cracking and thermal sleeve erosion-corrosion problems, a unique transition piece forging was specially designed, fabricated, and installed for each of the four steam generators during the 1995 outage. This paper discusses the design, fabrication, and installation of themore » transition piece forgings at Salem Unit 1, and the experiences gained from this project. It is believed that these experiences may help other utilities when planning similar replacements in the future.« less

Powder Cocaine and Crack Use in the United States: An Examination of Risk for Arrest and Socioeconomic Disparities in Use

PubMed Central

Palamar, Joseph J.; Davies, Shelby; Ompad, Danielle C.; Cleland, Charles M.; Weitzman, Michael

2015-01-01

Background In light of the current sentencing disparity (18:1) between crack and powder cocaine possession in the United States, we examined socioeconomic correlates of use of each, and relations between use and arrest, to determine who may be at highest risk for arrest and imprisonment. Methods We conducted secondary data analyses on the National Survey on Drug Use and Health, 2009–2012. Data were analyzed for adults age ≥18 to determine associations between use and arrest. Socioeconomic correlates of lifetime and annual use of powder cocaine and of crack were delineated using multivariable logistic regression and correlates of frequency of recent use were examined using generalized negative binomial regression. Results Crack users were at higher risk than powder cocaine users for reporting a lifetime arrest or multiple recent arrests. Racial minorities were at low risk for powder cocaine use and Hispanics were at low risk for crack use. Blacks were at increased risk for lifetime and recent crack use, but not when controlling for other socioeconomic variables. However, blacks who did use either powder cocaine or crack tended to use at higher frequencies. Higher education and higher family income were negatively associated with crack use although these factors were sometimes risk factors for powder cocaine use. Conclusions Crack users are at higher risk of arrest and tend to be of lower socioeconomic status compared to powder cocaine users. These findings can inform US Congress as they review the proposed Smarter Sentencing Act of 2014, which would help eliminate cocaine-related sentencing disparities. PMID:25702933

Meteorite Unit Models for Structural Properties

NASA Astrophysics Data System (ADS)

Agrawal, Parul; Carlozzi, Alexander A.; Karajeh, Zaid S.; Bryson, Kathryn L.

2017-10-01

To assess the threat posed by an asteroid entering Earth’s atmosphere, one must predict if, when, and how it fragments during entry. A comprehensive understanding of the asteroid material properties is needed to achieve this objective. At present, the meteorite material found on earth are the only objects from an entering asteroid that can be used as representative material and be tested inside a laboratory. Due to complex composition, it is challenging and expensive to obtain reliable material properties by means of laboratory test for a family of meteorites. In order to circumvent this challenge, meteorite unit models are developed to determine the effective material properties including Young’s modulus, compressive and tensile strengths and Poisson’s ratio, that in turn would help deduce the properties of asteroids. The meteorite unit model is a representative volume that accounts for diverse minerals, porosity, cracks and matrix composition.The Young’s Modulus and Poisson’s Ratio in the meteorite units are calculated by performing several hundreds of Monte Carlo simulations by randomly distributing the various phases inside these units. Once these values are obtained, cracks are introduced in these units. The size, orientation and distribution of cracks are derived by CT-scans and visual scans of various meteorites. Subsequently, simulations are performed to attain stress-strain relations, strength and effective modulus values in the presence of these cracks. The meteorite unit models are presented for H, L and LL ordinary chondrites, as well as for terrestrial basalt. In the case of the latter, data from the simulations is compared with experimental data to validate the methodology. These meteorite unit models will be subsequently used in fragmentation modeling of full scale asteroids.

Successful performance of a refinery with Eureka unit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirotani, Y.; Takeuchi, T.; Miyabuchi, Y.

1981-03-01

Since starting in February, 1976, 3,400,000 Kl of vacuum residue (13,000,000 Kl of crude oil equivalent) has been successfully processed in the Eureka unit of Fuji Oil refinery complex and more than 2,500,000 Kl of cracked oil and 1,000,000 tons of pitch have been produced. The operation rate has been 94 to 98% except for the annual shutdown period for inspection. The cracked oil is easily desulfurized to make naphta, diesel oil and a large amount of gas oil (low sulfur fuel oil, 0.1 wt % sulfur). As for the desulfurization of cracked oil, the increase in H/sub 2/ consumptionmore » and the decline of catalyst life are observed. However, the operation conditions do not differ much from those for straight run fractions. Processing both hydrotreated and untreated cracked heavy oil (CHO) with FCC unit has proved to be possible. In case of untreated CHO, however, it causes a slight increase in make up catalyst and coke yield. It is demonstrated that heavy crude oils, such as Bachaquero, can effectively be processed in this system. No additional pollution problems have occurred by introducing an Eureka unit to the refinery, although it is located in the district where the most stringent environmental regulations are urged.« less

Sensing sheet: the response of full-bridge strain sensors to thermal variations for detecting and characterizing cracks

NASA Astrophysics Data System (ADS)

Tung, S.-T.; Glisic, B.

2016-12-01

Sensing sheets based on large-area electronics consist of a dense array of unit strain sensors. This new technology has potential for becoming an effective and affordable monitoring tool that can identify, localize and quantify surface damage in structures. This research contributes to their development by investigating the response of full-bridge unit strain sensors to thermal variations. Overall, this investigation quantifies the effects of temperature on thin-film full-bridge strain sensors monitoring uncracked and cracked concrete. Additionally, an empirical formula is developed to estimate crack width given an observed strain change and a measured temperature change. This research led to the understanding of the behavior of full-bridge strain sensors installed on cracked concrete and exposed to temperature variations. It proves the concept of the sensing sheet and its suitability for application in environments with variable temperature.

Gum formation tendencies of olefinic structures in gasoline and synergistic effect of sulphur compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nagpal, J.M.; Joshi, G.C.; Aswal, D.S.

1995-04-01

The high octane gasoline pool contains varying amounts of cracked naphthas as an important ingredient in formulating high octane lead free gasoline. The cracked naphthas are largely from Fluidized Catalytic Cracking (FCC) units and to lesser extend from thermal cracking units. While the role of olefinic unsaturation in gum formation during storage of gasoline has been extensively studied, there is little published work on contribution of individual olefin types in storage stability and gum formation tendency of gasoline containing these compound types. In the present work we report our results on storage stability and gum formation tendency of different olefinmore » types present in cracked naphthas through model compound matrix. It is found that cyclic olefins and cyclic diolefins are the most prolific gum formers. We have also studied the role of sulfur compounds present in the gasolines on gum formation tendency of olefins. While thiols enhance gum formation from all olefinic types, sulfides and disulfides interact depending on the structure of olefins. These can have either an accelerating, or inhibiting effect on gum formation.« less

Coke formation in the thermal cracking of hydrocarbons. 4: Modeling of coke formation in naphtha cracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reyniers, G.C.; Froment, G.F.; Kopinke, F.D.

1994-11-01

An extensive experimental program has been carried out in a pilot unit for the thermal cracking of hydrocarbons. On the basis of the experimental information and the insight in the mechanisms for coke formation in pyrolysis reactors, a mathematical model describing the coke formation has been derived. This model has been incorporated in the existing simulation tools at the Laboratorium voor Petrochemische Techniek, and the run length of an industrial naphtha cracking furnace has been accurately simulated. In this way the coking model has been validated.

Fractography and mechanisms of environmentally enhanced fatigue crack propagation of a reactor pressure vessel steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Torronen, K.; Kemppainen, M.

1981-10-01

This paper describes the findings and interpretations of the fractographic survey conducted for the International Cyclic Crack Growth Rate (ICCGR) cooperative group round-robin specimens. Specimens of A533B pressure vessel steel were tested at several laboratories in the United States and elsewhere with the same nominal test parameters. A rather wide scatter of the results was found. A fractographic and metallographic survey was carried out in order to clarify the scatter and to evaluate the micromechanism of the crack growth. The fractographic findings are reported in detail and correlated to the crack growth behavior. A hydrogen-assisted crack propagation mechanism based onmore » the fractography is proposed and applied to the observed crack growth behavior.« less

Elastostatic stress analysis of orthotropic rectangular center-cracked plates

NASA Technical Reports Server (NTRS)

Gyekenyesi, G. S.; Mendelson, A.

1972-01-01

A mapping-collocation method was developed for the elastostatic stress analysis of finite, anisotropic plates with centrally located traction-free cracks. The method essentially consists of mapping the crack into the unit circle and satisfying the crack boundary conditions exactly with the help of Muskhelishvili's function extension concept. The conditions on the outer boundary are satisfied approximately by applying the method of least-squares boundary collocation. A parametric study of finite-plate stress intensity factors, employing this mapping-collocation method, is presented. It shows the effects of varying material properties, orientation angle, and crack-length-to-plate-width and plate-height-to-plate-width ratios for rectangular orthotropic plates under constant tensile and shear loads.

NDT of railway components using induction thermography

NASA Astrophysics Data System (ADS)

Netzelmann, U.; Walle, G.; Ehlen, A.; Lugin, S.; Finckbohner, M.; Bessert, S.

2016-02-01

Induction or eddy current thermography is used to detect surface cracks in ferritic steel. The technique is applied to detect surface cracks in rails from a moving test car. Cracks were detected at a train speed between 2 and 15 km/h. An automated demonstrator system for testing railway wheels after production is described. While the wheel is rotated, a robot guides the detection unit consisting of inductor and infrared camera over the surface.

Meteorite Material Model for Structural Properties

NASA Technical Reports Server (NTRS)

Agrawal, Parul; Carlozzi, Alexander A.; Karajeh, Zaid S.; Bryson, Kathryn L.

2017-01-01

To assess the threat posed by an asteroid entering Earth's atmosphere, one must predict if, when, and how it fragments during entry. A comprehensive understanding of the asteroid material properties is needed to achieve this objective. At present, the meteorite material found on earth are the only objects from an entering asteroid that can be used as representative material and be tested inside a laboratory setting. Due to complex petrology, it is technically challenging and expensive to obtain reliable material properties by means of laboratory test for a family of meteorites. In order to circumvent this challenge, meteorite unit models are developed to determine the effective material properties including Youngs modulus, compressive and tensile strengths and Poissons ratio, that in turn would help deduce the properties of asteroids. The meteorite unit is a representative volume that accounts for diverse minerals, porosity, cracks and matrix composition. The Youngs Modulus and Poissons Ratio in the meteorite units are calculated by performing several hundreds of Monte-Carlo simulations by randomly distributing the various phases inside these units. Once these values are obtained, cracks are introduced in these meteorite units. The size, orientation and distribution of cracks are derived by extensive CT-scans and visual scans of various meteorites from the same family. Subsequently, simulations are performed to attain stress-strain relations, strength and effective modulus values in the presence of these cracks. The meteorite unit models are presented for H, L and LL ordinary chondrites, as well as for terrestrial basalt. In the case of the latter, data from the simulations is compared with experimental data to validate the methodology. These material models will be subsequently used in fragmentation modeling of full scale asteroids.

A numerical investigation of the scale-up effects on flow, heat transfer, and kinetics processes of FCC units.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, S. L.

1998-08-25

Fluid Catalytic Cracking (FCC) technology is the most important process used by the refinery industry to convert crude oil to valuable lighter products such as gasoline. Process development is generally very time consuming especially when a small pilot unit is being scaled-up to a large commercial unit because of the lack of information to aide in the design of scaled-up units. Such information can now be obtained by analysis based on the pilot scale measurements and computer simulation that includes controlling physics of the FCC system. A Computational fluid dynamic (CFD) code, ICRKFLO, has been developed at Argonne National Laboratorymore » (ANL) and has been successfully applied to the simulation of catalytic petroleum cracking risers. It employs hybrid hydrodynamic-chemical kinetic coupling techniques, enabling the analysis of an FCC unit with complex chemical reaction sets containing tens or hundreds of subspecies. The code has been continuously validated based on pilot-scale experimental data. It is now being used to investigate the effects of scaled-up FCC units. Among FCC operating conditions, the feed injection conditions are found to have a strong impact on the product yields of scaled-up FCC units. The feed injection conditions appear to affect flow and heat transfer patterns and the interaction of hydrodynamics and cracking kinetics causes the product yields to change accordingly.« less

Model Verification and Validation Concepts for a Probabilistic Fracture Assessment Model to Predict Cracking of Knife Edge Seals in the Space Shuttle Main Engine High Pressure Oxidizer

NASA Technical Reports Server (NTRS)

Pai, Shantaram S.; Riha, David S.

2013-01-01

Physics-based models are routinely used to predict the performance of engineered systems to make decisions such as when to retire system components, how to extend the life of an aging system, or if a new design will be safe or available. Model verification and validation (V&V) is a process to establish credibility in model predictions. Ideally, carefully controlled validation experiments will be designed and performed to validate models or submodels. In reality, time and cost constraints limit experiments and even model development. This paper describes elements of model V&V during the development and application of a probabilistic fracture assessment model to predict cracking in space shuttle main engine high-pressure oxidizer turbopump knife-edge seals. The objective of this effort was to assess the probability of initiating and growing a crack to a specified failure length in specific flight units for different usage and inspection scenarios. The probabilistic fracture assessment model developed in this investigation combined a series of submodels describing the usage, temperature history, flutter tendencies, tooth stresses and numbers of cycles, fatigue cracking, nondestructive inspection, and finally the probability of failure. The analysis accounted for unit-to-unit variations in temperature, flutter limit state, flutter stress magnitude, and fatigue life properties. The investigation focused on the calculation of relative risk rather than absolute risk between the usage scenarios. Verification predictions were first performed for three units with known usage and cracking histories to establish credibility in the model predictions. Then, numerous predictions were performed for an assortment of operating units that had flown recently or that were projected for future flights. Calculations were performed using two NASA-developed software tools: NESSUS(Registered Trademark) for the probabilistic analysis, and NASGRO(Registered Trademark) for the fracture mechanics analysis. The goal of these predictions was to provide additional information to guide decisions on the potential of reusing existing and installed units prior to the new design certification.

Shrink-swell behavior of soil across a vertisol catena

USDA-ARS?s Scientific Manuscript database

Shrinking and swelling of soils and the associated formation and closing of cracks can vary spatially within the smallest hydrologic unit subdivision utilized in surface hydrology models. Usually in the application of surface hydrology models, cracking is not considered to vary within a hydrologic u...

HIV seroprevalence among street-recruited injection drug and crack cocaine users in 16 US municipalities.

PubMed Central

Kral, A H; Bluthenthal, R N; Booth, R E; Watters, J K

1998-01-01

OBJECTIVES: This study deter- mined human immunodeficiency virus (HIV) seroprevalence and factors associated with HIV infection among street-recruited injection drug users and crack cocaine smokers. METHODS: An analysis was performed on HIV serologies and risk behaviors of 6402 injection drug users and 3383 crack smokers in 16 US municipalities in 1992 and 1993. RESULTS: HIV seroprevalence was 12.7% among injection drug users and 7.5% among crack smokers. Most high-seroprevalence municipalities (>25%) were located along the eastern seaboard of the United States. In high-seroprevalence municipalities, but not in others, HIV seroprevalence was higher for injection drug users than for crack smokers. Among injection drug users, cocaine injection, use of speedballs (cocaine or amphetamines with heroin), and sexual risk behaviors were independently associated with HIV infection. Among crack smokers, sexual risk behaviors were associated with HIV infection. CONCLUSIONS: Injection drug users and crack smokers are at high risk for HIV infection. PMID:9584014

49 CFR 393.207 - Suspension systems.

Code of Federal Regulations, 2010 CFR

2010-10-01

... bar. No torsion bar or torsion bar suspension shall be cracked or broken. (f) Air suspensions. The air... the controls are either located on the trailer, or the power unit and trailer combination are not....207 Suspension systems. (a) Axles. No axle positioning part shall be cracked, broken, loose or missing...

Cracking the Credit Hour

ERIC Educational Resources Information Center

Laitinen, Amy

2012-01-01

The basic currency of higher education--the credit hour--represents the root of many problems plaguing America's higher education system: the practice of measuring time rather than learning. "Cracking the Credit Hour" traces the history of this time-based unit, from the days of Andrew Carnegie to recent federal efforts to define a credit…

75 FR 54700 - Sentencing Guidelines for United States Courts

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-08

... involving 5 grams (or more) of crack cocaine, and the 10-year mandatory minimum applied to offenses involving 50 grams (or more) of crack cocaine. Section 2 of the Act raised these quantities to 28 grams and 280 grams, respectively. The Commission requests comment on what temporary amendments to the...

Fuzzy Logic for Determination of Crack Severity in Defense Applications

DTIC Science & Technology

2010-03-31

FUZZY LOGIC FOR DETERMINATION OF CRACK SEVERITY IN DEFENSE APPLICATIONS Vijay Sharma , Harpreet Singh, Arati M. Dixit, Ahmed Mekki Department of... Vijay Sharma ; Harpreet Singh; Arati M. Dixit; Ahmed Mekki 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S

Stress analysis for structures with surface cracks

NASA Technical Reports Server (NTRS)

Bell, J. C.

1978-01-01

Two basic forms of analysis, one treating stresses around arbitrarily loaded circular cracks, the other treating stresses due to loads arbitrarily distributed on the surface of a half space, are united by a boundary-point least squares method to obtain analyses for stresses from surface cracks in places or bars. Calculations were for enough cases to show how effects from the crack vary with the depth-to-length ratio, the fractional penetration ratio, the obliquity of the load, and to some extent the fractional span ratio. The results include plots showing stress intensity factors, stress component distributions near the crack, and crack opening displacement patterns. Favorable comparisons are shown with two kinds of independent experiments, but the main method for confirming the results is by wide checking of overall satisfaction of boundary conditions, so that external confirmation is not essential. Principles involved in designing analyses which promote dependability of the results are proposed and illustrated.

Lining seam elimination algorithm and surface crack detection in concrete tunnel lining

NASA Astrophysics Data System (ADS)

Qu, Zhong; Bai, Ling; An, Shi-Quan; Ju, Fang-Rong; Liu, Ling

2016-11-01

Due to the particularity of the surface of concrete tunnel lining and the diversity of detection environments such as uneven illumination, smudges, localized rock falls, water leakage, and the inherent seams of the lining structure, existing crack detection algorithms cannot detect real cracks accurately. This paper proposed an algorithm that combines lining seam elimination with the improved percolation detection algorithm based on grid cell analysis for surface crack detection in concrete tunnel lining. First, check the characteristics of pixels within the overlapping grid to remove the background noise and generate the percolation seed map (PSM). Second, cracks are detected based on the PSM by the accelerated percolation algorithm so that the fracture unit areas can be scanned and connected. Finally, the real surface cracks in concrete tunnel lining can be obtained by removing the lining seam and performing percolation denoising. Experimental results show that the proposed algorithm can accurately, quickly, and effectively detect the real surface cracks. Furthermore, it can fill the gap in the existing concrete tunnel lining surface crack detection by removing the lining seam.

Doing Drugs and Dropping Out: A Report Prepared for the Use of the Subcommittee on Economic Growth, Trade, and Taxes of the Joint Economic Committee, Congress of the United States. 102d Congress, 1st Session.

ERIC Educational Resources Information Center

Joint Economic Committee, Washington, DC.

This report assesses the societal costs of substance abuse--especially cocaine and crack addition--and dropping out of school. It is organized around three themes: (1) the impact of cocaine and crack abuse in terms of crime, public spending, and lost productivity; (2) policies that move addicts away from crack; and (3) policies that reduce the…

Simulating the effect of slab features on vapor intrusion of crack entry

PubMed Central

Yao, Yijun; Pennell, Kelly G.; Suuberg, Eric M.

2012-01-01

In vapor intrusion screening models, a most widely employed assumption in simulating the entry of contaminant into a building is that of a crack in the building foundation slab. Some modelers employed a perimeter crack hypothesis while others chose not to identify the crack type. However, few studies have systematically investigated the influence on vapor intrusion predictions of slab crack features, such as the shape and distribution of slab cracks and related to this overall building foundation footprint size. In this paper, predictions from a three-dimensional model of vapor intrusion are used to compare the contaminant mass flow rates into buildings with different foundation slab crack features. The simulations show that the contaminant mass flow rate into the building does not change much for different assumed slab crack shapes and locations, and the foundation footprint size does not play a significant role in determining contaminant mass flow rate through a unit area of crack. Moreover, the simulation helped reveal the distribution of subslab contaminant soil vapor concentration beneath the foundation, and the results suggest that in most cases involving no biodegradation, the variation in subslab concentration should not exceed an order of magnitude, and is often significantly less than this. PMID:23359620

Steam generator issues in the United States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strosnider, J.R.

1997-02-01

Alloy 600 steam generator tubes in the US have exhibited degradation mechanisms similar to those observed in other countries. Effective programs have been implemented to address several degradation mechanisms including: wastage; mechanical wear; pitting; and fatigue. These degradation mechanisms are fairly well understood as indicated by the ability to effectively mitigate/manage them. Stress corrosion cracking (SCC) is the dominant degradation mechanism in the US. SCC poses significant inspection and management challenges to the industry and the regulators. The paper also addresses issues of research into SCC, inspection programs, plugging, repair strategies, water chemistry, and regulatory control. Emerging issues in themore » US include: parent tube cracking at sleeve joints; detection and repair of circumferential cracks; free span cracking; inspection and cracking of dented regions; and severe accident analysis.« less

76 FR 24960 - Sentencing Guidelines for United States Courts

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-03

... 2010, Public Law 111-220 (the ``Act''). The Act reduced the statutory penalties for cocaine base... other drugs, i.e., the base offense levels for crack cocaine are set in the Drug Quantity Table so that..., offenses involving 28 grams or more of crack cocaine are assigned a base offense level of 26, offenses...

40 CFR Table 29 to Subpart Uuu of... - HAP Emission Limits for Sulfur Recovery Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... Recovery Units 29 Table 29 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 29 Table 29 to Subpart UUU of Part 63—HAP Emission Limits for Sulfur Recovery Units As stated in...

40 CFR Table 22 to Subpart Uuu of... - Inorganic HAP Emission Limits for Catalytic Reforming Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... Catalytic Reforming Units 22 Table 22 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 22 Table 22 to Subpart UUU of Part 63—Inorganic HAP Emission Limits for Catalytic Reforming Units...

40 CFR Table 22 to Subpart Uuu of... - Inorganic HAP Emission Limits for Catalytic Reforming Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... Catalytic Reforming Units 22 Table 22 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 22 Table 22 to Subpart UUU of Part 63—Inorganic HAP Emission Limits for Catalytic Reforming Units...

40 CFR Table 29 to Subpart Uuu of... - HAP Emission Limits for Sulfur Recovery Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... Recovery Units 29 Table 29 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 29 Table 29 to Subpart UUU of Part 63—HAP Emission Limits for Sulfur Recovery Units As stated in...

40 CFR Table 15 to Subpart Uuu of... - Organic HAP Emission Limits for Catalytic Reforming Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... Catalytic Reforming Units 15 Table 15 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 15 Table 15 to Subpart UUU of Part 63—Organic HAP Emission Limits for Catalytic Reforming Units As...

40 CFR Table 15 to Subpart Uuu of... - Organic HAP Emission Limits for Catalytic Reforming Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... Catalytic Reforming Units 15 Table 15 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 15 Table 15 to Subpart UUU of Part 63—Organic HAP Emission Limits for Catalytic Reforming Units As...

Progressive Failure of a Unidirectional Fiber-Reinforced Composite Using the Method of Cells: Discretization Objective Computational Results

NASA Technical Reports Server (NTRS)

Pineda, Evan J.; Bednarcyk, Brett A.; Waas, Anthony M.; Arnold, Steven M.

2012-01-01

The smeared crack band theory is implemented within the generalized method of cells and high-fidelity generalized method of cells micromechanics models to capture progressive failure within the constituents of a composite material while retaining objectivity with respect to the size of the discretization elements used in the model. An repeating unit cell containing 13 randomly arranged fibers is modeled and subjected to a combination of transverse tension/compression and transverse shear loading. The implementation is verified against experimental data (where available), and an equivalent finite element model utilizing the same implementation of the crack band theory. To evaluate the performance of the crack band theory within a repeating unit cell that is more amenable to a multiscale implementation, a single fiber is modeled with generalized method of cells and high-fidelity generalized method of cells using a relatively coarse subcell mesh which is subjected to the same loading scenarios as the multiple fiber repeating unit cell. The generalized method of cells and high-fidelity generalized method of cells models are validated against a very refined finite element model.

Suppressing Crack Formation in Particulate Systems by Utilizing Capillary Forces

PubMed Central

Schneider, Monica; Maurath, Johannes; Fischer, Steffen B.; Weiß, Moritz; Willenbacher, Norbert; Koos, Erin

2017-01-01

Cracks, formed during the drying of particulate films, can reduce the effectiveness or even render products useless. We present a novel, generic approach to suppress crack formation in thin films made from hard particle suspensions, which are otherwise highly susceptible to cracking, using the capillary force between particles present when a trace amount of an immiscible liquid is added to a suspension. This secondary liquid preserves the particle cohesion, modifying the structure and increasing the drying rate. Crack-free films can be produced at thicknesses much greater than the critical cracking thickness for a suspension without capillary interactions, and even persists after sintering. This capillary suspension strategy is applicable to a broad range of materials including suspensions of metals, semiconductive and ceramic oxides or glassy polymeric particles and can be easily implemented in many industrial processes since it is based on well-established unit operations. Promising fields of application include ceramic foils and printed electronic devices. PMID:28263554

40 CFR Table 30 to Subpart Uuu of... - Operating Limits for HAP Emissions From Sulfur Recovery Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... Sulfur Recovery Units 30 Table 30 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 30 Table 30 to Subpart UUU of Part 63—Operating Limits for HAP Emissions From Sulfur Recovery...

40 CFR Table 29 to Subpart Uuu of... - HAP Emission Limits for Sulfur Recovery Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... Units 29 Table 29 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 29 Table 29 to Subpart UUU of Part 63—HAP Emission Limits for Sulfur Recovery Units As stated in § 63.1568...

40 CFR Table 29 to Subpart Uuu of... - HAP Emission Limits for Sulfur Recovery Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... Units 29 Table 29 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 29 Table 29 to Subpart UUU of Part 63—HAP Emission Limits for Sulfur Recovery Units As stated in § 63.1568(a)(1...

40 CFR Table 29 to Subpart Uuu of... - HAP Emission Limits for Sulfur Recovery Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... Units 29 Table 29 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 29 Table 29 to Subpart UUU of Part 63—HAP Emission Limits for Sulfur Recovery Units As stated in § 63.1568(a)(1...

Analytical Modelling of Transverse Matrix Cracking of [plus or minus Theta/90(sub n)](sub s) Composite Laminates Under Multiaxial Loading

NASA Technical Reports Server (NTRS)

Mayugo, J A.; Camanho, P. P.; Maimi, P.; Davila, C. G.

2010-01-01

An analytical model based on the analysis of a cracked unit cell of a composite laminate subjected to multiaxial loads is proposed to predict the onset and accumulation of transverse matrix cracks in the 90(sub n) plies of uniformly stressed [plus or minus Theta/90(sub n)](sub s) laminates. The model predicts the effect of matrix cracks on the stiffness of the laminate, as well as the ultimate failure of the laminate, and it accounts for the effect of the ply thickness on the ply strength. Several examples describing the predictions of laminate response, from damage onset up to final failure under both uniaxial and multiaxial loads, are presented.

Too much FCC catalyst activity can cut yields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wichers, W.R.; Upson, L.

1984-03-19

For many people working in the field of catalytic cracking, high equilibrium catalyst activity is inherently good. It is surprising how many times this line of reasoning is accepted by the refiner. There also seems to be something psychologically satisfying in seeing an equilibrium catalyst report where the catalyst activity is reported as a high number. Generally, everyone is happy when the reported activity of equilibrium catalyst is increasing and unhappy when it is going down. In the past, increasing catalyst activity did result in improved operations. For units that operated with substantial amounts of bed cracking, higher activity catalystmore » allowed the amount of bed cracking to be reduced and the relative amount of cracking that occurred in the riser to be increased. The switch from bed to riser cracking decreased catalytic coke make and gasoline overcracking, thus reducing regenerator temperature and improving gasoline yields.« less

Meteorite Material Model for Structural Properties

NASA Astrophysics Data System (ADS)

Agrawal, P.; Carlozzi, A. A.; Karajeh, Z. S.; Bryson, K. L.

2017-07-01

In order to prepare material models for the entire family of asteroids, meteorite units are developed for ordinary chondrites. The meteorite unit is a representative volume that accounts for diverse minerals, porosity, cracks and matrix composition.

Passive wireless antenna sensors for crack detection and shear/compression sensing

NASA Astrophysics Data System (ADS)

Mohammad, Irshad

Despite the fact that engineering components and structures are carefully designed against fatigue failures, 50 to 90% of mechanical failures are due to fatigue crack development. The severity of the failure depends on both the crack length and its orientation. Many types of sensors are available that can detect fatigue crack propagation. However, crack orientation detection has been rarely reported in the literature. We evaluated a patch antenna sensor capable of detecting crack propagation as well as crack orientation changes. The aim of these sensors would be to evaluate the real-time health condition of metallic structures to avoid catastrophic failures. The proposed crack sensing system consists of a dielectric substrate with a ground plane on one side of the substrate and an antenna patch printed on the other side of the substrate. The ground plane and the antenna patch, both conductive in nature, form an electromagnetic resonant cavity that radiates at distinct frequencies. These frequencies are monitored to evaluate the condition of cracks. A wireless sensor array can be realized by implementing a wireless interrogation unit. The scientific merits of this research are: 1) high sensitivity: it was demonstrated that the antenna sensors can detect crack growth with a sub-millimeter resolution; 2) passive wireless operation: based on microstrip antennas, the antenna sensors encode the sensing information in the backscattered antenna signal and thus can transmit the information without needing a local battery; 3) thin and conformal: the entire sensor unit is less than a millimeter thick and highly conformal; 4) crack orientation detection: the crack orientation on the structure can be precisely evaluated based on a single parameter, which only few sensors can accomplish. In addition to crack detection, the patch antenna sensors are also investigated for measuring shear and pressure forces, with an aim to study the formation, diagnostics and prevention of foot ulcers in diabetic patients. These sensors were vertically integrated and embedded in the insole of shoes for measuring plantar pressure/shear distribution. The scientific merits of this proposed research are: 1) simultaneous shear/pressure measurement : current smart shoe technology can only measure shear and pressure separately due to the size of the shear sensor. The proposed sensor can measure shear and pressure deformation simultaneously; 2) high sensitivity and spatial resolution: these sensors are very sensitive and have compact size that enables measuring stress distribution with fine spatial resolution; 3) passive and un-tethered operation: the sensor transponder was mounted on the top surface of the shoe to facilitate wireless interrogation of the sensor array embedded in the insole of the shoe, eliminating external wiring completely.

Change of Hot Cracking Susceptibility in Welding of High Strength Aluminum Alloy AA 7075

NASA Astrophysics Data System (ADS)

Holzer, M.; Hofmann, K.; Mann, V.; Hugger, F.; Roth, S.; Schmidt, M.

High strength aluminum alloys are known as hard to weld alloys due to their high hot crack susceptibility. However, they have high potential for applications in light weight constructions of automotive industry and therefore it is needed to increase weldability. One major issue is the high hot cracking susceptibility. Vaporization during laser beam welding leads to a change of concentration of the volatile elements magnesium and zinc. Hence, solidification range of the weld and therefore hot cracking susceptibility changes. Additionally, different welding velocities lead to changed solidification conditions with certain influence on hot cracking. This paper discusses the influence of energy per unit length during laser beam welding of AA 7075 on the change of element concentration in the weld seam and the resulting influence on hot cracking susceptibility. Therefore EDS-measurements of weld seams generated with different velocities are performed to determine the change of element concentration. These quantitative data is used to numerically calculate the solidification range in order to evaluate its influence on the hot cracking susceptibility. Besides that, relative hot crack length and mechanical properties are measured. The results increase knowledge about welding of high strength aluminum alloy AA 7075 and hence support further developing of the welding process.

Identification of breathing cracks in a beam structure with entropy

NASA Astrophysics Data System (ADS)

Wimarshana, Buddhi; Wu, Nan; Wu, Christine

2016-04-01

A cantilever beam with a breathing crack is studied to detect and evaluate the crack using entropy measures. Closed cracks in engineering structures lead to proportional complexities to their vibration responses due to weak bi-linearity imposed by the crack breathing phenomenon. Entropy is a measure of system complexity and has the potential in quantifying the complexity. The weak bi-linearity in vibration signals can be amplified using wavelet transformation to increase the sensitivity of the measurements. A mathematical model of harmonically excited unit length steel cantilever beam with a breathing crack located near the fixed end is established, and an iterative numerical method is applied to generate accurate time domain dynamic responses. The bi-linearity in time domain signals due to the crack breathing are amplified by wavelet transformation first, and then the complexities due to bi-linearity is quantified using sample entropy to detect the possible crack and estimate the crack depth. It is observed that the method is capable of identifying crack depths even at very early stages of 3% with the increase in the entropy values more than 10% compared with the healthy beam. The current study extends the entropy based damage detection of rotary machines to structural analysis and takes a step further in high-sensitivity structural health monitoring by combining wavelet transformation with entropy calculations. The proposed technique can also be applied to other types of structures, such as plates and shells.

Detection and Analysis of Enamel Cracks by Quantitative Light-induced Fluorescence Technology.

PubMed

Jun, Mi-Kyoung; Ku, Hye-Min; Kim, Euiseong; Kim, Hee-Eun; Kwon, Ho-Keun; Kim, Baek-Il

2016-03-01

The ability to accurately detect tooth cracks and quantify their depth would allow the prediction of crack progression and treatment success. The aim of this in vitro study was to determine the capabilities of quantitative light-induced fluorescence (QLF) technology in the detection of enamel cracks. Ninety-six extracted human teeth were selected for examining naturally existing or suspected cracked teeth surfaces using a photocuring unit. QLF performed with a digital camera (QLF-D) images were used to assess the ability to detect enamel cracks based on the maximum fluorescence loss value (ΔFmax, %), which was then analyzed using the QLF-D software. A histologic evaluation was then performed in which the samples were sectioned and observed with the aid of a polarized light microscope. The relationship between ΔFmax and the histology findings was assessed based on the Spearman rank correlation. The sensitivity and specificity were calculated to evaluate the validity of using QLF-D to analyze enamel inner-half cracks and cracks extending to the dentin-enamel junction. There was a strong correlation between the results of histologic evaluations of enamel cracks and the ΔFmax value, with a correlation coefficient of 0.84. The diagnostic accuracy of QLF-D had a sensitivity of 0.87 and a specificity of 0.98 for enamel inner-half cracks and a sensitivity of 0.90 and a specificity of 1.0 for cracks extending to the dentin-enamel junction. These results indicate that QLF technology would be a useful clinical tool for diagnosing enamel cracks, especially given that this is a nondestructive method. Copyright © 2016 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rejent, J.A.; Vianco, P.T.; Woodrum, R.A.

Aging analyses were performed on solder joints from two radar units: (1) a laboratory, N57 tube-type radar unit and (2) a field-returned, B61-0, tube-type radar unit. The cumulative temperature environments experienced by the units during aging were calculated from the intermetallic compound layer thickness and the mean Pb-rich phase particle size metrics for solder joints in the units, assuming an aging time of 35 years for both radars. Baseline aging metrics were obtained from a laboratory test vehicle assembled at AS/FM and T; the aging kinetics of both metrics were calculated from isothermal aging experiments. The N57 radar unit interconnectmore » board solder joints exhibited very little aging. The eyelet solder joints did show cracking that most likely occurred at the time of assembly. The eyelet, SA1126 connector solder joints, showed some delamination between the Cu pad and underlying laminate. The B61 field-returned radar solder joints showed a nominal degree of aging. Cracking of the eyelet solder joints was observed. The Pb-rich phase particle measurements indicated additional aging of the interconnects as a result of residual stresses. Cracking of the terminal pole connector, pin-to-pin solder joint was observed; but it was not believed to jeopardize the electrical functionality of the interconnect. Extending the stockpile lifetime of the B61 tube-type radar by an additional 20 years would not be impacted by the reliability of the solder joints with respect to further growth of the intermetallic compound layer. Additional coarsening of the Pb-rich phase will increase the joints' sensitivity to thermomechanical fatigue.« less

76 FR 41332 - Sentencing Guidelines for the United States Courts

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-13

... 1B1.10 that is in effect on the date on which the court reduces the defendant's term of imprisonment.... Part A amended the Drug Quantity Table in 2D1.1 for crack cocaine and made related revisions to... possessed more than 5 grams of crack cocaine was sentenced under 2D1.1.''. The Commentary to 1B1.10...

Practical Applications of Fracture Mechanics

DTIC Science & Technology

1980-05-01

Department British AerospaceRoyal Aircraft Establishment Manchester DivisioFarnborough, Hampshire United Kingdom n U nited K ingdom Anit e r Kin1o Francis...Bulkhead (Grange) 385 (6) Crack Propagation Analysis of Flat Stiffened Pa,"is (Schwarmann) 3-88 (7) Crack Propagation Analysis of Pressurized Fusel:. e ...modeling basis for microcrack growth. Major issues as to the applicability of fracture mechanic. e ,"thodoloqy, surface retardation due to machining

40 CFR 63.1575 - What reports must I submit and when?

Code of Federal Regulations, 2010 CFR

2010-07-01

... cracking units that are served by a single wet scrubber emission control device (e.g., a Venturi scrubber... requirements applicable to the unit that is operating and the wet scrubber emission control device do not apply...

Noninvasive cross-sectional visualization of enamel cracks by optical coherence tomography in vitro.

PubMed

Imai, Kanako; Shimada, Yasushi; Sadr, Alireza; Sumi, Yasunori; Tagami, Junji

2012-09-01

Current methods for the detection of enamel cracks are not very sensitive. Optical coherence tomography (OCT) is a promising diagnostic method for creating cross-sectional imaging of internal biological structures by measuring echoes of backscattered light. In this study, swept-source OCT (SS-OCT), a variant of OCT that sweeps the near-infrared wavelength at a rate of 30 kHz over a span of 110 nm centered at 1,330 nm, was examined as a diagnostic tool for enamel cracks. Twenty extracted human teeth were visually evaluated without magnification. SS-OCT was conducted on locations in which the presence of an enamel crack was suspected under visual inspection using a photocuring unit as transillumination. The teeth were then sectioned with a diamond saw and directly viewed under a confocal laser scanning microscope (CLSM). Using SS-OCT, the presence and extent of enamel cracks were clearly visualized on images based on backscattering signals. The extension of enamel cracks beyond the dentinoenamel junction could also be confirmed. The diagnostic accuracy of SS-OCT was shown to be superior to that of conventional visual inspection--the area under the receiver operating characteristic curve--for the detection of enamel crack and whole-thickness enamel crack; visual inspection: 0.69 and 0.56, SS-OCT: 0.85 and 0.77, respectively). Enamel cracks can be clearly detected because of increased backscattering of light matching the location of the crack, and the results correlated well with those from the CLSM. Copyright © 2012 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Emerging patterns of crack use in Mexico City.

PubMed

Valdez, Avelardo; Kaplan, Charles; Nowotny, Kathryn M; Natera-Rey, Guillermina; Cepeda, Alice

2015-08-01

Recent studies in Mexico have documented a significant increase in crack cocaine use, indicating the potential for an emerging drug epidemic. Ethnographic observations and interviews were used describe the profiles and patterns of use among street-recruited crack users in Mexico City. The data came from an international research collaboration funded by the National Institutes of Health. A polythetic typology was developed based on five dimensions central to categorizing patterns of crack use behavior: frequency of use, duration of use, context, social networks, and social contracts. Four types of users were discovered applying these dimensions: dabblers, stable users, crack heads, and old heads. Although several similarities were documented between patterns of crack use in Mexico and those in the United States and Western Europe, several key aspects distinguished crack users in this population: (1) self-regulated use; (2) non-linear progression of crack; and (3) the influence of the dimensions pertaining to setting, social networks, and social contract as contributing to understanding of the previous two. Further, we provide a discussion of how specific contextual factors in Mexico may be giving rise to these emerging patterns. Compared to the U.S. and Europe, this study finds that the majority of crack users were able to self-regulate their use without major disruption to daily social functioning. As crack use spreads in Mexico and other Latin American countries, we need to recognize the importance of social context in developing more tailored health and social responses that are specific to these developing countries. Copyright © 2015 Elsevier B.V. All rights reserved.

40 CFR Table 43 to Subpart Uuu of... - Requirements for Reports

Code of Federal Regulations, 2014 CFR

2014-07-01

... to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 43 Table 43 to Subpart UUU of Part 63—Requirements for Reports As stated in § 63.1575(a), you shall meet each...

40 CFR Table 43 to Subpart Uuu of... - Requirements for Reports

Code of Federal Regulations, 2012 CFR

2012-07-01

... to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 43 Table 43 to Subpart UUU of Part 63—Requirements for Reports As stated in § 63.1575(a), you shall meet each...

Degree of acculturation and the risk of crack cocaine smoking among Hispanic Americans.

PubMed

Wagner-Echeagaray, F A; Schütz, C G; Chilcoat, H D; Anthony, J C

1994-11-01

Epidemiologic data from three national surveys conducted in 1988, 1990, and 1991 were used to investigate the association between acculturation and use of crack cocaine among Hispanic Americans living in the United States. Poststratification and conditional logistic regression were used to hold constant shared aspects of neighborhood environment, age, sex, and education. The analyses showed a strong inverse relationship between degree of acculturation and crack smoking among Mexican Americans (relative odds = 0.12, 95% confidence interval = 0.04, 0.34) but not among other Hispanics in the study population. This observed variation within the US Hispanic American population deserves special attention in future research.

Degree of acculturation and the risk of crack cocaine smoking among Hispanic Americans.

PubMed Central

Wagner-Echeagaray, F A; Schütz, C G; Chilcoat, H D; Anthony, J C

1994-01-01

Epidemiologic data from three national surveys conducted in 1988, 1990, and 1991 were used to investigate the association between acculturation and use of crack cocaine among Hispanic Americans living in the United States. Poststratification and conditional logistic regression were used to hold constant shared aspects of neighborhood environment, age, sex, and education. The analyses showed a strong inverse relationship between degree of acculturation and crack smoking among Mexican Americans (relative odds = 0.12, 95% confidence interval = 0.04, 0.34) but not among other Hispanics in the study population. This observed variation within the US Hispanic American population deserves special attention in future research. PMID:7977926

Multifunctional two-stage riser fluid catalytic cracking process.

PubMed

Zhang, Jinhong; Shan, Honghong; Chen, Xiaobo; Li, Chunyi; Yang, Chaohe

This paper described the discovering process of some shortcomings of the conventional fluid catalytic cracking (FCC) process and the proposed two-stage riser (TSR) FCC process for decreasing dry gas and coke yields and increasing light oil yield, which has been successfully applied in 12 industrial units. Furthermore, the multifunctional two-stage riser (MFT) FCC process proposed on the basis of the TSR FCC process was described, which were carried out by the optimization of reaction conditions for fresh feedstock and cycle oil catalytic cracking, respectively, by the coupling of cycle oil cracking and light FCC naphtha upgrading processes in the second-stage riser, and the specially designed reactor for further reducing the olefin content of gasoline. The pilot test showed that it can further improve the product quality, increase the diesel yield, and enhance the conversion of heavy oil.

[Contributions of ludic care in nursing to chemical detoxification due to the use of crack cocaine].

PubMed

Pavanatto, Paola Aparecida; Gehlen, Maria Helena; Ilha, Silomar; Zamberlan, Claudia; Rangel, Rosiane Filipin; Nietsche, Elisabeta Albertina

2015-06-01

to understand the contributions of ludic care in nursing by stimulating the acceptance of chemical detoxification from crack on the perception of people in the detoxification process. an exploratory, descriptive study with a qualitative approach, performed with five people hospitalized for chemical detoxification from crack, from March to July 2013 in a chemical detox unit of a midsize hospital in the central region of Rio Grande do Sul. Data was collected using a semi-structured interview and was subjected to content analysis. Two categories emerged: Ludic care in nursing as a stimulus to the acceptance of chemical detoxification; Ludic care in nursing in the promotion for healthy living after chemical detoxification. ludic care in nursing proved to enhance the acceptance of chemical detoxification from crack in the reality investigated.

Heterogeneous kinetic modeling of the catalytic conversion of cycloparaffins

NASA Astrophysics Data System (ADS)

Al-Sabawi, Mustafa N.

The limited availability of high value light hydrocarbon feedstocks along with the rise in crude prices has resulted in the international recognition of the vast potential of Canada's oil sands. With the recent expansion of Canadian bitumen production come, however, many technical challenges, one of which is the significant presence of aromatics and cycloparaffins in bitumen-derived feedstocks. In addition to their negative environmental impact, aromatics limit fluid catalytic cracking (FCC) feedstock conversion, decrease the yield and quality of valuable products such as gasoline and middle distillates, increase levels of polyaromatic hydrocarbons prone to form coke on the catalyst, and ultimately compromise the FCC unit performance. Although cycloparaffins do not have such negative impacts, they are precursors of aromatics as they frequently undergo hydrogen transfer reactions. However, cycloparaffin cracking chemistry involves other competing reactions that are complex and need much investigation. This dissertation provides insights and understanding of the fundamentals of the catalytic cracking of cycloparaffins using carefully selected model compounds such as methylcyclohexane (MCH) and decalin. Thermal and catalytic cracking of these cycloparaffins on FCC-type catalysts are carried out using the CREC Riser Simulator under operating conditions similar to those of the industrial FCC units in terms of temperature, reaction time, reactant partial pressure and catalyst-to-hydrocarbon ratio. The crystallite size of the supported zeolites is varied between 0.4 and 0.9 microns, with both activity and selectivity being monitored. Catalytic conversions ranged between 4 to 16 wt% for MCH and between 8 to 27 wt% for decalin. Reaction pathways of cycloparaffins are determined, and these include ring-opening, protolytic cracking, isomerization, hydrogen transfer and transalkylation. The yields and selectivities of over 60 and 140 products, formed during MCH and decalin catalytic conversions respectively, are reported. Using these data, heterogeneous kinetic models accounting for intracrystallite molecular transport, adsorption and thermal and catalytic cracking of both cycloparaffin reactants are established. Results show that undesirable hydrogen transfer reactions are more pronounced and selectively favoured against other reactions at lower reaction temperatures, while the desirable ring-opening and cracking reactions predominate at the higher reaction temperatures. Moreover, results of the present work show that while crystallite size may have an effect on the overall conversion in some situations, there is a definite effect on the selectivity of products obtained during the cracking of MCH and decalin and the cracking of MCH in a mixture with co-reactants such as 1,3,5-triisopropylbenzene. Keywords. cycloparaffins, naphthenes, fluid catalytic cracking, kinetic modeling, Y-zeolites, diffusion, adsorption, ring-opening, hydrogen transfer, catalyst selectivity.

40 CFR Table 32 to Subpart Uuu of... - Requirements for Performance Tests for HAP Emissions From Sulfur Recovery Units Not Subject to...

Code of Federal Regulations, 2011 CFR

2011-07-01

... Sulfur Oxides 32 Table 32 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 32 Table 32 to Subpart UUU of Part 63—Requirements for Performance Tests for HAP Emissions From Sulfur...

