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Determination of Strength for Reliability Analysis of Multilayer Ceramic Capacitors

Description: A Nanoindenter<sup>TM</sup> equipped with a Vickers indenter was used to measure fracture toughness of Multilayer Capacitors (MLCs) and BaTiO<sub>3</sub> blanks. Strength of blanks of 6.3 x 4.7 x 1.1 mm<sup>3</sup> was measured by performing three-point flexure using a 4 mm support span. The size of the strength limiting pores in the flexure tests was compared to pore sizes measured on polished MLC cross sections, and it was found that much larger pores were present in the 3-point flexure specimens. Strength distributions for the MLCs were generated using the measured fracture toughness values, assuming the measured pores or second phase inclusions were strength limiting.
Date: January 25, 1999
Creator: Breder, K.; Bridge, R.J.; Kirkland, T.P.; Riester, L. & Wereszczak, A.A.
Partner: UNT Libraries Government Documents Department

CONSTRAINT EFFECT IN FRACTURE WHAT IS IT

Description: The meaning of the phrase 'constraint effect in fracture' has changed in the past two decades from 'contained plasticity' to a broader description of 'dependence of fracture toughness value on geometry of test specimen or structure'. This paper will first elucidate the fundamental mechanics reasons for the apparent 'constraint effects in fracture', followed by outlining a straightforward approach to overcoming this problem in both brittle (elastic) and ductile (elastic-plastic) fracture. It is concluded by discussing the major difference in constraint effect on fracture event in elastic and elastic-plastic materials.
Date: October 29, 2008
Creator: Lam, P & Prof. Yuh J. Chao, P
Partner: UNT Libraries Government Documents Department

Determining the toughness of ceramics from Vickers indentationsusing the crack-opening displacements: An experimental study

Description: Recently, a method for evaluating the fracture toughness of ceramics has been proposed based on the computed crack-opening displacements of cracks emanating from Vickers hardness indentations. In order to verify this method, experiments were carried out to determine the toughness of a commercial silicon carbide ceramic, Hexaloy SA, by measuring the crack-opening profiles of such Vickers indentation cracks. While the obtained toughness value of Ko = 2.3 MPavm was within 10% of that measured using conventional fracture toughness testing, the computed crack-opening profiles corresponding to this toughness displayed poor agreement with those measured experimentally, raising concerns about the suitability of this method for determining the toughness of ceramics. The effects of subsurface cracking and cracking during loading are considered as possible causes of such discrepancies, with the former based on evidence observed for secondary radial cracking which affected the crack opening profile and deduced toughness values.
Date: October 30, 2002
Creator: Kruzic, J.J. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Anisotropic Damage Analysis of HY100 Steel Under Quasistatic Loading Conditions

Description: The effect of MnS inclusion orientation on damage evolution and fracture toughness in HYlOO steel is investigated in the context of anisotropic damage modeling at the continuum level. Experimental notched-bar data sets are analyzed and modeled using finite element calculations with constitutive behavior that assumes isotropic elastoplastic behavior in conjunction with anisotropic damage.
Date: January 1, 2001
Creator: Laboratory, Los Alamos National
Partner: UNT Libraries Government Documents Department

Tailoring the intergranular phases in silicon nitride for improved toughness

Description: Intergranular glass phases can have a significant influence on fracture resistance (R-curve behavior) of Si nitride ceramics and appears to be related to debonding of the {beta}-Si{sub 3}N{sub 4}/oxynitride-glass interfaces. Applying the results from {beta}- Si{sub 3}N{sub 4}-whisker/oxynitride-glass model systems, self- reinforced Si nitrides with different sintering additive ratios were investigated. Si nitrides sintered with a lower Al{sub 2}O{sub 3}: Y{sub 2}O{sub 3} additive ratio exhibited higher stead-state fracture toughness together with a steeply rising R-curve. Analytical electron microscopy suggested that the different fracture behavior is related to the Al content in the SiAlON growth band on the elongated grains, which could result in differences in interfacial bonding structures between the grains and the intergranular glass.
Date: December 31, 1996
Creator: Sun, E. Y.; Becher, P. F.; Plucknett, K. P.; Waters, S. B.; Hirao, K. & Brito, M. E.
Partner: UNT Libraries Government Documents Department

The roles of atomic-scale dynamics and structure in the brittle fracture of silica

