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Description: Bridged crack models using beam theory formulation have proved to be effective in the modeling of quasistatic delamination crack growth in through thickness reinforced structures. In this paper, we model dynamic crack propagation in these structures with the beam theory formulation. Steady state crack propagation characteristics unique to the dynamic case are first identified. Dynamic crack propagation and the energetics of steady state dynamic crack growth for a Double Cantilever beam (DCB) configuration loaded with a flying wedge is examined next. We find that steady state crack growth is attainable for this loading configuration provided certain conditions are satisfied.
Date: February 1, 2001
Creator: SRIDHAR, N. & AL, ET
Partner: UNT Libraries Government Documents Department

Screening Test Results of Fatigue Properties of type 316LN Stainless Steel in Mercury

Description: Fully reversed, load-controlled uniaxial push-pull fatigue tests at room temperature have been performed in air and in mercury on specimens of type 316LN stainless steel. The results indicate a significant influence of mercury on fatigue properties. Compared to specimens tested in air, specimens tested in mercury had reproducibly shorter fatigue lives (by a factor of 2-3), and fracture faces exhibiting intergranular cracking. Preliminary indications are that crack initiation in each environment is similar, but mercury significantly accelerates crack propagation.
Date: May 20, 1999
Creator: Pawel, S. J.
Partner: UNT Libraries Government Documents Department

Application of damage models in metal forming

Description: The development of damage models in the analysis of metal forming processes, to characterize the formability limits, is an important area of ongoing research. In this paper, two energy-based damage models for the simulation of crack initiation in metal forming processes are presented. The first one is an isotropic damage model with two damage variables. The second one is an anisotropic model with a damage characteristic tensor. The damage models are developed within the general framework of continuum thermodynamics for irreversible processes by identifying a proper set of internal variables together with their associated generalized forces. An approach is proposed to account for microcrack opening and closing. A viscoplastic regularization algorithm is used to take into account the strain rate effect and to improve numerical stability. Both models have been incorporated into the finite element code, LAGAMINE. The models were applied to simulations of upsetting of collar cylinders and nonisothermal hemispherical punch stretching. The results of the analyses were validated by comparing the finite element simulations with experimentally obtained data.
Date: June 1, 1995
Creator: Zhu, Y. Y. & Zacharia, T.
Partner: UNT Libraries Government Documents Department

Environment-assisted-cracking under measured and/or controlled ectrochemical potential

Description: Longer-term stress corrosion cracking (SCC) experiments, described in the activity plan E-20-56, are well underway at LLNL to evaluate the SCC susceptibility of candidate corrosion-resistant inner container materials in a 90°ºC acidic brine containing 5 weight percent (wt%) NaCl using fatigue-precracked wedge-loaded double-cantilever-beam (DCB) specimens. The results of a recent localized corrosion study have revealed that the propensity to pitting and crevice corrosion in susceptible alloys is characterized by "critical potentials" obtained from the cyclic potentiodynamic polarization (CPP) experiments described in the activity plan E-20-43/44. It is also well known that the tendency to SCC can be influenced by the electrochemical potential. But the role of electrochemistry in SCC has not been explored to a large extent. Therefore, the proposed activity is aimed at evaluating the SCC behavior of susceptible container materials under measured and/or controlled electrochemical potential in repository-relevant environments using DCB and slow-strain-rate (SSR) test specimens. The magnitude of the controlled potential will be selected based on the measured "critical potentials" obtained from the CPP experiment performed earlier in a similar environment. The resultant data will enable the mechanistic understanding of the cracking process in materials of interest under the synergistic influence of applied stress and corrosive medium, which will be utilized in developing and validating the SCC models for long-term performance assessment.
Date: November 7, 1997
Creator: Roy, A
Partner: UNT Libraries Government Documents Department