40 CFR Table 32 to Subpart Uuu of... - Requirements for Performance Tests for HAP Emissions From Sulfur Recovery Units Not Subject to...

Code of Federal Regulations, 2014 CFR

2014-07-01

... Sulfur Oxides 32 Table 32 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 32 Table 32 to Subpart UUU of Part 63—Requirements for Performance Tests for HAP Emissions From...

40 CFR Table 32 to Subpart Uuu of... - Requirements for Performance Tests for HAP Emissions From Sulfur Recovery Units Not Subject to...

Code of Federal Regulations, 2013 CFR

2013-07-01

... Sulfur Oxides 32 Table 32 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 32 Table 32 to Subpart UUU of Part 63—Requirements for Performance Tests for HAP Emissions From...

40 CFR Table 32 to Subpart Uuu of... - Requirements for Performance Tests for HAP Emissions From Sulfur Recovery Units Not Subject to...

Code of Federal Regulations, 2012 CFR

2012-07-01

... Sulfur Oxides 32 Table 32 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 32 Table 32 to Subpart UUU of Part 63—Requirements for Performance Tests for HAP Emissions From...

Fatigue Crack Growth Database for Damage Tolerance Analysis

NASA Technical Reports Server (NTRS)

Forman, R. G.; Shivakumar, V.; Cardinal, J. W.; Williams, L. C.; McKeighan, P. C.

2005-01-01

The objective of this project was to begin the process of developing a fatigue crack growth database (FCGD) of metallic materials for use in damage tolerance analysis of aircraft structure. For this initial effort, crack growth rate data in the NASGRO (Registered trademark) database, the United States Air Force Damage Tolerant Design Handbook, and other publicly available sources were examined and used to develop a database that characterizes crack growth behavior for specific applications (materials). The focus of this effort was on materials for general commercial aircraft applications, including large transport airplanes, small transport commuter airplanes, general aviation airplanes, and rotorcraft. The end products of this project are the FCGD software and this report. The specific goal of this effort was to present fatigue crack growth data in three usable formats: (1) NASGRO equation parameters, (2) Walker equation parameters, and (3) tabular data points. The development of this FCGD will begin the process of developing a consistent set of standard fatigue crack growth material properties. It is envisioned that the end product of the process will be a general repository for credible and well-documented fracture properties that may be used as a default standard in damage tolerance analyses.

40 CFR Table 37 to Subpart Uuu of... - Requirements for Performance Tests for Bypass Lines

Code of Federal Regulations, 2012 CFR

2012-07-01

... Bypass Lines 37 Table 37 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 37 Table 37 to Subpart UUU of Part 63—Requirements for Performance Tests for Bypass Lines As...

40 CFR Table 37 to Subpart Uuu of... - Requirements for Performance Tests for Bypass Lines

Code of Federal Regulations, 2014 CFR

2014-07-01

... Bypass Lines 37 Table 37 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 37 Table 37 to Subpart UUU of Part 63—Requirements for Performance Tests for Bypass Lines As...

40 CFR Table 42 to Subpart Uuu of... - Additional Information for Initial Notification of Compliance Status

Code of Federal Regulations, 2010 CFR

2010-07-01

... Notification of Compliance Status 42 Table 42 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 42 Table 42 to Subpart UUU of Part 63—Additional Information for Initial Notification of...

40 CFR Table 40 to Subpart Uuu of... - Requirements for Installation, Operation, and Maintenance of Continuous Opacity Monitoring...

Code of Federal Regulations, 2013 CFR

2013-07-01

... Systems 40 Table 40 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 40 Table 40 to Subpart UUU of Part 63—Requirements for Installation, Operation, and Maintenance of...

40 CFR Table 40 to Subpart Uuu of... - Requirements for Installation, Operation, and Maintenance of Continuous Opacity Monitoring...

Code of Federal Regulations, 2011 CFR

2011-07-01

... Systems 40 Table 40 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 40 Table 40 to Subpart UUU of Part 63—Requirements for Installation, Operation, and Maintenance of Continuous...

40 CFR Table 40 to Subpart Uuu of... - Requirements for Installation, Operation, and Maintenance of Continuous Opacity Monitoring...

Code of Federal Regulations, 2014 CFR

2014-07-01

... Systems 40 Table 40 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 40 Table 40 to Subpart UUU of Part 63—Requirements for Installation, Operation, and Maintenance of...

40 CFR Table 40 to Subpart Uuu of... - Requirements for Installation, Operation, and Maintenance of Continuous Opacity Monitoring...

Code of Federal Regulations, 2012 CFR

2012-07-01

... Systems 40 Table 40 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 40 Table 40 to Subpart UUU of Part 63—Requirements for Installation, Operation, and Maintenance of...

40 CFR Table 42 to Subpart Uuu of... - Additional Information for Initial Notification of Compliance Status

Code of Federal Regulations, 2011 CFR

2011-07-01

... Notification of Compliance Status 42 Table 42 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 42 Table 42 to Subpart UUU of Part 63—Additional Information for Initial Notification of...

40 CFR Table 40 to Subpart Uuu of... - Requirements for Installation, Operation, and Maintenance of Continuous Opacity Monitoring...

Code of Federal Regulations, 2010 CFR

2010-07-01

... Systems 40 Table 40 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 40 Table 40 to Subpart UUU of Part 63—Requirements for Installation, Operation, and Maintenance of Continuous...

40 CFR Table 37 to Subpart Uuu of... - Requirements for Performance Tests for Bypass Lines

Code of Federal Regulations, 2013 CFR

2013-07-01

... Bypass Lines 37 Table 37 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 37 Table 37 to Subpart UUU of Part 63—Requirements for Performance Tests for Bypass Lines As...

A study of creep crack growth in 2219-T851

NASA Astrophysics Data System (ADS)

Bensussan, Philippe L.; Jablonski, David A.; Pelloux, Regis M.

1984-01-01

Creep crack growth rates were measured in high strength 2219-T851 aluminum alloy with a computerized fully automated test procedure. Crack growth tests were performed on CT specimens with side grooves. The experimental set-up is described. During a test, the specimen is cyclically loaded on a servohydraulic testing machine under computer control, maintained at maximum load for a given hold time at each cycle, unloaded, and then reloaded. Crack lengths are obtained from compliance measurements recorded during each unloading. It is shown that the measured crack growth rates per cycle do represent creep crack growth rates per unit time for hold times longer than 10 seconds. The validity of LEFM concepts for side-grooved specimens is reviewed, and compliance and stress intensity factor calibrations for such specimens are reported. For the range of testing conditions of this study, 2219-T851 is shown to be creep brittle in terms of concepts of fracture mechanics of creeping solids. It is found that, under these testing conditions, a correlation exists between the creep crack growth rates under plane strain conditions and the stress intensity factor ( da/dt = A K 3.8 at 175 °C) for simple K histories in a regime of steady or quasi-steady state crack growth. The micromechanisms of fracture are determined to be of complex nature. The fracture mode is observed to be mixed inter- and transgranular, the relative amount of intergranular fracture decreasing as K and da/dt increase.

Catalytic cracking of Mayan gas oil and selected hydrotreated products: Topical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wells, J.W.; Zagula, E.J.; Brinkman, D.W.

1988-01-01

The catalytic cracking of a Mayan vacuum gas oil and the products from mild, moderate, and severe hydrotreating of this gas oil was evaluated over a low-metal equilibrium catalyst in a microconfined bed unit (MCBU). Results obtained with the Mayan feedstocks are compared with those of an earlier study conducted with similar feedstocks obtained from a Wilmington (CA) crude oil. Two levels of catalytic cracking severity were used in the evaluation. Performance and product analysis showed that hydrotreating improves the yields obtained from catalytic cracking and the quality of the resultant products. In contrast to results obtained with the Wilmingtonmore » feedstocks, conversion and gasoline yield do not improve with severity of the hydrotreating of the Mayan vacuum gas oils. The insensitivity of the cracking performance to hydrotreating severity may reflect the more facile removal of polar compounds (heteroatom compounds) on hydrotreating of the Mayan gas oil in comparison to the Wilmington. Sulfur and nitrogen contents of the liquid products (gasoline, light cycle oil, heavy cycle oil) decreased as the severity of the feed hydrotreating increased. 7 refs., 12 figs., 15 tabs.« less

Demonstrating damage tolerance of composite airframes

NASA Technical Reports Server (NTRS)

Poe, Clarence C., Jr.

1993-01-01

Commercial transport aircraft operating in the United States are certified by the Federal Aviation Authority to be damage tolerant. On 28 April 1988, Aloha Airlines Flight 243, a Boeing 727-200 airplane, suffered an explosive decompression of the fuselage but landed safely. This event provides very strong justification for the damage tolerant design criteria. The likely cause of the explosive decompression was the linkup of numerous small fatigue cracks that initiated at adjacent fastener holes in the lap splice joint at the side of the body. Actually, the design should have limited the damage size to less than two frame spacings (about 40 inches), but this type of 'multi-site damage' was not originally taken into account. This cracking pattern developed only in the high-time airplanes (many flights). After discovery in the fleet, a stringent inspection program using eddy current techniques was inaugurated to discover these cracks before they linked up. Because of concerns about safety and the maintenance burden, the lap-splice joints of these high-time airplanes are being modified to remove cracks and prevent new cracking; newer designs account for 'multi-site damage'.

40 CFR Table 37 to Subpart Uuu of... - Requirements for Performance Tests for Bypass Lines

Code of Federal Regulations, 2010 CFR

2010-07-01

... Bypass Lines 37 Table 37 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 37 Table 37 to Subpart UUU of Part 63—Requirements for Performance Tests for Bypass Lines As stated in § 63...

40 CFR Table 44 to Subpart Uuu of... - Applicability of NESHAP General Provisions to Subpart UUU

Code of Federal Regulations, 2011 CFR

2011-07-01

... Provisions to Subpart UUU 44 Table 44 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 44 Table 44 to Subpart UUU of Part 63—Applicability of NESHAP General Provisions to Subpart UUU As...

40 CFR Table 44 to Subpart Uuu of... - Applicability of NESHAP General Provisions to Subpart UUU

Code of Federal Regulations, 2010 CFR

2010-07-01

... Provisions to Subpart UUU 44 Table 44 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 44 Table 44 to Subpart UUU of Part 63—Applicability of NESHAP General Provisions to Subpart UUU As...

40 CFR Table 36 to Subpart Uuu of... - Work Practice Standards for HAP Emissions From Bypass Lines

Code of Federal Regulations, 2011 CFR

2011-07-01

... Emissions From Bypass Lines 36 Table 36 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 36 Table 36 to Subpart UUU of Part 63—Work Practice Standards for HAP Emissions From Bypass Lines...

40 CFR Table 37 to Subpart Uuu of... - Requirements for Performance Tests for Bypass Lines

Code of Federal Regulations, 2011 CFR

2011-07-01

... Bypass Lines 37 Table 37 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 37 Table 37 to Subpart UUU of Part 63—Requirements for Performance Tests for Bypass Lines As stated in § 63...

40 CFR Table 36 to Subpart Uuu of... - Work Practice Standards for HAP Emissions From Bypass Lines

Code of Federal Regulations, 2010 CFR

2010-07-01

... Emissions From Bypass Lines 36 Table 36 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 36 Table 36 to Subpart UUU of Part 63—Work Practice Standards for HAP Emissions From Bypass Lines...

Imposed Thermal Fatigue and Post-Thermal-Cycle Wear Resistance of Biomimetic Gray Cast Iron by Laser Treatment

NASA Astrophysics Data System (ADS)

Sui, Qi; Zhou, Hong; Zhang, Deping; Chen, Zhikai; Zhang, Peng

2017-08-01

The present study aims to create coupling biomimetic units on gray cast iron substrate by laser surface treatment (LST). LSTs for single-step (LST1) and two-step (LST2) processes, were carried out on gray cast iron in different media (air and water). Their effects on microstructure, thermal fatigue, and post-thermal-cycle wear (PTW) resistance on the specimens were studied. The tests were carried out to examine the influence of crack-resistance behavior as well as the biomimetic surface on its post-thermal-cycle wear behavior and different units, with different laser treatments for comparison. Results showed that LST2 enhanced the PTW behaviors of gray cast iron, which then led to an increase in its crack resistance. Among the treated cast irons, the one treated by LST2 in air showed the lowest residual stress, due to the positive effect of the lower steepness of the thermal gradient. Moreover, the same specimen showed the best PTW performance, due to its superior crack resistance and higher hardness as a result of it.

Inroads in the Non-Invasive Diagnostics of Ballistic Impact Damage

DTIC Science & Technology

2006-11-01

2004; Wells, et al., 2002), Ti - 6Al - 4V metallic armor materials (Wells, et al., 2004) and, most recently, on a ballistic gelatin target (Wells, 2006...spiral cracking outside of the penetration cavity in a Ti - 6Al - 4V sample disk. This type of volumetric damage characterization information, otherwise...visualization of the penetration cavity and spiral cracking in a Ti - 6Al - 4V sample. 4 Figure 8. Quantitative 3-D unit damage fraction

40 CFR Table 4 to Subpart Uuu of... - Requirements for Performance Tests for Metal HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2013 CFR

2013-07-01

... (NSPS) for Particulate Matter (PM) 4 Table 4 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 4 Table 4 to Subpart UUU of Part 63—Requirements for Performance Tests...

40 CFR Table 4 to Subpart Uuu of... - Requirements for Performance Tests for Metal HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2012 CFR

2012-07-01

... (NSPS) for Particulate Matter (PM) 4 Table 4 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 4 Table 4 to Subpart UUU of Part 63—Requirements for Performance Tests...

40 CFR Table 4 to Subpart Uuu of... - Requirements for Performance Tests for Metal HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2014 CFR

2014-07-01

... (NSPS) for Particulate Matter (PM) 4 Table 4 to Subpart UUU of Part 63 Protection of Environment... Units Pt. 63, Subpt. UUU, Table 4 Table 4 to Subpart UUU of Part 63—Requirements for Performance Tests...

75 FR 67019 - Presidential Determination on Major Illicit Drug Transit or Major Illicit Drug Producing...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-01

... base, and crack cocaine, primarily from Bolivia; and marijuana. The United States recognizes Brazil's... high- potency marijuana that is trafficked to the United States. The frequent mixing of methamphetamine... and synthetic drugs including marijuana, MDMA, and methamphetamine are produced in Canada and...

Exposed Ice in the Northern Mid-Latitudes of Mars

NASA Technical Reports Server (NTRS)

Allen, Carlton C.

2007-01-01

Ice-Rich Layer: Polygonal features with dimensions of approximately 100 meters, bounded by cracks, are commonly observed on the martian northern plains. These features are generally attributed to thermal cracking of ice-rich sediments, in direct analogy to polygons in terrestrial polar regions. We mapped polygons in the northern mid-latitudes (30 to 65 N) using MOC and HiRISE images. Polygons are scattered across the northern plains, with a particular concentration in western Utopia Planitia. This region largely overlaps the Late Amazonian Astapus Colles unit, characterized by polygonal terrain and nested pits consistent with periglacial and thermokarst origins. Bright and Dark Polygonal Cracks: An examination of all MOC images (1997 through 2003) covering the study area demonstrated that, at latitudes of 55 to 65 N, most of the imaged polygons show bright bounding cracks. We interpret these bright cracks as exposed ice. Between 40 and 55 N, most of the imaged polygons show dark bounding cracks. These are interpreted as polygons from which the exposed ice has been removed by sublimation. The long-term stability limit for exposed ice, even in deep cracks, apparently lies near 55 N. Bright and Dark Spots: Many HiRISE and MOC frames showing polygons in the northern plains also show small numbers of bright and dark spots, particularly in western Utopia Planitia. Many of the spots are closely associated with collapse features suggestive of thermokarst. The spots range from tens to approximately 100 meters in diameter. The bright spots are interpreted as exposed ice, due to their prevalence on terrain mapped as ice rich. The dark spots are interpreted as former bright spots, which have darkened as the exposed ice is lost by sublimation. The bright spots may be the martian equivalents of pingos, ice-cored mounds found in periglacial regions on Earth. Terrestrial pingos from which the ice core has melted often collapse to form depressions similar to the martian dark spots. Future Observations: The SHARAD radar should be able to confirm the presence and measure the depth of the interpreted ice-rich layer that forms the Astapus Colles unit. If this layer is confirmed it will strengthen the interpretation of bright polygon cracks and bright spots as exposed ice. HiRISE images of the northern plains are showing unprecedented details of the polygonal cracks. Future HiRISE images that include bright spots, compared to MOC images taken years earlier, will illustrate the temporal stability of the spots. The CRISM spectrometer, with multiple spectral bands and a spatial resolution around 20 meters, should allow mineralogical identification of the material exposed in the polygonal bounding cracks and in the bright spots.

Heat-shock properties in yttrium-oxide films synthesized from metal-ethylenediamine tetraacetic acid complex through flame-spray apparatus

NASA Astrophysics Data System (ADS)

Xin, D. Y.; Komatsu, Keiji; Abe, Keita; Costa, Takashi; Ikeda, Yutaka; Nakamura, Atsushi; Ohshio, Shigeo; Saitoh, Hidetoshi

2017-03-01

Recently, a new deposition technique using a metal-ethylenediamine tetraacetic acid (EDTA) complex has been developed. In this study, the heat-shock properties of metal-oxide films synthesized from a metal-EDTA complex were investigated. Y2O3 films were synthesized on stainless-steel (SUS) substrate from EDTA•Y•H through the combustion of H2-O2 gas. A cyclic heat-shock test was conducted on the fabricated Y2O3 films through exposure to the H2-O2 flame. The existence of Y2O3 crystals was confirmed. Surface cracks or damages were not observed in the samples after the cyclic thermal test. Although the number of cross-sectional cracks, crack lengths, and cracks per unit area was increased by the heat shock, delaminations were not observed in the Y2O3 films. The results show that the prepared Y2O3 films have high thermal-shock resistance and are suitable for use as thermal barrier coatings.

Nitrile O-ring Cracking: A Case of Vacuum Flange O-ring Failures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dees, Craig

2016-07-01

A review of recent nitrile O-ring failures in ISO-KF vacuum flange connections in glovebox applications is presented. An investigation of a single “isolated” o-ring failure leads to the discovery of cracked nitrile o-rings in a glovebox atmospheric control unit. The initial cause of the o-ring failure is attributed to ozone degradation. However, additional investigation reveals nitrile o-ring cracking on multiple gloveboxes and general purpose piping, roughly 85% of the nitrile o-rings removed for inspection show evidence of visible cracking after being in service for 18 months or less. The results of material testing and ambient air testing is presented, elevatedmore » ozone levels are not found. The contributing factors of o-ring failure, including nitrile air sensitivity, inadequate storage practices, and poor installation techniques, are discussed. A discussion of nitrile o-ring material properties, the benefits and limitations, and alternate materials are discussed. Considerations for o-ring material selection, purchasing, storage, and installation are presented in the context of lessons learned from the nitrile o-ring cracking investigation. This paper can be presented in 20 minutes and does not require special accommodations or special audio visual devices.« less

Phase transformation and sustained load crack growth in ZrO[sub 2] + 3 mol% Y[sub 2]O[sub 3]: Experiments and kinetic modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, H.; Gao, M.; Wei, R.P.

1995-01-01

To better understand environmentally assisted crack growth (SCG) in yttria stabilized zirconia, experimental studies were undertaken to characterize the kinetics of crack growth and the associated stress/moisture induced phase transformation in ZrO[sub 2] + 3 mol% Y[sub 2]O[sub 3] (3Y-TZP) in water, dry nitrogen and toluene from 3 to 70 C. The results showed that crack growth in water depended strongly on stress intensity factor (K[sub 1]) and temperature (T) and involved the transformation of a thin layer of material near the crack tip from the tetragonal (t) to the monoclinic (m) phase. These results, combined with literature data onmore » moisture-induced phase transformation, suggested that crack growth enhancement by water is controlled by the rate of this transformation and reflects the environmental cracking susceptibility of the transformed m-phase. A model was developed to link subcritical crack growth (SCG) rate to the kinetics of t [yields] m phase transformation. The SCG rate is expressed as an exponential function of stress-free activation energy, a stress-dependent contribution in terms of the mode 1 stress intensity factor K[sub I] and actuation volume, and temperature. The stress-free activation energies for water and the inert environments were determined to be 82 [+-] 3 and 169 [+-] 4 kJ/mol, respectively, at the 95% confidence level, and the corresponding activation volumes were 14 and 35 unit cells. The decreases in activation energy and activation volume may be attributed to a change in surface energy by water.« less

40 CFR 63.1578 - Who implements and enforces this subpart?

Code of Federal Regulations, 2010 CFR

2010-07-01

... National Emission Standards for Hazardous Air Pollutants for Petroleum Refineries: Catalytic Cracking Units.... (1) Approval of alternatives to the non-opacity emission limitations and work practice standards in...

Catalytic cracking of a Wilmington vacuum oil gas and selected hydrotreated products: Topical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wells, J.W.; Zagula, E.J.

1987-05-01

The catalytic cracking of a Wilmington vacuum gas oil and the products from mild hydrotreating and severe hydrotreating of this gas oil was evaluated over a low metal equilibrium catalyst in a microconfined bed unit (MCBU). Two levels of catalytic cracking severity were evaluated for these three samples. The performance and product analysis showed that hydrotreating improves the quality of catalytic cracker feedstock and the resultant products. The results also indicated that a level of hydrotreating exists above which the quality of the liquid products and the yields of coke and heavy oil are not affected significantly by the severitymore » of the catalytic cracking process. As expected, the sulfur and nitrogen content of the liquid products (gasolines, light cycle oil, and heavy cycle oil) were found to decrease as the severity of the feed hydrotreating increased. The distribution of sulfur and nitrogen in the liquid products was found to be independent of cracking conditions or product yields for a given level of hydrogenation. Analysis of the gas products shows that the degree of hydrogen transfer increases with the severity of hydrogenation. As cracking severity increases, the apparent degree of hydrogen transfer decreases, and the concentration of olefinic compounds increases relative to the saturated compounds. In the future, these results will be compared to similar results from a Mayan vacuum gas oil. 10 refs., 17 figs., 10 tabs.« less

Salinity effects on the dynamics and patterns of desiccation cracks

NASA Astrophysics Data System (ADS)

Shokri, N.; Zhou, P.

2012-12-01

Cracking arising from desiccation is a ubiquitous phenomenon encountered in various industrial and geo-environmental applications including drying of clayey soil, cement, ceramics, gels, and many more colloidal suspensions. Presence of cracks in muddy sediments modifies the characteristics of the medium such as pore structure, porosity, and permeability which in turn influence various flow and transport processes. Thus it remains a topic of great interest in many disciplines to describe the dynamics of desiccation cracking under various boundary conditions. To this end, we conducted a comprehensive study to investigate effects of NaCl concentrations on cracking dynamics and patterns during desiccation of Bentonite. Mixtures of Bentonite and NaCl solutions were prepared with NaCl concentration varying from 2 to 10 percent in 0.5 percent increment (totally 17 configurations). The slurry was placed in a Petri dish mounted on a digital balance to record the evaporation dynamics. The atmospheric conditions were kept constant using an environmental chamber. An automatic camera was used to record the dynamics of macro-cracks (mm scale) at the surface of desiccating clay each minute. The obtained results illustrate the significant effects of salt concentration on the initiation, propagation, morphology and general dynamics of macro-cracks. We found that higher salt concentrations results in larger macro cracks' lengths attributed to the effects of NaCl on compressing the electric double layer of particles at increasing electrolyte concentrations which reduce considerably the repulsive forces among the particles and causing instability of the slurry and flocculation of the colloidal particles. Rheological measurements by means of a stress controlled rheometer revealed that the yield stress of the slurry decreases as NaCl concentration increases which may indicate aggregation of larger units in the slurry as a result of flocculation causing larger cracks' lengths due to drying. At the end of each round of the experiment, a detailed visualization was conducted using Scanning Electron Microscopy to investigate the patterns and morphology of cracks at micro-scale as influenced by the salt concentration. Our results provide new insights and finding about the effects of salt concentrations on desiccation cracks at different scales ranging from a few mm to few microns.

Finite Element Optimization for Nondestructive Evaluation on a Graphics Processing Unit for Ground Vehicle Hull Inspection

DTIC Science & Technology

2013-08-22

4 cores, where the code may simultaneously run on the multiple cores or the graphics processing unit (or GPU – to be more specific on an NVIDIA ...allowed to get accurate crack shapes. DISCLAIMER Reference herein to any specific commercial company , product, process, or service by trade name

Fatigue Behavior of Long and Short Cracks in Wrought and Powder Aluminum Alloys.

DTIC Science & Technology

1984-05-01

PROGRAM ELEMENT. PROJECT. TASK AREA & WORK UNIT NUMBERS Robert 0. Ritchie, Department of Materials Science and Mineral Engineering, University of 2306/ Al ...Chemical Compositions in wt% of Alloys Si Fe Cu Mn Mg Cr Zn Ti Zr Al 2024 0.50 0.50 4.50 0.50 1.50 0.10 0.25 0.15 -- balance 2124 0.20 0.30 4.50 0.50 1.50...been applied by Suresh et al .41 to rationalize the microstructural effects of precipitation hardening on fatigue crack growth in 7075 alloys. The

Experience with ethylene plant computer control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nasi, M.; Darby, M.L.; Sourander, M.

This article discusses the control strategies, results and opinions of management and operations of a computer based ethylene plant control system. The ethylene unit contains 9 cracking heaters, and its nameplate capacity is 200,000 tpa ethylene. Reports on control performance during different unit loading and using different feedstock types. By converting the yield and utility consumption benefits due to computer control into monetary units, the payback time of the system is less than 2 yrs.

Experimental study on compressive strength of sediment brick masonry

NASA Astrophysics Data System (ADS)

Woen, Ean Lee; Malek, Marlinda Abdul; Mohammed, Bashar S.; Chao-Wei, Tang; Tamunif, Muhammad Thaqif

2018-02-01

The effects of pre-wetted unit bricks, mortar type and slenderness ratio of prisms on the compressive strength and failure mode of newly developed sediment brick have been evaluated and compared to clay brick and cement-sand bricks. The results show that pre-wetted sediment brick masonry exhibits higher compressive strength of up to 20% compared to the dry sediment masonry. Using cement-lime mortar leads to lower compressive strength compared to cement mortar. However, the sediment brick masonry with the cement lime mortar exhibit higher compressive strength in comparison with cement mortar masonry. More of diagonal shear cracks have been observed in the failure mode of the sediment bricks masonry compared to clay and cement-sand bricks masonry that show mostly vertical cracks and crushing. The sediment unit bricks display compressive strength in between clay and cement-sand bricks.

40 CFR Table 1 to Subpart Uuu of... - Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... waste heat boiler in which you burn auxiliary or in supplemental liquid or solid fossil fuel, the... British thermal units (lb/million Btu) of heat input attributable to the liquid or solid fossil fuel; and... auxiliary or supplemental liquid or solid fossil fuel, the incremental rate of PM must not exceed 43.0 g/GJ...

PFC2D simulation of thermally induced cracks in concrete specimens

NASA Astrophysics Data System (ADS)

Liu, Xinghong; Chang, Xiaolin; Zhou, Wei; Li, Shuirong

2013-06-01

The appearance of cracks exposed to severe environmental conditions can be critical for concrete structures. The research is to validate Particle Flow Code(PFC2D) method in the context of concrete thermally-induced cracking simulations. First, concrete was discreted as meso-level units of aggregate, cement mortar and the interfaces between them. Parallel bonded-particle model in PFC2D was adapted to describe the constitutive relation of the cementing material. Then, the concrete mechanics meso-parameters were obtained through several groups of biaxial tests, in order to make the numerical results comply with the law of the indoor test. The concrete thermal meso-parameters were determined by compared with the parameters in the empirical formula through the simulations imposing a constant heat flow to the left margin of concrete specimens. At last, a case of 1000mm×500mm concrete specimen model was analyzed. It simulated the formation and development process of the thermally-induced cracks under the cold waves of different durations and temperature decline. Good agreements in fracture morphology and process were observed between the simulations, previous studies and laboratory data. The temperature decline limits during cold waves were obtained when its tensile strength was given as 3MPa. And it showed the feasibility of using PFC2D to simulate concrete thermally-induced cracking.

Residual Life and Strength Predictions and Life-Enhancement of Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okada, H.; Atluri, S.N.

1998-09-01

In this paper, a method to quantitatively evaluate the T{sub {var_epsilon}}* integral directly from the measured near-tip displacement field for laboratory specimens made of metallic materials, is presented. This is the first time that such an attempt became a success. In order to develop the procedure, we carefully examine the nature of T{sub {var_epsilon}}* Hence, the nature of T{sub {var_epsilon}}* is further revealed. Following Okada and Atluri (1997), the relationship between energy balance statements for a cracked plate and the T{sub {var_epsilon}}* is discussed. It is concluded that T{sub {var_epsilon}}* quantifies the deformation energy dissipated near crack tip region [anmore » elongating strip of height e] per unit crack extension. In the evaluation of T{sub {var_epsilon}}* integral directly from measured displacement field, the use of deformation theory plasticity (J2-D theory) and the truncation of the near crack integral path on the experimental studies of Omori et el. (1995) are presented, and these show a good agreement with the results of finite element analysis.« less

On the role of particle cracking in flow and fracture of metal matrix composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brockenbrough, J.R.; Zok, F.W.

1995-01-01

The flow response of particle-reinforced metal matrix composites is studied using finite element methods. Unit cells containing either intact or cracked particles in a power law hardening matrix are used to determine the corresponding asymptotic flow strengths. The effects of the hardening exponent and the elastic mismatch between the particles and the matrix on the flow response are examined. For comparison, the flow response of power law hardening solids containing penny-shaped cracks is also evaluated. The latter results are found to be in reasonable agreement with those corresponding to composites that contain low volume fractions of cracked particles. The asymptoticmore » results are used to develop a one-dimensional constitutive law for composites which undergo progressive damage during tensile straining. This law is used to evaluate the strain at the onset of plastic instability. It is proposed that the instability strain be used as a measure of tensile ductility when the particle content is low and the particles are uniformly distributed through the matrix.« less

Insights Gained from Ultrasonic Testing of Piping Welds Subjected to the Mechanical Stress Improvement Process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, Michael T.; Cinson, Anthony D.; Crawford, Susan L.

2010-12-01

Pacific Northwest National Laboratory (PNNL) is assisting the United States Nuclear Regulatory Commission (NRC) in developing a position on the management of primary water stress corrosion cracking (PWSCC) in leak-before-break piping systems. Part of this involves determining whether inspections alone, or inspections plus mitigation, are needed. This work addresses the reliability of ultrasonic testing (UT) of cracks that have been mitigated by the mechanical stress improvement process (MSIP). The MSIP has been approved by the NRC (NUREG-0313) since 1986 and modifies residual stresses remaining after welding with compressive, or neutral, stresses near the inner diameter surface of the pipe. Thismore » compressive stress is thought to arrest existing cracks and inhibit new crack formation. To evaluate the effectiveness of the MSIP and the reliability of ultrasonic inspections, flaws were evaluated both before and after MSIP application. An initial investigation was based on data acquired from cracked areas in 325-mm-diameter piping at the Ignalina Nuclear Power Plant (INPP) in Lithuania. In a follow-on exercise, PNNL acquired and evaluated similar UT data from a dissimilar metal weld (DMW) specimen containing implanted thermal fatigue cracks. The DMW specimen is a carbon steel nozzle-to-safe end-to-stainless steel pipe section that simulates a pressurizer surge nozzle. The flaws were implanted in the nozzle-to-safe end Alloy 82/182 butter region. Results are presented on the effects of MSIP on specimen surfaces, and on UT flaw responses.« less

40 CFR 63.1560 - What is the purpose of this subpart?

Code of Federal Regulations, 2010 CFR

2010-07-01

... Standards for Hazardous Air Pollutants for Petroleum Refineries: Catalytic Cracking Units, Catalytic... from petroleum refineries. This subpart also establishes requirements to demonstrate initial and continuous compliance with the emission limitations and work practice standards. ...

Advances of two-stage riser catalytic cracking of heavy oil for maximizing propylene yield (TMP) process.

PubMed

Chaohe, Yang; Xiaobo, Chen; Jinhong, Zhang; Chunyi, Li; Honghong, Shan

Two-stage riser catalytic cracking of heavy oil for maximizing propylene yield (TMP) process proposed by State Key Laboratory of Heavy oil Processing, China University of Petroleum, can remarkably enhance the propylene yield and minimize the dry gas and coke yields, and obtain high-quality light oils (gasoline and diesel). It has been commercialized since 2006. Up to now, three TMP commercial units have been put into production and other four commercial units are under design and construction. The commercial data showed that taking paraffinic based Daqing (China) atmospheric residue as the feedstock, the propylene yield reached 20.31 wt%, the liquid products yield (the total yield of liquefied petroleum gas, gasoline, and diesel) was 82.66 wt%, and the total yield of dry gas and coke was 14.28 wt%. Moreover, the research octane number of gasoline could be up to 96.

Health hazard evaluation report HETA 83-248-1515, Arco Philadelphia refinery, Philadelphia, Pennsylvania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewis, F.A.; Parrish, G.

1984-10-01

A bulk sample of fractionator residue was analyzed for polynuclear aromatic (PNA) compounds at the catalytic cracking unit of ARCO Philadelphia Refinery (SIC-2911), Philadelphia, Pennsylvania in May, 1983. The study was requested by the Atlantic Independent Union to determine if skin rashes and skin irritation occurring among refinery workers were caused by PNA in the fractionators. The authors conclude that a health hazard from exposure to chemicals at the cracking unit may exist. No specific chemical agent can be identified. Dust from the catalyst and oily residues that could contaminate workers shoes and clothing may have contributed to some ofmore » the dermatitis cases. Recommendations include laundering workers coveralls by dry cleaning to insure the removal of oily residues, providing workers with oil resistant or oil proof work boots, and repairing the ventilator in the sample preparation room adjacent to the block house.« less

Failure analysis of glass-ceramic insulators of shock tested vacuum (neutron) tubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spears, R.K.

1980-08-25

Eight investigative techniques were used to examine the glass-ceramic insulators in vacuum (neutron) tubes. The insulators were extracted from units that had been subjected to low temperature mechanical shock tests. Two of the three units showed reduced neutron output after these tests and an insulator on one of these two was cracked completely through which probably occurred during shock testing. The objective of this study was to determine if any major differences existed between the insulators of these tubes. After eight analyses, it was concluded that no appreciable differences existed. It appeared that cracking of the one glass-ceramic sample wasmore » initiated at inner-sleeve interface voids. For this sample, the interface void density was much higher than is presently acceptable. All insulators were made with glass-ceramic having a Na/sub 2/O content of 4.6 wt%. An increased Na/sub 2/O content will cause an increase in the coefficient of expansion and will reduce the residual stress level since the molybdenum has a higher coefficient of thermal expansion than the insulator. Thus, it is believed that a decrease in interface voids and an increase in Na/sub 2/O should aid in reduced cracking of the insulator during these tests.« less

Proceedings of the 1980 Army Science Conference, United States Military Academy, West Point, New York, 17-20 June 1980. Volume 2. Principal Authors E through M.

DTIC Science & Technology

1980-07-21

is under pressure, ignition could result when the explosive extrudes into the crack. This has been suggested as a possible ignition mechanism when...to occur when thu explosive is extruded Into cracks in the conf:inlng steel case while the munition is under pressure. This latter sequence of events...SESSIONS routine. They ate a hot lunch and dinner on the aircraft at the usual U.S. ’times, plus a breakfast snack at 0810 CET. No alcoholic beverages

40 CFR Table 1 to Subpart Uuu of... - Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... heat boiler in which you burn auxiliary or in supplemental liquid or solid fossil fuel, the incremental... thermal units (lb/million Btu) of heat input attributable to the liquid or solid fossil fuel; and the... supplemental liquid or solid fossil fuel, the incremental rate of PM must not exceed 43.0 g/GJ (0.10 lb/million...

40 CFR Table 5 to Subpart Uuu of... - Initial Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... waste heat boiler in which you burn auxiliary or supplemental liquid or solid fossil fuel, the... thermal units (lb/million Btu) of heat input attributable to the liquid or solid fossil fuel; and the.../million Btu) of heat input attributable to the liquid or solid fossil fuel. As part of the Notification of...

40 CFR Table 1 to Subpart Uuu of... - Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... heat boiler in which you burn auxiliary or in supplemental liquid or solid fossil fuel, the incremental... thermal units (lb/million Btu) of heat input attributable to the liquid or solid fossil fuel; and the... supplemental liquid or solid fossil fuel, the incremental rate of PM must not exceed 43.0 g/GJ (0.10 lb/million...

40 CFR Table 5 to Subpart Uuu of... - Initial Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... waste heat boiler in which you burn auxiliary or supplemental liquid or solid fossil fuel, the... thermal units (lb/million Btu) of heat input attributable to the liquid or solid fossil fuel; and the.../million Btu) of heat input attributable to the liquid or solid fossil fuel. As part of the Notification of...

Application of Extra Virgin Olive Oil to Prevent Nipple Cracking in Lactating Women.

PubMed

Cordero, María José Aguilar; Villar, Norma Mur; Barrilao, Rafael Guisado; Cortés, Manuel Eduardo Cortés; López, Antonio Manuel Sánchez

2015-12-01

It is well established that extra virgin olive oil (EVOO), applied to the skin, has healing and anti-inflammatory properties. To evaluate the effectiveness of EVOO in the prevention of nipple cracking in lactating women. Experimental, prospective, randomized study of 300 lactating women, admitted to the postpartum unit of the city's general hospital (Cienfuegos, Cuba). The study was carried out in 2012. Eligible patients were randomized into two groups of 150 women. In Group 1, EVOO was applied on the nipple after feeding, and in Group 2, drops of breast milk were applied to the nipple after feeding. Clinical evaluations were made during the first week of treatment and after the first month. All women who initiated breastfeeding were considered eligible to be included in this study; breastfeeding was characterized as the moment of mother-child interaction with suction on the nipple. Efficacy was evaluated quantitatively, as the absence of cracks in the nipple during the first 2 weeks of lactation using as the proportion of women with or without nipple cracks, and if present, whether they were moderate or slight. The quantitative efficacy was 97.3% and no adverse effects occurred in mothers and newborns during the administration of EVOO. EVOO helps prevent nipple cracking in lactating women. It has been shown to have protective effects when breastfeeding presents technical difficulties. This conclusion is borne out by the frequency distribution results obtained, which reflect a significantly higher proportion of nipple cracking in the population that was not treated with EVOO. Use EVOO to prevent nipple cracking during breastfeeding by administering 3 drops on each nipple after each feeding. Decreased nipple cracking will reduce pain and enhance breastfeedinging by administering 3 drops on each nipple after each feeding, improving the health of mothers and infants. © 2015 Sigma Theta Tau International.

Subcritical crack propagation due to chemical rock weakening: macroscale chemo-plasticity and chemo-elasticity modeling

NASA Astrophysics Data System (ADS)

Hueckel, T.; Hu, M.

2015-12-01

Crack propagation in a subcritically stressed rock subject to chemically aggressive environment is analyzed and numerically simulated. Chemically induced weakening is often encountered in hydraulic fracturing of low-permeability oil/gas reservoirs and heat reservoirs, during storage of CO2 and nuclear waste corroding canisters, and other circumstances when rock matrix acidizing is involved. Upon acidizing, mineral mass dissolution is substantially enhanced weakening the rock and causing crack propagation and eventually permeability changes in the medium. The crack process zone is modeled mathematically via a chemo-plastic coupling and chemo-elastic coupling model. In plasticity a two-way coupling is postulated between mineral dissolution and a yield limit of rock matrix. The rate of dissolution is described by a rate law, but the mineral mass removal per unit volume is also a function of a variable internal specific surface area, which is in turn affected by the micro-cracking (treated as a plastic strain). The behavior of the rock matrix is modeled as rigid-plastic adding a chemical softening capacity to Cam-Clay model. Adopting the Extended Johnson's approximation of processes around the crack tip, the evolution of the stress field and deformation as a function of the chemically enhanced rock damage is modeled in a simplified way. In addition, chemical reactive transport is made dependent on plastic strain representing micro-cracking. Depending on mechanical and chemical boundary conditions, the area of enhanced chemical softening is near or somewhat away from the crack tip.In elasticity, chemo-mechanical effect is postulated via a chemical volumetric shrinkage strain proportional to mass removal variable, conceived analogously to thermal expansion. Two versions are considered: of constant coefficient of shrinkage and a variable one, coupled to deviatoric strain. Airy Potential approach used for linear elasticity is extended considering an extra term, which is uncoupled or coupled to strain. The later case requires iterations with solution of reactive transport equation. A decrease of stress intensity factor with time of reaction is well reproduced.

Fatigue crack growth model RANDOM2 user manual, appendix 1

NASA Technical Reports Server (NTRS)

Boyce, Lola; Lovelace, Thomas B.

1989-01-01

The FORTRAN program RANDOM2 is documented. RANDOM2 is based on fracture mechanics using a probabilistic fatigue crack growth model. It predicts the random lifetime of an engine component to reach a given crack size. Included in this user manual are details regarding the theoretical background of RANDOM2, input data, instructions and a sample problem illustrating the use of RANDOM2. Appendix A gives information on the physical quantities, their symbols, FORTRAN names, and both SI and U.S. Customary units. Appendix B includes photocopies of the actual computer printout corresponding to the sample problem. Appendices C and D detail the IMSL, Ver. 10(1), subroutines and functions called by RANDOM2 and a SAS/GRAPH(2) program that can be used to plot both the probability density function (p.d.f.) and the cumulative distribution function (c.d.f.).

Chemical Safety Alert: Hazards of Delayed Coker Unit (DCU) Operations

EPA Pesticide Factsheets

EPA and OSHA jointly publish this Chemical Safety Alert/Safety and Health Information Bulletin (CSA/SHIB) to increase awareness. DCU is a severe form of thermal cracking requiring high temperatures for long periods, for refining crude oils.

Flexible separator for alkaline batteries

NASA Technical Reports Server (NTRS)

Sheibley, D. W.

1977-01-01

Device is fabricated from low-cost readily-available commercial-materials by automated methods utilizing conventional paper coating processes. Flexibility of unit prevents cracking and disintegration caused by electrode warpage and dendrite growth, major causes of early battery failure with present separators.

Submittal of Final Post-Closure Inspection Letter Report for Corrective Action Unit 112: Area 23 Hazardous Waste Trenches, Nevada Test Site, Nevada, Revision 0, December 2007; DOE/NV--1103

DOE Office of Scientific and Technical Information (OSTI.GOV)

NSTec Environmental Restoration

This letter serves as the post-closure monitoring letter report for the above Corrective Action Unit (CAU) for the period October 2006-September 2007. Quarterly inspections were conducted on December 20,2006; March 29,2007; June 13,2007; and September 27, 2007, to observe the condition of the gate, use restriction warning signs, monuments, fencing, trenches, soil covers, and monitoring well covers. The first inspection was conducted on December 20,2006. Signs, fencing, riprap, monuments, and monitoring well covers were in excellent condition. No cracking, erosion, or subsidence was observed on the covers. No issues or concerns were identified, and no corrective actions were recommended. Themore » second inspection was conducted on March 29,2007. Signs, fencing, riprap, monuments, and monitoring well covers were in excellent condition. No cracking, erosion, or subsidence was observed on the covers. Vegetation that was observed to be growing in several locations on the cover was the only identified concern, for which removal was recommended. Vegetation was removed on May 24,2007. The third inspection was conducted on June 13,2007. Signs, fencing, riprap, monuments, and monitoring well covers were in excellent condition. No cracking, erosion, or subsidence was observed on the covers. No issues or concerns were identified, and no corrective actions were recommended. The fourth inspection was conducted on September 27,2007. Signs, fencing, riprap, monuments, and monitoring well covers were in excellent condition. No cracking, erosion, or subsidence was observed on the covers. No issues or concerns were identified, and no corrective actions were recommended. The post-closure inspection checklists for CAU 112 are attached. Photographs and field notes taken during site inspections are maintained in the project files.« less

75 FR 44236 - Agency Information Collection Activities; Submission to OMB for Review and Approval; Comment...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-28

..., Catalytic Cracking, Reforming and Sulfur Units (Renewal); EPA ICR Number 1844.04, OMB Control Number 2060... ICR Number 1844.04, OMB Control Number 2060-0554. ICR Status: This ICR is scheduled to expire on...

Creation of an ODOT specification for patching or overlay of bridge decks.

DOT National Transportation Integrated Search

2009-09-01

Bridge deck cracking is a huge problem in the United States, and various agencies have sponsored research endeavoring to determine the underlying problems. A number of causes have been identified, including thermal movement, plastic shrinkage, and ea...

Bridge deck cracking and composite action analyses : final report, March 2010.

DOT National Transportation Integrated Search

2010-03-01

According to the American Society of Civil Engineers Report Card (ASCE, 2005), United States infrastructure received a grade point average of "D"(i.e., poor rating) in 2005. Moreover, the National Bridge Inventory (Federal Highway Administration, 200...

7 CFR 51.491 - Wet slip.

Code of Federal Regulations, 2013 CFR

2013-01-01

..., CERTIFICATION, AND STANDARDS) United States Standards for Grades of Cantaloups 1 Definitions § 51.491 Wet slip. Wet slip means a condition present at time of packing in which the stem scar is abnormally large... cracks at the edge of the stem scar. ...

7 CFR 51.491 - Wet slip.

Code of Federal Regulations, 2014 CFR

2014-01-01

..., CERTIFICATION, AND STANDARDS) United States Standards for Grades of Cantaloups 1 Definitions § 51.491 Wet slip. Wet slip means a condition present at time of packing in which the stem scar is abnormally large... cracks at the edge of the stem scar. ...

Cohesive zone finite element analysis of crack initiation from a butt joint’s interface corner

DOE PAGES

Reedy, E. D.

2014-09-06

The Cohesive zone (CZ) fracture analysis techniques are used to predict the initiation of crack growth from the interface corner of an adhesively bonded butt joint. In this plane strain analysis, a thin linear elastic adhesive layer is sandwiched between rigid adherends. There is no preexisting crack in the problem analyzed, and the focus is on how the shape of the traction–separation (T–U) relationship affects the predicted joint strength. Unlike the case of a preexisting interfacial crack, the calculated results clearly indicate that the predicted joint strength depends on the shape of the T–U relationship. Most of the calculations usedmore » a rectangular T–U relationship whose shape (aspect ratio) is defined by two parameters: the interfacial strength σ* and the work of separation/unit area Γ. The principal finding of this study is that for a specified adhesive layer thickness, there is any number of σ*, Γ combinations that generate the same predicted joint strength. For each combination there is a corresponding CZ length. We developed an approximate CZ-like elasticity solution to show how such combinations arise and their connection with the CZ length.« less

Prevalence of Salmonella in 11 Spices Offered for Sale from Retail Establishments and in Imported Shipments Offered for Entry to the United States.