Description: We modeled the initiation of fracture in vitreous silica at various strain rates using molecular dynamics simulations. We avoided biasing the location for fracture initiation within the sample so that we could study the effects of dynamics and structure on determining the path to fracture, defined as the particular bonds that break during the course of fracture. We sought to show that the path to fracture would be primarily determined by the local variations in the structure of the vitreous phase at low strain rates, with diminished sensitivity on structural variations at higher strain rates. However, the results of our model indicate that the path to fracture is dependent not only on the initial structure of the system and the applied strain rate, but also on the initial phase of the thermal vibrations. This underscores the importance of atomic dynamics in determining the path to fracture in brittle materials and provides a justification for extending the analysis of fracture surfaces to the near-atomic scale.
Date: December 31, 1995
Creator: Swiler, T.P.; Varghese, T. & Simmons, J.H.
Partner: UNT Libraries Government Documents Department

Ductile damage model with void coalescence

Description: A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. Underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. Implementation of the model in hydrocodes is discussed.
Date: March 1, 1995
Creator: Tonks, D.L.
Partner: UNT Libraries Government Documents Department

New perspectives on the fracture of Nicalon fibers

Description: Experimental studies have been conducted to examine the strength and fracture behavior of monofiliment Nicalon{sup 3} SiC fibers ranging in diameter from 8 to 22 {mu}m. The effects of varying fiber diameter, flaw location and flaw population on the tensile behavior of individual fibers were investigated using fractography. Results indicate that variations in fiber diameter influence the apparent fiber fracture toughness K{sub 1c}, with higher K{sub 1c} values observed for decreasing fiber diameters. Observations also suggest that the location of the critical flaw may play a role in the fracture of Nicalon fibers. In addition to surface flaws, three distinct internal flaw populations are seen to cause fracture in Nicalon fibers.
Date: November 1, 1997
Creator: Taylor, S.T.; Lowe, T.C. & Butt, D.P.
Partner: UNT Libraries Government Documents Department

Nondestructive and Localized Measurements of Stress-Strain Curves and Fracture Toughness of Ferritic Steels at Various Temperatures Using Innovative Stress-Strain Microprobe Technology. Final Report for Period 8/13/1996--06/16/1999

Description: The results presented in this report demonstrate the capabilities of Advanced Technology Corporation's patented Portable/In Situ Stress-Strain Microprobe (TM) (SSM) System and its Automated Ball Indentation (ABI) test techniques to nondestructively measure the yield strength, the stress-strain curve, and the fracture toughness of ferritic steel samples and components in a reliable and accurate manner.
Date: October 29, 1999
Creator: Haggag, Fahmy M.
Partner: UNT Libraries Government Documents Department

Transient and steady-state erosion of in-situ reinforced silicon nitride

Description: Relative to most other materials silicon nitride is very erosion resistant. However, the resulting surface flaws degrade strength - a serious concern for component designers. AlliedSignal Ceramic Components GS-44 in-situ reinforced silicon nitride was eroded in a slinger apparatus. Both transient (extremely low level) and steady-state erosion regimes were investigated. Alumina particles with effective average diameters of 140 Jim and 63 {mu}m were used at velocities of 50 m/s, 100 m/s, and 138 m/s. Biaxial tensile strength was measured. Strength decreased by about 15% after a very small erodent dosage and then remained virtually constant with further erosion. In-situ reinforcement produces R-curve behavior in which the fracture toughness increases with crack size. The effect of this is quite dramatic with strength loss being significantly less than expected for a normal silicon nitride with constant fracture toughness.
Date: October 1, 1994
Creator: Karasek, K.R.; Whalen, P.J.; Rateick, R.G. Jr.; Hamilton, A.C. & Routbort, J.L.
Partner: UNT Libraries Government Documents Department

FRACTURE TOUGHNESS OF 6.4 MM (0.25 INCH) ARC-CAST MOLOBDENUM AND MOLYBDENUM-TZM PLATE AT ROOM TEMPERATURE AND 300 DEGREES C

