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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

The rate of fatigue-crack propagation in two aluminum alloys

Description: From Summary: "A general method has been developed for determination of fatigue-crack propagation rates. In order to provide a check on the theoretical predictions and to evaluate certain empirical constants appearing in the expression for the rate of fatigue-crack propagation, an extensive series of tests has been conducted. Sheet specimens, 2 inches and 12 inches wide, of 2024-T3 and 7075-T6 aluminum alloys were tested in repeated tension with constant-amplitude loading."
Date: September 1958
Creator: McEvily, Arthur J., Jr. & Illg, Walter
Partner: UNT Libraries Government Documents Department

Fatigue-crack-propagation and residual-static-strength results on full-scale transport-airplane wings

Description: Report presenting results of fatigue-crack-propagation studies conducted during fatigue tests of nine complete wings from C-46 airplanes. Static tests of the wings with fatigue failures are also described. Results regarding fatigue-crack propagation and residual static strength testing are provided.
Date: December 1956
Creator: Whaley, Richard E.; McGuigan, M. J., Jr. & Bryan, D. F.
Partner: UNT Libraries Government Documents Department

Fatigue-Crack Propagation in Aluminum Alloy Box Beams

Description: Report presenting fatigue testing of eighteen box beams constructed according to four designs in order to study fatigue-crack propagation and accompanying stress redistribution. Two designs had stiffeners riveted to the cover, one had stiffeners bonded to the cover, and one had an integrally stiffened cover machined from a plate. Results regarding crack initiation, crack propagation, and stress distribution are provided.
Date: August 1956
Creator: Hardrath, Herbert F.; Leybold, Herbert A.; Landers, Charles B. & Hauschild, Louis W.
Partner: UNT Libraries Government Documents Department

Further Investigation of Fatigue-Crack Propagation in Aluminum-Alloy Box Beams

Description: Report presenting testing of twenty-one box beams constructed according to nine designs that were subjected to fatigue tests at one load level to study fatigue-crack propagation and accompanying stress redistribution. Six designs had stiffeners riveted to the skin, two had integrally stiffened covers, and one had stiffeners bonded to the skin. Results regarding crack initiation, crack propagation, and stresses are provided.
Date: June 1958
Creator: Hardrath, Herbert F. & Leybold, Herbert 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

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

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

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

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

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

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

Iron Aluminide Composites

Description: Iron aluminides with the B2 structure are highly oxidation and corrosion resistant. They are thermodynamically compatible with a wide range of ceramics such as TiC, WC, TiB{sub 2}, and ZrB{sub 2}. In addition, liquid iron aluminides wet these ceramics very well. Therefore, FeAl/ceramic composites may be produced by techniques such as liquid phase sintering of powder mixtures, or pressureless melt infiltration of ceramic powders with liquid FeAl. These techniques, the resulting microstructure, and their advantages as well as limitations are described. Iron aluminide composites can be very strong. Room temperature flexure strengths as high as 1.8 GPa have been observed for FeAl/WC. Substantial gains in strength at elevated temperatures (1073 K) have also been demonstrated. Above 40 vol.% WC the room temperature flexure strength becomes flaw-limited. This is thought to be due to processing flaws and limited interfacial strength. The fracture toughness of FeAl/WC is unexpectedly high and follows a mile of mixtures. Interestingly, sufficiently thin (&lt; 1 {micro}m) FeAl ligaments between adjacent WC particles fracture not by cleavage, but in a ductile manner. For these thin ligaments the dislocation pile-ups formed during deformation are not long enough to nucleate cleavage fracture, and their fracture mode is therefore ductile. For several reasons, this brittle-to-ductile size transition does not improve the fracture toughness of the composites significantly. However, since no cleavage cracks are nucleated in sufficiently thin FeAl ligaments, slow crack growth due to ambient water vapor does not occur. Therefore, as compared to monolithic iron aluminizes, environmental embrittlement is dramatically reduced in iron aluminide composites.
Date: November 20, 1998
Creator: Schneibel, J.H.
Partner: UNT Libraries Government Documents Department

Investigation of the effect of microstructure on the R-Curve behavior of metal-ceramic composites

Description: An investigation was made into the effect of microstructure on the peak toughness and shape of the crack growth resistance curves for two ceramic-metal composites. An Al{sup 2}O{sup 3}/Al composite formed by Reactive Metal Penetration was used along with an AlN/Al composite formed using a reactive infiltration technique. The results indicate that the toughness increases with an increase in the volume fraction of the metal phase for a particular composite composition, and the peak toughness and shape of the R-Curve also depend on the composite microstructure and metal composition.
Date: July 1, 1995
Creator: Ellerby, D.T.; Flinn, B.D.; Scott, W.D.; Bordia, R.K.; Ewsuk, K.G.; Loehman, R.E. et al.
Partner: UNT Libraries Government Documents Department