PubMed

Zhang, Guodong; Hu, Lijun; Pouillot, Régis; Tatavarthy, Aparna; Doren, Jane M Van; Kleinmeier, Daria; Ziobro, George C; Melka, David; Wang, Hua; Brown, Eric W; Strain, Errol; Bunning, Vincent K; Musser, Steven M; Hammack, Thomas S

2017-10-04

The U.S. Food and Drug Administration conducted a survey to evaluate Salmonella prevalence and aerobic plate counts in packaged (dried) spices offered for sale at retail establishments in the United States. The study included 7,250 retail samples of 11 spice types that were collected during November 2013 to September 2014 and October 2014 to March 2015. No Salmonella-positive samples (based on analysis of 125 g) were found among retail samples of cumin seed (whole or ground), sesame seed (whole, not roasted or toasted, and not black), and white pepper (ground or cracked), for prevalence estimates of 0.00% with 95% Clopper and Pearson's confidence intervals of 0.00 to 0.67%, 0.00 to 0.70%, and 0.00 to 0.63%, respectively. Salmonella prevalence estimates (confidence intervals) for the other eight spice types were 0.19% (0.0048 to 1.1%) for basil leaf (whole, ground, crushed, or flakes), 0.24% (0.049 to 0.69%) for black pepper (whole, ground, or cracked), 0.56% (0.11 to 1.6%) for coriander seed (ground), 0.19% (0.0049 to 1.1%) for curry powder (ground mixture of spices), 0.49% (0.10 to 1.4%) for dehydrated garlic (powder, granules, or flakes), 0.15% (0.0038 to 0.83%) for oregano leaf (whole, ground, crushed, or flakes), 0.25% (0.03 to 0.88%) for paprika (ground or cracked), and 0.64% (0.17 to 1.6%) for red pepper (hot red pepper, e.g., chili, cayenne; ground, cracked, crushed, or flakes). Salmonella isolates were serotyped, and genomes were sequenced. Samples of these same 11 spice types were also examined from shipments of imported spices offered for entry to the United States from 1 October 2011 to 30 September 2015. Salmonella prevalence estimates (based on analysis of two 375-g composite samples) for shipments of imported spices were 1.7 to 18%. The Salmonella prevalence estimates for spices offered for sale at retail establishments for all of the spice types except dehydrated garlic and basil were significantly lower than estimates for shipments of imported spice offered for entry.

Humanizing folk devils using ethnography.

PubMed

Myers, Peter L

2018-01-01

The sociological concepts of the "moral panic" and the deviant "folk devil" apply to the drug panics in the United States over methamphetamine, heroin, and crack cocaine. Mothers or pregnant women who smoke crack cocaine, and their babies, are assigned exaggerated "demonic" attributes that result in stigma and societal rejection. Otherwise, ethnographic studies of drug users demonstrate realities that are other than what might be considered were one to merely look at their use and the consequences. These considerations are examined with respect to the image of folk devils, methadone program attendees, smokers of "blunts," opium den habitués, and others grouped together as negative influences as a result of their drug habits.

Thermal gradients in Southwestern United States and the effect on bridge bearing loads : final report.

DOT National Transportation Integrated Search

2017-05-01

Thermal gradients became a component of bridge design after soffit cracking in prestressed concrete bridges was attributed to nonlinear temperature distribution through the depth of the bridge. While the effect of thermal gradient on stress distribut...

Fatigue Resistant Design Criteria for MD SHA Cantilevered Mast Arm Signal Structure : Research Summary

DOT National Transportation Integrated Search

2017-12-01

Over the past two decades, wind induced fatigue cracking of highway signs, luminaires, and traffic signal support structures have been increasingly reported all over the United States. While fatalities associated with these failures have been limited...

A new procedure for refurbishment of power plant Superalloy 617 by pulsed Nd:YAG laser process

NASA Astrophysics Data System (ADS)

Taheri, Naser; Naffakh-Moosavy, Homam; Ghaini, Farshid Malek

2017-06-01

The present study has evaluated the surface rejuvenation of aged Inconel 617 superalloy by both GTAW and pulsed Nd:YAG laser techniques. The gas tungsten arc welding (GTAW) by heat input per unit length [Q/V(J/mm)] of 280, 291.67, 309.74 and 225.48 (J/mm), and the pulse Nd:YAG laser process by the 15.71, 19.43 and 22.32 (J/mm), were employed. The Rosenthal equation was used for calculation of mushy zone (MZ) and partially-melted zone (PMZ). Size of MZ and PMZ in GTAW are more than 31 and 6 times than that of formed in pulsed Nd:YAG laser. According to the characterizations, solidification and liquation cracks were observed in these areas produced by GTAW whereas no cracks were identified in laser treated samples. Also, line scan EDS analyses demonstrated the interdendritic chromium and molybdenum segregation, which facilitated formation of hot cracks. With reduction in heat input per unit length, the hardness increased and the size of solidified metal microstructure reduced in pulse Nd:YAG laser. These comparative results showed that pulse Nd:YAG laser can easily be utilized as a new rejuvenation technique for aged Alloy 617 in comparison to the conventional processes due to extremely narrow MZ and HAZ and better surface soundness and mechanical properties.

Main steam-line break core shroud loading calculations for BWRs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shoop, U.; Feltus, M.A.; Baratta, A.J.

1995-12-31

In July 1994, the U.S. Nuclear regulatory Commission sent out Generic Letter 94-03 to all boiling water reactors in the United States, informing them of intergranular stress corrosion cracking of core shrouds found in 2 reactors. The letter directed all to perform safety analysis of the BWR units. Penn State performed scoping calculations to determine the forces experienced by the core shroud during a main-stream line break transient.

Processing and Applications of Depleted Uranium Alloy Products

DTIC Science & Technology

1976-09-01

temperal,,r at the wheel-metal interface, thus tending to produce surface cracks and in some cases to burn the metal. Data on speeds and feeds inr...comprehensive current resource of technical information on the development and utilization of advcnlod metal- or ceramic-base materials. The Center is operated...under the sponsorship of the Department of Defense. Neither the United Staxes Government nor any person acting on be ilf of the United States Government

Bridging micro to macroscale fracture properties in highly heterogeneous brittle solids: weak pinning versus fingering

NASA Astrophysics Data System (ADS)

Vasoya, Manish; Lazarus, Véronique; Ponson, Laurent

2016-10-01

The effect of strong toughness heterogeneities on the macroscopic failure properties of brittle solids is investigated in the context of planar crack propagation. The basic mechanism at play is that the crack is locally slowed down or even trapped when encountering tougher material. The induced front deformation results in a selection of local toughness values that reflect at larger scale on the material resistance. To unravel this complexity and bridge micro to macroscale in failure of strongly heterogeneous media, we propose a homogenization procedure based on the introduction of two complementary macroscopic properties: An apparent toughness defined from the loading required to make the crack propagate and an effective fracture energy defined from the rate of energy released by unit area of crack advance. The relationship between these homogenized properties and the features of the local toughness map is computed using an iterative perturbation method. This approach is applied to a circular crack pinned by a periodic array of obstacles invariant in the radial direction, which gives rise to two distinct propagation regimes: A weak pinning regime where the crack maintains a stationary shape after reaching an equilibrium position and a fingering regime characterized by the continuous growth of localized regions of the fronts while the other parts remain trapped. Our approach successfully bridges micro to macroscopic failure properties in both cases and illustrates how small scale heterogeneities can drastically affect the overall failure response of brittle solids. On a broader perspective, we believe that our approach can be used as a powerful tool for the rational design of heterogeneous brittle solids and interfaces with tailored failure properties.

The Remote Detection of Incipient Catastrophic Failure in Large Landslides

NASA Astrophysics Data System (ADS)

Petley, D.; Bulmer, M. H.; Murphy, W.; Mantovani, F.

2001-12-01

Landslide movement is commonly associated with brittle failure and ductile deformation. Kilburn and Petley (2001) proposed that cracking in landslides occurs due to downslope stress acting on the deforming horizon. If the assumption that a given crack event breaks a fixed distance of unbroken rock or soil the rate of cracking becomes equivalent to the number of crack events per unit time. Where crack growth (not nucleation) is occurring, the inverse rate of displacement changes linearly with time. Failure can be assumed to be the time at which displacement rates become infinitely large. Thus, for a slope heading towards catastrophic failure due to the development of a failure plane, this relationship would be linear, with the point at which failure will occur being the time when the line intercepts the x-axis. Increasing rates of deformation associated with ductile processes of crack nucleation would yield a curve with a negative gradient asymptopic to the x-axis. This hypothesis is being examined. In the 1960 movement of the Vaiont slide, Italy, although the rate of movement was accelerating, the plot of 1/deformation against time shows that it was increasing towards a steady state deformation. This movement has been associated with a low accumulated strain ductile phase of movement. In the 1963 movement event, the trend is linear. This was associated with a brittle phase of movement. A plot of 1/deformation against time for movement of the debris flow portion of the Tessina landslide (1998) shows a curve with a negative gradient asymptopic to the x-axis. This indicates that the debris flow moved as a result of ductile deformation processes. Plots of movement data for the Black Ven landslide over 1999 and 2001 also show curves that correlate with known deformation and catastrophic phases. The model results suggest there is a definable deformation pattern that is diagnostic of landslides approaching catastrophic failure. This pattern can be differentiated from landslides that are undergoing ductile deformation and those that are suffering crack nucleation.

Dynamic Analysis with Fibre Optic Sensors for Structural Health Monitoring

DTIC Science & Technology

2006-10-01

cracked thick aluminum plate repaired with a bonded composite patch using transmission-type extrinsic Fabry – Perot interferometric optical fiber...and optical filtering have been used to demodulate returned Bragg signals. Due to the passive nature of the interrogation unit, system bandwidth is

KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons electrowelds a crack formed in the insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

NASA Image and Video Library

2003-09-16

KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons electrowelds a crack formed in the insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons prepares to electroweld a crack formed in the insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

NASA Image and Video Library

2003-09-16

KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons prepares to electroweld a crack formed in the insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons prepares to electroweld a crack found on an insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

NASA Image and Video Library

2003-09-16

KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons prepares to electroweld a crack found on an insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

Softening non-metallic crystals by inhomogeneous elasticity.

PubMed

Howie, P R; Thompson, R P; Korte-Kerzel, S; Clegg, W J

2017-09-14

High temperature structural materials must be resistant to cracking and oxidation. However, most oxidation resistant materials are brittle and a significant reduction in their yield stress is required if they are to be resistant to cracking. It is shown, using density functional theory, that if a crystal's unit cell elastically deforms in an inhomogeneous manner, the yield stress is greatly reduced, consistent with observations in layered compounds, such as Ti 3 SiC 2 , Nb 2 Co 7 , W 2 B 5 , Ta 2 C and Ta 4 C 3 . The mechanism by which elastic inhomogeneity reduces the yield stress is explained and the effect demonstrated in a complex metallic alloy, even though the electronegativity differences within the unit cell are less than in the layered compounds. Substantial changes appear possible, suggesting this is a first step in developing a simple way of controlling plastic flow in non-metallic crystals, enabling materials with a greater oxidation resistance and hence a higher temperature capability to be used.

Transenamel and transdentinal penetration of hydrogen peroxide applied to cracked or microabrasioned enamel.

PubMed

Briso, A L F; Lima, A P B; Gonçalves, R S; Gallinari, M O; dos Santos, P H

2014-01-01

The present study evaluated transenamel and transdentinal penetration of hydrogen peroxide during tooth whitening recognized in altered enamel by the presence of cracks or microabrasion. We used 72 experimental units (n=20) obtained from bovine incisors: GI-sound enamel; GII-teeth showing visible enamel cracks (4 mm to 5.7 mm in length); and GIII-microabrasioned enamel. The 12 remaining specimens were used to analyze the enamel surface morphology using scanning electron microscopy. The specimens were cylindrical and 5.7 mm in diameter and 3.5 mm thick. A product based on 35% hydrogen peroxide was used for bleaching, following the manufacturer's recommendations for use. To quantify the H2O2 penetration, the specimens were placed in artificial pulp chambers containing an acetate buffer solution. After bleaching, the solution was collected and adequately proportioned with leucocrystal violet, peroxidase enzyme, and deionized water. The resulting solution was evaluated using ultraviolet visible reflectance spectrophotometer equipment. The data were analyzed by analysis of variance (ANOVA) and Fisher's PLSD at a significance level of 0.05, and significant differences in the penetration of peroxide in different substrate conditions were observed (p<0.0001). The penetration of hydrogen peroxide was more intense in cracked teeth. The group in which the enamel was microabraded showed intermediate values when compared to the control group. Microabrasion and the presence of cracks in the enamel make this substrate more susceptible to penetration of hydrogen peroxide during in-office whitening.

A simulation model for risk assessment of turbine wheels

NASA Technical Reports Server (NTRS)

Safie, Fayssal M.; Hage, Richard T.

1991-01-01

A simulation model has been successfully developed to evaluate the risk of the Space Shuttle auxiliary power unit (APU) turbine wheels for a specific inspection policy. Besides being an effective tool for risk/reliability evaluation, the simulation model also allows the analyst to study the trade-offs between wheel reliability, wheel life, inspection interval, and rejection crack size. For example, in the APU application, sensitivity analysis results showed that the wheel life limit has the least effect on wheel reliability when compared to the effect of the inspection interval and the rejection crack size. In summary, the simulation model developed represents a flexible tool to predict turbine wheel reliability and study the risk under different inspection policies.

A simulation model for risk assessment of turbine wheels

NASA Astrophysics Data System (ADS)

Safie, Fayssal M.; Hage, Richard T.

A simulation model has been successfully developed to evaluate the risk of the Space Shuttle auxiliary power unit (APU) turbine wheels for a specific inspection policy. Besides being an effective tool for risk/reliability evaluation, the simulation model also allows the analyst to study the trade-offs between wheel reliability, wheel life, inspection interval, and rejection crack size. For example, in the APU application, sensitivity analysis results showed that the wheel life limit has the least effect on wheel reliability when compared to the effect of the inspection interval and the rejection crack size. In summary, the simulation model developed represents a flexible tool to predict turbine wheel reliability and study the risk under different inspection policies.

Investigation into Z-Pin Reinforced Composite Skin/Stiffener Debond under Monotonic and Cyclic Bending

NASA Astrophysics Data System (ADS)

Zhang, Xiangyang; Li, Yong; Van Hoa, Suong; Xiao, Jun; Chu, Qiyi

2018-02-01

Skin/stiffener debonding has been a longstanding concern for the users of stiffened composite panels in long-term service. Z-pinning technology is an emerging solution to reinforce the composite assembly joints. This work experimentally characterizes the progressive debonding of Z-pinned skin/stiffener interface with the skin under static bend loading. The three-stage failure process is identified as: flange edge debonding, pin/laminate debonding, and ultimate structural failure. Three different distribution patterns were compared in terms of the static debonding properties revealed the affirmative fact that locating pins in high normal stress regions, that is close to the flange edges in skin/stiffener structures, is more beneficial to utilize the full potential of Z-pinning reinforcement. The unit strip FE model was developed and demonstrated effective to analysis the effect of Z-pin distribution on the ultimate debond load. On the other hand, the evolution of fatigue cracks at Z-pinned skin/flange interface was investigated with a series of displacement-controlled fatigue bending tests and microscopic observations. Results show that Z-pinning postpones crack initiations at low displacement levels, and the remarkable crack-arresting function of pins enables the structure a prolonged fatigue life. However, pins become less effective when the maximum displacement exceeds the crack initiation level due to gradually pullout of pins.

Fracture Mechanics and Beam Theory Analyses of Semi-Elliptical Cracks Originating in the Base of Rail.

DOT National Transportation Integrated Search

2012-04-17

In May 2011, a derailment of a passenger train occurred in a tunnel in the northeast region of the United States. Fortunately, no serious injuries or fatalities resulted from this derailment. The probable cause of the derailment was determined to be ...

Non Contacting Evaluation of Strains and Cracking Using Optical and Infrared Imaging Techniques

DTIC Science & Technology

1988-08-22

Compatible Zenith Z-386 microcomputer with plotter II. 3-D Motion Measurinq System 1. Complete OPTOTRAK three dimensional digitizing system. System includes...acquisition unit - 16 single ended analog input channels 3. Data Analysis Package software (KINEPLOT) 4. Extra OPTOTRAK Camera (max 224 per system

78 FR 13905 - Government-Owned Inventions, Available for Licensing

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-01

... to the National Aeronautics and Space Administration, have been filed in the United States Patent and... Including Crack Arresting Barrier; NASA Case No.: MFS 32761-1-CIP: Eddy Current Minimizing Flow Plug for Use in Flow Conditioning and Flow Metering. Sumara M. Thompson-King, Deputy General Counsel. [FR Doc...

7 CFR 51.2655 - Damage.

Code of Federal Regulations, 2010 CFR

2010-01-01

... FRESH FRUITS, VEGETABLES AND OTHER PRODUCTS 1,2 (INSPECTION, CERTIFICATION, AND STANDARDS) United States... within the stem cavity when deep or not well healed, or when the appearance is affected to a greater... deep or not well healed, or when the crack has weakened the cherry to the extent that it is likely to...

40 CFR Table 11 to Subpart Uuu of... - Requirements for Performance Tests for Organic HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2012 CFR

2012-07-01

...) for Carbon Monoxide (CO) 11 Table 11 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL..., Subpt. UUU, Table 11 Table 11 to Subpart UUU of Part 63—Requirements for Performance Tests for Organic...

40 CFR Table 11 to Subpart Uuu of... - Requirements for Performance Tests for Organic HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2013 CFR

2013-07-01

...) for Carbon Monoxide (CO) 11 Table 11 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL..., Subpt. UUU, Table 11 Table 11 to Subpart UUU of Part 63—Requirements for Performance Tests for Organic...

40 CFR Table 11 to Subpart Uuu of... - Requirements for Performance Tests for Organic HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2014 CFR

2014-07-01

...) for Carbon Monoxide (CO) 11 Table 11 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL..., Subpt. UUU, Table 11 Table 11 to Subpart UUU of Part 63—Requirements for Performance Tests for Organic...

Double Mantle Plume Upwelling—A Possible Formation Mechanism of Beta Plateau and Devana Chasma,Venus

NASA Astrophysics Data System (ADS)

Ding, N.

2009-12-01

Ning Ding,Zuoxun Zeng,China University of Geosciences,Wuhan,430074,China NingDing.eagle@gmail.com Introduction:Venus represents a‘one plate planet’[1],and the uplift,fractures and volcanism in Beta Regio on Venus are considered to be formed by lithosphere uplift driven by a hot plume[2]. Based on the double peaking saddle landform,we suggest the tectonic pattern of double mantle plume upwelling to interpret the formation mechanism of Beta Plateau and Devana Chasma.We take a physical modeling to validate this possibility. Model:There is no ductile shear in Venus[3],so we use quartz sands to simulate the crust of Venus.We use two wood stickes 1.5cm in diameter rising from the rubber canvas slowly and straight till about half of the model,then falling down slowly and straight.The base is a hard rubber plate,in the center of which,there are two holes 3cm in diameter,and the distance between them is 5cm.The holes are covered by rubber canvas.We use the quartz sands in colours of white, red and black with particle size of 70 mess as the model materials. Result:Fig.1:At the beginning of the wood stickes upwelling,only fine radial cracks are formed above the upwelling from central to outside.With the upwelling continue,surface energy of the fine radial cracks increase and make the cracks unstable,finally,the fine radial cracks connect each other and form a fracture zone.And then the two mantle plume downwelling,the fracture zone is developed to form a chasma at the end. Fig.2:The four profiles all form reverse faults outside and normal faults inside.But the difference is the faults in the middle of the chasma goes deeper than others.It is the pattern of Beta Plateau where the tectonic rising is cut by Devana Chasma zone in the topographic features. Fig.3:From the tow fig., we can see two points similar:a.the elevation is high and distribution area is large around the area of two upwelling and it is high around the area of chasma,but the distribution area is small;b.both of them shows saddle shape and two highland connectting bya chasma. Discussion:Based on the‘Geology Map of V-17’,two highlands of Northern part of Devana Chasma,but the material Unit of North and South highland are different.The material Units of North highland are the oldest unit tt and t,the material Unit of South highland is pl and the material Unit of rift is r are both the youngest unit.From the Magellan SAR mosaic[5],we can clearly see Devana Chasma cut the material Unit of tt and pl.So the two highlands of Northern part of Devana Chasma are simultaneous formed.The younger material Unit of South highland of Northern part of Devana Chasma is because of the volcanic eruption of Theia Mons. Conclusion:The physical modeling validates the model of the double plume upwelling is a possible explanation. Acknowledgements:This research was supported by the National Teaching Bases For Geology(CUG)foundation funded. References:[1]I.López,Icarus2008[2]A.T.Basilevsky,Icarus2007[3]J.C.Aubele,2009,LPSC[4]A.V.Vezolainen,2003,Journalofgeophysicalres5earch[5]http://planetarynames.wr.usgs.gov/images/v17_comp&v29_comp.pdf Fig.1 Fig.2 Fig.3a,3b

NASA Astrophysics Data System (ADS)

2018-04-01

In what follows, because of the loading symmetry, we can specify the boundary conditions in terms of the patch edges at x1andx2 , leaving as understood the fact that the opposed patch is similarly loaded. Also, we leave as understood that the normal tractions are zero elsewhere than on the loaded patches, and that the shear tractions are zero everywhere on the crack surfaces. Because the stress functions are written as functions of σ, we use Eq. (3) to define the angles θ1 =cos-1(x1 / c) and θ2 =cos-1(x2 / c) . Then the patch edges on the unit circle, σ1 =eiθ1 and σ2 =eiθ2 , are used to calculate the stress intensities and crack surface displacements.

The fracture energy and some mechanical properties of a polyurethane elastomer.

NASA Technical Reports Server (NTRS)

Mueller, H. K.; Knauss, W. G.

1971-01-01

The energy required to form a unit of new surface in the fracture of a polyurethane elastomer is determined. The rate sensitivity of the material has been reduced by swelling it in toluene. This paper primarily describes the experimental work of measuring the lower limit of the fracture energy. With this value and the creep compliance as a basis, the rate dependence of fracture energy for the unswollen material has been determined. It is thus shown that the dependence of the fracture energy on the rate of crack propagation can be explained by energy dissipation around the tip of the crack. Good agreement between the theoretically and experimentally determined relationships for the rate-sensitive fracture energy is demonstrated.

77 FR 64242 - Airworthiness Directives; The Boeing Company Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2012-10-19

... plc, P.O. Box 31, Derby, DE24 8BJ, United Kingdom; telephone 011 44 1332 242424; fax 011 44 1332... . For Bombardier service information identified in this proposed AD, contact Short Brothers PLC... investigation into the nature, cause, and extent of the cracking. If final action is later identified, based on...

78 FR 5505 - Turkey Point, Units 3 and 4; Application and Amendment to Facility Operating License Involving...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-25

...: You may access information and comment submissions related to this document, which the NRC possesses... access information related to this document, which the NRC possesses and are publicly available, by any... generation and the potential for stainless steel stress corrosion cracking is reduced. Therefore, the...

40 CFR Table 3 to Subpart Uuu of... - Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... system to measure and record the opacity of emissions from each catalyst regnerator vent. 4. Option 3: Ni... monitoring system to measure and record the gas flow rate 1. 5. Option 4: Ni lb/1,000 lbs of coke burn-off...

40 CFR Table 3 to Subpart Uuu of... - Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... system to measure and record the opacity of emissions from each catalyst regnerator vent. 4. Option 3: Ni... monitoring system to measure and record the gas flow rate 1. 5. Option 4: Ni lb/1,000 lbs of coke burn-off...

40 CFR 63.1565 - What are my requirements for organic HAP emissions from catalytic cracking units?

Code of Federal Regulations, 2013 CFR

2013-07-01

... operate at all times according to the procedures in the plan. (4) The emission limitations and operating... compliance with the emission limitations and work practice standards? You must: (1) Install, operate, and... ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS...

29 CFR 1919.71 - Unit proof test and examination of cranes.

Code of Federal Regulations, 2014 CFR

2014-07-01

..., including wire rope and wire rope terminals and connections, shall be checked with particular attention to sections of wire rope exposed to abnormal wear and to sections not normally exposed for examination. The provisions of § 1919.24 shall apply in wire rope examinations. Cracked or deformed hooks shall be discarded...

29 CFR 1919.71 - Unit proof test and examination of cranes.

Code of Federal Regulations, 2012 CFR

2012-07-01

..., including wire rope and wire rope terminals and connections, shall be checked with particular attention to sections of wire rope exposed to abnormal wear and to sections not normally exposed for examination. The provisions of § 1919.24 shall apply in wire rope examinations. Cracked or deformed hooks shall be discarded...

29 CFR 1919.71 - Unit proof test and examination of cranes.

Code of Federal Regulations, 2013 CFR

2013-07-01

..., including wire rope and wire rope terminals and connections, shall be checked with particular attention to sections of wire rope exposed to abnormal wear and to sections not normally exposed for examination. The provisions of § 1919.24 shall apply in wire rope examinations. Cracked or deformed hooks shall be discarded...

Human Trafficking and the Impact on National Security for the United States

DTIC Science & Technology

2006-03-15

governments in Southeast Asia to crack down on pedophile sex tourism – and many nations in that region have made progress.34 There is also a problem...Protection Project at Johns Hopkins University found that Cuba has “replaced Southeast Asia as a destination for pedophiles and sex tourists.” As

Advances in transient (pulsed) eddy current for inspection of multi-layer aluminum structures in the presence of ferrous fasteners

NASA Astrophysics Data System (ADS)

Desjardins, D. R.; Vallières, G.; Whalen, P. P.; Krause, T. W.

2012-05-01

An experimental investigation of the electromagnetic processes underlying transient (pulsed) eddy current inspection of aircraft wing structures in the vicinity of ferrous fasteners is performed. The separate effects of transient excitation of ferrous fastener and eddy currents induced in the surrounding aluminum structure are explored using a transmit-receive configuration with transient excitation of a steel rod, an aluminum plate with a bore hole and a steel rod through the bore hole. Observations are used to interpret results from a coupled driving and differential coil sensing unit applied to detect fatigue cracks emanating from bolt holes in aluminum structures with ferrous fasteners present. In particular, it is noted that abrupt magnetization of the fastener, by the probe's central driving unit, can transfer flux and consequently, induce strong eddy current responses deep within the aluminum structure in the vicinity of the bore hole. Rotation of the probe, centered over the fastener, permits detection of subsurface discontinuities, such as cracks, by the pair of differentially connected pickup coils.

Fatigue crack propagation in additively manufactured porous biomaterials.

PubMed

Hedayati, R; Amin Yavari, S; Zadpoor, A A

2017-07-01

Additively manufactured porous titanium implants, in addition to preserving the excellent biocompatible properties of titanium, have very small stiffness values comparable to those of natural bones. Although usually loaded in compression, biomedical implants can also be under tensional, shear, and bending loads which leads to crack initiation and propagation in their critical points. In this study, the static and fatigue crack propagation in additively manufactured porous biomaterials with porosities between 66% and 84% is investigated using compact-tension (CT) samples. The samples were made using selective laser melting from Ti-6Al-4V and were loaded in tension (in static study) and tension-tension (in fatigue study) loadings. The results showed that displacement accumulation diagram obtained for different CT samples under cyclic loading had several similarities with the corresponding diagrams obtained for cylindrical samples under compression-compression cyclic loadings (in particular, it showed a two-stage behavior). For a load level equaling 50% of the yield load, both the CT specimens studied here and the cylindrical samples we had tested under compression-compression cyclic loading elsewhere exhibited similar fatigue lives of around 10 4 cycles. The test results also showed that for the same load level of 0.5F y , the lower density porous structures demonstrate relatively longer lives than the higher-density ones. This is because the high bending stresses in high-density porous structures gives rise to local Mode-I crack opening in the rough external surface of the struts which leads to quicker formation and propagation of the cracks. Under both the static and cyclic loading, all the samples showed crack pathways which were not parallel to but made 45 ° angles with respect to the notch direction. This is due to the fact that in the rhombic dodecahedron unit cell, the weakest struts are located in 45 ° direction with respect to the notch direction. Copyright © 2017 Elsevier B.V. All rights reserved.

Qualitative and quantitative interpretation of SEM image using digital image processing.

PubMed

Saladra, Dawid; Kopernik, Magdalena

2016-10-01

The aim of the this study is improvement of qualitative and quantitative analysis of scanning electron microscope micrographs by development of computer program, which enables automatic crack analysis of scanning electron microscopy (SEM) micrographs. Micromechanical tests of pneumatic ventricular assist devices result in a large number of micrographs. Therefore, the analysis must be automatic. Tests for athrombogenic titanium nitride/gold coatings deposited on polymeric substrates (Bionate II) are performed. These tests include microshear, microtension and fatigue analysis. Anisotropic surface defects observed in the SEM micrographs require support for qualitative and quantitative interpretation. Improvement of qualitative analysis of scanning electron microscope images was achieved by a set of computational tools that includes binarization, simplified expanding, expanding, simple image statistic thresholding, the filters Laplacian 1, and Laplacian 2, Otsu and reverse binarization. Several modifications of the known image processing techniques and combinations of the selected image processing techniques were applied. The introduced quantitative analysis of digital scanning electron microscope images enables computation of stereological parameters such as area, crack angle, crack length, and total crack length per unit area. This study also compares the functionality of the developed computer program of digital image processing with existing applications. The described pre- and postprocessing may be helpful in scanning electron microscopy and transmission electron microscopy surface investigations. © 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society.

The J-2X Fuel Turbopump - Turbine Nozzle Low Cycle Fatigue Acceptance Rationale

NASA Technical Reports Server (NTRS)

Hawkins, Lakiesha V.; Duke, Gregory C.; Newman, Wesley R.; Reynolds, David C.

2011-01-01

The J-2X Fuel Turbopump (FTP) turbine, which drives the pump that feeds hydrogen to the J-2X engine for main combustion, is based on the J-2S design developed in the early 1970 s. Updated materials and manufacturing processes have been incorporated to meet current requirements. This paper addresses an analytical concern that the J-2X Fuel Turbine Nozzle Low Cycle Fatigue (LCF) analysis did not meet safety factor requirements per program structural assessment criteria. High strains in the nozzle airfoil during engine transients were predicted to be caused by thermally induced stresses between the vane hub, vane shroud, and airfoil. The heritage J-2 nozzle was of a similar design and experienced cracks in the same area where analysis predicted cracks in the J-2X design. Redesign options that did not significantly impact the overall turbine configuration were unsuccessful. An approach using component tests and displacement controlled fracture mechanics analysis to evaluate LCF crack initiation and growth rate was developed. The results of this testing and analysis were used to define the level of inspection on development engine test units. The programmatic impact of developing crack initiation/growth rate/arrest data was significant for the J-2X program. Final Design Certification Review acceptance logic will ultimately be developed utilizing this test and analytical data.

Metallurgical evaluation of a feedwater nozzle to safe-end weld

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowerman, B.S.; Czajkowski, C.J.; Roberts, T.C.

1999-11-01

Weld cracks in safety class systems are a serious concern, because these systems are part of the primary barrier providing containment of radioactive coolant. Loss of weld integrity yields leaks, or, under catastrophic failure, can be the basis for a severe loss of coolant accident. A circumferential indication was found by ultrasonic examination (UT) in the N4A-2 inlet feedwater nozzle to safe-end weld during the second refueling outage of River Bend Station Unit 1 in March 1989. The indication, approximately 15cm (6in) long with a reported maximum depth of 0.5cm (0.1in), was located in the Alloy 182 weld butter onmore » the safe-end side of the weld. (The safe-end base metal was ASME SA 508 Class 1 carbon steel.) The reported characteristics of the UT indication were indicative of intergranular stress corrosion cracking. This indication was reexamined during the second and third fuel cycles in March 1990 and September 1991, respectively, and during the third refuel outage in November 1990. Crack growth was reported during each examination. The safe-end was replaced during the fourth refueling outage in the summer of 1992. The US Nuclear Regulatory Commission (NRC) subsequently contracted with Brookhaven National laboratory (BNL) to conduct a confirmatory investigation to establish the failure mode and determine the root causes of cracking in the safe-end weld.« less

Metallurgical causes for the occurrence of creep damage in longitudinally seam-welded Cr-Mo high-energy piping

NASA Astrophysics Data System (ADS)

Zhou, Gang

A continuous occurrence of catastrophic failures, leaks and cracks of the Cr-Mo steam piping has created widespread utility concern for the integrity and serviceability of the seam-welded piping systems in power plants across USA. Cr-Mo steels are the materials widely used for elevated temperature service in fossil-fired generating stations. A large percentage of the power plant units with the Cr-Mo seam-welded steam piping have been in operation for a long duration such that the critical components of the units have been employed beyond the design life (30 or 40 years). This percentage will increase even more significantly in the near future. There is a strong desire to extend and thus there is a need to assess the remaining life of these units. Thus, understanding of the metallurgical causes for the failures and damage in the Cr-Mo seam-welded piping plays a major role in estimating possible life-extension and decision making on whether to operate, repair or replace. In this study, an optical metallographic method and a Cryo-Crack fractographic method have been developed for characterization and quantification of the damage in seam-welded steam piping. More than 500 metallographic assessments, from more than 25 power plants, have been accomplished using the optical metallographic method, and more than 200 fractographic specimens from 10 power plants have been evaluated using the "Cryo-Crack" fractographic technique. For comparison, "virgin" SA welds were fabricated using the Mohave welding procedure with re-N&T Mohave base metal with both "acid" and "basic" fluxes. The damage mechanism, damage distribution pattern, damage classification, correlation of the damage with the microstructural features of these SA welds and the impurity segregation patterns have been determined. A physical model for cavitation (leading to failure) in Cr-Mo SA weld metals and evaluation methodologies for high energy piping are proposed.

40 CFR Table 2 to Subpart Uuu of... - Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... daily average liquid-to-gas ratio above the limit established in the performance test. 4. Option 3: Ni.... Electrostatic precipitator Maintain the daily average Ni operating value no higher than the limit established...; maintain the monthly rolling average of the equilibrium catalyst Ni concentration no higher than the limit...

40 CFR Table 2 to Subpart Uuu of... - Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... daily average liquid-to-gas ratio above the limit established in the performance test. 4. Option 3: Ni.... Electrostatic precipitator Maintain the daily average Ni operating value no higher than the limit established...; maintain the monthly rolling average of the equilibrium catalyst Ni concentration no higher than the limit...

Fearing Prying U.S. Eyes, Canada's Colleges Crack Down On Computing

ERIC Educational Resources Information Center

Carnevale, Dan

2007-01-01

The USA Patriot Act is having far-reaching effects on the kinds of data that wind up on some academics' computers in Canada. Canadian colleges, responding to provincial laws passed in reaction to the Patriot Act, are preventing professors from entering the United States with students' private data on their laptops and limiting the locations of…

40 CFR 63.1565 - What are my requirements for organic HAP emissions from catalytic cracking units?

Code of Federal Regulations, 2010 CFR

2010-07-01

... according to the procedures in the plan. (4) The emission limitations and operating limits for organic HAP... work practice standards? You must: (1) Install, operate, and maintain a continuous monitoring system... operating limit in Table 9 of this subpart that applies to you according to the procedures in Table 11 of...

40 CFR 63.1565 - What are my requirements for organic HAP emissions from catalytic cracking units?

Code of Federal Regulations, 2011 CFR

2011-07-01

... according to the procedures in the plan. (4) The emission limitations and operating limits for organic HAP... work practice standards? You must: (1) Install, operate, and maintain a continuous monitoring system... operating limit in Table 9 of this subpart that applies to you according to the procedures in Table 11 of...

Ceramic transactions: Fractography of glasses and ceramics III. Volume 64

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varner, J.R.; Frechette, V.D.; Quinn, G.D.

1996-12-31

Reports are presented from the Third Annual Conference on the Fractography of Glasses and Ceramics. Topics include ceramics fracture mode, damage analysis, defect origin, deformation, crack evolution, and the use of laser raman spectroscopy for analysis of residual surface strains. Individual projects have been processed separately for the United States Department of Energy databases.

The influence of grain boundary geometry on intergranular crack propagation in Ni[sub 3]Al

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hui Lin; Pope, D.P.

1993-02-01

The distribution of grain boundary types along intergranular cracks in Ni[sub 3]Al was measured, by [Sigma] value, and compared to the distribution in the bulk, using statistically significant sample sizes. It was found that low angle ([Sigma] 1) and symmetrical [Sigma]3 boundaries (twins) are particularly strong, and all high angle boundaries, independent of their [Sigma] values are weak. In particular, low [Sigma], high angle boundaries, as a group, are also weak. These results are in qualitative agreement with predictions based on the structural unit model and imply that the fracture strength of an intergranularly brittle polycrystalline aggregate can be increasedmore » only by increasing the fraction of low angle and symmetrical [Sigma]3 boundaries.« less

Optical and Scanning Electron Microscopy of the Materials International Space Station Experiment (MISSE) Spacecraft Silicone Experiment

NASA Technical Reports Server (NTRS)

Hung, Ching-cheh; de Groh, Kim K.; Banks, Bruce A.

2012-01-01

Under a microscope, atomic oxygen (AO) exposed silicone surfaces are crazed and seen as "islands" separated by numerous crack lines, much analogous to mud-tile cracks. This research characterized and compared the degree of AO degradation of silicones by analyzing optical microscope images of samples exposed to low Earth orbit (LEO) AO as part of the Spacecraft Silicone Experiment. The Spacecraft Silicone Experiment consisted of eight DC 93-500 silicone samples exposed to eight different AO fluence levels (ranged from 1.46 to 8.43 10(exp 21) atoms/sq cm) during two different Materials International Space Station Experiment (MISSE) missions. Image analysis software was used to analyze images taken using a digital camera. To describe the morphological degradation of each AO exposed flight sample, three different parameters were selected and estimated: (1) average area of islands was determined and found to be in the 1000 to 3100 sq mm range; (2) total length of crack lines per unit area of the sample surface were determined and found to be in the range of 27 to 59 mm of crack length per sq mm of sample surface; and (3) the fraction of sample surface area that is occupied by crack lines was determined and found to be in the 25 to 56 percent range. In addition, average crack width can be estimated from crack length and crack area measurements and was calculated to be about 10 mm. Among the parameters studied, the fraction of sample surface area that is occupied by crack lines is believed to be most useful in characterizing the degree of silicone conversion to silicates by AO because its value steadily increases with increasing fluence over the entire fluence range. A series of SEM images from the eight samples exposed to different AO fluences suggest a complex sequence of surface stress due to surface shrinkage and crack formation, followed by re-distribution of stress and shrinking rate on the sample surface. Energy dispersive spectra (EDS) indicated that upon AO exposure, carbon content on the surface decreased relatively quickly at the beginning, to 32 percent of the pristine value for the least exposed sample in this set of experiments (1.46 10(exp 21) atoms/sq cm), but then decreased slowly, to 22 percent of the pristine value for the most exposed sample in this set of experiment (8.43 10(exp 21) atoms/sq cm). The oxygen content appears to increase at a slower rate. The least and most AO exposed samples were, respectively, 52 and 150 percent above the pristine values. The silicone samples with the greater AO exposure (7.75 10(exp 21) atoms/sq cm and higher) appear to have a surface layer which contains SiO2 with perhaps small amounts of unreacted silicone, CO and CO2 sealed inside.

Radial cracks around α-quartz inclusions in almandine: Constraints on the metamorphic history of the Oman mountains

NASA Astrophysics Data System (ADS)

Wendt, Anke S.; D'Arco, Philippe; Goffé, Bruno; Oberhänsli, Roland

1993-02-01

Radiating tensional cracks around α-quartz inclusions in almandine have been observed in metapelite samples from the southeastern Saih Hatat tectonic window, northeastern Oman Mountains. These almandines show an inclusion-rich (glaucophane + epidote) and strongly deformed core with inclusions of different mineral phases. The rim of the same almandines is inclusion-poor and shows only quartz, apatite, zircon, rutile and Ba sbnd Al phosphates as inclusions. Quartz and apatite inclusions in the rim are single crystals often surrounded by radial cracks. These radial cracks developed during uplift by the dilation of α-quartz (4-5 vol%) without a phase transformation. Subsequently, these cracks were filled with kaolinite, phengite (Si content 3.4 per formula unit, p.f.u.), chlorite and Fe oxides. We calculated the appearance of radial cracks without phase transformation using the mathematical procedure of Van der Molen and Van Roermund [1]. This calculation involves terms for thermal expansion, isothermal compressibility and shear modulus for the example of α-quartz and almandine for the same P and T interval during a retrograde path. Published geothermobarometric estimates give pressures of between 1.0 and 2.0 GPa and temperatures of between 450 and 600°C for the peak conditions for these rocks of the Saih Hatat tectonic window. On the basis of these P-T data we calculated different retrograde P-T paths in the α-quartz domain. Initiation of garnet fracturing is dependent on the P-T starting conditions and the component of isothermal compression of the retrograde path. The calculations yield a set of smooth monotonic curves whose exact position on the P-T plane between 0.1 and 0.6 GPa and 40 and 500°C depends on the initial P-T conditions and the component of isothermal compressibility of the retrograde P-T paths. This model can be used in general terms to estimate pressure and temperature for the following cases: (1) If independent evidence (such as petrological data) allow the determination of the final pressure at which radial cracks appeared, the initial inclusion pressure can be recalculated. (2) If the initial inclusion pressure is known (e.g. from petrological data), the conditions of radial cracking can be calculated, and the pair initial pressure-final pressure leads to an estimate of the shape of the retrograde P-T path as a function of its component of isothermal decompression. In the example from the northeastern Saih Hatat tectonic window the late syntectonic growth of albite + phengite + kaolinite suggests that the final pressure for fracturing ranged between 0.4 GPa and 0.5 GPa at temperatures of 300°C. These values correspond to high initial pressures of at least 2.0 GPa at a temperature of 550°C. The following geodynamic model is suggested: A regionally extended metamorphism led to the growth of inclusion-rich garnets in the rocks from the northeastern Saih Hatat tectonic window at depths of about 30 km ( < 0.1 GPa, about 450°C). Continuing prograde metamorphism at a depth of more than 60 km with P < 2.0 GPa and T ≈ 550°C affected a metapelite unit that is only exposed immediately south of As Sifah village. In this area, clear rims of almandine grew around the older garnets and entrapped mainly quartz and apatite. During uplift along a retrograde P-T path with a large component of isothermal decompression radial cracks around α-quartz inclusions developed in the rims of almandines at a depth of about 12 km (0.4-0.5 GPa, ⩾ 300°C).

NDE and DE of PWSCC Found in the J-Groove Weld of a Removed-From-Service Control Rod Drive Mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cumblidge, Stephen E.; Doctor, Steven R.; Schuster, George J.

2008-01-01

Studies conducted at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington focused on assessing the effectiveness of nondestructive examination (NDE) techniques for inspecting control rod drive mechanism (CRDM) nozzles and J-groove weldments. The primary objective of this work is to provide information to the United States Nuclear Regulatory Commission (US NRC) on the effectiveness of NDE methods as related to the in-service inspection of CRDM nozzles and J-groove weldments, and to enhance the knowledge base of primary water stress corrosion cracking (PWSCC) through destructive characterization of the CRDM assemblies. Two CRDM assemblies were removed from service, decontaminated, and thenmore » used in a series of laboratory NDE and DE measurements; this report addresses the following questions: 1) What did each NDE technique detect?, 2) What did each NDE technique miss?, 3) How accurately did each NDE technique characterize the detected flaws?, and finally 4) What were the basis for the NDE techniques performance? Two CRDM assemblies including the CRDM nozzle, the J-groove weld, buttering, and a portion of the ferritic head material were selected for this study. This paper focuses on a CRDM assembly that contained suspected PWSCC, based on in-service inspection data and through-wall leakage. The laboratory NDE measurements used to examine the CRDM assembly followed standard industry techniques for conducting in-service inspections of CRDM nozzles and the crown of the J-groove welds and buttering. These techniques included eddy current testing, time of flight diffraction ultrasound, and penetrant testing. In addition, other laboratory-based NDE methods were employed to conduct inspections of the CRDM assembly with particular emphasis on inspecting the J-groove weld and buttering. These techniques included volumetric ultrasonic inspection of the J-groove weld metal, visual testing via replicant material of the J-groove weld and high resolution photography of the J-groove weld crown and buttering. The results from these NDE studies were used to guide the development of the destructive characterization plan. The NDE studies found several crack-like indications. The NDE and DE studies determined that one of these was a through-weld radially-oriented PWSCC crack in the wetted surface of the J-groove weld, located at the transition point between the weld and the buttering. The crack was 6 mm long on the surface and quickly grew to 25 mm long at a depth of 8 mm, covering the length of the weld between the penetration tube and the carbon steel. The NDE studies found that only ET was able to detect the through-weld crack. The crack was oriented poorly for the ultrasonic testing, and was too tight for accurate PT or VT. The ET voltage response of the flaw was 30% that of a deep EDM notch. The DE performed on the crack consisted of slicing the crack into thin sections, polishing the sections, and then using optical and scanning electron microscopy (SEM) to characterize the crack. DE shows the crack was PWSCC and that it initiated on the wetted surface, grew and expanded through the weld metal, and exited into the annulus. The SEM examinations showed the crack followed the weld grain boundaries as it progressed through the weld. The crack was branched and discontinuous along its length.« less

Engineering Evaluation of International Low Impact Docking System Latch Hooks

NASA Technical Reports Server (NTRS)

Martinez, J.; Patin, R.; Figert, J.

2013-01-01

The international Low Impact Docking System (iLIDS) provides a structural arrangement that allows for visiting vehicles to dock with the International Space Station (ISS) (Fig 1). The iLIDS docking units are mechanically joined together by a series of active and passive latch hooks. In order to preserve docking capability at the existing Russian docking interfaces, the iLIDS latch hooks are required to conform to the existing Russian design. The latch hooks are classified as being fail-safe. Since the latch hooks are fail-safe, the hooks are not fracture critical and a fatigue based service life assessment will satisfy the structural integrity requirements. Constant amplitude fatigue testing to failure on four sets of active/passive iLIDS latch hooks was performed at load magnitudes of 10, 11, and 12 kips. Failure analysis of the hook fatigue failures identified multi-site fatigue initiation that was effectively centered about the hook mid-plane (consistent with the 3D model results). The fatigue crack initiation distribution implies that the fatigue damage accumulation effectively results in a very low aspect ratio surface crack (which can be simulated as thru-thickness crack). Fatigue damage progression resulted in numerous close proximity fatigue crack initiation sites. It was not possible to determine if fatigue crack coalescence occurs during cyclic loading or as result of the fast fracture response. The presence of multiple fatigue crack initiation sites on different planes will result in the formation of ratchet marks as the cracks coalesce. Once the stable fatigue crack becomes unstable and the fast fracture advances across the remaining ligament and the plane stress condition at a free-surface will result in failure along a 45 deg. shear plane (slant fracture) and the resulting inclined edge is called a shear lip. The hook thickness on the plane of fatigue crack initiation is 0.787". The distance between the shear lips on this plane was on the order of 0.48" and it was effectively centered about the mid-plane of the section. The numerous ratchet marks between the shear lips on the fracture initiation plane are indicative of multiple fatigue initiation sites within this region. The distribution of the fatigue damage about the centerline of the hook is consistent with the analytical results that demonstrate peak stress/strain response at the mid-plane that decreases in the direction of the hook outer surfaces. Scanning electron microscope images of the failed sections detected fatigue crack striations in close proximity to the free surface of the hook radius. These findings were documented at three locations on the fracture surface : 1) adjacent to the left shear lip, 2) adjacent to the right shear lip, and 3) near the centerline of the section. The features of the titanium fracture surface did not allow for a determination of a critical crack size via identification of the region where the fatigue crack propagation became unstable. The fracture based service life projections where benchmarked with strain-life analyses. The strainrange response in the hook radius was defined via the correlated finite element models and the modified method of universal slopes was incorporated to define the strain-life equation for the titanium alloy. The strain-life assessment confirmed that the fracture based projections were reasonable for the loading range of interest. Based upon the analysis and component level fatigue test data a preliminary service life capability for the iLIDS active and passive hooks of 2 lifetimes is projected (includes a scatter factor of 4).