Description: THE FRACTURE TOUGHNESS OF 6.4 mm (0.25 INCH) LOW CARBON ARC-CAST (LCAC) MOLYBDENUM AND ARC-CAST MOLYBDENUM-TZM ALLOY PLATE WERE MEASURED AT ROOM TEMPERATURE AND 300 DEGREES C USING COMPACT TNESION SPECIMENTS. THE EFFECT OF CRACK PLANE ORIENTATION (LONGITUDINAL VS. TRANSVERSE) AND ANNEALING PRACTICE (STRESS-RELIEVED VS. RECRYSTALLIZED) WERE EVALUATED. DEPENDING UPON THE TEST TEMPERATURE EITHER A STANDARD K[SUB]IC OR A J-INTEGRAL ANALYSIS WAS USED TO OBTAIN THE TOUGHNESS VALUE. AT ROOM TEMPERATURE, REGARDLESS OF ALLOY, ORIENTATION, OR MICROSTURECTURE, FRACTURE TOUGHNESS VALUES BETWEEN 15 AND 22 MPa m{sup 1/2} (14 AND 20 KSI IN{sup 1/2}) WERE MEASURED. THESE K[SUB]IC VALUES WERE CONSISTENT WITH MEASUREMENTS BY THE AUTHORS. INCREASING TEMPERATURE IMPROVES THE TOUGHNESS, DUE TO THE FACT THAT ONE TAKES ADVANTAGE OF THE DUCTIVE-BRITTLE TRANSITION BEHAVIOR OF MOLYBDENUM. AT 300 DEGREES C, THE FRACTURE TOUGHNESS OF RECRYSTALLIZED LCAC AND ARC-CAST TZM MOLYBDENUM WERE ALSO SIMILAR AT APPROXI MATELY 64 MPa m{sup 1/2} (58 KSI IN{sup 1/2}). IN THE STRESS-RELIEVED CONDITION, HOWEVER, THE TOUGHNESS OF ARC-CAST TZM (91 MPa m{sup 1/2}/83 KSI IN{sup 1/2}) WAS HIGHER THAN THAT OF THE LCAC MOLYBDENUM (74 MPa m{sup 1/2}/67 KSI IN{sup 1/2}).
Date: April 11, 2001
Creator: J. A. SHIELDS, JR.; LIPETZKY, P. & MUELLER, A. J.
Partner: UNT Libraries Government Documents Department

The limit of strength and toughness of steel

Description: The ideal structural steel combines high strength with high fracture toughness. This dissertation discusses the governing principles of strength and toughness, along with the approaches that can be used to improve these properties and the inherent limits to how strong and tough a steel can be.
Date: December 17, 2001
Creator: Guo, Zhen
Partner: UNT Libraries Government Documents Department

TRITIUM AND DECAY HELIUM EFFECTS ON THE FRACTURE TOUGHNESS PROPERTIES OF STAINLESS STEEL WELDMENTS

Description: J-Integral fracture toughness tests were conducted on tritium-exposed-and-aged Types 304L and 21-6-9 stainless steel weldments in order to measure the combined effects of tritium and its decay product, helium-3 on the fracture toughness properties. Initially, weldments have fracture toughness values about three times higher than base-metal values. Delta-ferrite phase in the weld microstructure improved toughness provided no tritium was present in the microstructure. After a tritium-exposure-and-aging treatment that resulted in {approx}1400 atomic parts per million (appm) dissolved tritium, both weldments and base metals had their fracture toughness values reduced to about the same level. The tritium effect was greater in weldments (67 % reduction vs. 37% reduction) largely because the ductile discontinuous delta-ferrite interfaces were embrittled by tritium and decay helium. Fracture toughness values decreased for both base metals and weldments with increasing decay helium content in the range tested (50-200 appm).
Date: August 31, 2007
Creator: Morgan, M; Scott West, S & Michael Tosten, M
Partner: UNT Libraries Government Documents Department

EFFECT OF TRITIUM AND DECAY HELIUM ON WELDMENT FRACTURE TOUGHNESS

Description: The fracture toughness data collected in this study are needed to assess the long-term effects of tritium and its decay product on tritium reservoirs. The results show that tritium and decay helium have negative effects on the fracture toughness properties of stainless steel and its weldments. The data and report from this study has been included in a material property database for use in tritium reservoir modeling efforts like the Technology Investment Program ''Lifecycle Engineering for Tritium Reservoirs''. A number of conclusions can be drawn from the data: (1) For unexposed Type 304L stainless steel, the fracture toughness of weldments was two to three times higher than the base metal toughness. (2) Tritium exposure lowered the fracture toughness properties of both base metals and weldments. This was characterized by lower J{sub Q} values and lower J-da curves. (3) Tritium-exposed-and-aged base metals and weldments had lower fracture toughness values than unexposed ones but still retained good toughness properties.
Date: September 26, 2006
Creator: Morgan, M; Scott West, S & Michael Tosten, M
Partner: UNT Libraries Government Documents Department

