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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

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

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

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

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

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

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

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

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

A comparison study on the densification behavior and mechanical properties of gelcast vs conventionally formed B{sub 4}C sintered conventionally and by microwaves

Description: The utilization of microwave energy for reaching high temperatures necessary to densify B{sub 4}C powder is compared with conventional means of sintering by evaluating the mechanical properties after densification. Microwave energy has been shown to be an effective means for achieving high sintered densities, even though temperatures of {approximately} 2,250 C are required. In this study, green preforms of B{sub 4}C specimens were sintered by both conventional and microwave heating. This study also utilized an advanced forming method called ``Gelcasting`` developed at ORNL. Gelcasting is a fluid forming process whereby high solids suspensions of powders containing dissolved monomers are cast into a mold, then polymerized or ``gelled`` in situ. This investigation compares microstructures and mechanical properties of both Gelcast B{sub 4}C and ``conventionally`` die-pressed B{sub 4}C. The microstructures and final mechanical properties of B{sub 4}C specimens are discussed.
Date: June 1, 1996
Creator: Menchhofer, P.A.; Kiggans, J.O.; Morrow, M.S. & Schechter, D.E.
Partner: UNT Libraries Government Documents Department

Ductile damage modeling based on void coalescence and percolation theories

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. The underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. The model is intended for hydrocode based computer simulation. An experimental program is underway to validate the model.
Date: September 1, 1995
Creator: Tonks, D.L.; Zurek, A.K. & Thissell, W.R.
Partner: UNT Libraries Government Documents Department

Techniques for in situ HVEM mechanical deformation of nanostructural materials

Description: We have developed two in-situ HVEM techniques which allow us to begin fundamental investigations into the mechanisms of deformation and fracture in nonstructured materials. A procedure for the observation of tensile deformation and failure in multilayers materials in cross-section is given and also the development of an in-situ HVEM nanoindentor of surfaces and films on surfaces in cross-section.
Date: August 7, 1995
Creator: Wall, M.A.; Barbee, T.W. Jr. & Dahmen, U.
Partner: UNT Libraries Government Documents Department

Ultrahigh carbon steels, Damascus steels, and superplasticity

Description: The processing properties of ultrahigh carbon steels (UHCSs) have been studied at Stanford University over the past twenty years. These studies have shown that such steels (1 to 2.1% C) can be made superplastic at elevated temperature and can have remarkable mechanical properties at room temperature. It was the investigation of these UHCSs that eventually brought us to study the myths, magic, and metallurgy of ancient Damascus steels, which in fact, were also ultrahigh carbon steels. These steels were made in India as castings, known as wootz, possibly as far back as the time of Alexander the Great. The best swords are believed to have been forged in Persia from Indian wootz. This paper centers on recent work on superplastic UHCSs and on their relation to Damascus steels. 32 refs., 6 figs.
Date: April 1, 1997
Creator: Sherby, O.D. & Wadsworth, J.
Partner: UNT Libraries Government Documents Department

Prediction of material strength and fracture of glass using the SPHINX smooth particle hydrodynamics code

Description: The design of many military devices involves numerical predictions of the material strength and fracture of brittle materials. The materials of interest include ceramics, that are used in armor packages; glass that is used in truck and jeep windshields and in helicopters; and rock and concrete that are used in underground bunkers. As part of a program to develop advanced hydrocode design tools, the authors have implemented a brittle fracture model for glass into the SPHINX smooth particle hydrodynamics code. The authors have evaluated this model and the code by predicting data from one-dimensional flyer plate impacts into glass, and data from tungsten rods impacting glass. Since fractured glass properties, which are needed in the model, are not available, the authors did sensitivity studies of these properties, as well as sensitivity studies to determine the number of particles needed in the calculations. The numerical results are in good agreement with the data.
Date: August 1, 1994
Creator: Mandell, D.A. & Wingate, C.A.
Partner: UNT Libraries Government Documents Department

Some new perspective on the strength and fracture of Nicalon fibers

Description: Nicalon{trademark} SiC fibers, processed by melt-spinning, are attractive reinforcing materials for high-temperature structural composites. This paper studies the effects of fiber diameter on fracture and statistical strength distribution of the fibers, by means of fractography on 8-22 {mu}m fibers fractured under tensile load. Flaw population and location effects are also studied.
Date: July 1, 1996
Creator: Taylor, S.T.; Zhu, Y.T.; Butt, D.P.; Stout, M.G.; Blumenthal, W.R. & Lowe, T.C.
Partner: UNT Libraries Government Documents Department