In vitro validation of a shape-optimized fiber-reinforced dental bridge.

PubMed

Chen, YungChung; Li, Haiyan; Fok, Alex

2011-12-01

To improve its mechanical performance, structural optimization had been used in a previous study to obtain an alternative design for a 3-unit inlay-retained fiber-reinforced composite (FRC) dental bridge. In that study, an optimized layout of the FRC substructure had been proposed to minimize stresses in the veneering composite and interfacial stresses between the composite and substructure. The current work aimed to validate in vitro the improved fracture resistance of the optimized design. All samples for the 3-unit inlay-retained FRC dental bridge were made with glass-fibers (FibreKor) as the substructure, surrounded by a veneering composite (GC Gradia). Two different FRC substructure designs were prepared: a conventional (n=20) and an optimized design (n=21). The conventional design was a straight beam linking one proximal box to the other, while the optimized design was a curved beam following the lower outline of the pontic. All samples were loaded to 400N on a universal test machine (MTS 810) with a loading speed of 0.2mm/min. During loading, the force and displacement were recorded. Meanwhile, a two-channel acoustic emission (AE) system was used to monitor the development of cracks during loading. The load-displacement curves of the two groups displayed significant differences. For the conventional design, there were numerous drops in load corresponding to local damage of the sample. For the optimized design, the load curves were much smoother. Cracks were clearly visible on the surface of the conventional group only, and the directions of those cracks were perpendicular to those of the most tensile stresses. Results from the more sensitive AE measurement also showed that the optimized design had, on average, fewer cracking events: 38 versus 2969 in the conventional design. The much lower number of AE events and smoother load-displacement curves indicated that the optimized FRC bridge design had a higher fracture resistance. It is expected that the optimized design will significantly improve the clinical performance of FRC bridges. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Status of ash (Fraxinus spp.) species in Alabama, Arkansas, Mississippi, and Louisiana, 2013

Treesearch

S.N. Oswalt

2015-01-01

The emerald ash borer (EAB; Agrilus planipennis) is an introduced Asian beetle species that was first detected in trees in the Fraxinus (ash) genus in the United States in 2002. Female EAB beetles lay between 40 to 70 eggs in cracks, crevices, and beneath bark flakes. The eggs hatch within about 2 weeks, larvae bore through the...

40 CFR Table 1 to Subpart Uuu of... - Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... incinerator or waste heat boiler in which you burn auxiliary or in supplemental liquid or solid fossil fuel... fossil fuel; and the opacity of emissions must not exceed 30 percent, except for one 6-minute average... burn auxiliary or supplemental liquid or solid fossil fuel, the incremental rate of PM must not exceed...

40 CFR Table 1 to Subpart Uuu of... - Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... incinerator or waste heat boiler in which you burn auxiliary or in supplemental liquid or solid fossil fuel... fossil fuel; and the opacity of emissions must not exceed 30 percent, except for one 6-minute average... burn auxiliary or supplemental liquid or solid fossil fuel, the incremental rate of PM must not exceed...

Three-dimensional Crack Depth Profile Assessment using Near-Field Surface Acoustic Wave Signal Response (Postprint)

DTIC Science & Technology

2012-02-01

release; distribution unlimited. See additional restrictions described on inside pages STINFO COPY AIR FORCE RESEARCH...LABORATORY MATERIALS AND MANUFACTURING DIRECTORATE WRIGHT-PATTERSON AIR FORCE BASE, OH 45433-7750 AIR FORCE MATERIEL COMMAND UNITED STATES AIR FORCE...AFRL/RXLP) Materials and Manufacturing Directorate, Air Force Research Laboratory Wright-Patterson Air Force Base, OH 45433-7750 Air Force

Residual Strength Characterization of Unitized Structures Fabricated Using Different Manufacturing Technologies

NASA Technical Reports Server (NTRS)

Seshadri, B. R.; Smith, S. W.; Johnston, W. M.

2008-01-01

This viewgraph presentation describes residual strength analysis of integral structures fabricated using different manufacturing procedures. The topics include: 1) Built-up and Integral Structures; 2) Development of Prediction Methodology for Integral Structures Fabricated using different Manufacturing Procedures; 3) Testing Facility; 4) Fracture Parameters Definition; 5) Crack Branching in Integral Structures; 6) Results and Discussion; and 7) Concluding Remarks.

Coast Guard Deepwater Program: Background, Oversight Issues, and Options for Congress

DTIC Science & Technology

2007-02-20

NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e . TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Congressional...Appendix E: NGSS Testimony . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Appendix F: Lockheed Martin Testimony...stopped at eight hulls (rather than the entire fleet of 49) due to deck cracking, hull buckling, and shaft alignment problems. These patrol boat

Fatigue-Crack Propagation through a Measured Residual Stress Field in Alloy Steel

DTIC Science & Technology

1978-02-01

LABORATORY BENE’T WEAPONS LABORATORY WATERVLIET, N. Y. 12189 AMCMS No. 36525000204 DA Project No. 579101900GR1 PRON No. GG-8-25791-GG-M7 APPROVED FOR...10. PROGRAM ELEMENT, PROJECT, TASK AREA a WORK UNIT NUMBERS AMCMS No. 36525000204 DA Proj. No. 579101900GR1 PRON No. 6G-8-25791-GG-ri7 n

Monitoring for pests and diseases in native oak woodlands: the case of acute oak decline in the United Kingdom

Treesearch

Nathan Brown; Stephen Parnell; Frank van den Bosch; Mike Jeger; Sandra Denman

2017-01-01

In recent years, a novel form of decline has been observed in southern and central England. This syndrome has been termed acute oak decline (AOD) and affects native oak, Quercus petraea and Q. robur. Typical symptoms include bark cracks that weep dark exudates, which are caused by necrotic patches in the...

KSC-02pd1131

NASA Image and Video Library

2002-07-10

KENNEDY SPACE CENTER, FLA. -- Scott Minnick, with United Space Alliance, places a fiber-optic camera inside the flow line on Endeavour. Minnick wears a special viewing apparatus that sees where the camera is going. The inspection is the result of small cracks being discovered on the LH2 Main Propulsion System (MPS) flow liners in other orbiters. Endeavour is next scheduled to fly on mission STS-113.

KSC-02pd1128

NASA Image and Video Library

2002-07-10

KENNEDY SPACE CENTER, FLA. -- Scott Minnick, with United Space Alliance, places a fiber-optic camera inside the flow line on Endeavour. Minnick wears a special viewing apparatus that sees where the camera is going. The inspection is the result of small cracks being discovered on the LH2 Main Propulsion System (MPS) flow liners in other orbiters. Endeavour is next scheduled to fly on mission STS-113.

Fast pyrolysis oil from pinewood chips co-processing with vacuum gas oil in an FCC unit for second generation fuel production

DOE PAGES

Pinho, Andrea de Rezende; de Almeida, Marlon B. B.; Mendes, Fabio Leal; ...

2016-10-15

Raw bio-oil produced from fast pyrolysis of pine woodchips was co-processed with standard Brazilian vacuum gasoil (VGO) and tested in a 200 kg•h -1 fluid catalytic cracking (FCC) demonstration-scale unit using a commercial FCC equilibrium catalyst. Two different bio-oil/VGO weight ratios were used: 5/95 and 10/90. Co-processing of raw bio-oil in FCC was shown to be technically feasible. Bio-oil could be directly co-processed with a regular gasoil FCC feed up to 10 wt%. The bio-oil and the conventional gasoil were cracked into valuable liquid products such as gasoline and diesel range products. Most of the oxygen present in the bio-oilmore » was eliminated as water and carbon monoxide as these yields were always higher than that of carbon dioxide. Product quality analysis shows that trace oxygenates, primarily alkyl phenols, in FCC gasoline and diesel products are present with or without co-processing oxygenated intermediates. The oxygenate concentrations increase with co-processing, but have not resulted in increased concerns with quality of fuel properties. The presence of renewable carbon was confirmed in gasoline and diesel cuts through 14C isotopic analysis, showing that renewable carbon is not only being converted into coke, CO, and CO 2, but also into valuable refining liquid products. Thus, gasoline and diesel could be produced from lignocellulosic raw materials through a conventional refining scheme, which uses the catalytic cracking process. As a result, the bio-oil renewable carbon conversion into liquid products (carbon efficiency) was approximately 30%, well above the efficiency found in literature for FCC bio-oil upgrading.« less

Fast pyrolysis oil from pinewood chips co-processing with vacuum gas oil in an FCC unit for second generation fuel production

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinho, Andrea de Rezende; de Almeida, Marlon B. B.; Mendes, Fabio Leal

Raw bio-oil produced from fast pyrolysis of pine woodchips was co-processed with standard Brazilian vacuum gasoil (VGO) and tested in a 200 kg•h -1 fluid catalytic cracking (FCC) demonstration-scale unit using a commercial FCC equilibrium catalyst. Two different bio-oil/VGO weight ratios were used: 5/95 and 10/90. Co-processing of raw bio-oil in FCC was shown to be technically feasible. Bio-oil could be directly co-processed with a regular gasoil FCC feed up to 10 wt%. The bio-oil and the conventional gasoil were cracked into valuable liquid products such as gasoline and diesel range products. Most of the oxygen present in the bio-oilmore » was eliminated as water and carbon monoxide as these yields were always higher than that of carbon dioxide. Product quality analysis shows that trace oxygenates, primarily alkyl phenols, in FCC gasoline and diesel products are present with or without co-processing oxygenated intermediates. The oxygenate concentrations increase with co-processing, but have not resulted in increased concerns with quality of fuel properties. The presence of renewable carbon was confirmed in gasoline and diesel cuts through 14C isotopic analysis, showing that renewable carbon is not only being converted into coke, CO, and CO 2, but also into valuable refining liquid products. Thus, gasoline and diesel could be produced from lignocellulosic raw materials through a conventional refining scheme, which uses the catalytic cracking process. As a result, the bio-oil renewable carbon conversion into liquid products (carbon efficiency) was approximately 30%, well above the efficiency found in literature for FCC bio-oil upgrading.« less

Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

NASA Astrophysics Data System (ADS)

Moradian, Zabihallah; Einstein, Herbert H.; Ballivy, Gerard

2016-03-01

Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g., hits and energy) to stress-strain plots of rocks let us detect cracking levels properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper, the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro- and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages (1) crack closure, (2) linear elastic deformation, (3) micro-crack initiation (white patch initiation), (4) micro-crack growth (stable crack growth), (5) micro-crack coalescence (macro-crack initiation), (6) macro-crack growth (unstable crack growth), (7) macro-crack coalescence and (8) failure.

Investigation of Cracks Found in Helicopter Longerons

NASA Technical Reports Server (NTRS)

Newman, John A.; Baughman, James M.; Wallace, Terryl A.

2009-01-01

Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurigical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.

Investigation of Helicopter Longeron Cracks

NASA Technical Reports Server (NTRS)

Newman, John A.; Baughman, James; Wallace, Terryl A.

2009-01-01

Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurgical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.

The growth of small corrosion fatigue cracks in alloy 2024

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Willard, Scott A.

1993-01-01

The corrosion fatigue crack growth characteristics of small surface and corner cracks in aluminum alloy 2024 is established. The damaging effect of salt water on the early stages of small crack growth is characterized by crack initiation at constituent particle pits, intergranular microcracking for a less than 100 micrometers, and transgranular small crack growth for a micrometer. In aqueous 1 percent NaCl and at a constant anodic potential of -700 mV(sub SCE), small cracks exhibit a factor of three increase in fatigue crack growth rates compared to laboratory air. Small cracks exhibit accelerated corrosion fatigue crack growth rates at low levels of delta-K (less than 1 MPa square root of m) below long crack delta-K (sub th). When exposed to Paris regime levels of crack tip stress intensity, small corrosion fatigue cracks exhibit growth rates similar to that observed for long cracks. Results suggest that crack closure effects influence the corrosion fatigue crack growth rates of small cracks (a less than or equal to 100 micrometers). This is evidenced by similar small and long crack growth behavior at various levels of R. Contrary to the corrosion fatigue characteristics of small cracks in high strength steels, no pronounced chemical crack length effect is observed for Al by 2024 exposed to salt water.

Surface faulting along the inland Itozawa normal fault (eastern Japan) and relation to the 2011 Tohoku-oki megathrust earthquake

NASA Astrophysics Data System (ADS)

Ferry, Matthieu; Tsutsumi, Hiroyuki; Meghraoui, Mustapha; Toda, Shinji

2013-04-01

The 11 March 2011 Mw 9 Tohoku-oki earthquake ruptured ~500 km length of the Japan Trench along the coast of eastern Japan and significantly impacted the stress regime within the crust. The resulting change in seismicity over the Japan mainland was exhibited by the 11 April 2011 Mw 6.6 Iwaki earthquake that ruptured the Itozawa and Yunodake faults. Trending NNW and NW, respectively, these 70-80° W-dipping faults bound the Iwaki basin of Neogene age and have been reactivated simultaneously both along 15-km-long sections. Here, we present initial results from a paleoseismic excavation performed across the Itozawa fault within the Tsunagi Valley at the northern third of the observed surface rupture. At the Tsunagi site, the rupture affects a rice paddy, which provides an ideally horizontal initial state to collect detailed and accurate measurements. The surface break is composed of a continuous 30-to-40-cm-wide purely extensional crack that separates the uplifted block from a gently dipping 1-to-2-m-wide strip affected by right-stepping en-echelon cracks and locally bounded by a ~0.1-m-high reverse scarplet. Total station across-fault topographic profiles indicate the pre-earthquake ground surface was vertically deformed by ~0.6 m while direct field examinations reveal that well-defined rice paddy limits have been left-laterally offset by ~0.1 m. The 12-m-long, 3.5-m-deep trench exposes the 30-to-40-cm-thick cultivated soil overlaying a 1-m-thick red to yellow silt unit, a 2-m-thick alluvial gravel unit and a basal 0.1-1-m-thick organic-rich silt unit. Deformation associated to the 2011 rupture illustrates down-dip movement along a near-vertical fault with a well-expressed bending moment at the surface and generalized warping. On the north wall, the intermediate gravel unit displays a deformation pattern similar to granular flow with only minor discrete faulting and no splay to be continuously followed from the main fault to the surface. On the south wall, warping dominates as well but with some strain localization along two major splays that exhibit 15-20 cm of vertical offset. On both walls, the basal silt unit is vertically deformed by ~0.6 m, similarly to what is observed for the 2011 rupture. Furthermore, the base of said silt unit exhibits indication for secondary faulting prior to the 2011 event and that resemble cracks observed at the present-day surface. This suggests that the Itozawa fault has already ruptured in a similar fashion in the late Pleistocene). Hence, recent activity of the Itozawa fault may be controlled entirely by large to giant earthquakes along the Japan Trench.

A Crack Growth Evaluation Method for Interacting Multiple Cracks

NASA Astrophysics Data System (ADS)

Kamaya, Masayuki

When stress corrosion cracking or corrosion fatigue occurs, multiple cracks are frequently initiated in the same area. According to section XI of the ASME Boiler and Pressure Vessel Code, multiple cracks are considered as a single combined crack in crack growth analysis, if the specified conditions are satisfied. In crack growth processes, however, no prescription for the interference between multiple cracks is given in this code. The JSME Post-Construction Code, issued in May 2000, prescribes the conditions of crack coalescence in the crack growth process. This study aimed to extend this prescription to more general cases. A simulation model was applied, to simulate the crack growth process, taking into account the interference between two cracks. This model made it possible to analyze multiple crack growth behaviors for many cases (e. g. different relative position and length) that could not be studied by experiment only. Based on these analyses, a new crack growth analysis method was suggested for taking into account the interference between multiple cracks.

Unified risk analysis of fatigue failure in ductile alloy components during all three stages of fatigue crack evolution process.

PubMed

Patankar, Ravindra

2003-10-01

Statistical fatigue life of a ductile alloy specimen is traditionally divided into three stages, namely, crack nucleation, small crack growth, and large crack growth. Crack nucleation and small crack growth show a wide variation and hence a big spread on cycles versus crack length graph. Relatively, large crack growth shows a lesser variation. Therefore, different models are fitted to the different stages of the fatigue evolution process, thus treating different stages as different phenomena. With these independent models, it is impossible to predict one phenomenon based on the information available about the other phenomenon. Experimentally, it is easier to carry out crack length measurements of large cracks compared to nucleating cracks and small cracks. Thus, it is easier to collect statistical data for large crack growth compared to the painstaking effort it would take to collect statistical data for crack nucleation and small crack growth. This article presents a fracture mechanics-based stochastic model of fatigue crack growth in ductile alloys that are commonly encountered in mechanical structures and machine components. The model has been validated by Ray (1998) for crack propagation by various statistical fatigue data. Based on the model, this article proposes a technique to predict statistical information of fatigue crack nucleation and small crack growth properties that uses the statistical properties of large crack growth under constant amplitude stress excitation. The statistical properties of large crack growth under constant amplitude stress excitation can be obtained via experiments.

Crack-tip-opening angle measurements and crack tunneling under stable tearing in thin sheet 2024-T3 aluminum alloy

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Sutton, M. A.

1993-01-01

The stable tearing behavior of thin sheets 2024-T3 aluminum alloy was studied for middle crack tension specimens having initial cracks that were: flat cracks (low fatigue stress) and 45 degrees through-thickness slant cracks (high fatigue stress). The critical crack-tip-opening angle (CTOA) values during stable tearing were measured by two independent methods, optical microscopy and digital image correlation. Results from the two methods agreed well. The CTOA measurements and observations of the fracture surfaces showed that the initial stable tearing behavior of low and high fatigue stress tests is significantly different. The cracks in the low fatigue stress tests underwent a transition from flat-to-slant crack growth, during which the CTOA values were high and significant crack tunneling occurred. After crack growth equal to about the thickness, CTOA reached a constant value of 6 deg and after crack growth equal to about twice the thickness, crack tunneling stabilized. The initial high CTOA values, in the low fatigue crack tests, coincided with large three-dimensional crack front shape changes due to a variation in the through-thickness crack tip constraint. The cracks in the high fatigue stress tests reach the same constant CTOA value after crack growth equal to about the thickness, but produced only a slightly higher CTOA value during initial crack growth. For crack growth on the 45 degree slant, the crack front and local field variables are still highly three-dimensional. However, the constant CTOA values and stable crack front shape may allow the process to be approximated with two-dimensional models.

40 CFR Table 6 to Subpart Uuu of... - Continuous Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... incinerator or waste heat boiler in which you burn auxiliary or supplemental liquid or solid fossil fuel, the... liquid or solid fossil fuel; and the opacity of emissions must not exceed 30 percent, except for one 6... liquid or solid fossil fuels (liters/hour or kilograms/hour) and the hours of operation during which...

40 CFR Table 6 to Subpart Uuu of... - Continuous Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... incinerator or waste heat boiler in which you burn auxiliary or supplemental liquid or solid fossil fuel, the... liquid or solid fossil fuel; and the opacity of emissions must not exceed 30 percent, except for one 6... liquid or solid fossil fuels (liters/hour or kilograms/hour) and the hours of operation during which...

An Enhanced Fuselage Ultrasound Inspection Approach for ISHM Purposes

DTIC Science & Technology

2012-03-01

daily reflections, this would not have been possible. Many thanks to the glorious Colombian Air Force “Asi se va a las Alturas” Francisco Ospina...ASIP Policies After the Aloha Accident, the public concerns increased and the United States Congress passed legislation known as the Aviation...Sensors: on- ground Optimization plus False Alarm Probability?, Useful Life?, Environmental Factors?, others Crack Found? FAA/USAF Approval of FMP

40 CFR Table 7 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

...-gas ratio above the limit established during the performance test. 4. Option 3: Ni lb/hr not subject to the NSPS for PM in 40 CFR 60.102. a. Continuous opacity monitoring system. The daily average Ni operating value must not exceed the site-specific Ni operating limit established during the performance test...

40 CFR Table 7 to Subpart Uuu of... - Continuous Compliance With Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

...-gas ratio above the limit established during the performance test. 4. Option 3: Ni lb/hr not subject to the NSPS for PM in 40 CFR 60.102. a. Continuous opacity monitoring system. The daily average Ni operating value must not exceed the site-specific Ni operating limit established during the performance test...

Environmental Impact Analysis Process. Environmental Assessment Proposed SMC Military Family Housing, San Pedro, California

DTIC Science & Technology

1998-12-01

paint conditions to be 98 percent intact, with cracking, flaking, and peeling noted on various exterior components of the units tested. The survey...paradisiaca var. seminifera Musa spp. banana bananas MYOPORACEAE Myoporum laetum Myoporum spp. myoporum myoporums MYRICACEAE Myrica...Chinese banyan common fig rubber plant Indian laurel fig rustyleaf fig white mulberry MUSACEAE Musa paradisiaca var. seminifera Musa spp. banana

Pacific Pediatric Advanced Care Initiative

DTIC Science & Technology

2010-10-01

cracked stopcock on the venous side c. Air introduced from medications infusing into the patient via a central venous line 6. After you have made sure...stopcock or pigtail. Withdraw volume to make venous pressures more negative History : Day 3 for a newborn infant with Group B sepsis. Eveything has...clinical laboratories, operating room, central supply, pharmacy, respiratory care, Neonatal Intensive Care Unit (NICU) nursing, Pediatric Intensive

Making the Merida Initiative Work

DTIC Science & Technology

2012-03-14

crack down on Mexican drug cartels through enhanced border security. The plan calls for additional personnel, increased intelligence capability and...Pentagon official.35 William Wechsler , Deputy Assistant Secretary of Defense for Counter-narcotics and Global Threats, testified to the Senate Armed...indirect support to units of the Mexican armed forces with counter-narco terrorism missions‖.36 Wechsler also stated, this is an emerging issue for DoD

Cyberspace Warfare: A New DoD Core Mission Area

DTIC Science & Technology

2013-05-01

information in the same way that people thrive on sumptuous cuisine . What sort of information? Stuff like how to crack passwords that open the portals... French , demonstrating the use of information to shape the strategic environment.”17 This united Northern Germany and Southern Germany as one nation...28 defeat their adversary in detail. On the other hand, the French elected to adopt a

Small fatigue cracks; Proceedings of the Second International Conference/Workshop, Santa Barbara, CA, Jan. 5-10, 1986

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ritchie, R.O.; Lankford, J.

Topics discussed in this volume include crack initiation and stage I growth, microstructure effects, crack closure, environment effects, the role of notches, analytical modeling, fracture mechanics characterization, experimental techniques, and engineering applications. Papers are presented on fatigue crack initiation along slip bands, the effect of microplastic surface deformation on the growth of small cracks, short fatigue crack behavior in relation to three-dimensional aspects and the crack closure effect, the influence of crack depth on crack electrochemistry and fatigue crack growth, and nondamaging notches in fatigue. Consideration is also given to models of small fatigue cracks, short crack theory, assessment ofmore » the growth of small flaws from residual strength data, the relevance of short crack behavior to the integrity of major rotating aero engine components, and the relevance of short fatigue crack growth data to the durability and damage tolerance analyses of aircraft.« less

Quantity Effect of Radial Cracks on the Cracking Propagation Behavior and the Crack Morphology

PubMed Central

Chen, Jingjing; Xu, Jun; Liu, Bohan; Yao, Xuefeng; Li, Yibing

2014-01-01

In this letter, the quantity effect of radial cracks on the cracking propagation behavior as well as the circular crack generation on the impacted glass plate within the sandwiched glass sheets are experimentally investigated via high-speed photography system. Results show that the radial crack velocity on the backing glass layer decreases with the crack number under the same impact conditions during large quantities of repeated experiments. Thus, the “energy conversion factor” is suggested to elucidate the physical relation between the cracking number and the crack propagation speed. Besides, the number of radial crack also takes the determinative effect in the crack morphology of the impacted glass plate. This study may shed lights on understanding the cracking and propagation mechanism in laminated glass structures and provide useful tool to explore the impact information on the cracking debris. PMID:25048684

Fatigue Crack Closure Analysis Using Digital Image Correlation

NASA Technical Reports Server (NTRS)

Leser, William P.; Newman, John A.; Johnston, William M.

2010-01-01

Fatigue crack closure during crack growth testing is analyzed in order to evaluate the critieria of ASTM Standard E647 for measurement of fatigue crack growth rates. Of specific concern is remote closure, which occurs away from the crack tip and is a product of the load history during crack-driving-force-reduction fatigue crack growth testing. Crack closure behavior is characterized using relative displacements determined from a series of high-magnification digital images acquired as the crack is loaded. Changes in the relative displacements of features on opposite sides of the crack are used to generate crack closure data as a function of crack wake position. For the results presented in this paper, remote closure did not affect fatigue crack growth rate measurements when ASTM Standard E647 was strictly followed and only became a problem when testing parameters (e.g., load shed rate, initial crack driving force, etc.) greatly exceeded the guidelines of the accepted standard.

Comparing the floquet stability of open and breathing fatigue cracks in an overhung rotordynamic system

NASA Astrophysics Data System (ADS)

Varney, Philip; Green, Itzhak

2017-11-01

Rotor cracks represent an uncommon but serious threat to rotating machines and must be detected early to avoid catastrophic machine failure. An important aspect of analyzing rotor cracks is understanding their influence on the rotor stability. It is well-known that the extent of rotor instability versus shaft speed is exacerbated by deeper cracks. Consequently, crack propagation can eventually result in an unstable response even if the shaft speed remains constant. Most previous investigations of crack-induced rotor instability concern simple Jeffcott rotors. This work advances the state-of-the-art by (a) providing a novel inertial-frame model of an overhung rotor, and (b) assessing the stability of the cracked overhung rotor using Floquet stability analysis. The rotor Floquet stability analysis is performed for both an open crack and a breathing crack, and conclusions are drawn regarding the importance of appropriately selecting the crack model. The rotor stability is analyzed versus crack depth, external viscous damping ratio, and rotor inertia. In general, this work concludes that the onset of instability occurs at lower shaft speeds for thick rotors, lower viscous damping ratios, and deeper cracks. In addition, when comparing commensurate cracks, the breathing crack is shown to induce more regions of instability than the open crack, though the open crack generally predicts an unstable response for shallower cracks than the breathing crack. Keywords: rotordynamics, stability, rotor cracks.

Surface Studies of Ultra Strength Drilling Steel after Corrosion Fatigue in Simulated Sour Environment

DOE Office of Scientific and Technical Information (OSTI.GOV)

M. Ziomek-Moroz; J.A. Hawk; R. Thodla

2012-05-06

The Unites States predicted 60% growth in energy demand by 2030 makes oil and natural gas primary target fuels for energy generation. The fact that the peak of oil production from shallow wells (< 5000 m) is about to be reached, thereby pushing the oil and natural gas industry into deeper wells. However, drilling to depths greater than 5000 m requires increasing the strength-to weight ratio of the drill pipe materials. Grade UD-165 is one of the ultra- high yield strength carbon steels developed for ultra deep drilling (UDD) activities. Drilling UDD wells exposes the drill pipes to Cl{sup -},more » HCO{sub 3}{sup -}/CO{sub 3}{sup 2-}, and H{sub 2}S-containig corrosive environments (i.e., sour environments) at higher pressures and temperatures compared to those found in conventional wells. Because of the lack of synergism within the service environment, operational stresses can result in catastrophic brittle failures characteristic for environmentally assisted cracking (EAC). Approximately 75% of all drill string failures are caused by fatigue or corrosion fatigue. Since there is no literature data on the corrosion fatigue performance of UD-165 in sour environments, research was initiated to better clarify the fatigue crack growth (FCGR) behavior of this alloy in UDD environments. The FCGR behavior of ultra-strength carbon steel, grade UD-165, was investigated by monitoring crack growth rate in deaerated 5%NaCl solution buffered with NaHCO{sub 3}/Na{sub 2}CO{sub 3} and in contact with H{sub 2}S. The partial pressure of H{sub 2}S (p{sub H2S}) was 0.83 kPa and pH of the solution was adjusted by NaOH to 12. The fatigue experiments were performed at 20 and 85 C in an autoclave with surface investigations augmented by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy. In this study, research focused on surface analyses supported by the fatigue crack growth rate measurements. Fig. 1 shows an SEM micrograph of the crack that propagated from the notch in the solution at 20 C. Accumulation of the corrosion products is visible along the crack. The EDX chemical analysis near the crack tip found iron, sulfur and oxygen in the passive layer. The surface of the sample after the fatigue test in the sour environment at 85{sup o}, Fig. 2, C looks different from that fatigued surface at 20 C. The crack propagates across the passive film that covers the surface fairly uniformly. Some spallation of the passive film is observed near the notch. The EDX chemical analysis of the passive film near the crack tip identified mainly iron, carbon and oxygen. It appears that temperature plays a very important role in formation of the passive film. This may be associated with different solubility of H{sub 2}S in the solution, which will be further studied.« less

A comparison of stress in cracked fibrous tissue specimens with varied crack location, loading, and orientation using finite element analysis.

PubMed

Peloquin, John M; Elliott, Dawn M

2016-04-01

Cracks in fibrous soft tissue, such as intervertebral disc annulus fibrosus and knee meniscus, cause pain and compromise joint mechanics. A crack concentrates stress at its tip, making further failure and crack extension (fracture) more likely. Ex vivo mechanical testing is an important tool for studying the loading conditions required for crack extension, but prior work has shown that it is difficult to reproduce crack extension. Most prior work used edge crack specimens in uniaxial tension, with the crack 90° to the edge of the specimen. This configuration does not necessarily represent the loading conditions that cause in vivo crack extension. To find a potentially better choice for experiments aiming to reproduce crack extension, we used finite element analysis to compare, in factorial combination, (1) center crack vs. edge crack location, (2) biaxial vs. uniaxial loading, and (3) crack-fiber angles ranging from 0° to 90°. The simulated material was annulus fibrosus fibrocartilage with a single fiber family. We hypothesized that one of the simulated test cases would produce a stronger stress concentration than the commonly used uniaxially loaded 90° crack-fiber angle edge crack case. Stress concentrations were compared between cases in terms of fiber-parallel stress (representing risk of fiber rupture), fiber-perpendicular stress (representing risk of matrix rupture), and fiber shear stress (representing risk of fiber sliding). Fiber-perpendicular stress and fiber shear stress concentrations were greatest in edge crack specimens (of any crack-fiber angle) and center crack specimens with a 90° crack-fiber angle. However, unless the crack is parallel to the fiber direction, these stress components alone are insufficient to cause crack opening and extension. Fiber-parallel stress concentrations were greatest in center crack specimens with a 45° crack-fiber angle, either biaxially or uniaxially loaded. We therefore recommend that the 45° center crack case be tried in future experiments intended to study crack extension by fiber rupture. Copyright © 2015 Elsevier Ltd. All rights reserved.

The Growth of Small Corrosion Fatigue Cracks in Alloy 7075

NASA Technical Reports Server (NTRS)

Piascik, Robert S.

2015-01-01

The corrosion fatigue crack growth characteristics of small (greater than 35 micrometers) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500×) crack length measurements in laboratory air and 1% sodium chloride (NaCl) environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN.

The Growth of Small Corrosion Fatigue Cracks in Alloy 7075

NASA Technical Reports Server (NTRS)

Piascik, R. S.

2001-01-01

The corrosion fatigue crack growth characteristics of small (less than 35 microns) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500X) crack length measurements in laboratory air and 1% NaCl environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN.

Engineering diagnostics for vortex-induced stay vanes cracks in a Francis turbine

NASA Astrophysics Data System (ADS)

D'Agostini Neto, Alexandre; Gissoni, Humberto, Dr.; Gonçalves, Manuel, Dr.; Cardoso, Rogério; Jung, Alexander, Dr.; Meneghini, Julio, Prof.

2016-11-01

Despite the fact that vortex-induced vibration (VIV) in hydraulic turbines components (especially in stay vanes) is a well-known phenomenon, it still remains challenging for operation and maintenance teams in several power plants around the world. Since the first publication of a similar problem in 1967, literature shows that at least 27 other turbines witnessed strong stay vane vibrations associated with vortex shedding. Recurrent stay vane cracks in a 250 MW Francis turbine in Brazil motivated an engineering study involving prototype measurements, structural and Computational Fluid Dynamics (CFD) analysis in order to determine a proper geometry modification that could eliminate the periodic vortex wake generated at the stay vanes trailing edge. First cracks appeared in 1978 just after the machine was put into operation. A study published in 1982 associated these cracks with dynamic excitations caused by the water flow at high flow conditions. New stay vane profiles were proposed and executed as well as improved welding recommendations. Cracks however, continued to appear requiring welding repairs roughly every two years. Although Voith Hydro was not the original equipment manufacturer for these units, the necessary information was available to study the issue and propose and execute new stay vane profiles. This paper details the approach taken for the study. First, indirect vibration measurements were used to determine vibration frequencies to help to characterize the affected mode shapes. These results were compared to finite element (FE) calculations. Strain gage measurements performed afterwards confirmed the conclusions of this analysis. Next, transient CFD calculations were run to reproduce the measured phenomenon and to serve as a basis for a new stay vane geometry. This modification was then implemented in the actual turbine stay vanes. A new set of indirect vibration measurements indicated the effectiveness of the proposed solution. Final confirmation will come from new strain gage measurements.

Novel dental adhesive resin with crack self-healing, antimicrobial and remineralization properties.

PubMed

Yue, Shichao; Wu, Junling; Zhang, Qiang; Zhang, Ke; Weir, Michael D; Imazato, Satoshi; Bai, Yuxing; Xu, Hockin H K

2018-05-18

Secondary caries at the tooth-restoration margins is a primary reason for restoration failure. Cracks at the margins lead to leakage which can trap bacteria, producing acids to cause caries. To date, there has been no report on developing an adhesive resin that has self-healing, antibacterial and remineralizing capabilities. The objectives of this study were to: (1) develop the first self-healing adhesive with antimicrobial and remineralizing capabilities, and (2) investigate the effects of incorporating microcapsules, dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP) for the first time. Self-healing microcapsules were synthesized with poly(urea-formaldehyde) (PUF) shells containing triethylene glycol dimethacrylate (TEGDMA) as the healing liquid. The new adhesive contained 7.5% microcapsules, 10% DMAHDM and 20% NACP. A single edge V-notched beam (SEVNB) method was used to measure the fracture toughness K IC and the autonomous crack-healing efficiency. An oral plaque microcosm biofilm model was tested. The new self-healing, antimicrobial and remineralizing dental adhesive matched the dentin bond strength of a commercial control (p > 0.1). The new adhesive achieved successful crack-healing, with an excellent K IC recovery of 67%. The new adhesive had strong antimicrobial activity, reducing biofilm colony-forming units by four orders of magnitude, and reducing biofilm acid production to 1/100th that of biofilms on the commercial control resin. A self-healing adhesive with antibacterial and remineralizing capabilities was developed for the first time. Excellent dentin bond strength, autonomous crack-healing and K IC recovery, and strong anti-biofilm properties were achieved for the new adhesive resin. The novel method of using triple agents (self-healing microcapsules + DMAHDM + NACP) is promising for applications in dental adhesives, cements, sealants and composites to combat the two main challenges: fracture and secondary caries. Copyright © 2018 Elsevier Ltd. All rights reserved.

The fragile elderly hip: Mechanisms associated with age-related loss of strength and toughness☆

PubMed Central

Reeve, Jonathan; Loveridge, Nigel

2014-01-01

Every hip fracture begins with a microscopic crack, which enlarges explosively over microseconds. Most hip fractures in the elderly occur on falling from standing height, usually sideways or backwards. The typically moderate level of trauma very rarely causes fracture in younger people. Here, this paradox is traced to the decline of multiple protective mechanisms at many length scales from nanometres to that of the whole femur. With normal ageing, the femoral neck asymmetrically and progressively loses bone tissue precisely where the cortex is already thinnest and is also compressed in a sideways fall. At the microscopic scale of the basic remodelling unit (BMU) that renews bone tissue, increased numbers of actively remodelling BMUs associated with the reduced mechanical loading in a typically inactive old age augments the numbers of mechanical flaws in the structure potentially capable of initiating cracking. Menopause and over-deep osteoclastic resorption are associated with incomplete BMU refilling leading to excessive porosity, cortical thinning and disconnection of trabeculae. In the femoral cortex, replacement of damaged bone or bone containing dead osteocytes is inefficient, impeding the homeostatic mechanisms that match strength to habitual mechanical usage. In consequence the participation of healthy osteocytes in crack-impeding mechanisms is impaired. Observational studies demonstrate that protective crack deflection in the elderly is reduced. At the most microscopic levels attention now centres on the role of tissue ageing, which may alter the relationship between mineral and matrix that optimises the inhibition of crack progression and on the role of osteocyte ageing and death that impedes tissue maintenance and repair. This review examines recent developments in the understanding of why the elderly hip becomes fragile. This growing understanding is suggesting novel testable approaches for reducing risk of hip fracture that might translate into control of the growing worldwide impact of hip fractures on our ageing populations. PMID:24412288

Laboratory Production of Biofuels and Biochemicals from a Rapeseed Oil through Catalytic Cracking Conversion.

PubMed

Ng, Siauw H; Shi, Yu; Heshka, Nicole E; Zhang, Yi; Little, Edward

2016-09-02

The work is based on a reported study which investigates the processability of canola oil (bio-feed) in the presence of bitumen-derived heavy gas oil (HGO) for production of transportation fuels through a fluid catalytic cracking (FCC) route. Cracking experiments are performed with a fully automated reaction unit at a fixed weight hourly space velocity (WHSV) of 8 hr(-1), 490-530 °C, and catalyst/oil ratios of 4-12 g/g. When a feed is in contact with catalyst in the fluid-bed reactor, cracking takes place generating gaseous, liquid, and solid products. The vapor produced is condensed and collected in a liquid receiver at -15 °C. The non-condensable effluent is first directed to a vessel and is sent, after homogenization, to an on-line gas chromatograph (GC) for refinery gas analysis. The coke deposited on the catalyst is determined in situ by burning the spent catalyst in air at high temperatures. Levels of CO2 are measured quantitatively via an infrared (IR) cell, and are converted to coke yield. Liquid samples in the receivers are analyzed by GC for simulated distillation to determine the amounts in different boiling ranges, i.e., IBP-221 °C (gasoline), 221-343 °C (light cycle oil), and 343 °C+ (heavy cycle oil). Cracking of a feed containing canola oil generates water, which appears at the bottom of a liquid receiver and on its inner wall. Recovery of water on the wall is achieved through washing with methanol followed by Karl Fischer titration for water content. Basic results reported include conversion (the portion of the feed converted to gas and liquid product with a boiling point below 221 °C, coke, and water, if present) and yields of dry gas (H2-C2's, CO, and CO2), liquefied petroleum gas (C3-C4), gasoline, light cycle oil, heavy cycle oil, coke, and water, if present.

Elastic/plastic analyses of advanced composites investigating the use of the compliant layer concept in reducing residual stresses resulting from processing

NASA Technical Reports Server (NTRS)

Arnold, Steven M.; Arya, Vinod K.; Melis, Matthew E.

1990-01-01

High residual stresses within intermetallic and metal matrix composite systems can develop upon cooling from the processing temperature to room temperature due to the coefficient of thermal expansion (CTE) mismatch between the fiber and matrix. As a result, within certain composite systems, radial, circumferential, and/or longitudinal cracks have been observed to form at the fiber-matrix interface. The compliant layer concept (insertion of a compensating interface material between the fiber and matrix) was proposed to reduce or eliminate the residual stress buildup during cooling and thus minimize cracking. The viability of the proposed compliant layer concept is investigated both elastically and elastoplastically. A detailed parametric study was conducted using a unit cell model consisting of three concentric cylinders to determine the required character (i.e., thickness and material properties) of the compliant layer as well as its applicability. The unknown compliant layer mechanical properties were expressed as ratios of the corresponding temperature dependent Ti-24Al-11Nb (a/o) matrix properties. The fiber properties taken were those corresponding to SCS-6 (SiC). Results indicate that the compliant layer can be used to reduce, if not eliminate, radial and circumferential residual stresses within the fiber and matrix and therefore also reduce or eliminate the radial cracking. However, with this decrease in in-plane stresses, one obtains an increase in longitudinal stress, thus potentially initiating longitudinal cracking. Guidelines are given for the selection of a specific compliant material, given a perfectly bonded system.

A nonlinear fracture mechanics approach to the growth of small cracks

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1983-01-01

An analytical model of crack closure is used to study the crack growth and closure behavior of small cracks in plates and at notches. The calculated crack opening stresses for small and large cracks, together with elastic and elastic plastic fracture mechanics analyses, are used to correlate crack growth rate data. At equivalent elastic stress intensity factor levels, calculations predict that small cracks in plates and at notches should grow faster than large cracks because the applied stress needed to open a small crack is less than that needed to open a large crack. These predictions agree with observed trends in test data. The calculations from the model also imply that many of the stress intensity factor thresholds that are developed in tests with large cracks and with load reduction schemes do not apply to the growth of small cracks. The current calculations are based upon continuum mechanics principles and, thus, some crack size and grain structure exist where the underlying fracture mechanics assumptions become invalid because of material inhomogeneity (grains, inclusions, etc.). Admittedly, much more effort is needed to develop the mechanics of a noncontinuum. Nevertheless, these results indicate the importance of crack closure in predicting the growth of small cracks from large crack data.

Radial Cracks Would Signal Wearout Of Turbine Blades

NASA Technical Reports Server (NTRS)

Paulus, Donald E.

1990-01-01

Nonfatal defects made to appear before fatal ones. Proposed to design turbine blades to crack radially before they crack chordwise. Advance radial cracking promoted in design by adjusting thermal stresses and net bending stresses. Prior appearance of radial crack or cracks in used blade serves as warning that more-threatening chordwise crack or cracks may subsequently appear. Blade replaced before it fails.

Edge-Cracking Behavior of CoCrFeMnNi High-Entropy Alloy During Hot Rolling

NASA Astrophysics Data System (ADS)

Won, Jong Woo; Kang, Minju; Kwon, Heoun-Jun; Lim, Ka Ram; Seo, Seong Moon; Na, Young Sang

2018-05-01

This work investigated edge-cracking behavior of equiatomic CoCrFeMnNi high-entropy alloy during hot rolling at rolling temperatures 500 ≤ T R ≤ 1000 °C. Edge cracks did not form in the material rolled at 500 °C, but widened and deepened into the inside of plate as T R increased from 500 °C. Edge cracks were most severe in the material rolled at 1000 °C. Mn-Cr-O type non-metallic inclusion and oxidation were identified as major factors that caused edge cracking. The inclusions near edge region acted as preferential sites for crack formation. Connection between inclusion cracks and surface cracks induced edge cracking. Rolling at T R ≥ 600 °C generated distinct inclusion cracks whereas they were not serious at T R = 500 °C, so noticeable edge cracks formed at T R ≥ 600 °C. At T R = 1000 °C, significant oxidation occurred at the crack surface. This accelerated edge crack penetration by embrittling the crack tip, so severe edge cracking occurred at T R = 1000 °C.

Gear crack propagation investigations

NASA Technical Reports Server (NTRS)

Lewicki, David G.; Ballarini, Roberto

1996-01-01

Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture ANalysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modeling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gages in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.

Mitigation of Crack Damage in Metallic Materials

NASA Technical Reports Server (NTRS)

Leser, Patrick E.; Newman, John A.; Smith, Stephen W.; Leser, William P.; Wincheski, Russell A.; Wallace, Terryl A.; Glaessgen, Edward H.; Piascik, Robert S.

2014-01-01

A system designed to mitigate or heal crack damage in metallic materials has been developed where the protected material or component is coated with a low-melting temperature film. After a crack is formed, the material is heated, melting the film which then infiltrates the crack opening through capillary action. Upon solidification, the healing material inhibits further crack damage in two ways. While the crack healing material is intact, it acts like an adhesive that bonds or bridges the crack faces together. After fatigue loading damages, the healing material in the crack mouth inhibits further crack growth by creating artificially-high crack closure levels. Mechanical test data show that this method sucessfully arrests or retards crack growth in laboratory specimens.

Shear fatigue crack growth - A literature survey

NASA Technical Reports Server (NTRS)

Liu, H. W.

1985-01-01

Recent studies of shear crack growth are reviewed, emphasizing test methods and data analyses. The combined mode I and mode II elastic crack tip stress fields are considered. The development and design of the compact shear specimen are described, and the results of fatigue crack growth tests using compact shear specimens are reviewed. The fatigue crack growth tests are discussed and the results of inclined cracks in tensile panels, center cracks in plates under biaxial loading, cracked beam specimens with combined bending and shear loading, center-cracked panels and double edge-cracked plates under cyclic shear loading are examined and analyzed in detail.

Inconel 690 is alloy of choice for steam-generator tubing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strauss, S.D.

1996-02-01

The product of two decades of research and plant application, Inconel 690 promises superior long-term resistance to tube cracking in comparison to alloy 600. Ongoing steam-generator management techniques applied at nuclear pressurized-water-reactor (PWR) plants focus on tube monitoring, inspection, and repair, and on water-chemistry control. Of greatest concern to owner/operators of steam generators (SGs) with recirculating (U-bend) rather than straight through tubes is corrosion of several forms, including pitting, thinning, and cracking. As problems persist and operating and maintenance (O and M) costs become prohibitive, managers must consider the remaining option: complete or partial SG replacement. Although replacement costs canmore » range upward of $100-million, this step restores full-power operation, simplifies inspection, shortens subsequent outages, increases unit availability, and reduces radiation exposure of maintenance personnel. Taken together, these can lead to economies over the long term.« less

Small-scale martian polygonal terrain: Implications for liquid surface water

USGS Publications Warehouse

Seibert, N.M.; Kargel, J.S.

2001-01-01

Images from the Mars Orbiter Camera (MOC) through August 1999 were analyzed for the global distribution of small-scale polygonal terrain not clearly resolved in Viking Orbiter imagery. With very few exceptions, small-scale polygonal terrain occurs at middle to high latitudes of the northern and southern hemisphere in Hesperian-age geologic units. The largest concentration of this terrain occurs in the Utopia basin in close association with scalloped depressions (interpreted as thermokarst) and appears to represent an Amazonia event. The morphology and occurence of small polygonal terrain suggest they are either mud desiccation cracks or ice-wedge polygons. Because the small-scale polygons in Utopia and Argyre Planitiae are associated with other cold-climate permafrost or glacial features, an ice-wedge model is preferred for these areas. Both cracking mechanisms work most effectively in water- or ice-rich finegrained material and may imply the seasonal or episodic existence of liquid water at the surface.

Three-Dimensional Analysis of Enamel Crack Behavior Using Optical Coherence Tomography.