TECHNICAL BASIS AND APPLICATION OF NEW RULES ON FRACTURE CONTROL OF HIGH PRESSURE HYDROGEN VESSEL IN ASME SECTION VIII, DIVISION 3 CODE

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

Estimation Uncertainty in the Determinatin of the Master Curve Reference Temperature

Description: The Master Curve Reference Temperature, T{sub 0}, characterizes the fracture performance of structural steels in the ductile-to-brittle transition region. For a given material, this reference temperature is estimated via fracture toughness testing. A methodology is presented to compute the standard error of an estimated T{sub 0} value from a finite sample of toughness data, in a unified manner for both constant temperature and multiple temperature test methods. Using the asymptotic properties of maximum likelihood estimators, closed-form expressions for the standard error of the estimate of T{sub 0} are presented for both test methods. This methodology includes statistically rigorous treatment of censored data, which represents an advance over the current ASTM E1921 methodology. Through Monte Carlo simulations of realistic constant temperature and multiple temperature test plans, the recommended likelihood-based procedure is shown to provide better statistical performance than the methods in the ASTM E1920 standards.
Date: November 15, 2006
Creator: Sham, TL & Eno, DR
Partner: UNT Libraries Government Documents Department

In-situ Fracture Studies and Modeling of the Toughening Mechanism Present in Wrought LCAC, TZM, and ODS Molybdenum Flat Products

Description: In-situ testing, ultrasonic C-scans, and metallography were used to show that a crack-divider delamination form of thin-sheet toughening occurs in wrought Low Carbon Arc Cast (LCAC) unalloyed molybdenum, Oxide Dispersion Strengthened (ODS) molybdenum, and TZM molybdenum at temperatures {ge} the Ductile to Brittle Transition Temperature (DBTT). Cracking along boundaries relieves mechanical constraint to free ligaments that may plastically stretch to produce toughening. Anisotropy in fracture toughness with lower values in the short-transverse direction is shown to produce the crack divider delaminations at the crack tip in the LT and TL orientations. The delamination zone increases with increasing stress-intensity to sizes significantly larger than the plastic zone, which leads to large increases in fracture toughness by the thin sheet toughening mechanism. Fracture in ODS Mo-alloys proceeds mainly along grain boundaries to produce small ligaments that exhibit ductility for both LT and TL orientations resulting in a lower DBTT and higher toughness values at lower temperatures than observed in LCAC and TZM. A combination of grain boundary fracture and cleavage is prevalent in LCAC molybdenum and TZM. The predominance for microcracking along grain boundaries to leave fine, ductile ligaments in ODS molybdenum can be attributed to a fine-grained microstructure with {approx} 1-2 {micro}m thickness of sheet-like grains. The presence of mixed grain boundary fracture and cleavage in LCAC and TZM can be attributed to a microstructure with a larger thickness of sheet-like grains (4-15 {micro}m).
Date: July 1, 2007
Creator: Cockerman, B. V. and Chan, K. S.
Partner: UNT Libraries Government Documents Department

Scalable File Systems for High Performance Computing Final Report

Description: Simulations of mode I interlaminar fracture toughness tests of a carbon-reinforced composite material (BMS 8-212) were conducted with LSDYNA. The fracture toughness tests were performed by U.C. Berkeley. The simulations were performed to investigate the validity and practicality of employing decohesive elements to represent interlaminar bond failures that are prevalent in carbon-fiber composite structure penetration events. The simulations employed a decohesive element formulation that was verified on a simple two element model before being employed to perform the full model simulations. Care was required during the simulations to ensure that the explicit time integration of LSDYNA duplicate the near steady-state testing conditions. In general, this study validated the use of employing decohesive elements to represent the interlaminar bond failures seen in carbon-fiber composite structures, but the practicality of employing the elements to represent the bond failures seen in carbon-fiber composite structures during penetration events was not established.
Date: October 3, 2007
Creator: Brandt, S A
Partner: UNT Libraries Government Documents Department