Stress corrosion cracking tests using double-cantilever-beam specimens

Description: Although a wide variety of degradation modes can occur in aqueous environments for corrosion-resistant metallic materials, localized corrosion such as pitting corrosion, crevice corrosion, SCC, and hydrogen embrinlement (HE) is considered to be the primary mode. The evaluation of the susceptibility of candidate corrosion-resistant container materials to pitting and crevice corrosion is well underway using electrochemical polarization techniques described in the Activity Plan E-20-43144. The proposed activity (E-20-56) is aimed at evaluating the SCC behavior of these materials in susceptible environments using the linearelastic-fracture-mechanics (LEFM) concept. The mechanical driving force for crack growth, or the stress distribution at the crack tip is quantified by the stress intensity factor, K, for the specific crack and loading geometry. The critical stress intensity factor for SCC, K<sub>ISCC</sub> for candidate materials will be evaluated in environments of interest, and their comparisons will be made to select the waste package inner container material having an optimum SCC resistance.
Date: October 25, 1996
Creator: Roy, A.
Partner: UNT Libraries Government Documents Department

Characterization of microstructure and crack propagation in alumina using orientation imaging microscopy (OIM). December 1996

Description: A more complete description requires the lattice orientations of a statistically significant number of grains, coupled with morphology such as grain size and shape; this can be obtained using orientation imaging microscopy (OIM), which uses crystallographic orientation data from Backscattered Electron Kikuchi patterns (BEKP) collected using a SEM. This report describes the OIM results for alumina; these include image quality maps, grain boundary maps, pole figures, and lattice misorientations depicted on MacKenzie plot and in Rodrigues space. High quality BEKP were obtained and the images and data readily reveal the grain morphology, texture, and grain boundary misorientations, including those for cracked boundaries. A larger number of grains should be measured to make statistical comparisons between materials with different processing histories.
Date: December 1, 1996
Creator: Glass, S.J.; Michael, J.R.; Readey, M.J.; Wright, S.I. & Field, D.P.
Partner: UNT Libraries Government Documents Department

On the expansion for surface displacement in the neighborhood of a crack tip

Description: It is shown that in the expansion of the crack opening displacement vs distance from the tip, there is no linear term present. This should lead to improved accuracy of the near tip fields and improved stress intensity factor results. The two-dimensional discussion should be able to be carried over to three dimensions.
Date: June 1, 1995
Creator: Gray, L.J. & Paulino, G.H.
Partner: UNT Libraries Government Documents Department

An Investigation of the Mechanism of IGA/SCC of Alloy 500 in Corrosion Accelerating Heated Crevice Environments. Technical progress report

Description: OAK-B135 An Investigation of the Mechanism of IGA/SCC of Alloy 500 in Corrosion Accelerating Heated Crevice Environments. Technical progress report Note: This report was submitted electronically even though Part II A indicates by ''PAPER''.
Date: March 1, 2000
Creator: Lumsden, Jesse
Partner: UNT Libraries Government Documents Department

Implications of early stages in the growth of stress corrosion cracking on component reliability

Description: Environment-induced crack growth generally progresses through several stages prior to component failure. Crack initiation, short crack growth, and stage 1 growth are early stages in crack development that are summarized in this paper. The implications of these stages on component reliability, derive from the extended time that the crack exists in the early stages because crack velocity is slow. The duration of the early stages provides a greater opportunity for corrective action if cracks can be detected. Several important factors about the value of understanding short crack behavior include: (1) life prediction requires a knowledge of the total life cycle of the crack including the early stages, (2) greater reliability is possible if the transition between short and long crack behavior is known component life after this transition is short and (3) remedial actions are more effective for short than long cracks.
Date: April 1, 1995
Creator: Jones, R.H. & Simonen, E.P.
Partner: UNT Libraries Government Documents Department

In situ measurement of fatigue-crack growth rates in a silicon carbide ceramic at elevated temperatures using a D.C. potential system

Description: The understanding of the mechanisms of fatigue-crack propagation in advanced ceramics at elevated temperatures (>800 degrees C) has in part been hampered by the experimental difficulty in directly measuring crack lengths, and hence crack-growth rates, at such high temperatures.
Date: October 12, 1999
Creator: Chen, D.; Gilbert, C.J. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Stress Corrosion Cracking of Annealed and Cold Worked Titanium Grade 7 and Alloy 22 in 110 C Concentrated Salt Environments