PubMed

Segarra, M S; Shimada, Y; Sadr, A; Sumi, Y; Tagami, J

2017-03-01

The aim of this study was to nondestructively analyze enamel crack behavior on different areas of teeth using 3D swept source-optical coherence tomography (SS-OCT). Ten freshly extracted human teeth of each type on each arch ( n = 80 teeth) were inspected for enamel crack patterns on functional, contact and nonfunctional, or noncontact areas using 3D SS-OCT. The predominant crack pattern for each location on each specimen was noted and analyzed. The OCT observations were validated by direct observations of sectioned specimens under confocal laser scanning microscopy (CLSM). Cracks appeared as bright lines with SS-OCT, with 3 crack patterns identified: Type I - superficial horizontal cracks; Type II - vertically (occluso-gingival) oriented cracks; and Type III - hybrid or complicated cracks, a combination of a Type I and Type III cracks, which may or may not be confluent with each other. Type II cracks were predominant on noncontacting surfaces of incisors and canines and nonfunctional cusps of posterior teeth. Type I and III cracks were predominant on the contacting surfaces of incisors, cusps of canines, and functional cusps of posterior teeth. Cracks originating from the dental-enamel junction and enamel tufts, crack deflections, and the initiation of new cracks within the enamel (internal cracks) were observed as bright areas. CLSM observations corroborated the SS-OCT findings. We found that crack pattern, tooth type, and the location of the crack on the tooth exhibited a strong correlation. We show that the use of 3D SS-OCT permits for the nondestructive 3D imaging and analysis of enamel crack behavior in whole human teeth in vitro. 3D SS-OCT possesses potential for use in clinical studies for the analysis of enamel crack behavior.

A fracture criterion for widespread cracking in thin-sheet aluminum alloys

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Dawicke, D. S.; Sutton, M. A.; Bigelow, C. A.

1993-01-01

An elastic-plastic finite-element analysis was used with a critical crack-tip-opening angle (CTOA) fracture criterion to model stable crack growth in thin-sheet 2024-T3 aluminum alloy panels with single and multiple-site damage (MSD) cracks. Comparisons were made between critical angles determined from the analyses and those measured with photographic methods. Calculated load against crack extension and load against crack-tip displacement on single crack specimens agreed well with test data even for large-scale plastic deformations. The analyses were also able to predict the stable tearing behavior of large lead cracks in the presence of stably tearing MSD cracks. Small MSD cracks significantly reduced the residual strength for large lead cracks.

ADAPTATION OF CRACK GROWTH DETECTION TECHNIQUES TO US MATERIAL TEST REACTORS

DOE Office of Scientific and Technical Information (OSTI.GOV)

A. Joseph Palmer; Sebastien P. Teysseyre; Kurt L. Davis

2015-04-01

A key component in evaluating the ability of Light Water Reactors to operate beyond 60 years is characterizing the degradation of materials exposed to radiation and various water chemistries. Of particular concern is the response of reactor materials to Irradiation Assisted Stress Corrosion Cracking (IASCC). Some test reactors outside the United States, such as the Halden Boiling Water Reactor (HBWR), have developed techniques to measure crack growth propagation during irradiation. The basic approach is to use a custom-designed compact loading mechanism to stress the specimen during irradiation, while the crack in the specimen is monitored in-situ using the Direct Currentmore » Potential Drop (DCPD) method. In 2012 the US Department of Energy commissioned the Idaho National Laboratory and the MIT Nuclear Reactor Laboratory (MIT NRL) to take the basic concepts developed at the HBWR and adapt them to a test rig capable of conducting in-pile IASCC tests in US Material Test Reactors. The first two and half years of the project consisted of designing and testing the loader mechanism, testing individual components of the in-pile rig and electronic support equipment, and autoclave testing of the rig design prior to insertion in the MIT Reactor. The load was applied to the specimen by means of a scissor like mechanism, actuated by a miniature metal bellows driven by pneumatic pressure and sized to fit within the small in-core irradiation volume. In addition to the loader design, technical challenges included developing robust connections to the specimen for the applied current and voltage measurements, appropriate ceramic insulating materials that can endure the LWR environment, dealing with the high electromagnetic noise environment of a reactor core at full power, and accommodating material property changes in the specimen, due primarily to fast neutron damage, which change the specimen resistance without additional crack growth. The project culminated with an in-pile demonstration at the MIT Reactor. The test rig and associated support equipment were used to apply loads to a representative Compact Tensile specimen during one MITR operating cycle, while measuring crack growth using the DCPD method. Although the test period was short (approximately 70 days), and the accumulated neutron dose relatively small, successful operation of the test rig was demonstrated. The specimen was cycled more than 8000 times (more than would be typical for a long term IASCC test), which was sufficient to propagate a crack of over 2 mm.« less

Status of the steam generator tube circumferential ODSCC degradation experienced at the Doel 4 plant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roussel, G.

1997-02-01

Since the 1991 outage, the Doel Unit 4 nuclear power plant is known to be affected by circumferential outside diameter intergranular stress corrosion cracking at the hot leg tube expansion transition. Extensive non destructive examination inspections have shown the number of tubes affected by this problem as well as the size of the cracks to have been increasing for the three cycles up to 1993. As a result of the high percentage of tubes found non acceptable for continued service after the 1993 in-service inspection, about 1,700 mechanical sleeves were installed in the steam generators. During the 1994 outage, allmore » the tubes sleeved during the 1993 outage were considered as potentially cracked to some extent at the upper hydraulic transition and were therefore not acceptable for continued service. They were subsequently repaired by laser welding. Furthermore all the tubes not sleeved during the 1993 outage were considered as not acceptable for continued service and were repaired by installing laser welded sleeves. During the 1995 outage, some unexpected degradation phenomena were evidenced in the sleeved tubes. This paper summarizes the status of the circumferential ODSCC experienced in the SG tubes of the Doel 4 plant as well as the other connected degradation phenomena.« less

Effects of underground mining and mine collapse on the hydrology of selected basins in West Virginia

USGS Publications Warehouse

Hobba, William A.

1993-01-01

The effects of underground mining and mine collapse on areal hydrology were determined at one site where the mined bed of coal lies above major streams and at two sites where the bed of coal lies below major streams. Subsidence cracks observed at land surface generally run parallel to predominant joint sets in the rocks. The mining and subsidence cracks increase hydraulic conductivity and interconnection of water-bearing rock units, which in turn cause increased infiltration of precipitation and surface water, decreased evapotranspiration, and higher base flows in some small streams. Water levels in observation wells in mined areas fluctuate as much as 100 ft annually. Both gaining and losing streams are found in mined areas. Mine pumpage and drainage can cause diversion of water underground from one basin to another. Areal and single-well aquifer tests indicated that near-surface rocks have higher transmissivity in a mine-subsided basin than in unmined basins. Increased infiltration and circulation through shallow subsurface rocks increase dissolved mineral loads in streams, as do treated and untreated contributions from mine pumpage and drainage. Abandoned and flooded underground mines make good reservoirs because of their increased transmissivity and storage. Subsidence cracks were not detectable by thermal imagery, but springs and seeps were detectable.

Stress-intensity factor equations for cracks in three-dimensional finite bodies

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Raju, I. S.

1981-01-01

Empirical stress intensity factor equations are presented for embedded elliptical cracks, semi-elliptical surface cracks, quarter-elliptical corner cracks, semi-elliptical surface cracks at a hole, and quarter-elliptical corner cracks at a hole in finite plates. The plates were subjected to remote tensile loading. Equations give stress intensity factors as a function of parametric angle, crack depth, crack length, plate thickness, and where applicable, hole radius. The stress intensity factors used to develop the equations were obtained from three dimensional finite element analyses of these crack configurations.

Analysis of surface cracks in finite plates under tension or bending loads

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Raju, I. S.

1979-01-01

Stress-intensity factors calculated with a three-dimensional, finite-element analysis for shallow and deep semielliptical surface cracks in finite elastic isotropic plates subjected to tension or bending loads are presented. A wide range of configuration parameters was investigated. The ratio of crack depth to plate thickness ranged from 0.2 to 0.8 and the ratio of crack depth to crack length ranged from 0.2 to 2.0. The effects of plate width on stress-intensity variations along the crack front was also investigated. A wide-range equation for stress-intensity factors along the crack front as a function of crack depth, crack length, plate thickness, and plate width was developed for tension and bending loads. The equation was used to predict patterns of surface-crack growth under tension or bending fatigue loads. A modified form of the equation was also used to correlate surface-crack fracture data for a brittle epoxy material within + or - 10 percent for a wide range of crack shapes and crack sizes.

On Generating Fatigue Crack Growth Thresholds

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Newman, James, Jr.; Forman, Royce G.

2003-01-01

The fatigue crack growth threshold, defining crack growth as either very slow or nonexistent, has been traditionally determined with standardized load reduction methodologies. These experimental procedures can induce load history effects that result in crack closure. This history can affect the crack driving force, i.e. during the unloading process the crack will close first at some point along the wake or blunt at the crack tip, reducing the effective load at the crack tip. One way to reduce the effects of load history is to propagate a crack under constant amplitude loading. As a crack propagates under constant amplitude loading, the stress intensity factor range, Delta K, will increase, as will the crack growth rate. da/dN. A fatigue crack growth threshold test procedure is experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R. The authors have chosen to study a ductile aluminum alloy where the plastic deformations generated during testing may be of the magnitude to impact the crack opening.

United States Air Force Summer Faculty Research Program for 1990. Program Management Report

DTIC Science & Technology

1991-06-05

propagation characteristics were extensively studied using pencil lead breaks in a center notch. For the fatigue studies center crack samples of 2024 - T351 ... aluminum specimens during fatigue cycling. The experimental procedure involved excitation of Rayleigh waves on the surface of each specimen and...Research Program (SFRP) provides opportunities for research in the physical sciences, engineering, and life sciences. The program has been effective

40 CFR Table 5 to Subpart Uuu of... - Initial Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... fossil fuel, the incremental rate of PM must not exceed 43.0 grams per Gigajoule (g/GJ) or 0.10 pounds... fossil fuel; and the opacity of emissions must not exceed 30 percent, except for one 6-minute average... lb/million Btu) of heat input attributable to the liquid or solid fossil fuel. As part of the...

40 CFR Table 6 to Subpart Uuu of... - Continuous Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... fossil fuel, the incremental rate of PM must not exceed 43.0 g/GJ (0.10 lb/million Btu) of heat input attributable to the liquid or solid fossil fuel; and the opacity of emissions must not exceed 30 percent... combustion of liquid or solid fossil fuels (liters/hour or kilograms/hour) and the hours of operation during...

40 CFR Table 6 to Subpart Uuu of... - Continuous Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... fossil fuel, the incremental rate of PM must not exceed 43.0 g/GJ (0.10 lb/million Btu) of heat input attributable to the liquid or solid fossil fuel; and the opacity of emissions must not exceed 30 percent... combustion of liquid or solid fossil fuels (liters/hour or kilograms/hour) and the hours of operation during...

40 CFR Table 5 to Subpart Uuu of... - Initial Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... fossil fuel, the incremental rate of PM must not exceed 43.0 grams per Gigajoule (g/GJ) or 0.10 pounds... fossil fuel; and the opacity of emissions must not exceed 30 percent, except for one 6-minute average... lb/million Btu) of heat input attributable to the liquid or solid fossil fuel. As part of the...

40 CFR Table 6 to Subpart Uuu of... - Continuous Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... fossil fuel, the incremental rate of PM must not exceed 43.0 g/GJ (0.10 lb/million Btu) of heat input attributable to the liquid or solid fossil fuel; and the opacity of emissions must not exceed 30 percent... combustion of liquid or solid fossil fuels (liters/hour or kilograms/hour) and the hours of operation during...

40 CFR Table 5 to Subpart Uuu of... - Initial Compliance With Metal HAP Emission Limits for Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... fossil fuel, the incremental rate of PM must not exceed 43.0 grams per Gigajoule (g/GJ) or 0.10 pounds... fossil fuel; and the opacity of emissions must not exceed 30 percent, except for one 6-minute average... lb/million Btu) of heat input attributable to the liquid or solid fossil fuel. As part of the...

40 CFR 63.1564 - What are my requirements for metal HAP emissions from catalytic cracking units?

Code of Federal Regulations, 2013 CFR

2013-07-01

... coke burn-off emission limit (Option 4). (2) Comply with each operating limit in Table 2 of this... the PM emission rate (lb/1,000 lbs of coke burn-off) for each run using Equations 1, 2, and 3 (if applicable) of this section as follows: ER11AP02.000 Where: Rc = Coke burn-off rate, kg/hr (lb/hr); Qr...

40 CFR 63.1564 - What are my requirements for metal HAP emissions from catalytic cracking units?

Code of Federal Regulations, 2014 CFR

2014-07-01

... coke burn-off emission limit (Option 4). (2) Comply with each operating limit in Table 2 of this... the PM emission rate (lb/1,000 lbs of coke burn-off) for each run using Equations 1, 2, and 3 (if applicable) of this section as follows: ER11AP02.000 Where: Rc = Coke burn-off rate, kg/hr (lb/hr); Qr...

40 CFR 63.1564 - What are my requirements for metal HAP emissions from catalytic cracking units?

Code of Federal Regulations, 2012 CFR

2012-07-01

... coke burn-off emission limit (Option 4). (2) Comply with each operating limit in Table 2 of this... the PM emission rate (lb/1,000 lbs of coke burn-off) for each run using Equations 1, 2, and 3 (if applicable) of this section as follows: ER11AP02.000 Where: Rc = Coke burn-off rate, kg/hr (lb/hr); Qr...

Prediction of Crack Growth Aqueous Environments.

DTIC Science & Technology

1983-06-01

one- dimensional one. The mathematical model for the electrical representation shown in Figure 1 requires solutions to a set of differential equations ... equation (5) is equivalent to that at a plane-parallel electrode. That is, it contains the info~rmation that would be available if it were possible to...concentration, and A" expresses the electrode electrolyte area per unit length that is actively engaged in reaction. The other parameters in equation (7

Cold Expansion Effects on Cracked Fastener Holes Under Constant Amplitude and Spectrum Loading in the 2024-T351 Aluminum Alloy

DTIC Science & Technology

2012-05-01

1 1.2. History of Fatigue Designs ................................................................................... 2 1.3...of design . 1.2. History of Fatigue Designs 1.2.1. Safe Life Design The United States Air Force (USAF) has primarily used two design paradigms...for fatigue thus far. These paradigms are the Safe Life, and the Damage Tolerance fatigue designs . The American Society for Metals (ASM) Handbook

High Strength Steel Weldment Reliability: Weld Metal Hydrogen Trapping.

DTIC Science & Technology

1998-02-01

Reliability : Weld Metal Hydrogen Trapping submitted to : United States Army Research Office Materials Science Division P.O. Box 12211 Research Triangle...Conf. Proc. of Welding and Related Technologies for the XXIth Century, November 1998, Kiev, Ukraine : "Hydrogen Assisted Cracking in...appendices (see appendix IV). Next TTCP workshop will be held from 6th to 8th October 1998, at CANMET , Ottawa, Ontario, Canada. 20 III. Figures 18

Waste tyre rubberized concrete: properties at fresh and hardened state.

PubMed

Aiello, M A; Leuzzi, F

2010-01-01

The main objective of this paper is to investigate the properties of various concrete mixtures at fresh and hardened state, obtained by a partial substitution of coarse and fine aggregate with different volume percentages of waste tyres rubber particles, having the same dimensions of the replaced aggregate. Workability, unit weight, compressive and flexural strength and post-cracking behaviour were evaluated and a comparison of the results for the different rubcrete mixtures were proposed in order to define the better mix proportions in terms of mechanical properties of the rubberized concrete. Results showed in this paper were also compared to data reported in literature. Moreover, a preliminary geometrical, physical and mechanical characterization on scrap tyre rubber shreds was made. The rubberized concrete mixtures showed lower unit weight compared to plain concrete and good workability. The results of compressive and flexural tests indicated a larger reduction of mechanical properties of rubcrete when replacing coarse aggregate rather than fine aggregate. On the other hand, the post-cracking behaviour of rubberized concrete was positively affected by the substitution of coarse aggregate with rubber shreds, showing a good energy absorption and ductility indexes in the range observed for fibrous concrete, as suggested by standard (ASTM C1018-97, 1997). 2010 Elsevier Ltd. All rights reserved.

Study on Dynamic Strain Aging and Low-Cycle Fatigue of Stainless Steel in Ultra-Supercritical Unit

NASA Astrophysics Data System (ADS)

Hongwei, Zhou; Yizhu, He; Jizu, Lv; Sixian, Rao

Dynamic strain aging (DSA) and low-cycle fatigue (LCF) behavior of TP347H stainless steel in ultra-supercritical unit were investigated at 550-650 °C. All the LCF tests were carried out under a fully-reversed, total axial strain control mode at the total strain amplitude from ±0.2% to ±1.0%. The effects of DSA in cyclic stress response, microstructure evolution and fatigue fracture surfaces and fatigue life were investigated in detail. The results show that DSA occurs during tensile, which is manifested as serrated flow in tensile stress-strain curves. The apparent activation energy for appearing of serrations in tensile stress-strain curves was 270 kJ/mol. Pipe diffusion of substitutional solutes such as Cr and Nb along the dislocation core, and strong interactions between segregated solutes and dislocations are considered as the mechanism of DSA. DSA partly restricts dislocation cross-slip, and dislocation cross-slip and planar-slip happen simultaneously during LCF. A lot of planar structures form, which is due to dislocation gliding on the special plane. This localized deformation structures result in many crack initiation sites. Meanwhile, DSA hardening increases cyclic stress response, accelerating crack propagation, which reduces high temperature strain fatigue life of steel.

Matrix cracking with irregular fracture fronts as observed in fiber reinforced ceramic composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, K.X.; Yeh, C.P.; Wyatt, K.W.

1998-01-01

As a result of matrix cracking in fiber reinforced composites, fracture planforms assume a wide variation of profiles due to the fact that fiber bridging strongly affects the behavior of local crack fronts. This observation raises the question on the legitimacy of commonly used penny-shaped crack solutions when applied to fiber reinforced composites. Accordingly, investigation of the effects of fracture front profiles on mechanical responses is the thrust of this paper. The authors start with the solution of a penny-shaped crack in a unidirectional, fiber reinforced composite, which demonstrates necessity of considering wavy fracture fronts in fiber reinforced composites. Amore » theoretical framework for fiber reinforced composites with irregular fracture fronts due to matrix cracking is then established via a micromechanics model. The difference between small crack-size matrix cracking and large crack-size matrix cracking is investigated in detail. It is shown that the bridging effect is insignificant when matrix crack size is small and solution of effective property are obtained using Mori-Tanaka`s method by treating cracks and reinforcing fibers as distinct, but interacting phases. When the crack size becomes large, the bridging effects has to be taken into consideration. With bridging tractions obtained in consistency with the micromechanics solution, and corresponding crack energy backed out, the effective properties are obtained through a modification of standard Mori-Tanaka`s treatment of multiphase composites. Analytical solutions show that the generalization of a crack density of a penny-shaped planform is insufficient in describing the effective responses of fiber-reinforced composites with matrix cracking. Approximate solutions that account for the effects of the irregularity of crack planforms are given in closed forms for several irregular crack planforms, including cracks of cross rectangle, polygon and rhombus.« less

Durability and life prediction modeling in polyimide composites

NASA Technical Reports Server (NTRS)

Binienda, Wieslaw K.

1995-01-01

Sudden appearance of cracks on a macroscopically smooth surface of brittle materials due to cooling or drying shrinkage is a phenomenon related to many engineering problems. Although conventional strength theories can be used to predict the necessary condition for crack appearance, they are unable to predict crack spacing and depth. On the other hand, fracture mechanics theory can only study the behavior of existing cracks. The theory of crack initiation can be summarized into three conditions, which is a combination of a strength criterion and laws of energy conservation, the average crack spacing and depth can thus be determined. The problem of crack initiation from the surface of an elastic half plane is solved and compares quite well with available experimental evidence. The theory of crack initiation is also applied to concrete pavements. The influence of cracking is modeled by the additional compliance according to Okamura's method. The theoretical prediction by this structural mechanics type of model correlates very well with the field observation. The model may serve as a theoretical foundation for future pavement joint design. The initiation of interactive cracks of quasi-brittle material is studied based on a theory of cohesive crack model. These cracks may grow simultaneously, or some of them may close during certain stages. The concept of crack unloading of cohesive crack model is proposed. The critical behavior (crack bifurcation, maximum loads) of the cohesive crack model are characterized by rate equations. The post-critical behavior of crack initiation is also studied.

Crack-closure and crack-growth measurements in surface-flawed titanium alloy Ti6Al-4V

NASA Technical Reports Server (NTRS)

Elber, W.

1975-01-01

The crack-closure and crack-growth characteristics of the titanium alloy Ti-6Al-4V were determined experimentally on surface-flawed plate specimens. Under cyclic loading from zero to tension, cracks deeper than 1 mm opened at approximately 50 percent of the maximum load. Cracks shallower than 1 mm opened at higher loads. The correlation between crack-growth rate and the total stress-intensity range showed a lower threshold behavior. This behavior was attributed to the high crack-opening loads at short cracks because the lower threshold was much less evident in correlations between the crack-growth rates and the effective stress-intensity range.

Crack deflection: Implications for the growth of long and short fatigue cracks

NASA Astrophysics Data System (ADS)

Suresh, S.

1983-11-01

The influences of crack deflection on the growth rates of nominally Mode I fatigue cracks are examined. Previous theoretical analyses of stress intensity solutions for kinked elastic cracks are reviewed. Simple elastic deflection models are developed to estimate the growth rates of nonlinear fatigue cracks subjected to various degrees of deflection, by incorporating changes in the effective driving force and in the apparent propagation rates. Experimental data are presented for intermediate-quenched and step-quenched conditions of Fe/2Si/0.1C ferrite-martensite dual phase steel, where variations in crack morphology alone influence considerably the fatigue crack propagation rates and threshold stress intensity range values. Such results are found to be in good quantitative agreement with the deflection model predictions of propagation rates for nonlinear cracks. Experimental information on crack deflection, induced by variable amplitude loading, is also provided for 2020-T651 aluminum alloy. It is demonstrated with the aid of elastic analyses and experiments that crack deflection models offer a physically-appealing rationale for the apparently slower growth rates of long fatigue cracks subjected to constant and variable amplitude loading and for the apparent deceleration and/or arrest of short cracks. The changes in the propagation rates of deflected fatigue cracks are discussed in terms of the local mode of crack advance, microstructure, effective driving force, growth mechanisms, mean stress, slip characteristics, and crack closure.

Characterization of Cracking and Crack Growth Properties of the C5A Aircraft Tie-Box Forging

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Smith, Stephen W.; Newman, John A.; Willard, Scott A.

2003-01-01

Detailed destructive examinations were conducted to characterize the integrity and material properties of two aluminum alloy (7075-T6) horizontal stabilizer tie box forgings removed.from US. Air Force C5A and C5B transport aircraft. The C5B tie box forging was,found to contain no evidence of cracking. Thirteen cracks were found in the CSA,forging. All but one of the cracks observed in the C5A component were located along the top cap region (one crack was located in the bottom cap region). The cracks in the C5A component initiated at fastener holes and propagated along a highly tunneled intergranular crack path. The tunneled crack growth configuration is a likelv result of surface compressive stress produced during peening of the .forging suijace. The tie box forging ,fatigue crack growth, fracture and stress corrosion cracking (SCC) properties were characterized. Reported herein are the results of laboratory air ,fatigue crack growth tests and 95% relative humidity SCC tests conducted using specimens machined from the C5A ,forging. SCC test results revealed that the C5A ,forging material was susceptible to intergranular environmental assisted cracking: the C5A forging material exhibited a SCC crack-tip stress-intensity factor threshold of less than 6 MPadn. Fracture toughness tests revealed that the C5A forging material exhibited a fracture toughness that was 25% less than the C5B forging. The C5A forging exhibited rapid laboratory air fatigue crack growth rates having a threshold crack-tip stress-intensity factor range of less than 0.8 MPa sup m. Detailed fractographic examinations revealed that the ,fatigue crack intergranular growth crack path was similar to the cracking observed in the C5A tie box forging. Because both fatigue crack propagation and SCC exhibit similar intergranular crack path behavior, the damage mechanism resulting in multi-site cracking of tie box forgings cannot be determined unless local cyclic stresses can be quantified.

Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

NASA Technical Reports Server (NTRS)

Bassani, J. L.; Erdogan, F.

1979-01-01

The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks is considered. For the semi-infinite crack the problem is solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses are calculated. For finite cracks the problem is reduced to a pair of integral equations. Numerical results are obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

Stress intensity factors in a hollow cylinder containing a radial crack

NASA Technical Reports Server (NTRS)

Delale, F.

1980-01-01

An exact formulation of the plane elasticity problem for a hollow cylinder or a disk containing a radial crack is given. The crack may be an external edge crack, an internal edge crack, or an embedded crack. It is assumed that on the crack surfaces the shear traction is zero and the normal traction is an arbitrary function of r. For various crack geometries and radius ratios, the numerical results are obtained for a uniform crack surface pressure, for a uniform pressure acting on the inside wall of the cylinder, and for a rotating disk.

Stress intensity factors in a hollow cylinder containing a radial crack

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1982-01-01

In this paper, an exact formulation of the plane elasticity problem for a hollow cylinder or a disk containing a radial crack is given. The crack may be an external edge crack, an internal edge crack, or an embedded crack. It is assumed that on the crack surfaces the shear traction is zero, and the normal traction is an arbitrary function of radius. For various crack geometries and radius ratios, the numerical results are obtained for a uniform crack surface pressure, for a uniform pressure acting on the inside wall of the cylinder, and for a rotating disk.

Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

NASA Technical Reports Server (NTRS)

Bassani, J. L.; Erdogan, F.

1978-01-01

The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks was considered. For the semi-infinite crack the problem was solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses were calculated. For finite cracks the problem was reduced to a pair of integral equations. Numerical results were obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

Evaluation of strength and failure of brittle rock containing initial cracks under lithospheric conditions

NASA Astrophysics Data System (ADS)

Li, Xiaozhao; Qi, Chengzhi; Shao, Zhushan; Ma, Chao

2018-02-01

Natural brittle rock contains numerous randomly distributed microcracks. Crack initiation, growth, and coalescence play a predominant role in evaluation for the strength and failure of brittle rocks. A new analytical method is proposed to predict the strength and failure of brittle rocks containing initial microcracks. The formulation of this method is based on an improved wing crack model and a suggested micro-macro relation. In this improved wing crack model, the parameter of crack angle is especially introduced as a variable, and the analytical stress-crack relation considering crack angle effect is obtained. Coupling the proposed stress-crack relation and the suggested micro-macro relation describing the relation between crack growth and axial strain, the stress-strain constitutive relation is obtained to predict the rock strength and failure. Considering different initial microcrack sizes, friction coefficients and confining pressures, effects of crack angle on tensile wedge force acting on initial crack interface are studied, and effects of crack angle on stress-strain constitutive relation of rocks are also analyzed. The strength and crack initiation stress under different crack angles are discussed, and the value of most disadvantaged angle triggering crack initiation and rock failure is founded. The analytical results are similar to the published study results. Rationality of this proposed analytical method is verified.

Short fatigue crack behavior in notched 2024-T3 aluminum specimens

NASA Technical Reports Server (NTRS)

Lee, J. J.; Sharpe, W. N., Jr.

1986-01-01

Single-edge, semi-circular notched specimens of Al 2024-T3, 2.3 mm thick, were cyclicly loaded at R-ratios of 0.5, 0.0, -1.0, and -2.0. The notch roots were periodically inspected using a replica technique which duplicates the bore surface. The replicas were examined under an optical microscope to determine the initiation of very short cracks and to monitor the growth of short cracks ranging in length from a few tens of microns to the specimen thickness. In addition to short crack growth measurements, the crack opening displacement (COD) was measured for surface cracks as short as 0.035 mm and for through-thickness cracks using the Interferometric Strain/Displacement Gage (ISDG), a laser-based optical technique. The growth rates of short cracks were faster than the long crack growth rates for R-ratios of -1.0 and -2.0. No significant difference between short and long crack growth rates was observed for R = 0.0. Short cracks had slower growth rates than long cracks for R = 0.5. The crack opening stresses measured for short cracks were smaller than those predicted for large cracks, with little difference appearing for positive R-ratios and large differences noted for negative R-ratios.

Mode I and mixed I/III crack initiation and propagation behavior of V-4Cr-4Ti alloy at 25{degrees}C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, H.X.; Kurtz, R.J.; Jones, R.H.

1997-04-01

The mode I and mixed-mode I/III fracture behavior of the production-scale heat (No. 832665) of V-4Cr-4Ti has been investigated at 25{degrees}C using compact tension (CT) specimens for a mode I crack and modified CT specimens for a mixed-mode I/III crack. The mode III to mode I load ratio was 0.47. Test specimens were vacuum annealed at 1000{degrees}C for 1 h after final machining. Both mode I and mixed-mode I/III specimens were fatigue cracked prior to J-integral testing. It was noticed that the mixed-mode I/III crack angle decreased from an initial 25 degrees to approximately 23 degrees due to crack planemore » rotation during fatigue cracking. No crack plane rotation occurred in the mode I specimen. The crack initiation and propagation behavior was evaluated by generating J-R curves. Due to the high ductility of this alloy and the limited specimen thickness (6.35 mm), plane strain requirements were not met so valid critical J-integral values were not obtained. However, it was found that the crack initiation and propagation behavior was significantly different between the mode I and the mixed-mode I/III specimens. In the mode I specimen crack initiation did not occur, only extensive crack tip blunting due to plastic deformation. During J-integral testing the mixed-mode crack rotated to an increased crack angle (in contrast to fatigue precracking) by crack blunting. When the crack initiated, the crack angle was about 30 degrees. After crack initiation the crack plane remained at 30 degrees until the test was completed. Mixed-mode crack initiation was difficult, but propagation was easy. The fracture surface of the mixed-mode specimen was characterized by microvoid coalescence.« less

A risk assessment method for multi-site damage

NASA Astrophysics Data System (ADS)

Millwater, Harry Russell, Jr.

This research focused on developing probabilistic methods suitable for computing small probabilities of failure, e.g., 10sp{-6}, of structures subject to multi-site damage (MSD). MSD is defined as the simultaneous development of fatigue cracks at multiple sites in the same structural element such that the fatigue cracks may coalesce to form one large crack. MSD is modeled as an array of collinear cracks with random initial crack lengths with the centers of the initial cracks spaced uniformly apart. The data used was chosen to be representative of aluminum structures. The structure is considered failed whenever any two adjacent cracks link up. A fatigue computer model is developed that can accurately and efficiently grow a collinear array of arbitrary length cracks from initial size until failure. An algorithm is developed to compute the stress intensity factors of all cracks considering all interaction effects. The probability of failure of two to 100 cracks is studied. Lower bounds on the probability of failure are developed based upon the probability of the largest crack exceeding a critical crack size. The critical crack size is based on the initial crack size that will grow across the ligament when the neighboring crack has zero length. The probability is evaluated using extreme value theory. An upper bound is based on the probability of the maximum sum of initial cracks being greater than a critical crack size. A weakest link sampling approach is developed that can accurately and efficiently compute small probabilities of failure. This methodology is based on predicting the weakest link, i.e., the two cracks to link up first, for a realization of initial crack sizes, and computing the cycles-to-failure using these two cracks. Criteria to determine the weakest link are discussed. Probability results using the weakest link sampling method are compared to Monte Carlo-based benchmark results. The results indicate that very small probabilities can be computed accurately in a few minutes using a Hewlett-Packard workstation.

Stress intensity factors in two bonded elastic layers containing cracks perpendicular to and on the interface. Part 1: Analysis

NASA Technical Reports Server (NTRS)

Lu, M. C.; Erdogan, F.

1980-01-01

The basic crack problem which is essential for the study of subcritical crack propagation and fracture of layered structural materials is considered. Because of the apparent analytical difficulties, the problem is idealized as one of plane strain or plane stress. An additional simplifying assumption is made by restricting the formulation of the problem to crack geometries and loading conditions which have a plane of symmetry perpendicular to the interface. The general problem is formulated in terms of a coupled system of four integral equations. For each relevant crack configuration of practical interest, the singular behavior of the solution near and at the ends and points of intersection of the cracks is investigated and the related characteristic equations are obtained. The edge crack terminating at and crossing the interface, the T-shaped crack consisting of a broken layer and a delamination crack, the cross-shaped crack which consists of a delamination crack intersecting a crack which is perpendicular to the interface, and a delamination crack initiating from a stress-free boundary of the bonded layers are some of the practical crack geometries considered.

A new fracture mechanics model for multiple matrix cracks of SiC fiber reinforced brittle-matrix composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okabe, T.; Takeda, N.; Komotori, J.

1999-11-26

A new model is proposed for multiple matrix cracking in order to take into account the role of matrix-rich regions in the cross section in initiating crack growth. The model is used to predict the matrix cracking stress and the total number of matrix cracks. The model converts the matrix-rich regions into equivalent penny shape crack sizes and predicts the matrix cracking stress with a fracture mechanics crack-bridging model. The estimated distribution of matrix cracking stresses is used as statistical input to predict the number of matrix cracks. The results show good agreement with the experimental results by replica observations.more » Therefore, it is found that the matrix cracking behavior mainly depends on the distribution of matrix-rich regions in the composite.« less

The Significance of Small Cracks in Fatigue Design Concepts as Related to Rotorcraft Metallic Dynamic Components

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.; Elber, W.

2000-01-01

In this paper the significance of the "small" crack effect as defined in fracture mechanics will be discussed as it relates to life managing rotorcraft dynamic components using the conventional safe-life, the flaw tolerant safe-life, and the damage tolerance design philosophies. These topics will be introduced starting with an explanation of the small-crack theory, then showing how small-crack theory has been used to predict the total fatigue life of fatigue laboratory test coupons with and without flaws, and concluding with how small cracks can affect the crack-growth damage tolerance design philosophy. As stated in this paper the "small" crack effect is defined in fracture mechanics where it has been observed that cracks on the order of 300 microns or less in length will propagate at higher growth rates than long cracks and also will grow at AK values below the long crack AK threshold. The small-crack effect is illustrated herein as resulting from a lack of crack closure and is explained based on continuum mechanics principles using crack-closure concepts in fracture mechanics.

Failure study of helium-cooled tungsten divertor plasma-facing units tested at DEMO relevant steady-state heat loads

NASA Astrophysics Data System (ADS)

Ritz, G.; Hirai, T.; Norajitra, P.; Reiser, J.; Giniyatulin, R.; Makhankov, A.; Mazul, I.; Pintsuk, G.; Linke, J.

2009-12-01

Tungsten was selected as armor material for the helium-cooled divertor in future DEMO-type fusion reactors and fusion power plants. After realizing the design and testing of them under cyclic thermal loads of up to ~14 MW m-2, the tungsten divertor plasma-facing units were examined by metallography; they revealed failures such as cracks at the thermal loaded and as-machined surfaces, as well as degradation of the brazing layers. Furthermore, in order to optimize the machining processes, the quality of tungsten surfaces prepared by turning, milling and using a diamond cutting wheel were examined. This paper presents a metallographic examination of the tungsten plasma-facing units as well as technical studies and the characterization on machining of tungsten and alternative brazing joints.

Fatigue crack tip deformation and fatigue crack propagation

NASA Technical Reports Server (NTRS)

Kang, T. S.; Liu, H. W.

1972-01-01

The effects of stress ratio, prestress cycling and plate thickness on the fatigue crack propagation rate are studied on 2024-T351 aluminum alloy. Fatigue crack propagation rate increases with the plate thickness and the stress ratio. Prestress cycling below the static yield strength has no noticeable effect on the fatigue crack propagation rate. However, prestress cycling above the static yield strength causes the material to strain harden and increases the fatigue crack propagation rate. Crack tip deformation is used to study the fatigue crack propagation. The crack tip strains and the crack opening displacements were measured from moire fringe patterns. The moire fringe patterns were obtained by a double exposure technique, using a very high density master grille (13,400 lines per inch).

Three-dimensional effects in interfacial crack propagation

NASA Astrophysics Data System (ADS)

Liechti, K. M.; Chai, Y.-S.; Liang, Y.-M.

1992-09-01

The paper describes the use of crack-opening interferometry for examining the variation in normal crack-opening displacements (NCOD) along the front of an interfacial crack in an edge-cracked bimaterial strip under biaxial loading. For the glass/epoxy combination considered here, the crack front was concave in the direction of crack growth, in contrast to previous observations with a glass/polyurethane/glass sandwich specimen and cracks in homogeneous materials. The NCOD were greatest in the interior of the specimen for all mode-mixes considered and the exponents in a power-law fit of NCOD versus distance from the crack front decreased toward the free surface. The exponents varied with mode-mix, suggesting that interfacial crack-front geometries could be similarly affected.

Concrete Cracking Prediction Including the Filling Proportion of Strand Corrosion Products.

PubMed

Wang, Lei; Dai, Lizhao; Zhang, Xuhui; Zhang, Jianren

2016-12-23

The filling of strand corrosion products during concrete crack propagation is investigated experimentally in the present paper. The effects of stirrups on the filling of corrosion products and concrete cracking are clarified. A prediction model of crack width is developed incorporating the filling proportion of corrosion products and the twisting shape of the strand. Experimental data on cracking angle, crack width, and corrosion loss obtained from accelerated corrosion tests of concrete beams are presented. The proposed model is verified by experimental data. Results show that the filling extent of corrosion products varies with crack propagation. The rust filling extent increases with the propagating crack until a critical width. Beyond the critical width, the rust-filling extent remains stable. Using stirrups can decrease the critical crack width. Stirrups can restrict crack propagation and reduce the rust filling. The tangent of the cracking angle increases with increasing corrosion loss. The prediction of corrosion-induced crack is sensitive to the rust-filling extent.

Effect of CT Specimen Thickness on the Mechanical Characteristics at the Crack Tip of Stress Corrosion Cracking in Ni-based Alloys

NASA Astrophysics Data System (ADS)

Yinghao, Cui; He, Xue; Lingyan, Zhao

2017-12-01

It’s important to obtain accurate stress corrosion crack(SCC) growth rate for quantitative life prediction of components in nuclear power plants. However, the engineering practice shows that the crack tip constraint effect has a great influence on the mechanical properties and crack growth rate of SCC at crack tip. To study the influence of the specimen thickness on the crack tip mechanical properties of SCC, the stress, strain and C integral at creep crack tip are analyzed under different specimens thickness. Results show that the cracked specimen is less likely to crack due to effect of crack tip constraint. When the thickness ratio B/W is larger than 0.1, the crack tip constraint is almost ineffective. Value of C integral is the largest when B/W is 0.25. Then specimen thickness has little effect on the value of C integral. The effect of specimen thickness on the value of C integral is less significant at higher thickness ratio.

Concrete Cracking Prediction Including the Filling Proportion of Strand Corrosion Products

PubMed Central

Wang, Lei; Dai, Lizhao; Zhang, Xuhui; Zhang, Jianren

2016-01-01

The filling of strand corrosion products during concrete crack propagation is investigated experimentally in the present paper. The effects of stirrups on the filling of corrosion products and concrete cracking are clarified. A prediction model of crack width is developed incorporating the filling proportion of corrosion products and the twisting shape of the strand. Experimental data on cracking angle, crack width, and corrosion loss obtained from accelerated corrosion tests of concrete beams are presented. The proposed model is verified by experimental data. Results show that the filling extent of corrosion products varies with crack propagation. The rust filling extent increases with the propagating crack until a critical width. Beyond the critical width, the rust-filling extent remains stable. Using stirrups can decrease the critical crack width. Stirrups can restrict crack propagation and reduce the rust filling. The tangent of the cracking angle increases with increasing corrosion loss. The prediction of corrosion-induced crack is sensitive to the rust-filling extent. PMID:28772367

Effects of External Hydrogen on Hydrogen Transportation and Distribution Around the Fatigue Crack Tip in Type 304 Stainless Steel

NASA Astrophysics Data System (ADS)

Chen, Xingyang; Zhou, Chengshuang; Cai, Xiao; Zheng, Jinyang; Zhang, Lin

2017-10-01

The effects of external hydrogen on hydrogen transportation and distribution around the fatigue crack tip in type 304 stainless steel were investigated by using hydrogen microprint technique (HMT) and thermal desorption spectrometry. HMT results show that some silver particles induced by hydrogen release are located near the fatigue crack and more silver particles are concentrated around the crack tip, which indicates that hydrogen accumulates in the vicinity of the crack tip during the crack growth in hydrogen gas environment. Along with the crack propagation, strain-induced α' martensite forms around the crack tip and promotes hydrogen invasion into the matrix, which will cause the crack initiation and propagation at the austenite/ α' martensite interface. In addition, the hydrogen content in the vicinity of the crack tip is higher than that at the crack edge far away from the crack tip, which is related to the stress state and strain-induced α' martensite.

Diffraction-based study of fatigue crack initiation and propagation in aerospace aluminum alloys

NASA Astrophysics Data System (ADS)

Gupta, Vipul K.

The crack initiation sites and microstructure-sensitive growth of small fatigue cracks are experimentally characterized in two precipitation-hardened aluminum alloys, 7075-T651 and 7050-T7451, stressed in ambient temperature moist-air (warm-humid) and -50°C dry N2 (cold-dry) environmental conditions. Backscattered electron imaging (BSE) and energy dispersive spectroscopy (EDS) of the fracture surfaces showed that Fe-Cu rich constituent particle clusters are the most common initiation sites within both alloys stressed in either environment. The crack growth within each alloy, on average, was observed to be slowed in the cold-dry environment than in the warm-humid environment, but only at longer crack lengths. Although no overwhelming effects of grain boundaries and grain orientations on small-crack growth were observed, crack growth data showed local fluctuations within individual grains. These observations are understood as crack propagation through the underlying substructure at the crack surface and frequent interaction with low/high-angle grain and subgrain boundaries, during cyclic loading, and, are further attributed to periodic changes in crack propagation path and multiple occurrences of crack-branching observed in the current study. SEM-based stereology in combination with electron backscattered diffraction (EBSD) established fatigue crack surface crystallography within the region from ˜1 to 50 mum of crack initiating particle clusters. Fatigue crack facets were parallel to a wide variety of crystallographic planes, with pole orientations distributed broadly across the irreducible stereographic triangle between the {001} and {101}-poles within both warm-humid and cold-dry environments. The results indicate environmentally affected fatigue cracking in both cases, given the similarity between the observed morphology and crystallography with that of a variety of aerospace aluminum alloys cracked in the presence of moist-air. There was no evidence of crystallographic {111} slip-plane cracking typical of the Stage I crack growth mode observed in single crystals and high purity polycrystals of face centered cubic metals, and which has presently been assumed for the present materials within fatigue crack initiation models. Rather, the facets tend to have near-Mode I spatial orientation, which is another indicator of the importance of environmentally affected fatigue damage. The results provide a physical basis to develop microstructurally-based next generation multi-stage fatigue (MSF) models that should include a new crack decohesion criteria based upon environmental fatigue cracking mechanisms. EBSD study of small-cracks in alloy 7050-T7451, stressed in warm-humid environment, showed that crack-path orientation changes and crack-branching occurred at both low/high-angle grain and subgrain boundaries. Single surface trace analysis suggests that the crack-path differs substantially from crystallographic slip-planes. EBSD-based observations of small-crack propagation through subgrain structure, either formed by cyclic plastic strain accumulation or pre-existing (typical of unrecrystallized grain structure in the present materials), suggest that subgrain structure plays a crucial role in small fatigue crack propagation. As mentioned earlier, local fluctuations in small-crack growth rates appear to be caused by frequent interaction with subgrain boundaries, and multiple occurrences of crack-branching and crack-path orientation changes at low/high-angle grain and subgrain boundaries. The aforementioned deviation from low-index {001}/{101}-planes and the occurrence of high-index cracking planes observed by EBSD/Stereology, in this study and others, are interpreted as trans-subgranular decohesion or inter-subgranular cracking, due to trapped hydrogen. In summary, the results provide a firmer experimental foundation for, and clearer understanding of, the mechanisms of environmental fatigue cracking of aluminum alloys, especially the role of inter-subgranular cracking, which had previously been advanced based upon fracture surface observations alone.

Fracture Toughness Evaluation of a Ni2MnGa Alloy Through Micro Indentation Under Magneto-Mechanical Loading

NASA Astrophysics Data System (ADS)

Goanţă, Viorel; Ciocanel, Constantin

2017-12-01

Ni2MnGa is a ferromagnetic alloy that exhibits the shape memory effect either induced by an externally applied magnetic field or mechanical stress. Due to the former, the alloy is commonly called magnetic shape memory alloy or MSMA. The microstructure of the MSMA consists of tetragonal martensite variants (three in the most general case) that are characterized by a magnetization vector which is aligned with the short side of the tetragonal unit cell. Exposing the MSMA to a magnetic field causes the magnetization vector to rotate and align with the external field, eventually leading to variant reorientation. The variant reorientation is observed macroscopically in the form of recoverable strain of up to 6% [1, 2]. As the magnetic field induced reorientation happens instantaneously [1, 3], MSMAs are suitable for fast actuation, sensing, or power harvesting applications. However, actuation applications are limited by the maximum actuation stress of the material that is about 3.5MPa at approximately 2 to 3% reorientation strain. During MSMA fatigue magneto-mechanical characterization studies [4, 5] it was observed that cracks nucleate and grow on the surface of material samples, after a relatively small number of cycles, leading to loss in material performance. This triggered the need for understanding the mechanisms that govern crack nucleation and growth in MSMAs, as well as the nature of the material, i.e. ductile or brittle. The experimental study reported in this paper was carried out to determine material's fracture toughness, the predominant crack growth directions, and the orientation of the cracks relative to the mechanical loading direction and to the material's microstructure. A fixture has been developed to allow Vickers micro indentation of 3mm by 3mm by 20mm Ni2MnGa samples exposed to different levels of magnetic field and/or mechanical stress. Using the measured characteristics of the impression generated during micro indentation, the lengths of propagated cracks, and appropriate equations (introduced in the paper), and the fracture toughness was evaluated as a function of the magneto-mechanical loading experienced by the material. The influence of the magneto-mechanical loading on the growth of already nucleated cracks has also been evaluated.

Healing of Fatigue Crack in 1045 Steel by Using Eddy Current Treatment

PubMed Central

Yang, Chuan; Xu, Wenchen; Guo, Bin; Shan, Debin; Zhang, Jian

2016-01-01

In order to investigate the methods to heal fatigue cracks in metals, tubular specimens of 1045 steel with axial and radial fatigue cracks were treated under the eddy current. The optical microscope was employed to examine the change of fatigue cracks of specimens before and after the eddy current treatment. The results show that the fatigue cracks along the axial direction of the specimen could be healed effectively in the fatigue crack initiation zone and the crack tip zone under the eddy current treatment, and the healing could occur within a very short time. The voltage breakdown and the transient thermal compressive stress caused by the detouring of eddy current around the fatigue crack were the main factors contributing to the healing in the fatigue crack initiation zone and the crack tip zone, respectively. Eddy current treatment may be a novel and effective method for crack healing. PMID:28773761

Vibration based algorithm for crack detection in cantilever beam containing two different types of cracks

NASA Astrophysics Data System (ADS)

Behzad, Mehdi; Ghadami, Amin; Maghsoodi, Ameneh; Michael Hale, Jack

2013-11-01

In this paper, a simple method for detection of multiple edge cracks in Euler-Bernoulli beams having two different types of cracks is presented based on energy equations. Each crack is modeled as a massless rotational spring using Linear Elastic Fracture Mechanics (LEFM) theory, and a relationship among natural frequencies, crack locations and stiffness of equivalent springs is demonstrated. In the procedure, for detection of m cracks in a beam, 3m equations and natural frequencies of healthy and cracked beam in two different directions are needed as input to the algorithm. The main accomplishment of the presented algorithm is the capability to detect the location, severity and type of each crack in a multi-cracked beam. Concise and simple calculations along with accuracy are other advantages of this method. A number of numerical examples for cantilever beams including one and two cracks are presented to validate the method.

