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The U.S. Nuclear Regulatory Commission staff has analyzed results from the weld residual stress round robin study, conducted in 2014. An uncertainty quantification scheme was applied to the dataset in order to compare and contrast results from independent analysts. The uncertainty quantification scheme provides a rigorous framework within which to make judgement calls about appropriate modeling guidelines and potential validation schemes. This paper will explore various options for guidelines and validation approaches, as informed by a statistical analysis of the dataset.

This paper presents a study on the roughness of glass fracture surfaces formed as a consequence of sub-critical crack growth. Double-cantilever-beam specimens were used in these studies to form fracture surfaces with areas under well-defined crack velocities and stress intensity factors. Roughness depends on crack velocity: the slower the velocity, the rougher the surface. Ranging from approximately 1 × 10 −10 m/s to approximately 10 m/s, the velocities were typical of those responsible for the formation of fracture mirrors in glass. Roughness measurements were made using atomic force microscopy on two glass compositions: silica glass and soda lime silica glass. For silica glass, the RMS roughness, R q , decreased from about 0.5 nm at a velocity of 1 × 10 −10 m/s to about 0.35 nm at a velocity of 10 m/s. For soda lime silica glass, the roughness decreased from about 2 nm to about 0.7 nm in a highly non-linear fashion over the same velocity range. We attributed the roughness and the change in roughness to microscopic stresses associated with nanometer scale compositional and structural variations within the glass microstructure. A theory developed to explain these results is in agreement with the data collected in the current paper. The RMS roughness of glass also depends on the area used to measure the roughness. As noted in other studies, fracture surfaces in glass exhibit a self-affine behavior. Over the velocities studied, the roughness exponent, ζ , was approximately 0.3 for silica glass and varied from 0.18 to 0.28 for soda lime silica glass. The area used for these measurements ranged from (0.5 μm) 2 to (5.0 μm) 2 . These values of the roughness exponent are consistent with values obtained when the scale of the measurement tool exceeds a critical size, as reported earlier in the literature.

As part of the xLPR (Extremely Low Probability of Rupture) project, the stress intensity factor (SIF) solutions required for crack growth calculations were updated. This involved extension of existing solutions and development of new solutions as well. For surface cracks, the Universal Weight Function Method (UWFM) was implemented to handle complex stress distributions. In addition, a crack transition model was developed to more accurately capture the surface to through-wall crack transition. Finally, solutions for idealized through-wall cracks were extended to various pipe sizes and longer crack lengths. In this paper, the SIF (K) solutions in xLPR Version 2.0 were validated against existing experimental data. The SIF modules in the xLPR code were used to simulate fatigue crack growth of circumferential cracks in pipes under bending up to wall penetration and to through-wall crack transition stage until idealized through-wall cracks were formed. The predicted fatigue crack growth results (mainly crack shape evolution) using the xLPR K-solutions provided good agreement with experimental data.

When Pb(Mg1/3Nb2/3)O3 (PMN) with 40 wt% excess PbO is sintered at 1050°C, the grains grow normally and have flat {100} surface segments with round edges. As PbTiO3 (PT) is added up to 8 mol%, the grain growth is still nearly normal, characterized by time invariant normalized size distributions, but the grain edges become more sharply curved. This normal growth behavior is consistent with relatively small surface step free energy as indicated by the round grain edges. As the PT content is increased above 10–35 mol%, the grain edges become sharp and abnormal grain growth occurs. This is consistent with the step free energy increasing with the PT content as indicated by the sharpening grain edges.