Description: Stress corrosion crack growth studies have been performed on annealed and cold worked Titanium Grade 7 and Alloy 22 in 110 C, aerated, concentrated, high pH salt environments characteristic of concentrated ground water. Following a very careful transition from fatigue precracking conditions to SCC conditions, the long term behavior under very stable conditions was monitored using reversing dc potential drop. Titanium Grade 7 exhibited continuous crack growth under both near-static and complete static loading conditions. Alloy 22 exhibited similar growth rates, but was less prone to maintain stable crack growth as conditions approached fully static loading.
Date: November 8, 2000
Creator: Andresen, P.
Partner: UNT Libraries Government Documents Department

Nonlinear Crack Growth Monitoring

Description: Oak Ridge National Laboratory has developed a new technique to monitor the growth of cracks in structural members, and to predict when failure due to this damage is imminent. This technique requires the measurement of global loadings and local deflections/strains at critical locations to indicate the increasing growth of hidden cracks with sufficient warning time prior to failure to take preventative action to correct the problem or retire the structure before failure. The techniques, as described in the referenced report have been proven on a laboratory scale to successfully detect the onset of failure due to fatigue cracking (including cracking of corroded samples), stress corrosion cracking, and low temperature creep crack growth, with a reasonable degree of warning before failure.
Date: March 27, 2001
Creator: Welch, D. E.
Partner: UNT Libraries Government Documents Department

Interfacial and near interfacial crack growth phenomena in metal bonded alumina

Description: Metal/ceramic interfaces can be found in many engineering applications including microelectronic packaging, multi-layered films, coatings, joints, and composite materials. In order to design reliable engineering systems that contain metal/ceramic interfaces, a comprehensive understanding of interfacial and near interfacial failure mechanisms is necessary.
Date: March 1, 2002
Creator: Kruzic, Jamie Joseph
Partner: UNT Libraries Government Documents Department

Results of High R-Ratio Fatigue Crack Growth Tests on 304 Stainless Steel in Low Oxygen Water

Description: Fatigue crack growth rate tests were performed on a 304 stainless steel compact tension (CT) specimen in water with 40-60 cc/kg H[sub]2. Data in the literature for CT tests show minor environmental effects in hydrogenated water, but higher effects in oxygenated water. However, the PWR data presented by Bernard, et al (1979) were taken at low stress ratios (R=0.05) and high stress intensity levels (delta K=16-41 MPa square root m). The purpose of these tests is to explore the crack growth rate characteristics of 304 SS in hydrogenated water at higher R values (0.7 and 0.83) and lower delta K values (11.0 and 7.7 MPa square root m). Each set of R, delta K conditions were tested at frequencies of 0.1, 0.01 and 0.001 Hz. The results show a pronounced effect on crack growth rates when compared to available literature data on air rates.
Date: August 1, 2002
Creator: Evans, W. M. & Wire, G. L.
Partner: UNT Libraries Government Documents Department


Description: A reduction of vibrations in mechanical seals increases the life of the seals in centrifugal pumps by minimizing fatigue damage. Mechanical seals consist of two smooth seal faces. one face is stationary with respect to the pump. The other rotates. Between the faces a fluid film evaporates as the fluid moves radially outward across the seal face. ideally, the film evaporates as it reaches the outer surface of the seal faces, thereby preventing leakage from the pump and effectively lubricating the two surfaces. Relative vibrations between the two surfaces affect the fluid film and lead to stresses on the seal faces, which lead to fatigue damage. As the fluid film breaks down impacts between the two seal faces create tensile stresses on the faces, which cycle at the speed of the motor rotation. These cyclic stresses provide the mechanism leading to fatigue crack growth. The magnitude of the stress is directly related to the rate of crack growth and time to failure of a seal. Related to the stress magnitude, vibration data is related to the life of mechanical seals in pumps.
Date: April 30, 2007
Creator: Leishear, R; Jerald Newton, J & David Stefanko, D
Partner: UNT Libraries Government Documents Department