Multifractality analysis of crack images from indirect thermal drying of thin-film dewatered sludge

NASA Astrophysics Data System (ADS)

Wang, Weiyun; Li, Aimin; Zhang, Xiaomin; Yin, Yulei

2011-07-01

Crack formation is inevitable during sludge drying because of the existence of uneven thermal stress. Experiments have been conducted to study crack pattern formation in thin film sludge. Crack images show that the thinner the sewage sludge film, the more even the crack distribution. The crack changes from a flaky texture to a banded structure with increasing thickness. Multifractal methods are proposed to analyze the crack image of four different thicknesses of dried sludge. Several parameters are conducted for quantification of the crack image and the results indicate that the width of spectra increases with thicker sludge film, that is to say, nonunifromity of crack distribution increases with increasing thickness, which proves that the multifractal method is sensitive enough to quantify the crack distribution and can be seen as a new approach for the changing research of crack images of sewage sludge drying.

Healing of Fatigue Crack in 1045 Steel by Using Eddy Current Treatment.

PubMed

Yang, Chuan; Xu, Wenchen; Guo, Bin; Shan, Debin; Zhang, Jian

2016-07-29

In order to investigate the methods to heal fatigue cracks in metals, tubular specimens of 1045 steel with axial and radial fatigue cracks were treated under the eddy current. The optical microscope was employed to examine the change of fatigue cracks of specimens before and after the eddy current treatment. The results show that the fatigue cracks along the axial direction of the specimen could be healed effectively in the fatigue crack initiation zone and the crack tip zone under the eddy current treatment, and the healing could occur within a very short time. The voltage breakdown and the transient thermal compressive stress caused by the detouring of eddy current around the fatigue crack were the main factors contributing to the healing in the fatigue crack initiation zone and the crack tip zone, respectively. Eddy current treatment may be a novel and effective method for crack healing.

Generating Fatigue Crack Growth Thresholds with Constant Amplitude Loads

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Newman, James C., J.; Forman, Royce G.

2002-01-01

The fatigue crack growth threshold, defining crack growth as either very slow or nonexistent, has been traditionally determined with standardized load reduction methodologies. Some experimental procedures tend to induce load history effects that result in remote crack closure from plasticity. This history can affect the crack driving force, i.e. during the unloading process the crack will close first at some point along the wake, reducing the effective load at the crack tip. One way to reduce the effects of load history is to propagate a crack under constant amplitude loading. As a crack propagates under constant amplitude loading, the stress intensity factor, K, will increase, as will the crack growth rate, da/dN. A fatigue crack growth threshold test procedure is developed and experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R.

Surface faulting along the inland Itozawa normal fault (eastern Japan) and relation to the 2011 Tohoku-oki megathrust earthquake

NASA Astrophysics Data System (ADS)

Ferry, M.; Tsutsumi, H.; Meghraoui, M.; Toda, S.

2012-12-01

The 11 March 2011 Mw 9 Tohoku-oki earthquake ruptured ~500 km length of the Japan Trench along the coast of eastern Japan and significantly impacted the stress regime within the crust. The resulting change in seismicity over the Japan mainland was exhibited by the 11 April 2011 Mw 6.6 Iwaki earthquake that ruptured the Itozawa and Yunodake faults. Trending NNW and NW, respectively, these 70-80° W-dipping faults bound the Iwaki basin of Neogene age and have been reactivated simultaneously both along 15-km-long sections. Here, we present initial results from a paleoseismic excavation performed across the Itozawa fault within the Tsunagi Valley at the northern third of the observed surface rupture. At the Tsunagi site, the rupture affects a rice paddy, which provides an ideally horizontal initial state to collect detailed and accurate measurements. The surface break is composed of a continuous 30-to-40-cm-wide purely extensional crack that separates the uplifted block from a gently dipping 1-to-2-m-wide strip affected by right-stepping en-echelon cracks and locally bounded by a ~0.1-m-high reverse scarplet. Total station across-fault topographic profiles indicate the pre-earthquake ground surface was vertically deformed by ~0.6 m while direct field examinations reveal that well-defined rice paddy limits have been left-laterally offset by ~0.1 m. The 12-m-long, 3.5-m-deep trench exposes the 30-to-40-cm-thick cultivated soil overlaying a 1-m-thick red to yellow silt unit, a 2-m-thick alluvial gravel unit and a basal 0.1-1-m-thick organic-rich silt unit. Deformation associated to the 2011 rupture illustrates down-dip movement along a near-vertical fault with a well-expressed bending moment at the surface and generalized warping. On the north wall, the intermediate gravel unit displays a deformation pattern similar to granular flow with only minor discrete faulting and no splay to be continuously followed from the main fault to the surface. On the south wall, warping dominates as well but with some strain localization along two major splays that exhibit 15-20 cm of vertical offset. On both walls, the basal silt unit is vertically deformed by ~0.6 m, similarly to what is observed for the 2011 rupture. Furthermore, the base of said silt unit exhibits indication for secondary faulting prior to the 2011 event and that resemble cracks observed at the present-day surface. This suggests that the Itozawa fault has already ruptured in a similar fashion; probably in the late Pleistocene-early Holocene (radiocarbon samples are being processed). Hence, recent activity of the Itozawa fault may be controlled entirely by large to giant earthquakes along the Japan Trench.

A viscoplastic study of crack-tip deformation and crack growth in a nickel-based superalloy at elevated temperature

NASA Astrophysics Data System (ADS)

Zhao, L. G.; Tong, J.

Viscoplastic crack-tip deformation behaviour in a nickel-based superalloy at elevated temperature has been studied for both stationary and growing cracks in a compact tension (CT) specimen using the finite element method. The material behaviour was described by a unified viscoplastic constitutive model with non-linear kinematic and isotropic hardening rules, and implemented in the finite element software ABAQUS via a user-defined material subroutine (UMAT). Finite element analyses for stationary cracks showed distinctive strain ratchetting behaviour near the crack tip at selected load ratios, leading to progressive accumulation of tensile strain normal to the crack-growth plane. Results also showed that low frequencies and superimposed hold periods at peak loads significantly enhanced strain accumulation at crack tip. Finite element simulation of crack growth was carried out under a constant Δ K-controlled loading condition, again ratchetting was observed ahead of the crack tip, similar to that for stationary cracks. A crack-growth criterion based on strain accumulation is proposed where a crack is assumed to grow when the accumulated strain ahead of the crack tip reaches a critical value over a characteristic distance. The criterion has been utilized in the prediction of crack-growth rates in a CT specimen at selected loading ranges, frequencies and dwell periods, and the predictions were compared with the experimental results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, S. Y.; Choo, Hahn; Liaw, Peter K

The combined effects of overload-induced enlarged compressive residual stresses and crack tip blunting with secondary cracks are suggested to be responsible for the observed changes in the crack opening load and resultant post-overload transient crack growth behavior [Lee SY, Liaw PK, Choo H, Rogge RB, Acta Mater 2010;59:485-94]. In this article, in situ neutron diffraction experiments were performed to quantify the influence of the combined effects by investigating the internal-stress evolution at various locations away from the crack tip. In the overload-retardation period, stress concentration occurs in the crack blunting region (an overload point) until a maximum crack arrest loadmore » is reached. The stress concentration is then transferred from the blunting region to the propagating crack tip (following the overload), requiring a higher applied load, as the closed crack is gradually opened. The transfer phenomena of the stress concentration associated with a crack opening process account for the nonlinearity of strain response in the vicinity of the crack tip. The delaying action of stress concentration at the crack tip is understood in conjunction with the concept of a critical stress (i.e. the stress required to open the closed crack behind the crack tip). A linear relationship between {Delta}{var_epsilon}{sub eff} and {Delta}K{sub eff} provides experimental support for the hypothesis that {Delta}K{sub eff} can be considered as the fatigue crack tip driving force.« less

Experimental Study on the Growth, Coalescence and Wrapping Behaviors of 3D Cross-Embedded Flaws Under Uniaxial Compression

NASA Astrophysics Data System (ADS)

Zhou, Xiao-Ping; Zhang, Jian-Zhi; Wong, Louis Ngai Yuen

2018-05-01

The crack initiation, growth, wrapping and coalescence of two 3D pre-existing cross-embedded flaws in PMMA specimens under uniaxial compression are investigated. The stress-strain curves of PMMA specimens with 3D cross-embedded flaws are obtained. The tested PMMA specimens exhibit dominant elastic deformation and eventual brittle failure. The experimental results show that four modes of crack initiation and five modes of crack coalescence are observed. The initiations of oblique secondary crack and anti-wing crack in 3D cracking behaviors are first reported as well as the coalescence of anti-wing cracks. Moreover, two types of crack wrapping are found. Substantial wrapping of petal cracks, which includes open and closed modes of wrapping, appears to be the major difference between 2D and 3D cracking behaviors of pre-existing flaws, which are also first reported. Petal crack wraps symmetrically from either the propagated wing cracks or the coalesced wing cracks. Besides, only limited growth of petal cracks is observed, and ultimate failure of specimens is induced by the further growth of the propagated wing crack. The fracture mechanism of the tested PMMA specimens is finally revealed. In addition, the initiation stress and the peak stress versus the geometry of two 3D pre-existing cross-embedded flaws are also investigated in detail.

Modeling of heat flow and effective thermal conductivity of fractured media: Analytical and numerical methods

NASA Astrophysics Data System (ADS)

Nguyen, S. T.; Vu, M.-H.; Vu, M. N.; Tang, A. M.

2017-05-01

The present work aims to modeling the thermal conductivity of fractured materials using homogenization-based analytical and pattern-based numerical methods. These materials are considered as a network of cracks distributed inside a solid matrix. Heat flow through such media is perturbed by the crack system. The problem of heat flow across a single crack is firstly investigated. The classical Eshelby's solution, extended to the thermal conduction problem of an ellipsoidal inclusion embedding in an infinite homogeneous matrix, gives an analytical solution of temperature discontinuity across a non-conducting penny-shaped crack. This solution is then validated by the numerical simulation based on the finite elements method. The numerical simulation allows analyzing the effect of crack conductivity. The problem of a single crack is then extended to a medium containing multiple cracks. Analytical estimations for effective thermal conductivity, that take into account the interaction between cracks and their spatial distribution, are developed for the case of non-conducting cracks. Pattern-based numerical method is then employed for both cases non-conducting and conducting cracks. In the case of non-conducting cracks, numerical and analytical methods, both account for the spatial distribution of the cracks, fit perfectly. In the case of conducting cracks, the numerical analyzing of crack conductivity effect shows that highly conducting cracks weakly affect heat flow and the effective thermal conductivity of fractured media.

On the finite element modeling of the asymmetric cracked rotor

NASA Astrophysics Data System (ADS)

AL-Shudeifat, Mohammad A.

2013-05-01

The advanced phase of the breathing crack in the heavy duty horizontal rotor system is expected to be dominated by the open crack state rather than the breathing state after a short period of operation. The reason for this scenario is the expected plastic deformation in crack location due to a large compression stress field appears during the continuous shaft rotation. Based on that, the finite element modeling of a cracked rotor system with a transverse open crack is addressed here. The cracked rotor with the open crack model behaves as an asymmetric shaft due to the presence of the transverse edge crack. Hence, the time-varying area moments of inertia of the cracked section are employed in formulating the periodic finite element stiffness matrix which yields a linear time-periodic system. The harmonic balance method (HB) is used for solving the finite element (FE) equations of motion for studying the dynamic behavior of the system. The behavior of the whirl orbits during the passage through the subcritical rotational speeds of the open crack model is compared to that for the breathing crack model. The presence of the open crack with the unbalance force was found only to excite the 1/2 and 1/3 of the backward critical whirling speed. The whirl orbits in the neighborhood of these subcritical speeds were found to have nearly similar behavior for both open and breathing crack models. While unlike the breathing crack model, the subcritical forward whirling speeds have not been observed for the open crack model in the response to the unbalance force. As a result, the behavior of the whirl orbits during the passage through the forward subcritical rotational speeds is found to be enough to distinguish the breathing crack from the open crack model. These whirl orbits with inner loops that appear in the neighborhood of the forward subcritical speeds are then a unique property for the breathing crack model.

High speed thin plate fatigue crack monitor

NASA Technical Reports Server (NTRS)

Wincheski, Buzz A. (Inventor); Heyman, Joseph S. (Inventor); Namkung, Min (Inventor); Fulton, James P. (Inventor)

1996-01-01

A device and method are provided which non-destructively detect crack length and crack geometry in thin metallic plates. A non-contacting vibration apparatus produces resonant vibrations without introducing extraneous noise. Resulting resonant vibration shifts in cracked plates are correlated to known crack length in plates with similar resonant vibration shifts. In addition, acoustic emissions of cracks at resonance frequencies are correlated to acoustic emissions from known crack geometries.

Surface-crack growth: Models, experiments, and structures; Proceedings of the Symposium, Sparks, NV, Apr. 25, 1988

NASA Technical Reports Server (NTRS)

Reuter, Walter G. (Editor); Underwood, John H. (Editor); Newman, James C., Jr. (Editor)

1990-01-01

The present volume on surface-crack growth modeling, experimental methods, and structures, discusses elastoplastic behavior, the fracture analysis of three-dimensional bodies with surface cracks, optical measurements of free-surface effects on natural surfaces and through cracks, an optical and finite-element investigation of a plastically deformed surface flaw under tension, fracture behavior prediction for rapidly loaded surface-cracked specimens, and surface cracks in thick laminated fiber composite plates. Also discussed are a novel study procedure for crack initiation and growth in thermal fatigue testing, the growth of surface cracks under fatigue and monotonically increasing load, the subcritical growth of a surface flaw, surface crack propagation in notched and unnotched rods, and theoretical and experimental analyses of surface cracks in weldments.

Dynamic response of a cracked atomic force microscope cantilever used for nanomachining

PubMed Central

2012-01-01

The vibration behavior of an atomic force microscope [AFM] cantilever with a crack during the nanomachining process is studied. The cantilever is divided into two segments by the crack, and a rotational spring is used to simulate the crack. The two individual governing equations of transverse vibration for the cracked cantilever can be expressed. However, the corresponding boundary conditions are coupled because of the crack interaction. Analytical expressions for the vibration displacement and natural frequency of the cracked cantilever are obtained. In addition, the effects of crack flexibility, crack location, and tip length on the vibration displacement of the cantilever are analyzed. Results show that the crack occurs in the AFM cantilever that can significantly affect its vibration response. PACS: 07.79.Lh; 62.20.mt; 62.25.Jk PMID:22335820

Dynamic ductile fracture of a central crack

NASA Technical Reports Server (NTRS)

Tsai, Y. M.

1976-01-01

A central crack, symmetrically growing at a constant speed in a two dimensional ductile material subject to uniform tension at infinity, is investigated using the integral transform methods. The crack is assumed to be the Dugdale crack, and the finite stress condition at the crack tip is satisfied during the propagation of the crack. Exact expressions of solution are obtained for the finite stress condition at the crack tip, the crack shape, the crack opening displacement, and the energy release rate. All those expressions are written as the product of explicit dimensional quantities and a nondimensional dynamic correction function. The expressions reduce to the associated static results when the crack speed tends to zero, and the nondimensional dynamic correction functions were calculated for various values of the parameter involved.

Interaction of a penny-shaped crack and an external circular crack in a transversely isotropic composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, Y.M.

1998-12-31

The interaction of a penny-shaped crack and an external circular crack in a transversely isotropic composite is investigated using the techniques of Hankel transform and multiplying factors. The boundary conditions of the problem have three different parts. The stress intensity factors at the inner and the outer crack tips are obtained in exact expressions as the products of a dimensional quantity and nondimensional functions. The presence of a penny-shaped crack is shown to have a strong effect on the magnitude of the stress intensity of the external circular crack. The crack surface displacement is also obtained and evaluated numerically formore » different values of the ratio of the inner crack radius to the external crack radius.« less

Automatic crack detection method for loaded coal in vibration failure process

PubMed Central

Li, Chengwu

2017-01-01

In the coal mining process, the destabilization of loaded coal mass is a prerequisite for coal and rock dynamic disaster, and surface cracks of the coal and rock mass are important indicators, reflecting the current state of the coal body. The detection of surface cracks in the coal body plays an important role in coal mine safety monitoring. In this paper, a method for detecting the surface cracks of loaded coal by a vibration failure process is proposed based on the characteristics of the surface cracks of coal and support vector machine (SVM). A large number of cracked images are obtained by establishing a vibration-induced failure test system and industrial camera. Histogram equalization and a hysteresis threshold algorithm were used to reduce the noise and emphasize the crack; then, 600 images and regions, including cracks and non-cracks, were manually labelled. In the crack feature extraction stage, eight features of the cracks are extracted to distinguish cracks from other objects. Finally, a crack identification model with an accuracy over 95% was trained by inputting the labelled sample images into the SVM classifier. The experimental results show that the proposed algorithm has a higher accuracy than the conventional algorithm and can effectively identify cracks on the surface of the coal and rock mass automatically. PMID:28973032

Automatic crack detection method for loaded coal in vibration failure process.

PubMed

Li, Chengwu; Ai, Dihao

2017-01-01

In the coal mining process, the destabilization of loaded coal mass is a prerequisite for coal and rock dynamic disaster, and surface cracks of the coal and rock mass are important indicators, reflecting the current state of the coal body. The detection of surface cracks in the coal body plays an important role in coal mine safety monitoring. In this paper, a method for detecting the surface cracks of loaded coal by a vibration failure process is proposed based on the characteristics of the surface cracks of coal and support vector machine (SVM). A large number of cracked images are obtained by establishing a vibration-induced failure test system and industrial camera. Histogram equalization and a hysteresis threshold algorithm were used to reduce the noise and emphasize the crack; then, 600 images and regions, including cracks and non-cracks, were manually labelled. In the crack feature extraction stage, eight features of the cracks are extracted to distinguish cracks from other objects. Finally, a crack identification model with an accuracy over 95% was trained by inputting the labelled sample images into the SVM classifier. The experimental results show that the proposed algorithm has a higher accuracy than the conventional algorithm and can effectively identify cracks on the surface of the coal and rock mass automatically.

Stress intensity factors in two bonded elastic layers containing cracks perpendicular to and on the interface. I Analysis. II - Solution and results

NASA Technical Reports Server (NTRS)

Lu, M.-C.; Erdogan, F.

1983-01-01

The basic crack problem which is essential for the study of subcritical crack propagation and fracture of layered structural materials is considered. Because of the apparent analytical difficulties, the problem is idealized as one of plane strain or plane stress. An additional simplifying assumption is made by restricting the formulation of the problem to crack geometries and loading conditions which have a plane of symmetry perpendicular to the interface. The general problem is formulated in terms of a coupled systems of four integral equations. For each relevant crack configuration of practical interest, the singular behavior of the solution near and at the ends and points of intersection of the cracks is investigated and the related characteristic equations are obtained. The edge crack terminating at and crossing the interface, the T-shaped crack consisting of a broken layer and a delamination crack, the cross-shaped crack which consists of a delamination crack intersecting a crack which is perpendicular to the interface, and a delamination crack initiating from a stress-free boundary of the bonded layers are some of the practical crack geometries considered. Previously announced in STAR as N80-18428 and N80-18429

Fracture analysis of stiffened panels under biaxial loading with widespread cracking

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Dawicke, D. S.

1995-01-01

An elastic-plastic finite-element analysis with a critical crack-tip-opening angle (CTOA) fracture criterion was used to model stable crack growth and fracture of 2024-T3 aluminum alloy (bare and clad) panels for several thicknesses. The panels had either single or multiple-site damage (MSD) cracks subjected to uniaxial or biaxial loading. Analyses were also conducted on cracked stiffened panels with single or MSD cracks. The critical CTOA value for each thickness was determined by matching the failure load on a middle-crack tension specimen. Comparisons were made between the critical angles determined from the finite-element analyses and those measured with photographic methods. Predicted load-against-crack extension and failure loads for panels under biaxial loading, panels with MSD cracks, and panels with various number of stiffeners were compared with test data, whenever possible. The predicted results agreed well with the test data even for large-scale plastic deformations. The analyses were also able to predict stable tearing behavior of a large lead crack in the presence of MSD cracks. The analyses were then used to study the influence of stiffeners on residual strength in the presence of widespread fatigue cracking. Small MSD cracks were found to greatly reduce the residual strength for large lead cracks even for stiffened panels.

Fracture analysis of stiffened panels under biaxial loading with widespread cracking

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1995-01-01

An elastic-plastic finite-element analysis with a critical crack-tip opening angle (CTOA) fracture criterion was used to model stable crack growth and fracture of 2024-T3 aluminum alloy (bare and clad) panels for several thicknesses. The panels had either single or multiple-site damage (MSD) cracks subjected to uniaxial or biaxial loading. Analyses were also conducted on cracked stiffened panels with single or MSD cracks. The critical CTOA value for each thickness was determined by matching the failure load on a middle-crack tension specimen. Comparisons were made between the critical angles determined from the finite-element analyses and those measured with photographic methods. Predicted load-against-crack extension and failure loads for panels under biaxial loading, panels with MSD cracks, and panels with various numbers of stiffeners were compared with test data whenever possible. The predicted results agreed well with the test data even for large-scale plastic deformations. The analyses were also able to predict stable tearing behavior of a large lead crack in the presence of MSD cracks. The analyses were then used to study the influence of stiffeners on residual strength in the presence of widespread fatigue cracking. Small MSD cracks were found to greatly reduce the residual strength for large lead cracks even for stiffened panels.

Initial Reactivity of Linkages and Monomer Rings in Lignin Pyrolysis Revealed by ReaxFF Molecular Dynamics.

PubMed

Zhang, Tingting; Li, Xiaoxia; Guo, Li

2017-10-24

The initial conversion pathways of linkages and their linked monomer units in lignin pyrolysis were investigated comprehensively by ReaxFF MD simulations facilitated by the unique VARxMD for reaction analysis. The simulated molecular model contains 15 920 atoms and was constructed on the basis of Adler's softwood lignin model. The simulations uncover the initial conversion ratio of various linkages and their linked aryl monomers. For linkages and their linked monomer aryl rings of α-O-4, β-O-4 and α-O-4 & β-5, the C α /C β ether bond cracking dominates the initial pathway accounting for at least up to 80% of their consumption. For the linkage of β-β & γ-O-α, both the C α -O ether bond cracking and its linked monomer aryl ring opening are equally important. Ring-opening reactions dominate the initial consumption of other 4-O-5, 5-5, β-1, β-2, and β-5 linkages and their linked monomers. The ether bond cracking of C α -O and C β -O occurs at low temperature, and the aryl ring-opening reactions take place at relatively high temperature. The important intermediates leading to the stable aryl ring opening are the phenoxy radicals, the bridged five-membered and three-membered rings and the bridged six-membered and three-membered rings. In addition, the reactivity of a linkage and its monomer aryl ring may be affected by other linkages. The ether bond cracking of α-O-4 and β-O-4 linkages can activate its neighboring linkage or monomer ring through the formed phenoxy radicals as intermediates. The important intermediates revealed in this article should be of help in deepening the understanding of the controlling mechanism for producing aromatic chemicals from lignin pyrolysis.

Microstructural characterization of hydrogen induced cracking in TRIP-assisted steel by EBSD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laureys, A., E-mail: Aurelie.Laureys@UGent.be; Depover, T.; Petrov, R.

2016-02-15

The present work evaluates hydrogen induced cracking by performing an elaborate EBSD (Electron BackScatter Diffraction) study in a steel with transformation induced plasticity (TRIP-assisted steel). This type of steel exhibits a multiphase microstructure which undergoes a deformation induced phase transformation. Additionally, each microstructural constituent displays a different behavior in the presence of hydrogen. The aim of this study is to obtain a better understanding on the mechanisms governing hydrogen induced crack initiation and propagation in the hydrogen saturated multiphase structure. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The tests were interrupted at stresses justmore » after reaching the tensile strength, i.e. before macroscopic failure of the material. This allowed to study hydrogen induced crack initiation and propagation by SEM (Scanning Electron Microscopy) and EBSD. A correlation was found between the presence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. Initiation seems to occur mostly by martensite decohesion. High strain regions surrounding the hydrogen induced crack tips indicate that further crack propagation may have occurred by the HELP (hydrogen-enhanced localized plasticity) mechanism. Small hydrogen induced cracks located nearby the notch are typically S-shaped and crack propagation was dominantly transgranularly. The second stage of crack propagation consists of stepwise cracking by coalescence of small hydrogen induced cracks. - Highlights: • Hydrogen induced cracking in TRIP-assisted steel is evaluated by EBSD. • Tensile tests were conducted on notched hydrogen saturated samples. • Crack initiation occurs by a H-Enhanced Interface DEcohesion (HEIDE) mechanism. • Crack propagation involves growth and coalescence of small cracks. • Propagation is governed by the characteristics of phases on the crack path.« less

Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

NASA Technical Reports Server (NTRS)

Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

1998-01-01

The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

Universal Shapes formed by Interacting Cracks

NASA Astrophysics Data System (ADS)

Fender, Melissa; Lechenault, Frederic; Daniels, Karen

2011-03-01

Brittle failure through multiple cracks occurs in a wide variety of contexts, from microscopic failures in dental enamel and cleaved silicon to geological faults and planetary ice crusts. In each of these situations, with complicated curvature and stress geometries, pairwise interactions between approaching cracks nonetheless produce characteristically curved fracture paths known in the geologic literature as en passant cracks. While the fragmentation of solids via many interacting cracks has seen wide investigation, less attention has been paid to the details of individual crack-crack interactions. We investigate the origins of this widely observed crack pattern using a rectangular elastic plate which is notched on each long side and then subjected to quasistatic uniaxial strain from the short side. The two cracks propagate along approximately straight paths until the pass each other, after which they curve and release a lenticular fragment. We find that, for materials with diverse mechanical properties, the shape of this fragment has an aspect ratio of 2:1, with the length scale set by the initial cracks offset s and the time scale set by the ratio of s to the pulling velocity. The cracks have a universal square root shape, which we understand by using a simple geometric model and the crack-crack interaction.

Photomultiplier tube failure under hydrostatic pressure in future neutrino detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chambliss, K.; Diwan, M.; Simos, N.

Failure of photomultiplier tubes (PMTs) under hydrostatic pressure is a concern in neutrino detection, specifically, in the proposed Long-Baseline Neutrino Experiment project. Controlled hydrostatic implosion tests were performed on prototypic PMT bulbs of 10-inch diameter and recorded using high speed filming techniques to capture failures in detail. These high-speed videos were analyzed frame-by-frame in order to identify the origin of a crack, measure the progression of individual crack along the surface of the bulb as it propagates through the glass, and estimate crack velocity. Crack velocity was calculated for each individual crack, and an average velocity was determined for allmore » measurable cracks on each bulb. Overall, 32 cracks were measured in 9 different bulbs tested. Finite element modeling (FEM) of crack formation and growth in prototypic PMT shows stress concentration near the middle section of the PMT bulbs that correlates well with our crack velocity measurements in that section. The FEM model predicts a crack velocity value that is close to the terminal crack velocity reported. Our measurements also reveal significantly reduced crack velocities compared to terminal crack velocities measured in glasses using fracture mechanics testing and reported in literature.« less

Photomultiplier tube failure under hydrostatic pressure in future neutrino detectors

DOE PAGES

Chambliss, K.; Diwan, M.; Simos, N.; ...

2014-10-09

Failure of photomultiplier tubes (PMTs) under hydrostatic pressure is a concern in neutrino detection, specifically, in the proposed Long-Baseline Neutrino Experiment project. Controlled hydrostatic implosion tests were performed on prototypic PMT bulbs of 10-inch diameter and recorded using high speed filming techniques to capture failures in detail. These high-speed videos were analyzed frame-by-frame in order to identify the origin of a crack, measure the progression of individual crack along the surface of the bulb as it propagates through the glass, and estimate crack velocity. Crack velocity was calculated for each individual crack, and an average velocity was determined for allmore » measurable cracks on each bulb. Overall, 32 cracks were measured in 9 different bulbs tested. Finite element modeling (FEM) of crack formation and growth in prototypic PMT shows stress concentration near the middle section of the PMT bulbs that correlates well with our crack velocity measurements in that section. The FEM model predicts a crack velocity value that is close to the terminal crack velocity reported. Our measurements also reveal significantly reduced crack velocities compared to terminal crack velocities measured in glasses using fracture mechanics testing and reported in literature.« less

Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

NASA Technical Reports Server (NTRS)

Chen, QI; Liu, Hao-Wen

1988-01-01

Fatigue crack growth in large grain Al alloy was studied. Fatigue crack growth is caused primarily by shear decohesion due to dislocation motion in the crack tip region. The crack paths in the large crystals are very irregular and zigzag. The crack planes are often inclined to the loading axis both in the inplane direction and the thickness direction. The stress intensity factors of such inclined cracks are approximated from the two dimensional finite element calculations. The plastic deformation in a large crystal is highly anisotropic, and dislocation motion in such crystals are driven by the resolved shear stress. The resolved shear stress intensity coefficient in a crack solid, RSSIC, is defined, and the coefficients for the slip systems at a crack tip are evaluated from the calculated stress intensity factors. The orientations of the crack planes are closely related to the slip planes with the high RSSIC values. If a single slip system has a much higher RSSIC than all the others, the crack will follow the slip plane, and the slip plane becomes the crack plane. If two or more slip systems have a high RSSIC, the crack plane is the result of the decohesion processes on these active slip planes.

Fretting Fatigue with Cylindrical-On-Flat Contact: Crack Nucleation, Crack Path and Fatigue Life

PubMed Central

Noraphaiphipaksa, Nitikorn; Manonukul, Anchalee; Kanchanomai, Chaosuan

2017-01-01

Fretting fatigue experiments and finite element analysis were carried out to investigate the influence of cylindrical-on-flat contact on crack nucleation, crack path and fatigue life of medium-carbon steel. The location of crack nucleation was predicted using the maximum shear stress range criterion and the maximum relative slip amplitude criterion. The prediction using the maximum relative slip amplitude criterion gave the better agreement with the experimental result, and should be used for the prediction of the location of crack nucleation. Crack openings under compressive bulk stresses were found in the fretting fatigues with flat-on-flat contact and cylindrical-on-flat contacts, i.e., fretting-contact-induced crack openings. The crack opening stress of specimen with flat-on-flat contact was lower than those of specimens with cylindrical-on-flat contacts, while that of specimen with 60-mm radius contact pad was lower than that of specimen with 15-mm radius contact pad. The fretting fatigue lives were estimated by integrating the fatigue crack growth curve from an initial propagating crack length to a critical crack length. The predictions of fretting fatigue life with consideration of crack opening were in good agreement with the experimental results. PMID:28772522

In silico simulation of liver crack detection using ultrasonic shear wave imaging.

PubMed

Nie, Erwei; Yu, Jiao; Dutta, Debaditya; Zhu, Yanying

2018-05-16

Liver trauma is an important source of morbidity and mortality worldwide. A timely detection and precise evaluation of traumatic liver injury and the bleeding site is necessary. There is a need to develop better imaging modalities of hepatic injuries to increase the sensitivity of ultrasonic imaging techniques for sites of hemorrhage caused by cracks. In this study, we conduct an in silico simulation of liver crack detection and delineation using an ultrasonic shear wave imaging (USWI) based method. We simulate the generation and propagation of the shear wave in a liver tissue medium having a crack using COMSOL. Ultrasound radio frequency (RF) signal synthesis and the two-dimensional speckle tracking algorithm are applied to simulate USWI in a medium with randomly distributed scatterers. Crack detection is performed using the directional filter and the edge detection algorithm rather than the conventional inversion algorithm. Cracks with varied sizes and locations are studied with our method and the crack localization results are compared with the given crack. Our pilot simulation study shows that, by using USWI combined with a directional filter cum edge detection technique, the near-end edge of the crack can be detected in all the three cracks that we studied. The detection errors are within 5%. For a crack of 1.6 mm thickness, little shear wave can pass through it and the far-end edge of the crack cannot be detected. The detected crack lengths using USWI are all slightly shorter than the actual crack length. The robustness of our method in detecting a straight crack, a curved crack and a subtle crack of 0.5 mm thickness is demonstrated. In this paper, we simulate the use of a USWI based method for the detection and delineation of the crack in liver. The in silico simulation helps to improve understanding and interpretation of USWI measurements in a physical scattered liver medium with a crack. This pilot study provides a basis for improved insights in future crack detection studies in a tissue phantom or liver.

Surface crack problems in plates

NASA Technical Reports Server (NTRS)

Joseph, P. F.; Erdogan, F.

1989-01-01

The mode I crack problem in plates under membrane loading and bending is reconsidered. The purpose is to examine certain analytical features of the problem further and to provide some new results. The formulation and the results given by the classical and the Reissner plate theories for through and part-through cracks are compared. For surface cracks the three-dimensional finite element solution is used as the basis of comparison. The solution is obtained and results are given for the crack/contact problem in a plate with a through crack under pure bending and for the crack interaction problem. Also, a procedure is developed to treat the problem of subcritical crack growth and to trace the evolution of the propagating crack.

Seeding Cracks Using a Fatigue Tester for Accelerated Gear Tooth Breaking

NASA Technical Reports Server (NTRS)

Nenadic, Nenad G.; Wodenscheck, Joseph A.; Thurston, Michael G.; Lewicki, David G.

2011-01-01

This report describes fatigue-induced seeded cracks in spur gears and compares them to cracks created using a more traditional seeding method, notching. Finite element analysis (FEA) compares the effective compliance of a cracked tooth to the effective compliance of a notched tooth where the crack and the notch are of the same depth. In this analysis, cracks are propagated to the desired depth using FRANC2D and effective compliances are computed in ANSYS. A compliance-based feature for detecting cracks on the fatigue tester is described. The initiated cracks are examined using both nondestructive and destructive methods. The destructive examination reveals variability in the shape of crack surfaces.

Research progress on expansive soil cracks under changing environment.

PubMed

Shi, Bei-xiao; Zheng, Cheng-feng; Wu, Jin-kun

2014-01-01

Engineering problems shunned previously rise to the surface gradually with the activities of reforming the natural world in depth, the problem of expansive soil crack under the changing environment becoming a control factor of expansive soil slope stability. The problem of expansive soil crack has gradually become a research hotspot, elaborates the occurrence and development of cracks from the basic properties of expansive soil, and points out the role of controlling the crack of expansive soil strength. We summarize the existing research methods and results of expansive soil crack characteristics. Improving crack measurement and calculation method and researching the crack depth measurement, statistical analysis method, crack depth and surface feature relationship will be the future direction.

Sub-10-micrometer toughening and crack tip toughness of dental enamel.

PubMed

Ang, Siang Fung; Schulz, Anja; Pacher Fernandes, Rodrigo; Schneider, Gerold A

2011-04-01

In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip's toughness (K(I0),K(III0)), the crack's closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine enamel was studied using atomic force microscopy (AFM). The mode I crack tip toughness K(I0) of cracks along enamel rod boundaries and across enamel rods exhibit a similar range of values: K(I0,Ir)=0.5-1.6MPa m(0.5) (based on Irwin's 'near-field' solution) and K(I0,cz)=0.8-1.5MPa m(0.5) (based on the cohesive zone solution of the Dugdale-Muskhelishvili (DM) crack model). The mode III crack tip toughness K(III0,Ir) was computed as 0.02-0.15MPa m(0.5). The crack-closure stress at the crack tip was computed as 163-770 MPa with a cohesive zone length and width 1.6-10.1μm and 24-44 nm utilizing the cohesive zone solution. Toughening elements were observed under AFM and SEM: crack bridging due to protein ligament and hydroxyapatite fibres (micro- and nanometer scale) as well as microcracks were identified. Crown Copyright © 2010. Published by Elsevier Ltd. All rights reserved.

21 CFR 137.190 - Cracked wheat.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 21 Food and Drugs 2 2011-04-01 2011-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting... such wheat, other than moisture, remain unaltered. Cracked wheat contains not more than 15 percent of...

United States Air Force Graduate Student Research Program for 1990. Program Management Report

DTIC Science & Technology

1992-06-05

were extensively studied using pencil lead breaks in a center notch. For the fatigue studies center crack samples of 2024 - T351 aluminum were used...Research Program (SFRP) provides opportunities for research in the physical sciences, engineering, and life sciences. The program has been effective ...positive effect on teaching. (WRDC/FDL) Several mentioned the opportunity for introduction to research interests of the Air Force and the opportunity to work

40 CFR 63.1564 - What are my requirements for metal HAP emissions from catalytic cracking units?

Code of Federal Regulations, 2010 CFR

2010-07-01

... with the PM emission limit (Option 2); (iii) You can elect to comply with the Nickel (Ni) lb/hr emission limit (Option 3); or (iv) You can elect to comply with the Ni lb/1,000 lbs of coke burn-off... coke burn. ER11AP02.004 (iii) If you elect Option 3 in paragraph (a)(1)(iii) of this section, the Ni lb...

40 CFR Table 4 to Subpart Uuu of... - Requirements for Performance Tests for Metal HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2010 CFR

2010-07-01

... 4 of § 63.1564. 4. Option 3: Ni lb/hr a. Measure concentration of Ni and total metal HAP. Method 29 (40 CFR part 60, appendix A). b. Compute Ni emission rate (lb/hr). Equation 5 of § 63.1564. c. Determine the equilibrium catalyst Ni concentration. XRF procedure in appendix A to this subpart1; or EPA...

40 CFR 63.1564 - What are my requirements for metal HAP emissions from catalytic cracking units?

Code of Federal Regulations, 2011 CFR

2011-07-01

... with the PM emission limit (Option 2); (iii) You can elect to comply with the Nickel (Ni) lb/hr emission limit (Option 3); or (iv) You can elect to comply with the Ni lb/1,000 lbs of coke burn-off... coke burn. ER11AP02.004 (iii) If you elect Option 3 in paragraph (a)(1)(iii) of this section, the Ni lb...

40 CFR Table 4 to Subpart Uuu of... - Requirements for Performance Tests for Metal HAP Emissions From Catalytic Cracking Units Not...

Code of Federal Regulations, 2011 CFR

2011-07-01

... 4 of § 63.1564. 4. Option 3: Ni lb/hr a. Measure concentration of Ni and total metal HAP. Method 29 (40 CFR part 60, appendix A). b. Compute Ni emission rate (lb/hr). Equation 5 of § 63.1564. c. Determine the equilibrium catalyst Ni concentration. XRF procedure in appendix A to this subpart1; or EPA...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Surendra; Jauriqui, Leanne; Sloan, Trista

We have used Process Compensated Resonant Testing (PCRT) for studying structural integrity and functional performance of ceramic balls used in various auxiliary power units (APUs), propulsion engines, and defense and space missiles. The results show that PCRT is successful in sorting acceptable parts from parts with defects such as micro-structural changes, C-cracks, and scuffs. However, PCRT suffers from limitations, generally not determining the type, size or location of the anomaly. The pursuit of improvements to PCRT is an on-going process.

Yemen: Background and U.S. Relations

DTIC Science & Technology

2009-07-07

In a speech to the Atlantic Council of the United States, CIA Director Michael Hayden stated that “Yemen is another country of concern, a place where...Saleh has pledged to crack down on the southern separatist movement. In a pivotal speech in May 2009, Saleh remarked: “Now, the popular committees...will face the apostate elements. I call them apostate, vandalizing, and hireling elements. They are not new since they were products of the sedition

Fracture Mechanics Analysis for Short Cracks

DTIC Science & Technology

1990-02-01

OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION I(if applicable ) United Technologies Res. Ctr. JF S 6c ADDRESS (City. State, and ZIP Code) 7b...plastic fracture mechanics ( EPFM ) with the pioneering works of Hult and McClintock (Ref. 3), Dugdale (Ref. 4), Barenblatt (Ref. 5), Bilby, Cottrell and...Swinden (Refs. 6 and 7), Rice (Ref. 8), and Hutchinson (Ref. 9). EPFM is applica- ble and needed especially for high toughness and low strength

Stable tearing behavior of a thin-sheet material with multiple cracks

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Newman, J. C., Jr.; Sutton, M. A.; Amstutz, B. E.

1994-01-01

Fracture tests were conducted on 2.3mm thick, 305mm wide sheets of 2024-T3 aluminum alloy with 1-5 collinear cracks. The cracks were introduced (crack history) into the specimens by three methods: (1) saw cutting; (2) fatigue precracking at a low stress range; and (3) fatigue precracking at a high stress range. For the single crack tests, the initial crack history influenced the stress required for the onset of stable crack growth and the first 10mm of crack growth. The effect on failure stress was about 4 percent or less. For the multiple crack tests, the initial crack history was shown to cause differences of more than 20 percent in the link-up stress and 13 percent in failure stress. An elastic-plastic finite element analysis employing the Crack Tip Opening Angle (CTOA) fracture criterion was used to predict the fracture behavior of the single and multiple crack tests. The numerical predictions were within 7 percent of the observed link-up and failure stress in all the tests.

Influence of crack history on the stable tearing behavior of a thin-sheet material with multiple cracks

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Newman, J. C., Jr.; Sutton, M. A.; Amstutz, B. E.

1994-01-01

Fracture tests were conducted on 2.3mm thick, 305mm wide sheets of 2024-T3 aluminum alloy with from one to five collinear cracks. The cracks were introduced (crack history) into the specimens by three methods: saw cutting, fatigue precracking at a low stress range, and fatigue precracking at a high stress range. For the single crack tests, the initial crack history influenced the stress required for the onset of stable crack growth and the first 10mm of crack growth. The effect on failure stress was about 4 percent or less. For the multiple crack tests, the initial crack history was shown to cause differences of more than 20 percent in the link-up stress and 13 percent in failure stress. An elastic-plastic finite element analysis employing the CTOA fracture criterion was used to predict the fracture behavior of the single and multiple crack tests. The numerical predictions were within 7 percent of the observed link-up and failure stress in all the tests.

Corrosion pitting and environmentally assisted small crack growth

PubMed Central

Turnbull, Alan

2014-01-01

In many applications, corrosion pits act as precursors to cracking, but qualitative and quantitative prediction of damage evolution has been hampered by lack of insights into the process by which a crack develops from a pit. An overview is given of recent breakthroughs in characterization and understanding of the pit-to-crack transition using advanced three-dimensional imaging techniques such as X-ray computed tomography and focused ion beam machining with scanning electron microscopy. These techniques provided novel insights with respect to the location of crack development from a pit, supported by finite-element analysis. This inspired a new concept for the role of pitting in stress corrosion cracking based on the growing pit inducing local dynamic plastic strain, a critical factor in the development of stress corrosion cracks. Challenges in quantifying the subsequent growth rate of the emerging small cracks are then outlined with the potential drop technique being the most viable. A comparison is made with the growth rate for short cracks (through-thickness crack in fracture mechanics specimen) and long cracks and an electrochemical crack size effect invoked to rationalize the data. PMID:25197249

Automatic Detection and Evaluation of Solar Cell Micro-Cracks in Electroluminescence Images Using Matched Filters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spataru, Sergiu; Hacke, Peter; Sera, Dezso

A method for detecting micro-cracks in solar cells using two dimensional matched filters was developed, derived from the electroluminescence intensity profile of typical micro-cracks. We describe the image processing steps to obtain a binary map with the location of the micro-cracks. Finally, we show how to automatically estimate the total length of each micro-crack from these maps, and propose a method to identify severe types of micro-cracks, such as parallel, dendritic, and cracks with multiple orientations. With an optimized threshold parameter, the technique detects over 90 % of cracks larger than 3 cm in length. The method shows great potentialmore » for quantifying micro-crack damage after manufacturing or module transportation for the determination of a module quality criterion for cell cracking in photovoltaic modules.« less

Fracture Analysis of Semi-Elliptical Surface Cracks in Ductile Materials

NASA Technical Reports Server (NTRS)

Daniewicz, S. R.; Newman, J. C., Jr.; Leach, A. M.

2004-01-01

Accurate life assessment of structural components may require advanced life prediction criteria and methodologies. Structural components often exhibit several different types of defects, among the most prevalent being surface cracks. A semi-elliptical surface crack subjected to monotonic loading will exhibit stable crack growth until the crack has reached a critical size, at which the crack loses stability and fracture ensues (Newman, 2000). The shape and geometry of the flaw are among the most influential factors. When considering simpler crack configurations, such as a through-the-thickness crack, a three-dimensional (3D) geometry may be modeled under the approximation of two-dimensional (2D) plane stress or plane strain. The more complex surface crack is typically modeled numerically with the Finite Element Method (FEM). A semi-elliptical surface crack is illustrated in Figure 1-1.

Characterization of Cracking Mechanisms of Carbon Anodes Used in Aluminum Industry by Optical Microscopy and Tomography

NASA Astrophysics Data System (ADS)

Amrani, Salah; Kocaefe, Duygu; Kocaefe, Yasar; Bhattacharyay, Dipankar; Bouazara, Mohamed; Morais, Brigitte

2016-10-01

The objective of this work is to understand the different mechanisms of crack formation in dense anodes used in the aluminum industry. The first approach used is based on the qualitative characterization of the surface cracks and the depth of these cracks. The second approach, which constitutes a quantitative characterization, is carried out by determining the distribution of the crack width along its length as well as the percentage of the surface containing cracks. A qualitative analysis of crack formation was also carried out using 3D tomography. It was observed that mixing and forming conditions have a significant effect on crack formation in green anodes. The devolatilization of pitch during baking causes the formation and propagation of cracks in baked anodes in which large particles control the direction of crack propagation.

Modeling the Interactions Between Multiple Crack Closure Mechanisms at Threshold

NASA Technical Reports Server (NTRS)

Newman, John A.; Riddell, William T.; Piascik, Robert S.

2003-01-01

A fatigue crack closure model is developed that includes interactions between the three closure mechanisms most likely to occur at threshold; plasticity, roughness, and oxide. This model, herein referred to as the CROP model (for Closure, Roughness, Oxide, and Plasticity), also includes the effects of out-of plane cracking and multi-axial loading. These features make the CROP closure model uniquely suited for, but not limited to, threshold applications. Rough cracks are idealized here as two-dimensional sawtooths, whose geometry induces mixed-mode crack- tip stresses. Continuum mechanics and crack-tip dislocation concepts are combined to relate crack face displacements to crack-tip loads. Geometric criteria are used to determine closure loads from crack-face displacements. Finite element results, used to verify model predictions, provide critical information about the locations where crack closure occurs.