The microstructures of thick plasma-sprayed yttria-stabilized zirconia (8% mass fraction yttria) deposits were studied in a series of Porod small-angle neutron scattering (SANS) and multiple small-angle neutron scattering (MSANS) experiments. Three main void components were identified in the deposits: intrasplat cracks, interlamellar planar pores, and globular pores. The SANS and MSANS measurements were analyzed using the traditional theory for Porod scattering and a recently developed three-component model for MSANS evaluation. The average size, volume fraction, internal surface area, and orientation distribution for each void component within the deposits were determined. This study focused on gaining a better understanding of the effects of initial feedstock particle size and annealing temperatures on the microstructure of deposits sprayed under equivalent particle-impact conditions. Quantitative results are presented for each of four deposit samples: one prepared using the as-received feedstock particle wide-size distribution and three prepared from feedstock powder of different and relatively narrow particle size ranges with average sizes of 32, 47, and 88 μm. Except for the coarse (88 μm) feedstock powder, only mild monotonic variations were found in the microstructural anisotropies, the porosities (13 ± 1%), and the internal surface areas in the as-sprayed deposits. The internal surface area was independent of the feedstock particle size, even with the coarse feedstock. When the deposits were annealed at high temperatures (1100 and 1400 °C), the microstructures were altered with a reduction of the total internal surface area and a mild coarsening of the voids. These changes in the microstructural evolution were well-captured and described by the three-component model. The results were compared and related with those obtained from scanning electron microscopy images and elastic moduli measurements.

Properties of actual graded materials were characterized with a new procedure based on inverse analysis. This procedure utilizes indirect experimental records obtained from instrumented micro-indentation and extracts key properties of indented specimen through the Kalman filter technique. The graded material is composed of mixture of Yittria Partially Stabilized Zirconia (PSZ) and NiCrAlY and it possesses varying elastic � /plastic properties through its thickness. This procedure enables determination of the compositional profile and the effective mechanical property without resorting to complex experimental measurements. It relies solely on the load � /displacement records of instrumented spherical indentation and the inverse analysis during the post-processing. The graded specimens were fabricated by plasma spray deposition process under controlled feeding of PSZ and NiCrAlY powders. Prior to testing of the graded materials, single phased coatings were made with each component and analyzed. This process allows consistent material constants to be used in the graded material analysis. Here PSZ and NiCrAlY were assumed to be elastic and elastic � /plastic, respectively. The elastic moduli of both materials were estimated with a common indentation method while the plastic properties of NiCrAlY were determined by modifying the inverse method proposed for the graded materials. The latter procedure represents a new indentation method for characterization of homogeneous elastic � /plastic materials. Once the properties of constituents were identified, the properties of graded material were estimated with the Kalman filter technique. The indented load � /displacement relations simulated from finite element analysis with the estimated properties and that of measured record showed excellent agreement, which assures a high degree of accuracy in the current measurement procedure. # 2002 Elsevier Science B.V. All rights reserved.

We have studied single crystals of β-Si3N4 with polarization-resolved Raman spectroscopy in order to unambiguously obtain the symmetry character of zone center optical phonon modes. By applying ultraviolet excitation radiation, approaching resonance condition, we have overcome the usual difficulties with overwhelming fluorescence obscuring Raman spectra of β-Si3N4 in the visible. Superior extinction ratios have been achieved and the application of group theory allows us to assign ten out of eleven Raman-active modes in excellent correlation with recent theoretical results. The probable nature of the eleventh mode is discussed.

The mechanisms controlling normal and exaggerated grain growth in lead magnesium niobate–lead titanate (PMN–PT) ceramics have been investigated by varying the PbO-based liquid-phase volume fraction from 0.03 to 0.6 and sintering temperature from 900° to 1100°C. There is a transition in matrix grain growth rate and matrix grain shape with liquid fraction; samples with liquid volume fractions less than ∼0.15 show relatively small equiaxed grains resulting from grain-to-grain impingement. Samples with higher liquid fractions show significantly larger, facetted, cube-shaped grains, whose size is independent of liquid fraction, indicating that a surface nucleation rate mechanism controls growth in this regime. Exaggerated grains were found in the high liquid fraction samples. Electron backscatter diffraction showed that all of the exaggerated grains contained 60°〈111〉 twins but none of the normal matrix grains contained twins. The reentrant angles in the twinned grains give them a growth advantage over untwinned grains, resulting in a population of exaggerated grains.