Description: As a part of an ongoing activity to develop ASME Code rules for the hydrogen infrastructure, the ASME Boiler and Pressure Vessel Code Committee approved new fracture control rules for Section VIII, Division 3 vessels in 2006. These rules have been incorporated into new Article KD-10 in Division 3. The new rules require determining fatigue crack growth rate and fracture resistance properties of materials in high pressure hydrogen gas. Test methods have been specified to measure these fracture properties, which are required to be used in establishing the vessel fatigue life. An example has been given to demonstrate the application of these new rules.
Date: April 30, 2007
Creator: Rawls, G
Partner: UNT Libraries Government Documents Department

Rolling Contact Fatigue of Ceramics

Description: High hardness, low coefficient of thermal expansion and high temperature capability are properties also suited to rolling element materials. Silicon nitride (Si{sub 3}N{sub 4}) has been found to have a good combination of properties suitable for these applications. However, much is still not known about rolling contact fatigue (RCF) behavior, which is fundamental information to assess the lifetime of the material. Additionally, there are several test techniques that are employed internationally whose measured RCF performances are often irreconcilable. Due to the lack of such information, some concern for the reliability of ceramic bearings still remains. This report surveys a variety of topics pertaining to RCF. Surface defects (cracks) in Si{sub 3}N{sub 4} and their propagation during RCF are discussed. Five methods to measure RCF are then briefly overviewed. Spalling, delamination, and rolling contact wear are discussed. Lastly, methods to destructively (e.g., C-sphere flexure strength testing) and non-destructively identify potential RCF-limiting flaws in Si{sub 3}N{sub 4} balls are described.
Date: September 1, 2006
Creator: Wereszczak, Andrew A; Wang, W.; Wang, Y.; Hadfield, M.; Kanematsu, W.; Kirkland, Timothy Philip et al.
Partner: UNT Libraries Government Documents Department


Description: Unlike the common belief that crack propagation behavior can be predicted successfully by employing fracture criteria based on a constant crack tip opening displacement or angle (CTOD/CTOA), this paper shows that the initially non-constant portion of the CTOD/CTOA plays an essential role in predicting the fracture load for a growing crack. Three- and two-dimensional finite element analyses indicate that a severe underestimate of the experimental load vs. crack extension curve would occur if a constant CTOD/CTOA criterion is used. However, the use of a simplified, bilinear CTOD/CTOA criterion including its non-constant portion will closely duplicate the test data. Furthermore, as a result of using the experimental data from J-integral test with various crack length to specimen width ratios (a/W), it is demonstrated that the CTOD/CTOA is crack tip constraint dependent. The initially higher values of the CTOD/CTOA are in fact a natural consequence of crack growth process which is refl ected by the J-resistance curve and its slope (tearing modulus).
Date: July 19, 2004
Creator: LAM, POH-SANG
Partner: UNT Libraries Government Documents Department

Application of the Two-Parameter J-A2 Description to Ductile Crack Growth

Description: Typical ASTM fracture testing determines J-integral resistance (J-R) curve or fracture toughness (JIC) based on specimens with high constraint geometry such as those specified in ASTM E1737-96. A three-term asymptotic solution with two parameters J and A2 (a constraint parameter) has been developed for characterizing the constraint effect of various geometries. The present paper extends the J-A2 characterization of a stationary crack tip to the regime of stable crack growth. Similar to the concept of J-controlled crack growth, the J-A2 description can be approximately used to characterize ductile crack growth under certain amount of crack extension. The region of J-A2 controlled crack growth is much larger than that controlled by J-integral alone. From the relationships between A2 and the test data, JIC and tearing modulus (TR), the coefficients used to define a J-R curve can be determined. For non-standard specimens or actual structures, once the constraint parameter A2 is determined, the J-R curves appropriate for these geometries can then be obtained. A procedure of transferring J-R curves determined from the standard ASTM procedure to non-standard specimens or flawed structures is outlined in the paper.
Date: July 8, 1999
Creator: Lam, P.S.
Partner: UNT Libraries Government Documents Department