Fatigue pre-cracking and fracture toughness in polycrystalline tungsten and molybdenum

NASA Astrophysics Data System (ADS)

Taguchi, Katsuya; Nakadate, Kazuhito; Matsuo, Satoru; Tokunaga, Kazutoshi; Kurishita, Hiroaki

2018-01-01

Fatigue pre-cracking performance and fracture toughness in polycrystalline tungsten (W) and molybdenum (Mo) have been investigated in relation to grain boundary (GB) configuration with respect to the crack advance direction. Sub-sized, single edge notched bend (SENB) specimens with three different orientations, R-L (ASTM notation) for a forged Mo rod and L-S and T-S for a rolled W plate, were pre-cracked in two steps: fully uniaxial compression fatigue loading to provoke crack initiation and its stable growth from the notch root, and subsequent 3-point bend (3PB) fatigue loading to extend the crack. The latter step intends to minimize the influence of the residual tensile stresses generated during compression fatigue by moving the crack tip away from the plastic zone. It is shown that fatigue pre-cracking performance, especially pre-crack extension behavior, is significantly affected by the specimen orientation. The R-L orientation, giving the easiest cracking path, permitted crack extension completely beyond the plastic zone, while the L-S and T-S orientations with the thickness cracking direction of the rolled plate sustained the crack lengths around or possibly within the plastic zone size due to difficulty in crack advance through an aligned grain structure. Room temperature fracture toughness tests revealed that the 3PB fatigued specimens exhibited appreciably higher fracture toughness by about 30% for R-L, 40% for L-S and 60% for T-S than the specimens of each orientation pre-cracked by compression fatigue only. This indicates that 3PB fatigue provides the crack tip front out of the residual tensile stress zone by crack extension or leads to reduction in the residual stresses at the crack tip front. Strong dependence of fracture toughness on GB configuration was evident. The obtained fracture toughness values are compared with those in the literature and its strong GB configuration dependence is discussed in connection with the appearance of pop-in.

A preliminary study of crack initiation and growth at stress concentration sites

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Gallagher, J. P.; Hartman, G. A.; Rajendran, A. M.

1982-01-01

Crack initiation and propagation models for notches are examined. The Dowling crack initiation model and the E1 Haddad et al. crack propagation model were chosen for additional study. Existing data was used to make a preliminary evaluation of the crack propagation model. The results indicate that for the crack sizes in the test, the elastic parameter K gave good correlation for the crack growth rate data. Additional testing, directed specifically toward the problem of small cracks initiating and propagating from notches is necessary to make a full evaluation of these initiation and propagation models.

Analysis and prediction of Multiple-Site Damage (MSD) fatigue crack growth

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Newman, J. C., Jr.

1992-01-01

A technique was developed to calculate the stress intensity factor for multiple interacting cracks. The analysis was verified through comparison with accepted methods of calculating stress intensity factors. The technique was incorporated into a fatigue crack growth prediction model and used to predict the fatigue crack growth life for multiple-site damage (MSD). The analysis was verified through comparison with experiments conducted on uniaxially loaded flat panels with multiple cracks. Configuration with nearly equal and unequal crack distribution were examined. The fatigue crack growth predictions agreed within 20 percent of the experimental lives for all crack configurations considered.

Investigation of eddy current examination on OD fatigue crack for steam generator tubes

NASA Astrophysics Data System (ADS)

Kong, Yuying; Ding, Boyuan; Li, Ming; Liu, Jinhong; Chen, Huaidong; Meyendorf, Norbert G.

2015-03-01

The opening width of fatigue crack was very small, and conventional Bobbin probe was very difficult to detect it in steam generator tubes. Different sizes of 8 fatigue cracks were inspected using bobbin probe rotating probe. The analysis results showed that, bobbin probe was not sensitive for fatigue crack even for small through wall crack mixed with denting signal. On the other hand, the rotating probe was easily to detect all cracks. Finally, the OD phase to depth curve for fatigue crack using rotating probe was established and the results agreed very well with the true crack size.

In situ investigation of high humidity stress corrosion cracking of 7075 aluminum alloy by three-dimensional (3D) X-ray synchrotron tomography

DOE PAGES

Singh, S. S.; Williams, J. J.; Lin, M. F.; ...

2014-05-14

In situ X-ray synchrotron tomography was used to investigate the stress corrosion cracking behavior of under-aged Al–Zn–Mg–Cu alloy in moisture. The discontinuous surface cracks (crack jumps) mentioned in the literature are actually a single continuous and tortuous crack when observed in three dimension (3D). Contrary to 2D measurements made at the surface which suggest non-uniform crack growth rates, 3D measurements of the crack length led to a much more accurate measurement of crack growth rates.

Dynamics of a fluid-driven crack in three dimensions by the finite difference method

NASA Astrophysics Data System (ADS)

Chouet, Bernard

1986-12-01

The finite difference method is applied to the study of the dynamics of a three-dimensional fluid-filled crack excited into resonance by the sudden failure of a small barrier of area ΔS on the crack surface. The impulse response of the crack is examined for various ratios of crack width to crack length and for several values of the crack stiffness C = (b/μ)(L/d), where b is the bulk modulus of the fluid, μ is the rigidity of the solid, and L and d are the crack length and crack thickness, respectively. The motion of the crack is characterized by distinct time scales representing the duration of brittle failure and the periods of acoustic resonance in the lateral and longitudinal dimensions of the source. The rupture has a duration proportional to the area of crack expansion and is the trigger responsible for the excitation of the crack into resonance; the resonant periods are proportional to the crack stiffness and to the width and length of the crack. The crack wave sustaining the resonance is analogous to the tube wave propagating in a fluid-filled borehole. It is dispersive, showing a phase velocity that decreases with increasing wavelength. Its wave speed is always lower than the acoustic velocity of the fluid and shows a strong dependence on the crack stiffness, decreasing as the stiffness increases. The initial motion of the crack surface is an opening, and the radiated far-field compressional wave starts with a strong but brief compression which has a duration proportional to the crack stiffness and size of the rupture area; the amplitude of this pulse increases with the area of rupture but decreases with increasing stiffness. Flow into the newly created cavity triggers a pressure drop in the fluid, which produces a partial collapse of the wall propagated over the crack surface at the speed of the crack wave. The collapse of the crack surface generates a weak long-period component of dilatation following the compressional first motion in the far-field P wave train; the dilatational component is clearer in the signal from stiffer cracks when seen in the direction of the rupture. The energy loss by radiation is stronger for high frequencies, resulting in a progressive enrichment of the crack response in lower frequencies over the duration of resonance. These source characteristics translate into a far-field signature that is marked by a high-frequency content near its onset and dominated by a longer-period component in its coda. The source duration shows a strong dependence on the fluid viscosity and associated viscous damping at the crack wall.

Hydrogen enhanced crack growth in 18 Ni maraging steels

NASA Technical Reports Server (NTRS)

Hudak, S. J., Jr.; Wei, R. P.

1976-01-01

The kinetics of sustained-load subcritical crack growth for 18 Ni maraging steels in high-purity hydrogen are examined using the crack-tip stress intensity factor K as a measure of crack driving force. Crack growth rate as a function of stress intensity exhibited a clearly defined K-independent stage (Stage II). Crack growth rates in an 18 Ni (grade 250) maraging steel are examined for temperatures from -6 to +100 C. A critical temperature was observed above which crack growth rates became diminishingly small. At lower temperatures the activation energy for Stage II crack growth was found to be 16.7 plus or minus 3.3 kJ/mole. Temperature and hydrogen partial pressure are shown to interact in a complex manner to determine the apparent Kth (stress intensity level below which no observable crack growth occurs) and the crack growth behavior. Comparison of results on '250' and '300' grades of 18 Ni maraging steel indicate a significant influence of alloy composition and/or strength level on the crack growth behavior.

Theoretical predicting of permeability evolution in damaged rock under compressive stress

NASA Astrophysics Data System (ADS)

Vu, M. N.; Nguyen, S. T.; To, Q. D.; Dao, N. H.

2017-05-01

This paper outlines an analytical model of crack growth induced permeability changes. A theoretical solution of effective permeability of cracked porous media is derived. The fluid flow obeys Poisseuille's law along the crack and Darcy's law in the porous matrix. This solution exhibits a percolation threshold for any type of crack distribution apart from a parallel crack distribution. The physical behaviour of fluid flow through a cracked porous material is well reproduced by the proposed model. The presence of this effective permeability coupling to analytical expression of crack growth under compression enables the modelling of the permeability variation due to stress-induced cracking in a porous rock. This incorporation allows the prediction of the permeability change of a porous rock embedding an anisotropic crack distribution from any initial crack density, that is, lower, around or upper to percolation threshold. The interaction between cracks is not explicitly taken into account. The model is well applicable both to micro- and macrocracks.

Crack propagation in teeth: a comparison of perimortem and postmortem behavior of dental materials and cracks.

PubMed

Hughes, Cris E; White, Crystal A

2009-03-01

This study presents a new method for understanding postmortem heat-induced crack propagation patterns in teeth. The results demonstrate that patterns of postmortem heat-induced crack propagation differ from perimortem and antemortem trauma-induced crack propagation patterns. Dental material of the postmortem tooth undergoes dehydration leading to a shrinking and more brittle dentin material and a weaker dentin-enamel junction. Dentin intertubule tensile stresses are amplified by the presence of the pulp cavity, and initiates crack propagation from the internal dentin, through the dentin-enamel junction and lastly the enamel. In contrast, in vivo perimortem and antemortem trauma-induced crack propagation initiates cracking from the external surface of the enamel toward the dentin-enamel junction where the majority of the energy of the crack is dissipated, eliminating the crack's progress into the dentin. These unique patterns of crack propagation can be used to differentiate postmortem taphonomy-induced damage from antemortem and perimortem trauma in teeth.

Definitive diagnosis of early enamel and dentin cracks based on microscopic evaluation.

PubMed

Clark, David J; Sheets, Cherilyn G; Paquette, Jacinthe M

2003-01-01

The diagnoses of cracked teeth and incomplete coronal fracture have historically been symptom based. The dental operating microscope at 16x magnification can fundamentally change a clinician's ability to diagnose such conditions. Clinicians have been observing cracks under extreme magnification for nearly a decade. Patterns have become clear that can lead to appropriate treatment prior to symptoms or to devastation to tooth structure. Conversely, many cracks are not structural and can lead to misdiagnosis and overtreatment. Methodic microscopic examination, an understanding of crack progression, and an appreciation of the types of cracks will guide a doctor to make appropriate decisions. Teeth can have structural cracks in various stages. To date, diagnosis and treatment are very often at end stage of crack development. This article gives new guidelines for recognition, visualization, classification, and treatment of cracked teeth based on the routine use of 16x magnification. The significance of enamel cracks as they relate to dentinal cracks is detailed.

Modeling of crack bridging in a unidirectional metal matrix composite

NASA Technical Reports Server (NTRS)

Ghosn, Louis J.; Kantzos, Pete; Telesman, Jack

1991-01-01

The effective fatigue crack driving force and crack opening profiles were determined analytically for fatigue tested unidirectional composite specimens exhibiting fiber bridging. The crack closure pressure due to bridging was modeled using two approaches; the fiber pressure model and the shear lag model. For both closure models, the Bueckner weight function method and the finite element method were used to calculate crack opening displacements and the crack driving force. The predicted near crack tip opening profile agreed well with the experimentally measured profiles for single edge notch SCS-6/Ti-15-3 metal matrix composite specimens. The numerically determined effective crack driving force, Delta K(sup eff), was calculated using both models to correlate the measure crack growth rate in the composite. The calculated Delta K(sup eff) from both models accounted for the crack bridging by showing a good agreement between the measured fatigue crack growth rates of the bridged composite and that of unreinforced, unbridged titanium matrix alloy specimens.

Modeling of crack bridging in a unidirectional metal matrix composite

NASA Technical Reports Server (NTRS)

Ghosn, Louis J.; Kantzos, Pete; Telesman, Jack

1992-01-01

The effective fatigue crack driving force and crack opening profiles were determined analytically for fatigue tested unidirectional composite specimens exhibiting fiber bridging. The crack closure pressure due to bridging was modeled using two approaches: the fiber pressure model and the shear lag model. For both closure models, the Bueckner weight function method and the finite element method were used to calculate crack opening displacements and the crack driving force. The predicted near crack tip opening profile agreed well with the experimentally measured profiles for single edge notch SCS-6/Ti-15-3 metal matrix composite specimens. The numerically determined effective crack driving force, Delta K(eff), was calculated using both models to correlate the measure crack growth rate in the composite. The calculated Delta K(eff) from both models accounted for the crack bridging by showing a good agreement between the measured fatigue crack growth rates of the bridged composite and that of unreinforced, unbridged titanium matrix alloy specimens.

Dynamic delamination crack propagation in a graphite/epoxy laminate

NASA Technical Reports Server (NTRS)

Grady, J. E.; Sun, C. T.

1991-01-01

Dynamic delamination crack propagation in a (90/0) 5s Graphite/Epoxy laminate with an embedded interfacial crack was investigated experimentally using high speed photography. The dynamic motion was produced by impacting the beamlike laminate specimen with a silicon rubber ball. The threshold impact velocities required to initiate dynamic crack propagation in laminates with varying initial crack positions were determined. The crack propagation speeds were estimated from the photographs. Results show that the through the thickness position of the embedded crack can significantly affect the dominant mechanism and the threshold impact velocity for the onset of crack movement. If the initial delamination is placed near the top of bottom surface of the laminate, local buckling of the delaminated plies may cause instability of the crack. If the initial delamination lies on the midplane, local buckling does not occur and the initiation of crack propagation appears to be dominated by Mode II fracture. The crack propagation and arrest observed was seen to be affected by wave motion within the delamination region.

Modeling Transverse Cracking in Laminates With a Single Layer of Elements Per Ply

NASA Technical Reports Server (NTRS)

Van Der Meer, Frans P.; Davila, Carlos G.

2012-01-01

The objective of the present paper is to investigate the ability of mesolevel X-FEM models with a single layer of elements per ply to capture accurately all aspects of matrix cracking. In particular, we examine whether the model can predict the insitu ply thickness effect on crack initiation and propagation, the crack density as a function of strain, the strain for crack saturation, and the interaction between delamination and transverse cracks. Results reveal that the simplified model does not capture correctly the shear-lag relaxation of the stress field on either side of a crack, which leads to an overprediction of the crack density. It is also shown, however, that after onset of delamination many of the inserted matrix cracks close again, and that the density of open cracks becomes similar to the density predicted by the detailed model. The degree to which the spurious cracks affect the global response is quantified and the reliability of the mesolevel approach with a single layer of elements per ply is discussed.

Crack classification and evolution in anisotropic shale during cyclic loading tests by acoustic emission

NASA Astrophysics Data System (ADS)

Wang, Miaomiao; Tan, Chengxuan; Meng, Jing; Yang, Baicun; Li, Yuan

2017-08-01

Characterization and evolution of the cracking mode in shale formation is significant, as fracture networks are an important element in shale gas exploitation. In this study we determine the crack modes and evolution in anisotropic shale under cyclic loading using the acoustic emission (AE) parameter-analysis method based on the average frequency and RA (rise-time/amplitude) value. Shale specimens with bedding-plane orientations parallel and perpendicular to the axial loading direction were subjected to loading cycles with increasing peak values until failure occurred. When the loading was parallel to the bedding plane, most of the cracks at failure were shear cracks, while tensile cracks were dominant in the specimens that were loaded normal to the bedding direction. The evolution of the crack mode in the shale specimens observed in the loading-unloading sequence except for the first cycle can be divided into three stages: (I) no or several cracks (AE events) form as a result of the Kaiser effect, (II) tensile and shear cracks increase steadily at nearly equal proportions, (III) tensile cracks and shear cracks increase abruptly, with more cracks forming in one mode than in the other. As the dominant crack motion is influenced by the bedding, the failure mechanism is discussed based on the evolution of the different crack modes. Our conclusions can increase our understanding of the formation mechanism of fracture networks in the field.

Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy

PubMed Central

Withers, P. J.

2015-01-01

To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored. PMID:25624521

Thermoelastic analysis of matrix crack growth in particulate composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sridhar, N.; Rickman, J.M.; Srolovitz, D.J.

1995-04-01

The authors examine the conditions under which differences in thermal expansion between a particle and the matrix lead to crack growth within the matrix. Using linear elasticity fracture mechanics, they obtain closed-form, analytical results for the case of a penny shaped crack present in the matrix interacting with a spherical inclusion which is misfitting with respect to the matrix. A simple and direct relationship is established between the strain energy release rate, the crack size, the crack orientation with respect to the inclusion, the crack/inclusion separation, the degree of thermal expansion mismatch and the elastic properties of the medium. Themore » authors also analyze the size to which these cracks can grow and find that for a given misfit strain and material properties, crack growth is inhibited beyond a certain critical crack size. They find that beyond this critical size, the elastic strain energy released upon crack growth is no longer sufficient to compensate for the energy expended in extending the crack, since the crack is growing into the rapidly decreasing stress field. The modification of the above conditions for crack growth due to the superposition of an external stress field has also been analyzed. The preferred orientation of these cracks as a function of misfit strain is predicted. The implication of these results for thermal cycling are analyzed.« less

The noncontinuum crack tip deformation behavior of surface microcracks

NASA Astrophysics Data System (ADS)

Morris, W. L.

1980-07-01

The crack tip opening displacement (CTOD) of small surface fatigue cracks (lengths of the grain size) in Al 2219-T851 depends upon the location of a crack relative to the grain boundaries. Both CTOD and crack tip closure stress are greatest when the crack tip is a large distance from the next grain boundary in the direction of crack propagation. Contrary to behavioral trends predicted by continuum fracture mechanics, crack length has no detectable effect on the contribution of plastic deformation to CTOD. It is apparent from these observations that the region of significant plastic deformation is confined by the grain boundaries, resulting in a plastic zone size that is insensitive to crack length and to external load.

Cracking of Clay Due to Contact with Waste Chlorinated Solvents

NASA Astrophysics Data System (ADS)

Otero, M.; Ayral, D.; Shipan, J.; Goltz, M. N.; Huang, J.; Demond, A. H.

2012-12-01

Clays are known to crack upon desiccation. Desiccation cracks of up to 3 cm wide have been reported in natural soils. This raises the question if a similar behavior is seen when a dense non-aqueous phase liquids (DNAPL) waste is in contact with clay. The contact with organic liquids causes the clay structure to shrink, leading to the formation of cracks. Moreover, DNAPL waste not only contains the organic liquid solvent but also includes surface-active solutes or surfactants. Such solutes can enhance the interaction of the organic solvents with the clay. This research will assess whether or not contact with chlorinated organic waste causes cracking. In order to evaluate the possibility of cracking in the clay, microcosms have been constructed that mimic aquifer systems, consisting of a saturated layer of sand, a saturated layer of bentonite clay and a 2.5 cm layer of either pure chlorinated solvents or DNAPL waste. The onset of cracking for the microcosm with tetrachloroethylene (PCE) waste as the DNAPL layer occurred after ten days of contact. Similarly, at eight days, cracks were observed in a microcosm containing trichloroethylene (TCE) waste . Forty-four days later, the length and number of cracks have grown considerably; with a total crack length of 50 cm on a surface of 80 cm2 in the microcosm containing PCE waste. On the other hand it took approximately 161 days for the clay layer in the microcosm containing pure PCE to crack. To quantity the degree of cracking, crack maps were developed using the image software, Image J. Characteristics like crack length, crack aperture, and the percentage of total length for a range of apertures were calculated using this software. For example, for the PCE waste microcosm, it was calculated that 3.7% of the crack length had an aperture of 100-300 microns, 15.1% of the crack length had an aperture of 300-500 microns, 29.7% of the crack length had an aperture of 500-700 microns, 40.1% of the crack length had an aperture of 700-900 microns, 6.3% had an aperture of 900-1,100 microns and 5.1% had an aperture of over 1,100 microns. These data suggest that aquitards in the field might crack when in contact with the DNAPL waste. Moreover, it is apparent that the waste contains solutes that accelerate the cracking of the clay layer. Thus, models examining the impact of storage in low permeability layers need to consider the possible impact of cracking.

Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth

NASA Technical Reports Server (NTRS)

Telesman, Jack; Gabb, Tim; Ghosn, Louis J.

2016-01-01

Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress intensity parameter, Kmax, was developed by incorporating into the formulation the remaining stress level concept as measured by simple stress relaxation tests. The newly proposed parameter, Ksrf, did an excellent job in correlating the dwell crack growth rates for the four heat treatments which were shown to have similar intrinsic environmental cyclic fatigue crack growth resistance.

Mixed-mode stress intensity factors for kink cracks with finite kink length loaded in tension and bending: application to dentin and enamel.

PubMed

Bechtle, Sabine; Fett, Theo; Rizzi, Gabriele; Habelitz, Stefan; Schneider, Gerold A

2010-05-01

Fracture toughness resistance curves describe a material's resistance against crack propagation. These curves are often used to characterize biomaterials like bone, nacre or dentin as these materials commonly exhibit a pronounced increase in fracture toughness with crack extension due to co-acting mechanisms such as crack bridging, crack deflection and microcracking. The knowledge of appropriate stress intensity factors which depend on the sample and crack geometry is essential for determining these curves. For the dental biomaterials enamel and dentin it was observed that, under bending and tensile loading, crack propagation occurs under certain constant angles to the initial notch direction during testing procedures used for fracture resistance curve determination. For this special crack geometry (a kink crack of finite length in a finite body) appropriate geometric function solutions are missing. Hence, we present in this study new mixed-mode stress intensity factors for kink cracks with finite kink length within samples of finite dimensions for two loading cases (tension and bending) which were derived from a combination of mixed-mode stress intensity factors of kink cracks with infinitely small kinks and of slant cracks. These results were further applied to determine the fracture resistance curves of enamel and dentin by testing single edge notched bending (SENB) specimens. It was found that kink cracks with finite kink length exhibit identical stress fields to slant cracks as soon as the kink length exceeds 0.15 times the initial straight crack or notch length. The use of stress intensity factor solutions for infinitely small kink cracks for the determination of dentin fracture resistance curves (as was done by other researchers) leads to an overestimation of dentin's fracture resistance of up to 30%. Copyright 2010 Elsevier Ltd. All rights reserved.

Ply cracking in composite laminates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Youngmyong.

1989-01-01

Ply cracking behavior and accompanying stiffness changes in thermoset as well as thermoplastic matrix composites under various loading conditions are investigated. Specific topics addressed are: analytical model development for property degradations due to ply cracking under general in-plane loading; crack initiation and multiplication under static loading; and crack multiplication under cyclic loading. A model was developed to calculate the energy released due to ply cracking in a composite laminate subjected to general in-plane loading. The method is based on the use of a second order polynomial to represent the crack opening displacement and the concept of a through-the-thickness inherent flaw.more » The model is then used in conjunction with linear elastic fracture mechanics to predict the progressive ply cracking as well as first ply cracking. A resistance curve for crack multiplication is proposed as a means of characterizing the resistance to ply cracking in composite laminates. A methodology of utilizing the resistance curve to assess the crack density or overloading is also discussed. The method was applied to the graphite/thermoplastic polyimide composite to predict progressive ply cracking. However, unlike the thermoset matrix composites, a strength model is found to fit the experimental results better than the fracture mechanics based model. A set of closed form equations is also developed to calculate the accompanying stiffness changes due to the ply cracking. The effect of thermal residual stress is included in the analysis. A new method is proposed to characterize transverse ply cracking of symmetric balanced laminates under cyclic loading. The method is based on the concept of a through-the-thickness inherent flaw, the Paris law, and the resistance curve. Only two constants are needed to predict the crack density as a function of fatigue cycles.« less

Damage, crack growth and fracture characteristics of nuclear grade graphite using the Double Torsion technique

NASA Astrophysics Data System (ADS)

Becker, T. H.; Marrow, T. J.; Tait, R. B.

2011-07-01

The crack initiation and propagation characteristics of two medium grained polygranular graphites, nuclear block graphite (NBG10) and Gilsocarbon (GCMB grade) graphite, have been studied using the Double Torsion (DT) technique. The DT technique allows stable crack propagation and easy crack tip observation of such brittle materials. The linear elastic fracture mechanics (LEFM) methodology of the DT technique was adapted for elastic-plastic fracture mechanics (EPFM) in conjunction with a methodology for directly calculating the J-integral from in-plane displacement fields (JMAN) to account for the non-linearity of graphite deformation. The full field surface displacement measurement techniques of electronic speckle pattern interferometry (ESPI) and digital image correlation (DIC) were used to observe and measure crack initiation and propagation. Significant micro-cracking in the fracture process zone (FPZ) was observed as well as crack bridging in the wake of the crack tip. The R-curve behaviour was measured to determine the critical J-integral for crack propagation in both materials. Micro-cracks tended to nucleate at pores, causing deflection of the crack path. Rising R-curve behaviour was observed, which is attributed to the formation of the FPZ, while crack bridging and distributed micro-cracks are responsible for the increase in fracture resistance. Each contributes around 50% of the irreversible energy dissipation in both graphites.

Fatigue crack growth behaviour of semi-elliptical surface cracks for an API 5L X65 gas pipeline under tension

NASA Astrophysics Data System (ADS)

Shaari, M. S.; Akramin, M. R. M.; Ariffin, A. K.; Abdullah, S.; Kikuchi, M.

2018-02-01

The paper is presenting the fatigue crack growth (FCG) behavior of semi-elliptical surface cracks for API X65 gas pipeline using S-version FEM. A method known as global-local overlay technique was used in this study to predict the fatigue behavior that involve of two separate meshes each specifically for global (geometry) and local (crack). The pre-post program was used to model the global geometry (coarser mesh) known as FAST including the material and boundary conditions. Hence, the local crack (finer mesh) will be defined the exact location and the mesh control accordingly. The local mesh was overlaid along with the global before the numerical computation taken place to solve the engineering problem. The stress intensity factors were computed using the virtual crack closure-integral method (VCCM). The most important results is the behavior of the fatigue crack growth, which contains the crack depth (a), crack length (c) and stress intensity factors (SIF). The correlation between the fatigue crack growth and the SIF shows a good growth for the crack depth (a) and dissimilar for the crack length (c) where stunned behavior was resulted. The S-version FEM will benefiting the user due to the overlay technique where it will shorten the computation process.

Crackscope : automatic pavement cracking inspection system.

DOT National Transportation Integrated Search

2008-08-01

The CrackScope system is an automated pavement crack rating system consisting of a : digital line scan camera, laser-line illuminator, and proprietary crack detection and classification : software. CrackScope is able to perform real-time pavement ins...

Determination of crack depth in aluminum using eddy currents and GMR sensors

NASA Astrophysics Data System (ADS)

Lopes Ribeiro, A.; Pasadas, D.; Ramos, H. G.; Rocha, T.

2015-03-01

In this paper we use eddy currents to determine the depth of linear cracks in aluminum plates. A constant field probe is used to generate the spatially uniform excitation field and a single axis giant magneto-resistor (GMR) sensor is used to measure the eddy currents magnetic field. Different depths were machined in one aluminum plate with 4 mm of thickness. By scanning those cracks the magnetic field components parallel and perpendicular to the crack's line were measured when the eddy currents were launched perpendicularly to the crack's line. To characterize one crack in a plate of a given thickness and material, the experimental procedure was defined. The plate surface is scanned to detect and locate one crack. The acquired data enables the determination of the crack's length and orientation. A second scanning is performed with the excitation current perpendicular to the crack and the GMR sensing axis perpendicular and parallel to the crack's line.

Monitoring small-crack growth by the replication method

NASA Technical Reports Server (NTRS)

Swain, Mary H.

1992-01-01

The suitability of the acetate replication method for monitoring the growth of small cracks is discussed. Applications of this technique are shown for cracks growing at the notch root in semicircular-edge-notch specimens of a variety of aluminum alloys and one steel. The calculated crack growth rate versus Delta K relationship for small cracks was compared to that for large cracks obtained from middle-crack-tension specimens. The primary advantage of this techinque is that it provides an opportunity, at the completion of the test, to go backward in time towards the crack initiation event and 'zoom in' on areas of interest on the specimen surface with a resolution of about 0.1 micron. The primary disadvantage is the inability to automate the process. Also, for some materials, the replication process may alter the crack-tip chemistry or plastic zone, thereby affecting crack growth rates.

Surface cracks in a plate of finite width under tension or bending

NASA Technical Reports Server (NTRS)

Erdogan, F.; Boduroglu, H.

1984-01-01

The problem of a finite plate containing collinear surface cracks is considered and solved by using the line spring model with plane elasticity and Reissner's plate theory. The main focus is on the effect of interaction between two cracks or between cracks and stress-free plate boundaries on the stress intensity factors in an effort to provide extensive numerical results which may be useful in applications. Some sample results are obtained and are compared with the existing finite element results. Then the problem is solved for a single (internal) crack, two collinear cracks, and two corner cracks for wide range of relative dimensions. Particularly in corner cracks, the agreement with the finite element solution is surprisingly very good. The results are obtained for semi-elliptic and rectangular crack profiles which may, in practice, correspond to two limiting cases of the actual profile of a subcritically growing surface crack.

Surface cracks in a plate of finite width under extension or bending

NASA Technical Reports Server (NTRS)

Erdogan, F.; Boduroglu, H.

1984-01-01

In this paper the problem of a finite plate containing collinear surface cracks is considered. The problem is solved by using the line spring model with plane elasticity and Reissner's plate theory. The main purpose of the study is to investigate the effect of interaction between two cracks or between cracks and stress-free plate boundaries on the stress intensity factors and to provide extensive numerical results which may be useful in applications. First, some sample results are obtained and are compared with the existing finite element results. Then the problem is solved for a single (internal) crack, two collinear cracks and two corner cracks for wide range of relative dimensions. Particularly in corner cracks the agreement with the finite element solution is surprisingly very good. The results are obtained for semielliptic and rectangular crack profiles which may, in practice, correspond to two limiting cases of the actual profile of a subcritically growing surface crack.

Growth rate models for short surface cracks in AI 2219-T851

NASA Astrophysics Data System (ADS)

Morris, W. L.; James, M. R.; Buck, O.

1981-01-01

Rates of fatigue propagation of short Mode I surface cracks in Al 2219-T851 are measured as a function of crack length and of the location of the surface crack tips relative to the grain boundaries. The measured rates are then compared to values predicted from crack growth models. The crack growth rate is modeled with an underlying assumption that slip responsible for early propagation does not extend in significant amounts beyond the next grain boundary in the direction of crack propagation. Two models that contain this assumption are combined: 1) cessation of propagation into a new grain until a mature plastic zone is developed; 2) retardation of propagation by crack closure stress, with closure stress calculated from the location of a crack tip relative to the grain boundary. The transition from short to long crack growth behavior is also discussed.

Corrosion fatigue crack propagation in metals

NASA Technical Reports Server (NTRS)

Gangloff, Richard P.

1990-01-01

This review assesses fracture mechanics data and mechanistic models for corrosion fatigue crack propagation in structural alloys exposed to ambient temperature gases and electrolytes. Extensive stress intensity-crack growth rate data exist for ferrous, aluminum and nickel based alloys in a variety of environments. Interactive variables (viz., stress intensity range, mean stress, alloy composition and microstructure, loading frequency, temperature, gas pressure and electrode potential) strongly affect crack growth kinetics and complicate fatigue control. Mechanistic models to predict crack growth rates were formulated by coupling crack tip mechanics with occluded crack chemistry, and from both the hydrogen embrittlement and anodic dissolution/film rupture perspectives. Research is required to better define: (1) environmental effects near threshold and on crack closure; (2) damage tolerant life prediction codes and the validity of similitude; (3) the behavior of microcrack; (4) probes and improved models of crack tip damage; and (5) the cracking performance of advanced alloys and composites.

Variation of the distribution of crack lengths during corrosion fatigue

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishihara, S.; Miyao, K.; Shiozawa, K.

1984-07-01

The detailed initiation and growth behaviour of distributed cracks on a specimen surface was investigated during corrosion fatigue. It can be clarified that the changes of the distribution of crack lengths with stress cycling reflect the behaviour of initiation and growth of distributed cracks. The distribution of crack lengths for certain stress cycles could be explained by a statistical calculation which takes into account both the variation of number of cracks during stress cycling and the scatter of crack growth rate.

International Conference/Workshop on Small Fatigue Cracks (2nd) Held in Santa Barbara, California on 5-10 January 1986.

DTIC Science & Technology

1986-03-31

critical issues thus pertain to the determination of crack tip conditions, as a function of crack length, in terms of the coupled processes of fluid...transport and chemical/electrochemical reactions within the crack, and the determination of the origin of the environmentally-enhanced cracking rates in...Depth in Determining Crack Electrochemistry and Crack Growth" A. Turnbull, National Physical Laboratory, U.K., and R. C. Newmann, UMIST, U.K. 7:30 p.m.-7

Advanced Flaw Manufacturing and Crack Growth Control

NASA Astrophysics Data System (ADS)

Kemppainen, M.; Pitkänen, J.; Virkkunen, I.; Hänninen, H.

2004-02-01

Advanced artificial flaw manufacturing method has become available. The method produces true fatigue cracks, which are representative of most service-induced cracks. These cracks can be used to simulate behaviour of realistic cracks under service conditions. This paper introduces studies of the effects of different thermal loading cycles to crack opening and residual stress state as seen at the surface of the sample and in the ultrasonic signal. In-situ measurements were performed under dynamic thermal fatigue loading of a 20 mm long artificial crack.

Influence of surrounding environment on subcritical crack growth in marble

NASA Astrophysics Data System (ADS)

Nara, Yoshitaka; Kashiwaya, Koki; Nishida, Yuki; , Toshinori, Ii

2017-06-01

Understanding subcritical crack growth in rock is essential for determining appropriate measures to ensure the long-term integrity of rock masses surrounding structures and for construction from rock material. In this study, subcritical crack growth in marble was investigated experimentally, focusing on the influence of the surrounding environment on the relationship between the crack velocity and stress intensity factor. The crack velocity increased with increasing temperature and/or relative humidity. In all cases, the crack velocity increased with increasing stress intensity factor. However, for Carrara marble (CM) in air, we observed a region in which the crack velocity still increased with temperature, but the increase in the crack velocity with increasing stress intensity factor was not significant. This is similar to Region II of subcritical crack growth observed in glass in air. Region II in glass is controlled by mass transport to the crack tip. In the case of rock, the transport of water to the crack tip is important. In general, Region II is not observed for subcritical crack growth in rock materials, because rocks contain water. Because the porosity of CM is very low, the amount of water contained in the marble is also very small. Therefore, our results imply that we observed Region II in CM. Because the crack velocity increased in both water and air with increasing temperature and humidity, we concluded that dry conditions at low temperature are desirable for the long-term integrity of a carbonate rock mass. Additionally, mass transport to the crack tip is an important process for subcritical crack growth in rock with low porosity.

Inspecting cracks in foam insulation

NASA Technical Reports Server (NTRS)

Cambell, L. W.; Jung, G. K.

1979-01-01

Dye solution indicates extent of cracking by penetrating crack and showing original crack depth clearly. Solution comprised of methylene blue in denatured ethyl alcohol penetrates cracks completely and evaporates quickly and is suitable technique for usage in environmental or structural tests.

Internal state variable approach for predicting stiffness reductions in fibrous laminated composites with matrix cracks

NASA Technical Reports Server (NTRS)

Lee, Jong-Won; Allen, D. H.; Harris, C. E.

1989-01-01

A mathematical model utilizing the internal state variable concept is proposed for predicting the upper bound of the reduced axial stiffnesses in cross-ply laminates with matrix cracks. The axial crack opening displacement is explicitly expressed in terms of the observable axial strain and the undamaged material properties. A crack parameter representing the effect of matrix cracks on the observable axial Young's modulus is calculated for glass/epoxy and graphite/epoxy material systems. The results show that the matrix crack opening displacement and the effective Young's modulus depend not on the crack length, but on its ratio to the crack spacing.

Line spring model and its applications to part-through crack problems in plates and shells

NASA Technical Reports Server (NTRS)

Erdogan, Fazil; Aksel, Bulent

1988-01-01

The line spring model is described and extended to cover the problem of interaction of multiple internal and surface cracks in plates and shells. The shape functions for various related crack geometries obtained from the plane strain solution and the results of some multiple crack problems are presented. The problems considered include coplanar surface cracks on the same or opposite sides of a plate, nonsymmetrically located coplanar internal elliptic cracks, and in a very limited way the surface and corner cracks in a plate of finite width and a surface crack in a cylindrical shell with fixed end.

Line Spring Model and Its Applications to Part-Through Crack Problems in Plates and Shells

NASA Technical Reports Server (NTRS)

Erdogan, F.; Aksel, B.

1986-01-01

The line spring model is described and extended to cover the problem of interaction of multiple internal and surface cracks in plates and shells. The shape functions for various related crack geometries obtained from the plane strain solution and the results of some multiple crack problems are presented. The problems considered include coplanar surface cracks on the same or opposite sides of a plate, nonsymmetrically located coplanar internal elliptic cracks, and in a very limited way the surface and corner cracks in a plate of finite width and a surface crack in a cylindrical shell with fixed end.

Axial crack propagation and arrest in pressurized fuselage

NASA Technical Reports Server (NTRS)

Kosai, M.; Shimamoto, A.; Yu, C.-T.; Walker, S. I.; Kobayashi, A. S.; Tan, P.

1994-01-01

The crack arrest capability of a tear strap in a pressurized precracked fuselage was studied through instrumented axial rupture tests of small scale models of an idealized fuselage. Upon pressurization, rapid crack propagation initiated at an axial through crack along the stringer and immediately kinked due to the mixed modes 1 and 2 state caused by the one-sided opening of the crack flap. The diagonally running crack further turned at the tear straps. Dynamic finite element analysis of the rupturing cylinder showed that the crack kinked and also ran straight in the presence of a mixed mode state according to a modified two-parameter crack kinking criterion.

Application of the line-spring model to a cylindrical shell containing a circumferential or axial part-through crack

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1981-01-01

An approximate solution was obtained for a cylindrical shell containing a part-through surface crack. It was assumed that the shell contains a circumferential or axial semi-elliptic internal or external surface crack and was subjected to a uniform membrane loading or a uniform bending moment away from the crack region. A Reissner type theory was used to account for the effects of the transverse shear deformations. The stress intensity factor at the deepest penetration point of the crack was tabulated for bending and membrane loading by varying three dimensionless length parameters of the problem formed from the shell radius, the shell thickness, the crack length, and the crack depth. The upper bounds of the stress intensity factors are provided by the results of the elasticity solution obtained from the axisymmetric crack problem for the circumferential crack, and that found from the plane strain problem for a circular ring having a radial crack for the axial crack. The line-spring model gives the expected results in comparison with the elasticity solutions. Results also compare well with the existing finite element solution of the pressurized cylinder containing an internal semi-elliptic surface crack.

Analytical and experimental studies on detection of longitudinal, L and inverted T cracks in isotropic and bi-material beams based on changes in natural frequencies

NASA Astrophysics Data System (ADS)

Ravi, J. T.; Nidhan, S.; Muthu, N.; Maiti, S. K.

2018-02-01

An analytical method for determination of dimensions of longitudinal crack in monolithic beams, based on frequency measurements, has been extended to model L and inverted T cracks. Such cracks including longitudinal crack arise in beams made of layered isotropic or composite materials. A new formulation for modelling cracks in bi-material beams is presented. Longitudinal crack segment sizes, for L and inverted T cracks, varying from 2.7% to 13.6% of length of Euler-Bernoulli beams are considered. Both forward and inverse problems have been examined. In the forward problems, the analytical results are compared with finite element (FE) solutions. In the inverse problems, the accuracy of prediction of crack dimensions is verified using FE results as input for virtual testing. The analytical results show good agreement with the actual crack dimensions. Further, experimental studies have been done to verify the accuracy of the analytical method for prediction of dimensions of three types of crack in isotropic and bi-material beams. The results show that the proposed formulation is reliable and can be employed for crack detection in slender beam like structures in practice.

Stress Intensity Factors of Slanted Cracks in Bi-Material Plates

NASA Astrophysics Data System (ADS)

Ismail, Al Emran; Azhar Kamarudin, Kamarul; Nor, Nik Hisyamudin Muhd

2017-10-01

In this study, the stress intensity factors (SIF) of slanted cracks in bi-material plates subjected to mode I loading is numerically solved. Based on the literature survey, tremendous amount of research works are available studying the normal cracks in both similar and dissimilar plates. However, lack of SIF behavior for slanted cracks especially when it is embedded in bi-material plates. The slanted cracks are then modelled numerically using ANSYS finite element program. Two plates of different in mechanical properties are firmly bonded obliquely and then slanted edge cracks are introduced at the lower inclined edge. Isoparametric singular element is used to model the crack tip and the SIF is determined which is based on the domain integral method. Three mechanical mismatched and four slanted angles are used to model the cracks. According to the present results, the effects of mechanical mismatch on the SIF for normal cracks are not significant. However, it is played an important role when slanted angles are introduced. It is suggested that higher SIF can be obtained when the cracks are inclined comparing with the normal cracks. Consequently, accelerating the crack growth at the interface between two distinct materials.

Characteristics of lead induced stress corrosion cracking of alloy 690 in high temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chung, K.K.; Lim, J.K.; Watanabe, Yutaka

1996-10-01

Slow strain rate tests (SSRT) were conducted on alloy 690 in various lead chloride solutions and metal lead added to 100 ppm chloride solution at 288 C. The corrosion potential (rest potential) for the alloy was measured with SSRT tests. The cracking was observed by metallographic examination and electron probe micro analyzer. Also, the corrosion behavior of the alloy was evaluated by anodic polarized measurement at 30 C. Resulting from the tests, cracking was characterized by cracking behavior, crack length and crack growth rate, and lead effects on cracking. The cracking was mainly intergranular in mode, approximately from 60 ummore » to 450 um in crack length, and approximately 10{sup {minus}6} to 10{sup {minus}7} mmS-1 in crack velocity. The cracking was evaluated through the variation the corrosion potential in potential-time and lead behavior during SSRTs. The lead effect in corrosion was evaluated through active to passive transition behavior in anodic polarized curves. The corrosion reactions in the cracking region were confirmed by electron probe microanalysis. Alloy 690 is used for steam generation tubes in pressurized water reactors.« less

A probabilistic fatigue analysis of multiple site damage

NASA Technical Reports Server (NTRS)

Rohrbaugh, S. M.; Ruff, D.; Hillberry, B. M.; Mccabe, G.; Grandt, A. F., Jr.

1994-01-01

The variability in initial crack size and fatigue crack growth is incorporated in a probabilistic model that is used to predict the fatigue lives for unstiffened aluminum alloy panels containing multiple site damage (MSD). The uncertainty of the damage in the MSD panel is represented by a distribution of fatigue crack lengths that are analytically derived from equivalent initial flaw sizes. The variability in fatigue crack growth rate is characterized by stochastic descriptions of crack growth parameters for a modified Paris crack growth law. A Monte-Carlo simulation explicitly describes the MSD panel by randomly selecting values from the stochastic variables and then grows the MSD cracks with a deterministic fatigue model until the panel fails. Different simulations investigate the influences of the fatigue variability on the distributions of remaining fatigue lives. Six cases that consider fixed and variable conditions of initial crack size and fatigue crack growth rate are examined. The crack size distribution exhibited a dominant effect on the remaining fatigue life distribution, and the variable crack growth rate exhibited a lesser effect on the distribution. In addition, the probabilistic model predicted that only a small percentage of the life remains after a lead crack develops in the MSD panel.

Nonlinear ultrasonic imaging method for closed cracks using subtraction of responses at different external loads.

PubMed

Ohara, Yoshikazu; Horinouchi, Satoshi; Hashimoto, Makoto; Shintaku, Yohei; Yamanaka, Kazushi

2011-08-01

To improve the selectivity of closed cracks for objects other than cracks in ultrasonic imaging, we propose an extension of a novel imaging method, namely, subharmonic phased array for crack evaluation (SPACE) as well as another approach using the subtraction of responses at different external loads. By applying external static or dynamic loads to closed cracks, the contact state in the cracks varies, resulting in an intensity change of responses at cracks. In contrast, objects other than cracks are independent of external load. Therefore, only cracks can be extracted by subtracting responses at different loads. In this study, we performed fundamental experiments on a closed fatigue crack formed in an aluminum alloy compact tension (CT) specimen using the proposed method. We examined the static load dependence of SPACE images and the dynamic load dependence of linear phased array (PA) images by simulating the external loads with a servohydraulic fatigue testing machine. By subtracting the images at different external loads, we show that this method is useful in extracting only the intensity change of responses related to closed cracks, while canceling the responses of objects other than cracks. Copyright © 2010 Elsevier B.V. All rights reserved.

Analytical and numerical solutions for heat transfer and effective thermal conductivity of cracked media

NASA Astrophysics Data System (ADS)

Tran, A. B.; Vu, M. N.; Nguyen, S. T.; Dong, T. Q.; Le-Nguyen, K.

2018-02-01

This paper presents analytical solutions to heat transfer problems around a crack and derive an adaptive model for effective thermal conductivity of cracked materials based on singular integral equation approach. Potential solution of heat diffusion through two-dimensional cracked media, where crack filled by air behaves as insulator to heat flow, is obtained in a singular integral equation form. It is demonstrated that the temperature field can be described as a function of temperature and rate of heat flow on the boundary and the temperature jump across the cracks. Numerical resolution of this boundary integral equation allows determining heat conduction and effective thermal conductivity of cracked media. Moreover, writing this boundary integral equation for an infinite medium embedding a single crack under a far-field condition allows deriving the closed-form solution of temperature discontinuity on the crack and particularly the closed-form solution of temperature field around the crack. These formulas are then used to establish analytical effective medium estimates. Finally, the comparison between the developed numerical and analytical solutions allows developing an adaptive model for effective thermal conductivity of cracked media. This model takes into account both the interaction between cracks and the percolation threshold.

Crack networks in damaged glass

NASA Astrophysics Data System (ADS)

Mallet, Celine; Fortin, Jerome; Gueguen, Yves

2013-04-01

We investigate how cracks develop and propagate in synthetic glass samples. Cracks are introduced in glass by a thermal shock of 300oC. Crack network is documented from optical and electronic microscopy on these samples that have been submitted to a thermal shock only. Samples are cylinder of 80 mm length and 40 mm diameter. Sections were cut along the cylinder axis and perpendicular to it. Using SEM, crack lengths and apertures can be measured. Optical microscopy allows to get the crack distribution over the entire sample. The sample average crack length is 3 mm. The average aperture is 6 ± 3μm. There is however a clear difference between the sample core, where the crack network has approximatively a transverse isotrope symmetry and the outer ring, where cracks are smaller and more numerous. By measuring before and after the thermal treatment the radial P and S wave velocities in room conditions, we can determine the total crack density which is 0.24. Thermally cracked samples, as described above, were submitted to creep tests. Constant axial stress and lateral stress were applied. Several experiments were performed at different stress values. Samples are saturated for 48 hours (to get an homogeneous pore fluid distribution), the axial stress is increased up to 80% of the sample strength. Stress step tests were performed in order to get creep data. The evolution of strain (axial and radial strain) is measured using strain gages, gap sensors (for the global axial strain) and pore volume change (for the volumetric strain). Creep data are interpreted as evidence of sub-critical crack growth in the cracked glass samples. The above microstructural observations are used, together with a crack propagation model, to account for the creep behavior. Assuming that (i) the observed volumetric strain rate is due to crack propagation and (ii) crack aspect ratio is constant we calculate the creep rate. We obtain some value on the crack propagation during a 24 hours of constant stress test. At each of these test, crack propagate of 0.3 to 0.4 mm. From the initial average crack length of 3 mm, the crack reach the size of 5.8 mm at the end of a complete creep test (with 8 constant stress step of 24 hours).