Phase stability of thermal barrier deposits made from yttria partially stabilized zirconia (Y-PSZ) is a requirement for extended service lifetime. The response of Y-PSZ plasma-sprayed deposits to annealing at 1000, 1200, and 1400 °C with times from 1 to 1000 h has been evaluated using the Rietveld analysis of neutron diffraction data. Results show that the yttria concentration of the as-sprayed tetragonal zirconia component generally decreased with increasing annealing temperature and time. As the yttria content in the tetragonal phase approached a limiting concentration, about 3.5 mol.% of YO1,5, the tetragonal phase transformed into monoclinic phase on cooling. An increase in monoclinic phase content was clearly observed after annealing for 24 h at 1400 °C and was nearly 35% after 100 h at 1400 °C. A similar trend was observed at 1200 °C for longer annealing times, with monoclinic phase formation beginning after 400 h. At 1000 °C, experimental times were not sufficient for monoclinic phase to form, although a decrease in the yttria concentration in the tetragonal phase was observed.

Density, electron microscopy, elastic modulus, and small-angle neutron scattering studies are used to characterize the microstructures of yttria-stabilized zirconia plasma-sprayed deposits as a function of both feedstock morphology and annealing. In particular, anisotropic multiple small-angle neutron scattering data are combined with anisotropic Porod scattering results to quantify each of the three main porous components in these thermal barrier coating materials: intrasplat cracks, intersplat lamellar pores and globular pores. An inverse correlation between the volume of porosity and its surface area is confirmed for the as-sprayed deposits, as is a preferential annealing of intrasplat cracks at elevated temperatures. The average elastic modulus is correlated with the total void surface area while the elastic anisotropy is related more closely to the intersplat porosity. However, depending on the feedstock morphology, globular pores are also shown to play a surprisingly significant role in post-anneal deposit microstructures and properties.  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Summary Microstructural evolution in two in situ reinforced composite systems, one produced by partial reduction and the other by grain growth, has been examined over a range of size scales using light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Metal-ceramic matrix composites were formed by the partial reduction of Al2O3–Cr2O3 solid solutions to form Cr metal particles in an Al2O3–Cr2O3 matrix which had a lower Cr2O3 concentration. In a second system, grain growth of Si3N4 during liquid phase sintering produced large, whisker-like grains in a fine-grained Si3N4 matrix, bonded by an oxynitride phase. The mechanisms controlling microstructural evolution in these two systems were examined.

Metal-ceramic matrix composites were formed by the partial reduction of Al 2 O 3 -Cr 2 O 3 solid solutions to form Cr metal particles in an Al 2 O 3 -Cr 2 O 3 matrix which had a lower Cr 2 O 3 concentration. In Al 2 O 3 -Cr 2 O 3 solid solutions containing 10 and 25 wt.% Cr 2 O 3 , the microstructures produced by reduction are different from that expected from simple models of internal reduction or oxide scale formation. Grain boundary diffusion of individual grains. Small Cr particles were then observed to coarsen along some, but not all, grain boundaries by concomitant process known as ‘discontinuous coarsening’. The mechanisms controlling microstructural evolution in this system were examined.

In this paper we use atomic force microscopy to investigate the roughness of the mirror region in fracture specimens of silica glass. We demonstrate a decrease in surface RMS Roughness from about 0.5 nm to 0.4 nm with increasing stress intensity factor (0.5KIc to about 0.95KIc). Roughness occurs as a consequence of elastic interactions of the crack tip with nano scale inhomogenieties in the glass. These results contrast with the usual observation that roughness increases with increasing distance as the crack propagates from the fracture origin and into the mist and hackle regions. At low values of KI, crack surfaces are relatively smooth. It is only when cracks approach KIc that the roughness builds up in silica glass leading to the expected transition in surface topography as the crack gets longer. Introduction: The growth of cracks from small surface flaws is the principal cause of failure in glasses and ceramics; for this reason a substantial effort has been spent characterizing the nature of the surface flaws that initiate failure of glass objects. Such failures are important, not just for structural applications, but for any application in which ceramics or glasses are subjected to stresses as a consequence of the manufacturing process. For example, brittle fracture of ceramic parts in electronic components occurs as a consequence of built in residual stresses, usually due to the development of thermal mismatch stresses during component manufacture. Once a part has failed, the residual damage responsible for the failure is left behind on the surface. By examining this damage, it is possible to gain insight into the nature of the damage and the * Now at the University of Seville, Department of Materials Science, Seville, Spain