Fracture in Bulk Amorphous Alloys

Description: The fracture behavior of a Zr-based bulk amorphous alloy, Zr-10 AI-5 Ti-17.9 Cu-14.6 Ni, was examined by transmission electron microscopy (TEM) and x-ray diffraction for any evidence of crystallization preceding crack propagation. No evidence for crystallization was found in shear bands in compression specimens or at the fracture surface in tensile specimens. In- situ TEM deformation experiments were performed to more closely examine actual crack tip regions. During the in-situ deformation experiment controlled crack growth occurred to the point where the specimen was approximately 20 {micro}m thick at which point uncontrolled crack growth occurred. No evidence of any crystallization was found at the crack tips or the crack flanks. Subsequent scanning microscope examination showed that the uncontrolled crack growth region exhibited ridges and veins that appeared to have resulted from melting. Performing the deformations, both bulk and in-situ TEM, at liquid nitrogen temperatures (LN{sub 2}) resulted in an increase in the amount of controlled crack growth. The surface roughness of the bulk regions fractured at LN{sub 2} temperatures corresponded with the roughness of the crack propagation observed during the in-situ TEM experiment, suggesting that the smooth-appearing room temperature fracture sur-faces may also be a result of localized melting.
Date: November 30, 1998
Creator: Horton, J. A. & Wright, J. L.
Partner: UNT Libraries Government Documents Department

The effect of potential upon the high-temperature fatigue crack growth response of low-alloy steels. Part 1: Crack growth results

Description: Corrosion-fatigue crack propagation experiments were conducted on several low-alloy steels in elevated temperature aqueous environments, and experimental parameters included temperature, sulfur content of the steel, applied potential level, and dissolved hydrogen (and in one case, dissolved oxygen) concentration in the water. Specimen potentials were controlled potentiostatically, and the observation (or non-observation) of accelerated fatigue crack growth rates was a complex function of the above parameters. Electrochemical results and the postulated explanation for the complex behavior are given in Part II.
Date: April 1, 1997
Creator: James, L.A. & Moshier, W.C.
Partner: UNT Libraries Government Documents Department

[Localized fracture damage effects in toughened ceramics]. Final report

Description: The primary research goal was to investigate localized fracture damage due to single point cutting of ceramic materials and then to compare this to multipoint cutting during precision grinding of the same materials. Two test systems were designed and constructed for the single-point cutting tests. The first system used a PZT actuator for closed-loop load control. An acoustic emission data acquisition system was used for crack initiation detection. The second test system employed a high-precision diamond-turning machine for closed-loop position (cutting depth) control. A high stiffness load cell and data acquisition system were used for crack initiation detection. Microcutting tests were carried out on silicon, borosilicate glass and CVD silicon carbide. The crack initiation thresholds and the fracture damage distribution were determined as a function of the loading conditions using a Vickers diamond as the cutting tool. The grinding tests were done using a plunge-grinding technique with metal-bonded diamond wheels. Optical microscopy, surface roughness and specific cutting energy were measured in order to characterize the fracture damage as a function of the grinding infeed rate. Simulation models were developed in order to estimate the average grain-depth of cut in grinding so that the response could be compared to the single-point microcutting tests.
Date: December 31, 1997
Partner: UNT Libraries Government Documents Department

The effect of potential on the high-temperature fatigue crack growth response of low alloy steels: Part II, electrochemical results

Description: Environmentally assisted cracking (EAC) in low alloy steels was found to be dependent on externally applied potential in low sulfur steels in high temperature water. EAC could be turned on when the specimen was polarized anodically above a critical potential. However, hydrogen (H) additions inhibited the ability of potential to affect EAC. The behavior was related to formation of H ions during H oxidation at the crack mouth. A mechanism based on formation of H sulfide at the crack tip and H ions at the crack mouth is presented to describe the process by which sulfides and H ions affect the critical sulfide concentration at the crack tip.
Date: April 1, 1997
Creator: Moshier, W.C. & James, L.A.
Partner: UNT Libraries Government Documents Department

Residual stress measurement by successive extension of a slot: A literature review

Description: This report reviews the technical literature on techniques that employ successive extension of a slot and the resulting deformations to measure residual stress. Such techniques are known variously in the literature as the compliance or crack compliance method, the successive cracking method, the slotting method, and a fracture mechanics based approach. The report introduces the field and describes the basic aspects of these methods. The report then reviews all literature on the theoretical developments of the method. The theory portion first considers forward method solutions including fracture mechanics, finite element, analytical, and body force methods. Then it examines inverse solutions, including incremental inverses and series expansions. Next, the report reviews all experimental applications of slotting methods. Aspects reviewed include the specimen geometry and material, the details of making the slot, the method used to measure deformation, and the theoretical solutions used to solve for stress. Finally, the report makes a brief qualitative comparison between slotting methods and other residual stress measurement methods.
Date: May 1, 1997
Creator: Prime, M.B.
Partner: UNT Libraries Government Documents Department