Stress Intensity Factors for Part-Through Surface Cracks in Hollow Cylinders

NASA Technical Reports Server (NTRS)

Mettu, Sambi R.; Raju, Ivatury S.; Forman, Royce G.

1992-01-01

Flaws resulting from improper welding and forging are usually modeled as cracks in flat plates, hollow cylinders or spheres. The stress intensity factor solutions for these crack cases are of great practical interest. This report describes some recent efforts at improving the stress intensity factor solutions for cracks in such geometries with emphasis on hollow cylinders. Specifically, two crack configurations for cylinders are documented. One is that of a surface crack in an axial plane and the other is a part-through thumb-nail crack in a circumferential plane. The case of a part-through surface crack in flat plates is used as a limiting case for very thin cylinders. A combination of the two cases for cylinders is used to derive a relation for the case of a surface crack in a sphere. Solutions were sought which cover the entire range of the geometrical parameters such as cylinder thickness, crack aspect ratio and crack depth. Both the internal and external position of the cracks are considered for cylinders and spheres. The finite element method was employed to obtain the basic solutions. Power-law form of loading was applied in the case of flat plates and axial cracks in cylinders and uniform tension and bending loads were applied in the case of circumferential (thumb-nail) cracks in cylinders. In the case of axial cracks, the results for tensile and bending loads were used as reference solutions in a weight function scheme so that the stress intensity factors could be computed for arbitrary stress gradients in the thickness direction. For circumferential cracks, since the crack front is not straight, the above technique could not be used. Hence for this case, only the tension and bending solutions are available at this time. The stress intensity factors from the finite element method were tabulated so that results for various geometric parameters such as crack depth-to-thickness ratio (a/t), crack aspect ratio (a/c) and internal radius-to-thickness ratio (R/t) or the crack length-to-width ratio (2c/W) could be obtained by interpolation and extrapolation. Such complete tables were then incorporated into the NASA/FLAGRO computer program which is widely used by the aerospace community for fracture mechanics analysis.

A Study of Failure in Small Pressurized Cylindrical Shells Containing a Crack

NASA Technical Reports Server (NTRS)

Barwell, Craig A.; Eber, Lorenz; Fyfe, Ian M.

1998-01-01

The deformation in the vicinity of axial cracks in thin pressurized cylinders is examined using small experimental The deformation in the vicinity of axial cracks in thin pressurized cylinders is examined using small experimental models. The loading applied was either symmetric or unsymmetric about the crack plane, the latter being caused by structural constraints such as stringers. The objective was two fold - one, to provide the experimental results which will allow computer modeling techniques to be evaluated for deformations that are significantly different from that experienced by flat plates, and the other to examine the deformations and conditions associated with the onset of crack kinking which often precedes crack curving. The stresses which control crack growth in a cylindrical geometry depend on conditions introduced by the axial bulging, which is an integral part of this type of failure. For the symmetric geometry, both the hoop and radial strain just ahead off the crack, r = a, were measured and these results compared with those obtained from a variety of structural analysis codes, in particular STAGS [1], ABAQUS and ANSYS. In addition to these measurements, the pressures at the onset of stable and unstable crack growth were obtained and the corresponding crack deformations measured as the pressures were increased to failure. For the unsymmetric cases, measurements were taken of the crack kinking angle, and the displacements in the vicinity of the crack. In general, the strains ahead of the crack showed good agreement between the three computer codes and between the codes and the experiments. In the case of crack behavior, it was determined that modeling stable tearing with a crack-tip opening displacement fracture criterion could be successfully combined with the finite-element analysis techniques as used in structural analysis codes. The analytic results obtained in this study were very compatible with the experimental observations of crack growth. Measured crack kinking angles also showed good agreement with theories based on the maximum principle stress criterion.

A dynamic model of a cantilever beam with a closed, embedded horizontal crack including local flexibilities at crack tips

NASA Astrophysics Data System (ADS)

Liu, J.; Zhu, W. D.; Charalambides, P. G.; Shao, Y. M.; Xu, Y. F.; Fang, X. M.

2016-11-01

As one of major failure modes of mechanical structures subjected to periodic loads, embedded cracks due to fatigue can cause catastrophic failure of machineries. Understanding the dynamic characteristics of a structure with an embedded crack is helpful for early crack detection and diagnosis. In this work, a new three-segment beam model with local flexibilities at crack tips is developed to investigate the vibration of a cantilever beam with a closed, fully embedded horizontal crack, which is assumed to be not located at its clamped or free end or distributed near its top or bottom side. The three-segment beam model is assumed to be a linear elastic system, and it does not account for the nonlinear crack closure effect; the top and bottom segments always stay in contact at their interface during the beam vibration. It can model the effects of local deformations in the vicinity of the crack tips, which cannot be captured by previous methods in the literature. The middle segment of the beam containing the crack is modeled by a mechanically consistent, reduced bending moment. Each beam segment is assumed to be an Euler-Bernoulli beam, and the compliances at the crack tips are analytically determined using a J-integral approach and verified using commercial finite element software. Using compatibility conditions at the crack tips and the transfer matrix method, the nature frequencies and mode shapes of the cracked cantilever beam are obtained. The three-segment beam model is used to investigate the effects of local flexibilities at crack tips on the first three natural frequencies and mode shapes of the cracked cantilever beam. A stationary wavelet transform (SWT) method is used to process the mode shapes of the cracked cantilever beam; jumps in single-level SWT decomposition detail coefficients can be used to identify the length and location of an embedded horizontal crack.

New breathing functions for the transverse breathing crack of the cracked rotor system: Approach for critical and subcritical harmonic analysis

NASA Astrophysics Data System (ADS)

Al-Shudeifat, Mohammad A.; Butcher, Eric A.

2011-01-01

The actual breathing mechanism of the transverse breathing crack in the cracked rotor system that appears due to the shaft weight is addressed here. As a result, the correct time-varying area moments of inertia for the cracked element cross-section during shaft rotation are also determined. Hence, two new breathing functions are identified to represent the actual breathing effect on the cracked element stiffness matrix. The new breathing functions are used in formulating the time-varying finite element stiffness matrix of the cracked element. The finite element equations of motion are then formulated for the cracked rotor system and solved via harmonic balance method for response, whirl orbits and the shift in the critical and subcritical speeds. The analytical results of this approach are compared with some previously published results obtained using approximate formulas for the breathing mechanism. The comparison shows that the previously used breathing function is a weak model for the breathing mechanism in the cracked rotor even for small crack depths. The new breathing functions give more accurate results for the dynamic behavior of the cracked rotor system for a wide range of the crack depths. The current approach is found to be efficient for crack detection since the critical and subcritical shaft speeds, the unique vibration signature in the neighborhood of the subcritical speeds and the sensitivity to the unbalance force direction all together can be utilized to detect the breathing crack before further damage occurs.

Fatigue crack growth in unidirectional and cross-ply SCS-6/Timetal 21S titanium matrix composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herrmann, D.J.

1994-01-01

Fatigue crack growth in unidirectional and cross-ply SCS-6/ Timetal(R) 21S titanium matrix composite was investigated. Fatigue crack growth tests were performed on (0){sub 4}, (90){sub 4}, and (0/90){sub s} center notch specimens. The (0){sub 4} and (0/90){sub s} fatigue crack growth rates decreased initially. Specimens removed prior to failure were polished to the first row of fibers and intact fibers in the wake of the matrix crack were observed. These bridging fibers reduced the stress intensity range that the matrix material was subjected to, thus reducing the crack growth rate. The crack growth rate eventually increased as fibers failed inmore » the crack wake but the fatigue crack growth rate was still much slower than that of unreinforced Timetal(R) 21S. A model was developed to study the mechanics of a cracked unidirectional composite with any combination of intact and broken fibers in the wake of a matrix crack. The model was correlated to fatigue crack growth rate tests. The model was verified by comparing predicted displacements near the crack surface with Elber gage (1.5 mm gage length extensometer) measurements. The fatigue crack growth rate for the (90){sub 4} specimens was faster than that of unreinforced Timetal(registered trademark) 21S. Elber gage displacement measurements were in agreement with linear elastic fracture mechanics predictions, suggesting that linear elastic fracture mechanics may be applicable to transversely loaded titanium matrix composites.« less

Association Among Periodontitis and the Use of Crack Cocaine and Other Illicit Drugs.

PubMed

Antoniazzi, Raquel P; Zanatta, Fabricio B; Rösing, Cassiano K; Feldens, Carlos Alberto

2016-12-01

Crack cocaine can alter functions related to the immune system and exert a negative influence on progression and severity of periodontitis. The aim of this study is to compare periodontal status between crack cocaine users and crack cocaine non-users and investigate the association between crack cocaine and periodontitis after adjustments for confounding variables. This cross-sectional study evaluated 106 individuals exposed to crack cocaine and 106 never exposed, matched for age, sex, and tobacco use. An examiner determined visible plaque index (VPI), marginal bleeding index, supragingival dental calculus, probing depth (PD), clinical attachment level (CAL), and bleeding on probing (BOP). Logistic regression was used to model associations between crack cocaine and periodontitis (at least three sites with CAL >4 mm and at least two sites with PD >3 mm, not in the same site or tooth). Prevalence of periodontitis among crack non-users and crack users was 20.8% and 43.4%, respectively. Crack users had greater VPI, BOP, PD ≥3 mm, and CAL ≥4 mm than crack non-users. Periodontitis was associated with age >24 years, schooling ≤8 years, smoking, moderate/heavy alcohol use, and plaque rate ≥41%. Crack users had an approximately three-fold greater chance (odds ratio: 3.44; 95% confidence interval: 1.51 to 7.86) of periodontitis than non-users. Occurrence of periodontitis, visible plaque, and gingival bleeding was significantly higher among crack users, and crack use was associated with occurrence of periodontitis.

Small-crack effects in high-strength aluminum alloys

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Wu, X. R.; Venneri, S. L.; Li, C. G.

1994-01-01

The National Aeronautics and Space Administration and the Chinese Aeronautical Establishment participated in a Fatigue and Fracture Mechanics Cooperative Program. The program objectives were to identify and characterize crack initiation and growth of small cracks (10 microns to 2 mm long) in commonly used US and PRC aluminum alloys, to improve fracture mechanics analyses of surface- and corner-crack configurations, and to develop improved life-prediction methods. Fatigue and small-crack tests were performed on single-edgenotch tension (SENT) specimens and large-crack tests were conducted on center-crack tension specimens for constant-amplitude (stress ratios of -1, 0, and 0.5) and Mini-TWIST spectrum loading. The plastic replica method was used to monitor the initiation and growth of small fatigue cracks at the semicircular notch. Crack growth results from each laboratory on 7075-T6 bare and LC9cs clad aluminum alloys agreed well and showed that fatigue life was mostly crack propagation from a material defect (inclusion particles or void) or from the cladding layer. Finite-element and weight-function methods were used to determine stress intensity factors for surface and corner cracks in the SENT specimens. Equations were then developed and used in a crack growth and crack-closure model to correlate small- and large-crack data and to make life predictions for various load histories. The cooperative program produced useful experimental data and efficient analysis methods for improving life predictions. The results should ultimately improve aircraft structural reliability and safety.

3D ductile crack propagation within a polycrystalline microstructure using XFEM

NASA Astrophysics Data System (ADS)

Beese, Steffen; Loehnert, Stefan; Wriggers, Peter

2018-02-01

In this contribution we present a gradient enhanced damage based method to simulate discrete crack propagation in 3D polycrystalline microstructures. Discrete cracks are represented using the eXtended finite element method. The crack propagation criterion and the crack propagation direction for each point along the crack front line is based on the gradient enhanced damage variable. This approach requires the solution of a coupled problem for the balance of momentum and the additional global equation for the gradient enhanced damage field. To capture the discontinuity of the displacements as well as the gradient enhanced damage along the discrete crack, both fields are enriched using the XFEM in combination with level sets. Knowing the crack front velocity, level set methods are used to compute the updated crack geometry after each crack propagation step. The applied material model is a crystal plasticity model often used for polycrystalline microstructures of metals in combination with the gradient enhanced damage model. Due to the inelastic material behaviour after each discrete crack propagation step a projection of the internal variables from the old to the new crack configuration is required. Since for arbitrary crack geometries ill-conditioning of the equation system may occur due to (near) linear dependencies between standard and enriched degrees of freedom, an XFEM stabilisation technique based on a singular value decomposition of the element stiffness matrix is proposed. The performance of the presented methodology to capture crack propagation in polycrystalline microstructures is demonstrated with a number of numerical examples.

Estimate of Probability of Crack Detection from Service Difficulty Report Data.

DOT National Transportation Integrated Search

1995-09-01

The initiation and growth of cracks in a fuselage lap joint were simulated. Stochastic distribution of crack initiation and rivet interference were included. The simulation also contained a simplified crack growth. Nominal crack growth behavior of la...

Estimate of probability of crack detection from service difficulty report data

DOT National Transportation Integrated Search

1994-09-01

The initiation and growth of cracks in a fuselage lap joint were simulated. Stochastic distribution of crack initiation and rivet interference were included. The simulation also contained a simplified crack growth. Nominal crack growth behavior of la...

On ripple-load, stress-corrosion, and sustained-load cracking behavior in a high strength beta titanium alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pao, P.S.; Meyn, D.A.; Bayles, R.A.

1997-06-01

Both overaged and peakaged TIMETAL 21S beta titanium alloys exhibit significant ripple-load cracking susceptibility in salt water and in ambient air environments. At R = 0.90, the ripple-load cracking thresholds of the overaged alloy are 67% and 72% lower than the stress-corrosion cracking and sustained-load cracking thresholds. For the peakaged alloy, the reductions are 55% and 61%. The stress-corrosion cracking threshold in salt water and the sustained-load cracking threshold in air of peakaged TIMETAL 21S are significantly lower while the ripple-load cracking threshold is slightly lower than those of the overaged alloy. The stress-corrosion cracking, sustained-load cracking, and ripple-load crackingmore » resistance of peakaged TIMETAL 21S are significantly inferior to those of both beta-annealed Ti-6Al-4V and Ti-15V-3Cr-3Al-3Sn. The ripple-load cracking resistance of overaged TIMETAL 21S, though better than Ti-15V-3Cr-3Al-3Sn, is still inferior than that of beta-annealed Ti-6Al-4V.« less

The crack detection algorithm of pavement image based on edge information

NASA Astrophysics Data System (ADS)

Yang, Chunde; Geng, Mingyue

2018-05-01

As the images of pavement cracks are affected by a large amount of complicated noises, such as uneven illumination and water stains, the detected cracks are discontinuous and the main body information at the edge of the cracks is easily lost. In order to solve the problem, a crack detection algorithm in pavement image based on edge information is proposed. Firstly, the image is pre-processed by the nonlinear gray-scale transform function and reconstruction filter to enhance the linear characteristic of the crack. At the same time, an adaptive thresholding method is designed to coarsely extract the cracks edge according to the gray-scale gradient feature and obtain the crack gradient information map. Secondly, the candidate edge points are obtained according to the gradient information, and the edge is detected based on the single pixel percolation processing, which is improved by using the local difference between pixels in the fixed region. Finally, complete crack is obtained by filling the crack edge. Experimental results show that the proposed method can accurately detect pavement cracks and preserve edge information.

Nonlocal modeling and buckling features of cracked nanobeams with von Karman nonlinearity

NASA Astrophysics Data System (ADS)

Akbarzadeh Khorshidi, Majid; Shaat, Mohamed; Abdelkefi, Abdessattar; Shariati, Mahmoud

2017-01-01

Buckling and postbuckling behaviors of cracked nanobeams made of single-crystalline nanomaterials are investigated. The nonlocal elasticity theory is used to model the nonlocal interatomic effects on the beam's performance accounting for the beam's axial stretching via von Karman nonlinear theory. The crack is then represented as torsional spring where the crack severity factor is derived accounting for the nonlocal features of the beam. By converting the beam into an equivalent infinite long plate with an edge crack subjected to a tensile stress at the far field, the crack energy release rate, intensity factor, and severity factor are derived according to the nonlocal elasticity theory. An analytical solution for the buckling and the postbuckling responses of cracked nonlocal nanobeams accounting for the beam axial stretching according to von Karman nonlinear theory of kinematics is derived. The impacts of the nonlocal parameter on the critical buckling loads and the static nonlinear postbuckling responses of cracked nonlocal nanobeams are studied. The results indicate that the buckling and postbuckling behaviors of cracked nanobeams are strongly affected by the crack location, crack depth, nonlocal parameter, and length-to-thickness ratio.

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE PAGES

Gao, Yanfei

2015-11-30

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Yanfei

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

The stress intensity factors for a periodic array of interacting coplanar penny-shaped cracks

PubMed Central

Lekesiz, Huseyin; Katsube, Noriko; Rokhlin, Stanislav I.; Seghi, Robert R.

2013-01-01

The effect of crack interactions on stress intensity factors is examined for a periodic array of coplanar penny-shaped cracks. Kachanov’s approximate method for crack interactions (Int. J. Solid. Struct. 1987; 23(1):23–43) is employed to analyze both hexagonal and square crack configurations. In approximating crack interactions, the solution converges when the total truncation number of the cracks is 109. As expected, due to high density packing crack interaction in the hexagonal configuration is stronger than that in the square configuration. Based on the numerical results, convenient fitting equations for quick evaluation of the mode I stress intensity factors are obtained as a function of crack density and angle around the crack edge for both crack configurations. Numerical results for the mode II and III stress intensity factors are presented in the form of contour lines for the case of Poisson’s ratio ν =0.3. Possible errors for these problems due to Kachanov’s approximate method are estimated. Good agreement is observed with the limited number of results available in the literature and obtained by different methods. PMID:27175035

Quantitative Detection of Cracks in Steel Using Eddy Current Pulsed Thermography.

PubMed

Shi, Zhanqun; Xu, Xiaoyu; Ma, Jiaojiao; Zhen, Dong; Zhang, Hao

2018-04-02

Small cracks are common defects in steel and often lead to catastrophic accidents in industrial applications. Various nondestructive testing methods have been investigated for crack detection; however, most current methods focus on qualitative crack identification and image processing. In this study, eddy current pulsed thermography (ECPT) was applied for quantitative crack detection based on derivative analysis of temperature variation. The effects of the incentive parameters on the temperature variation were analyzed in the simulation study. The crack profile and position are identified in the thermal image based on the Canny edge detection algorithm. Then, one or more trajectories are determined through the crack profile in order to determine the crack boundary through its temperature distribution. The slope curve along the trajectory is obtained. Finally, quantitative analysis of the crack sizes was performed by analyzing the features of the slope curves. The experimental verification showed that the crack sizes could be quantitatively detected with errors of less than 1%. Therefore, the proposed ECPT method was demonstrated to be a feasible and effective nondestructive approach for quantitative crack detection.

Growing Crack in Antarctica Larsen C Ice Shelf Spotted by NASA MISR

NASA Image and Video Library

2016-08-31

Project MIDAS, a United Kingdom-based group that studies the Larsen Ice Shelf in Antarctica, reported Aug. 18, 2016, that a large crack in the Larsen C shelf has grown by another 13 miles (22 kilometers) in the past six months. The crack is now more than 80 miles (130 kilometers) long. Larsen C is the fourth largest ice shelf in Antarctica, with an area of about 19,300 square miles (50,000 square kilometers), greater than the size of Maryland. Computer modeling by Project MIDAS predicts that the crack will continue to grow and eventually cause between nine and twelve percent of the ice shelf to collapse, resulting in the loss of 2,300 square miles (6,000 square kilometers) of ice -- more than the area of Delaware. This follows the collapse of the Larsen B shelf in 2002 and the Larsen A shelf in 1995, which removed about 1,255 square miles (3,250 square kilometers) and 580 square miles (1,500 square kilometers) of ice, respectively. The Multiangle Imaging SpectroRadiometer (MISR) instrument aboard NASA's Terra satellite flew over Larsen C on Aug. 22, 2016. The MISR instrument views Earth with nine cameras pointed at different angles, which provides information about the texture of the surface. On the left is a natural-color image of the shelf from MISR's vertical-viewing camera. Antarctica is slowly emerging from its polar night, and the low light gives the scene a bluish tint. The Larsen C shelf is on the left, while thinner sea ice is present on the right. A variety of cracks are visible in the Larsen C shelf, all appearing roughly the same. The image is about 130 by 135 miles (210 by 220 kilometers) in size. On the right is a composite image made by combining data from MISR's 46-degree backward-pointing camera (plotted as blue), the vertical-pointing camera (plotted as green), and the 46-degree forward-pointing camera (plotted as red). This has the effect of highlighting surface roughness; smooth surfaces appear as blue-purple, while rough surfaces appear as orange. Clouds near the upper left appear multi-hued because their elevation above the surface causes the different angular views to be slightly displaced. In this composite, the difference between the rough sea ice and the smoother ice shelf is immediately apparent. An examination of the cracks in the ice shelf shows that the large crack Project MIDAS is tracking (indicated by an arrow) is orange in color, demonstrating that it is actively growing. These data were acquired during Terra orbit 88717 http://photojournal.jpl.nasa.gov/catalog/PIA20894

Subcritical crack growth along polymer interfaces

NASA Astrophysics Data System (ADS)

Gurumurthy, Charavana Kumara

2000-10-01

The adhesion characteristics have been investigated for a polyimide (PI)/model epoxy (ME) interface that is important for microelectronic applications. The fracture toughness (G*c) of this interface has been measured using an asymmetric double cantilever beam (ADCB) technique. The G*c is low, 10-25 J/m 2, and is sensitive to the mechanical phase angle psi. A modified ADCB setup has been used to measure the subcritical crack growth velocity v due to the stress-assisted water attack (SAWA) at various relative humidities (RH) and temperatures (T) as a function of its driving force (the strain energy release rate) G*. The threshold G* decreases remarkably. Above the threshold log v rises linearly with √ G* (a hydrolysis controlled regime) but then enters a regime where the crack velocity is almost independent of √G*, i.e., v = v* (a transport controlled regime). A model for SAWA has been developed based on thermally-activated kinetics for hydrolysis of the ester covalent bonds that bridge from one side to the other of the interface. A new technique has been developed for the determination of the fatigue crack growth under thermal (T) and hydro-thermal (HT) conditions as a function of the range in the strain energy release rate (DeltaG). Under T-fatigue, the fatigue crack growth per unit temperature cycle (da/dN) increases as a power of DeltaG, i.e., a Paris law relationship holds. The HT da/dN measured is higher than da/dN under T-fatigue conditions and has been successfully modeled as a summation of two components: (a) the da/dN due to T-fatigue and (b) the da/dN due to the SAWA along the interface for a given T-cycle. A surface modification procedure that converts a thin interpenetrated by a solvent cast ME is used to strengthen ME/PI interface. The G* c increases with the interpenetration distance w. Increasing w also improves the resistance of the PI/ME interface to SAWA with the threshold G* increasing and the water transport controlled velocity (v*) decreasing.

Time-domain fiber loop ringdown sensor and sensor network

NASA Astrophysics Data System (ADS)

Kaya, Malik

Optical fibers have been mostly used in fiber optic communications, imaging optics, sensing technology, etc. Fiber optic sensors have gained increasing attention for scientific and structural health monitoring (SHM) applications. In this study, fiber loop ringdown (FLRD) sensors were fabricated for scientific, SHM, and sensor networking applications. FLRD biosensors were fabricated for both bulk refractive index (RI)- and surface RI-based DNA sensing and one type of bacteria sensing. Furthermore, the effect of glucose oxidase (GOD) immobilization at the sensor head on sensor performance was evaluated for both glucose and synthetic urine solutions with glucose concentration between 0.1% and 10%. Detection sensitivities of the glucose sensors were achieved as low as 0.05%. For chemical sensing, heavy water, ranging from 97% to 10%, and several elemental solutions were monitored by using the FLRD chemical sensors. Bulk index-based FLRD sensing showed that trace elements can be detected in deionized water. For physical sensing, water and cracking sensors were fabricated and embedded into concrete. A partially-etched single-mode fiber (SMF) was embedded into a concrete bar for water monitoring while a bare SMF without any treatment was directly embedded into another concrete bar for monitoring cracks. Furthermore, detection sensitivities of water and crack sensors were investigated as 10 ml water and 0.5 mm surface crack width, respectively. Additionally fiber loop ringdown-fiber Bragg grating temperature sensors were developed in the laboratory; two sensor units for water, crack, and temperature sensing were deployed into a concrete cube in a US Department of Energy test bed (Miami, FL). Multi-sensor applications in a real concrete structure were accomplished by testing the six FLRD sensors. As a final stage, a sensor network was assembled by multiplexing two or three FLRD sensors in series and parallel. Additionally, two FLRD sensors were combined in series and parallel by using a 2x1 micro-electromechanical system optical switch to control sensors individually. For both configurations, contributions of each sensor to two or three coupled signals were simulated theoretically. Results show that numerous FLRD sensors can be connected in different configurations, and a sensor network can be built up for multi-function sensing applications.

Simulation and experiment for depth sizing of cracks in anchor bolts by ultrasonic phased array technology

NASA Astrophysics Data System (ADS)

Lin, Shan

2018-04-01

There have been lots of reports about the occurrence of cracks in bolts in aging nuclear and thermal power plants. Sizing of such cracks is crucial for assessing the integrity of bolts. Currently, hammering and visual tests are used to detect cracks in bolts. However, they are not applicable for sizing cracks. Although the tip diffraction method is well known as a crack sizing technique, reflection echoes from threads make it difficult to apply this technique to bolts. This paper addresses a method for depth sizing of cracks in bolts by means of ultrasonic phased array technology. Numerical results of wave propagation in bolts by the finite element method (FEM) shows that a peak associated within the vicinity of a crack tip can be observed in the curve of echo intensity versus refraction angle for deep cracks. The refraction angle with respect to this peak decreases as crack depth increases. Such numerical results are verified by experiments on bolt specimens that have electrical discharge machining notches or fatigue cracks with different depths. In the experiment, a 10-MHz linear array probe is used. Depth of cracks in bolts using the refraction angle associated with the peak is determined and compared to actual depths. The comparison shows that accurately determining a crack depth from the inspection results is possible.

Crack tip field and fatigue crack growth in general yielding and low cycle fatigue

NASA Technical Reports Server (NTRS)

Minzhong, Z.; Liu, H. W.

1984-01-01

Fatigue life consists of crack nucleation and crack propagation periods. Fatigue crack nucleation period is shorter relative to the propagation period at higher stresses. Crack nucleation period of low cycle fatigue might even be shortened by material and fabrication defects and by environmental attack. In these cases, fatigue life is largely crack propagation period. The characteristic crack tip field was studied by the finite element method, and the crack tip field is related to the far field parameters: the deformation work density, and the product of applied stress and applied strain. The cyclic carck growth rates in specimens in general yielding as measured by Solomon are analyzed in terms of J-integral. A generalized crack behavior in terms of delta is developed. The relations between J and the far field parameters and the relation for the general cyclic crack growth behavior are used to analyze fatigue lives of specimens under general-yielding cyclic-load. Fatigue life is related to the applied stress and strain ranges, the deformation work density, crack nucleus size, fracture toughness, fatigue crack growth threshold, Young's modulus, and the cyclic yield stress and strain. The fatigue lives of two aluminum alloys correlate well with the deformation work density as depicted by the derived theory. The general relation is reduced to Coffin-Manson low cycle fatigue law in the high strain region.

Evaluation of crack-sealing milled pavement in the effort to reduce transverse cracking.

DOT National Transportation Integrated Search

2015-01-01

To determine if crack sealing milled pavement prior to overlay will deter the : migration of transverse cracking, or have an effect on pavement performance, : when compared to an adjacent milled pavement that receives no crack sealing : treatment.

A stiffness derivative finite element technique for determination of crack tip stress intensity factors

NASA Technical Reports Server (NTRS)

Parks, D. M.

1974-01-01

A finite element technique for determination of elastic crack tip stress intensity factors is presented. The method, based on the energy release rate, requires no special crack tip elements. Further, the solution for only a single crack length is required, and the crack is 'advanced' by moving nodal points rather than by removing nodal tractions at the crack tip and performing a second analysis. The promising straightforward extension of the method to general three-dimensional crack configurations is presented and contrasted with the practical impossibility of conventional energy methods.

A crack-closure model for predicting fatigue-crack growth under aircraft spectrum loading

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1981-01-01

The development and application of an analytical model of cycle crack growth is presented that includes the effects of crack closure. The model was used to correlate crack growth rates under constant amplitude loading and to predict crack growth under aircraft spectrum loading on 2219-T851 aluminum alloy sheet material. The predicted crack growth lives agreed well with experimental data. The ratio of predicted to experimental lives ranged from 0.66 to 1.48. These predictions were made using data from an ASTM E24.06.01 Round Robin.

FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (UNIX VERSION)

NASA Technical Reports Server (NTRS)

Newman, J. C.

1994-01-01

Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied loads may be either tensile or compressive. Several standardized aircraft flight-load histories, such as TWIST, Mini-TWIST, FALSTAFF, Inverted FALSTAFF, Felix and Gaussian, are included as options. FASTRAN II also includes two other methods that will help the user input spectrum load histories. The two methods are: (1) a list of stress points, and (2) a flight-by-flight history of stress points. Examples are provided in the user manual. Developed as a research program, FASTRAN II has successfully predicted crack growth in many metallic materials under various aircraft spectrum loading. A computer program DKEFF which is a part of the FASTRAN II package was also developed to analyze crack growth rate data from laboratory specimens to obtain the effective stress-intensity factor against crack growth rate relations used in FASTRAN II. FASTRAN II is written in standard FORTRAN 77. It has been successfully compiled and implemented on Sun4 series computers running SunOS and on IBM PC compatibles running MS-DOS using the Lahey F77L FORTRAN compiler. Sample input and output data are included with the FASTRAN II package. The UNIX version requires 660K of RAM for execution. The standard distribution medium for the UNIX version (LAR-14865) is a .25 inch streaming magnetic tape cartridge in UNIX tar format. It is also available on a 3.5 inch diskette in UNIX tar format. The standard distribution medium for the MS-DOS version (LAR-14944) is a 5.25 inch 360K MS-DOS format diskette. The contents of the diskette are compressed using the PKWARE archiving tools. The utility to unarchive the files, PKUNZIP.EXE, is included. The program was developed in 1984 and revised in 1992. Sun4 and SunOS are trademarks of Sun Microsystems, Inc. IBM PC is a trademark of International Business Machines Corp. MS-DOS is a trademark of Microsoft, Inc. F77L is a trademark of the Lahey Computer Systems, Inc. UNIX is a registered trademark of AT&T Bell Laboratories. PKWARE and PKUNZIP are trademarks of PKWare, Inc.

FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (IBM PC VERSION)

NASA Technical Reports Server (NTRS)

Newman, J. C.

1994-01-01

Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied loads may be either tensile or compressive. Several standardized aircraft flight-load histories, such as TWIST, Mini-TWIST, FALSTAFF, Inverted FALSTAFF, Felix and Gaussian, are included as options. FASTRAN II also includes two other methods that will help the user input spectrum load histories. The two methods are: (1) a list of stress points, and (2) a flight-by-flight history of stress points. Examples are provided in the user manual. Developed as a research program, FASTRAN II has successfully predicted crack growth in many metallic materials under various aircraft spectrum loading. A computer program DKEFF which is a part of the FASTRAN II package was also developed to analyze crack growth rate data from laboratory specimens to obtain the effective stress-intensity factor against crack growth rate relations used in FASTRAN II. FASTRAN II is written in standard FORTRAN 77. It has been successfully compiled and implemented on Sun4 series computers running SunOS and on IBM PC compatibles running MS-DOS using the Lahey F77L FORTRAN compiler. Sample input and output data are included with the FASTRAN II package. The UNIX version requires 660K of RAM for execution. The standard distribution medium for the UNIX version (LAR-14865) is a .25 inch streaming magnetic tape cartridge in UNIX tar format. It is also available on a 3.5 inch diskette in UNIX tar format. The standard distribution medium for the MS-DOS version (LAR-14944) is a 5.25 inch 360K MS-DOS format diskette. The contents of the diskette are compressed using the PKWARE archiving tools. The utility to unarchive the files, PKUNZIP.EXE, is included. The program was developed in 1984 and revised in 1992. Sun4 and SunOS are trademarks of Sun Microsystems, Inc. IBM PC is a trademark of International Business Machines Corp. MS-DOS is a trademark of Microsoft, Inc. F77L is a trademark of the Lahey Computer Systems, Inc. UNIX is a registered trademark of AT&T Bell Laboratories. PKWARE and PKUNZIP are trademarks of PKWare, Inc.

Replica-based Crack Inspection

NASA Technical Reports Server (NTRS)

Newman, John A.; Smith, Stephen W.; Piascik, R. S.; Willard, Scott A.; Dawicke, David S.

2007-01-01

A surface replica-based crack inspection method has recently been developed for use in Space Shuttle main engine (SSME) hydrogen feedline flowliners. These flowliners exist to ensure favorable flow of liquid hydrogen over gimble joint bellows, and consist of two rings each containing 38 elongated slots. In the summer of 2002, multiple cracks ranging from 0.1 inches to 0.6 inches long were discovered; each orbiter contained at least one cracked flowliner. These long cracks were repaired and eddy current inspections ensured that no cracks longer than 0.075 inches were present. However, subsequent fracture-mechanics review of flight rationale required detection of smaller cracks, and was the driving force for development of higher-resolution inspection method. Acetate tape surface replicas have been used for decades to detect and monitor small cracks. However, acetate tape replicas have primarily been limited to laboratory specimens because complexities involved in making these replicas - requiring acetate tape to be dissolved with acetone - are not well suited for a crack inspection tool. More recently developed silicon-based replicas are better suited for use as a crack detection tool. A commercially available silicon-based replica product has been determined to be acceptable for use in SSME hydrogen feedlines. A method has been developed using this product and a scanning electron microscope for analysis, which can find cracks as small as 0.005 inches and other features (e.g., pits, scratches, tool marks, etc.) as small as 0.001 inches. The resolution of this method has been validated with dozens of cracks generated in a laboratory setting and this method has been used to locate 55 cracks (ranging in size from 0.040 inches to 0.004 inches) on space flight hardware. These cracks were removed by polishing away the cracked material and a second round of replicas confirmed the repair.

Modelling and measurement of crack closure and crack growth following overloads and underloads

NASA Technical Reports Server (NTRS)

Dexter, R. J.; Hudak, S. J.; Davidson, D. L.

1989-01-01

Ignoring crack growth retardation following overloads can result in overly conservative life predictions in structures subjected to variable amplitude fatigue loading. Crack closure is believed to contribute to the crack growth retardation, although the specific closure mechanism is dabatable. The delay period and corresponding crack growth rate transients following overload and overload/underload cycles were systematically measured as a function of load ratio and overload magnitude. These responses are correlated in terms of the local 'driving force' for crack growth, i.e. the effective stress intensity factor range. Experimental results are compared with the predictions of a Dugdale-type (1960) crack closure model, and improvements in the model are suggested.

Behavior of Ti-5Al-2.5Sn ELI titanium alloy sheet parent and weld metal in the presence of cracks at 20 K

NASA Technical Reports Server (NTRS)

Sullivan, T. L.

1971-01-01

Through- and surface-cracked specimens of two thicknesses were tested in uniaxial tension. Surface-cracked specimens were generally found to be stronger than through-cracked specimens with the same crack length. Apparent surface-crack fracture toughness calculated using the Anderson modified Irwin equation remained relatively constant for cracks as deep as 90 percent of the sheet thickness. Subcritical growth of surface cracks was investigated. Comparison of chamber and open air welds showed chamber welds to be slightly tougher. Both methods produced welds with toughness that compared favorably with that of the parent metal. Weld efficiencies were above 94 percent.

Environmental fatigue in aluminum-lithium alloys

NASA Technical Reports Server (NTRS)

Piascik, Robert S.

1992-01-01

Aluminum-lithium alloys exhibit similar environmental fatigue crack growth characteristics compared to conventional 2000 series alloys and are more resistant to environmental fatigue compared to 7000 series alloys. The superior fatigue crack growth behavior of Al-Li alloys 2090, 2091, 8090, and 8091 is due to crack closure caused by tortuous crack path morphology and crack surface corrosion products. At high R and reduced closure, chemical environment effects are pronounced resulting in accelerated near threshold da/dN. The beneficial effects of crack closure are minimized for small cracks resulting in rapid growth rates. Limited data suggest that the 'chemically small crack' effect, observed in other alloy system, is not pronounced in Al-Li alloys. Modeling of environmental fatigue in Al-Li-Cu alloys related accelerated fatigue crack growth in moist air and salt water to hydrogen embrittlement.

Visualization and Quantitative Analysis of Crack-Tip Plastic Zone in Pure Nickel

NASA Astrophysics Data System (ADS)

Kelton, Randall; Sola, Jalal Fathi; Meletis, Efstathios I.; Huang, Haiying

2018-05-01

Changes in surface morphology have long been thought to be associated with crack propagation in metallic materials. We have studied areal surface texture changes around crack tips in an attempt to understand the correlations between surface texture changes and crack growth behavior. Detailed profiling of the fatigue sample surface was carried out at short fatigue intervals. An image processing algorithm was developed to calculate the surface texture changes. Quantitative analysis of the crack-tip plastic zone, crack-arrested sites near triple points, and large surface texture changes associated with crack release from arrested locations was carried out. The results indicate that surface texture imaging enables visualization of the development of plastic deformation around a crack tip. Quantitative analysis of the surface texture changes reveals the effects of local microstructures on the crack growth behavior.

Growth rate of a penny-shaped crack in hydraulic fracturing of rocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abe, H.; Mura, T.; Keer, L.M.

1976-10-10

The stable growth of a crack created by the hydraulic pressurizing of a penny-shaped crack in a dry rock mass is investigated. The rock mass is infinitely extended, homogeneous, and isotropic. It is verified on the basis of the equations of fluid dynamics that the fracturing fluid cannot penetrate the entire domain of a crack when the crack is moving. The effects of various terms in the basic equations also are studied. The solution of some typical examples is given, and the significant effect of the stress intensity factor of the rock on the crack propagation is shown. When themore » crack is expanding under a constant flow rate, the classical solution by Sack is found to be approx. valid for very large cracks, and nevertheless the crack is stable. (11 refs.)« less

Growth rate of a penny-shaped crack in hydraulic fracturing of rocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abe, H.; Mura, T.; Keer, L.M.

1976-10-10

The stable growth of a crack created by the hydraulic pressurizing of a penny-shaped crack in a dry rock mass is investigated. The rock mass is infinitely extended, homogeneous, and isotropic. It is verified on the basis of the equations of fluid dynamics that the fracturing fluid cannot penetrate the entire domain of a crack when the crack is moving. The effects of various terms in the basic equations are also studied. The solution of some typical examples is given, and the significant effect of the stress intensity factor of the rock on the crack propagation is shown. When themore » crack is expanding under a constant flow rate, the classical solution by Sack is found to be approximately valid for very large cracks, and nevertheless the crack is stable.« less

Numerical computation of central crack growth in an active particle of electrodes influenced by multiple factors

NASA Astrophysics Data System (ADS)

Zhang, Yuwei; Guo, Zhansheng

2018-03-01

Mechanical degradation, especially fractures in active particles in an electrode, is a major reason why the capacity of lithium-ion batteries fades. This paper proposes a model that couples Li-ion diffusion, stress evolution, and damage mechanics to simulate the growth of central cracks in cathode particles (LiMn2O4) by an extended finite element method by considering the influence of multiple factors. The simulation shows that particles are likely to crack at a high discharge rate, when the particle radius is large, or when the initial central crack is longer. It also shows that the maximum principal tensile stress decreases and cracking becomes more difficult when the influence of crack surface diffusion is considered. The fracturing process occurs according to the following stages: no crack growth, stable crack growth, and unstable crack growth. Changing the charge/discharge strategy before unstable crack growth sets in is beneficial to prevent further capacity fading during electrochemical cycling.

Self-healing of early age cracks in cement-based materials by mineralization of carbonic anhydrase microorganism

PubMed Central

Qian, Chunxiang; Chen, Huaicheng; Ren, Lifu; Luo, Mian

2015-01-01

This research investigated the self-healing potential of early age cracks in cement-based materials incorporating the bacteria which can produce carbonic anhydrase. Cement-based materials specimens were pre-cracked at the age of 7, 14, 28, 60 days to study the repair ability influenced by cracking time, the width of cracks were between 0.1 and 1.0 mm to study the healing rate influenced by width of cracks. The experimental results indicated that the bacteria showed excellent repairing ability to small cracks formed at early age of 7 days, cracks below 0.4 mm was almost completely closed. The repair effect reduced with the increasing of cracking age. Cracks width influenced self-healing effectiveness significantly. The transportation of CO2and Ca2+ controlled the self-healing process. The computer simulation analyses revealed the self-healing process and mechanism of microbiologically precipitation induced by bacteria and the depth of precipitated CaCO3 could be predicted base on valid Ca2+. PMID:26583014

Autogenous healing of sea-water exposed mortar: Quantification through a simple and rapid permeability test

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palin, D., E-mail: d.palin@tudelft.nl; Jonkers, H. M.; Wiktor, V.

Concrete has an autogenous ability to heal cracks potentially contributing to its functional water tightness and durability. Here, we quantify the crack-healing capacity of sea-water submerged mortar specimens through a simple and rapid permeability test. Defined crack width geometries were created in blast furnace slag cement specimens allowing healed specimens to be quantified against unhealed specimens. Specimens with 0.2 mm wide cracks were not permeable after 28 days submersion. Specimens with 0.4 mm cracks had decreases in permeability of 66% after 28 days submersion, and 50–53% after 56 days submersion. Precipitation of aragonite and brucite in the cracks was themore » main cause of crack healing. Healing potential was dependent on the initial crack width, thermodynamic considerations and the amount of ions available in the crack. To our knowledge, this is the first study to quantify the functional autogenous healing capacity of cracked sea-water exposed cementitious specimens.« less

[Mechanism of the dentino-enamel junction on the resist-crack propagation of human teeth by the finite element method].

PubMed

Jingjing, Zheng; Tiezhou, Hou; Hong, Tao; Xueyan, Guo; Cui, Wu

2014-10-01

This study aims to identify the crack tip stress intensity factor of the propagation process, crack propagation path, and the changes in the shape of the crack tip by the finite element method. The finite element model of dentino-enamel junction was established with ANSYS software, and the length of the initial crack in the single edge was set to 0.1 mm. The lower end of the sample was fixed. The tensile load of 1 MPa with frequency of 5 Hz was applied to the upper end. The stress intensity factor, deflection angle, and changes in the shape of the crack tip in the crack propagation were calculated by ANSYS. The stress intensity factor suddenly and continuously decreased in dentino-enamel junction as the crack extended. A large skewed angle appeared, and the stress on crack tip was reduced. The dentino-enamel junction on human teeth may resist crack propagation through stress reduction.

Finite-Element Analysis of Crack Arrest Properties of Fiber Reinforced Composites Application in Semi-Elliptical Cracked Pipelines

NASA Astrophysics Data System (ADS)

Wang, Linyuan; Song, Shulei; Deng, Hongbo; Zhong, Kai

2018-04-01

In nowadays, repair method using fiber reinforced composites as the mainstream pipe repair technology, it can provide security for X100 high-grade steel energy long-distance pipelines in engineering. In this paper, analysis of cracked X100 high-grade steel pipe was conducted, simulation analysis was made on structure of pipes and crack arresters (CAs) to obtain the J-integral value in virtue of ANSYS Workbench finite element software and evaluation on crack arrest effects was done through measured elastic-plastic fracture mechanics parameter J-integral and the crack arrest coefficient K, in a bid to summarize effect laws of composite CAs and size of pipes and cracks for repairing CAs. The results indicate that the K value is correlated with laying angle λ, laying length L2/D1, laying thickness T1/T2of CAs, crack depth c/T1 and crack length a/c, and calculate recommended parameters for repairing fiber reinforced composite CAs in terms of two different crack forms.

Pavement crack detection combining non-negative feature with fast LoG in complex scene

NASA Astrophysics Data System (ADS)

Wang, Wanli; Zhang, Xiuhua; Hong, Hanyu

2015-12-01

Pavement crack detection is affected by much interference in the realistic situation, such as the shadow, road sign, oil stain, salt and pepper noise etc. Due to these unfavorable factors, the exist crack detection methods are difficult to distinguish the crack from background correctly. How to extract crack information effectively is the key problem to the road crack detection system. To solve this problem, a novel method for pavement crack detection based on combining non-negative feature with fast LoG is proposed. The two key novelties and benefits of this new approach are that 1) using image pixel gray value compensation to acquisit uniform image, and 2) combining non-negative feature with fast LoG to extract crack information. The image preprocessing results demonstrate that the method is indeed able to homogenize the crack image with more accurately compared to existing methods. A large number of experimental results demonstrate the proposed approach can detect the crack regions more correctly compared with traditional methods.

Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

NASA Technical Reports Server (NTRS)

Chen, Q.; Liu, H. W.

1988-01-01

Fatigue crack growth tests were carried out on large-grain Al 7029 aluminum alloy and the finite element method was used to calculate the stress field near the tip of a zigzag crack. The resolved shear stresses on all 12 slip systems were computed, and the resolved shear stress intensity coefficient (RSSIC) was defined. The RSSIC was used to analyze the irregular crack path and was correlated with the rate of single-slip-plane shear crack growth. Fatigue crack growth was found to be caused primarily by shear decohesion at a crack tip. When the RSSIC on a single-slip system was much larger than all the others, the crack followed a single-slip plane. When the RSSICs on two conjugate slip systems were comparable, a crack grew in a zigzag manner on these planes and the macrocrack-plane bisected the two active slip planes. The maximum RSSIC on the most active slip system is proposed as a parameter to correlate with the shear fatigue crack growth rate in large crystals.

Advances in Fatigue and Fracture Mechanics Analyses for Aircraft Structures

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1999-01-01

This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

Advances in Fatigue and Fracture Mechanics Analyses for Metallic Aircraft Structures

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

2000-01-01

This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked metallic structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

Fracture mechanics and surface chemistry investigations of environment-assisted crack growth

NASA Technical Reports Server (NTRS)

Wei, R. P.; Klier, K.; Simmons, G. W.; Chou, Y. T.

1984-01-01

It is pointed out that environment-assisted subcritical crack growth in high-strength steels and other high-strength alloys (particularly in hydrogen and in hydrogenous environments) is an important technological problem of long standing. This problem is directly related to issues of structural integrity, durability, and reliability. The terms 'hydrogen embrittlement' and 'stress corrosion cracking' have been employed to describe the considered phenomenon. This paper provides a summary of contributions made during the past ten years toward the understanding of environmentally assisted crack growth. The processes involved in crack growth are examined, and details regarding crack growth and chemical reactions are discussed, taking into account crack growth in steels exposed to water/water vapor, the effect of hydrogen, reactions involving hydrogen sulfide, and aspects of fracture surface morphology and composition. Attention is also given to the modeling of crack growth response, crack growth in gas mixtures, and the interaction of solute atoms with the crack-tip stress field.