Using Brillouin scattering, we have determined the complete set of elastic constants of the technologically important β-Si3N4. Availability of single crystals has allowed us to measure all five independent cij, which (in units of GPa) are: c11=433(3), c33=574(3), c13=127(5), c44=108(2), c66=119(4), and c12=c11−2c66=195(8), giving a bulk modulus of 259. Our values are compared with existing calculations and cij determined from nano-indentation results combined with empirical relations and trends in related materials.

An analytical strategy for quantifying the diffusion of 18O in small, melt-grown single-crystal Yba2Cu3O7-x superconductors by image depth profiling SIMS is presented. This technique was used to obtain data for both in-depth (along the c-axis) and lateral (in theab-plane) diffusion from one superconducting crystal. Cross-sectional images, generated from the image depth profiling data, revealed features of the diffusion processes that would not have been apparent in a standard depth profile. Retrospective selected area depth profiling was used to remove the influence of background species, edge effects and imperfections in the crystals, resulting in processed depth profiles with greater dynamic range. These techniques also were used to study the diffusion behavior of fluorine that was unexpectedly incorporated into the superconduting crystals during preparation. Finally, the influence of detector artifacts on the analytical results was evaluated.

The electric fatigue behavior of commercial lead zirconate titanate (PZT) was investigated by optical microscopy and instrumented Hertzian microindentation. Macroscopic delamination cracks were found near the electrodes after large numbers of electrical cycles. Additionally, macroscopics edge cracks were found to orientate from the boundary between electroded and unelectroded material. Instrumented Hertzian microindentation measurements on specimen cross sections show larger indentation depths just beneath the electrodes than in the center of the sample. This behavior may result form a higher microcrack density near the electrodes. The role of micro- and macrocracks in the electrical fatigue behavior of ferroelectric ceramics is discussed and compared to macroscopic material parameters and acoustic emissions.

Phase stability of the thermal barrier deposits made from yttria-partially-stabilized zirconia (Y-PSZ) is a requirement for extended service lifetime. The response of Y-PSZ plasma-sprayed deposits to annealing at 1000 °C, 1200 °C, and 1400 °C with times from 1 to 1000 hours has been evaluated using Rietveld analysis of neutron diffraction data. Results show that yttria concentration of the as-sprayed tetragonal zirconia component generally decreased with increasing annealing temperature and time. As the yttria content in the tetragonal phase approached a limiting concentration, the tetragonal phase transformed into monoclinic phase on cooling. An increase in monoclinic phase content was clearly observable after annealing 24 hours at 1400 °C and was nearly 35 % after 100 hours at 1400 °C. A similar trend was observed at 1200 °C for longer annealing times, with monoclinic phase formation beginning after 400 hours. At 1000 °C experimental times were not sufficient for monoclinic phase to form although a decrease in the yttria concentration in the tetragonal phase was observed. Keywords: neutron scattering, yttria-stabilized zirconia, phase composition, Rietveld analysis

A commercial hardness indenter has been modified to record load displacement as a spherical ball is elastically loaded onto the surface of the material to be measured. The resulting data are used to calculate the elastic modulus. This technique has been used to characterize the elastic modulus of zirconium oxide-8% yttrium oxide plasma sprayed deposits. Moduli were measured both on the cross section and on the plan section, and the differences were correlated with the microstructure. Since relatively small areas of the material were sampled by the indenter, local mapping of elastic modulus variations on the size scale of the microstructure was possible. A periodic variation in modulus with position in the cross section was found on a length scale that corresponded to the average plasma spray pass thickness. Elastic modulus variations also have been found on a macro scale through the thickness of freestanding plasma sprayed deposits. These large scale variations were probably a result of self annealing during the production of these thick samples. Finally, significant increases in elastic modulus have been found in samples annealed for a total of 2.5 h at 1100 °C. These changes have been correlated with small angle neutron scattering measurements of void surface area.

The techniques for processing Ba2YCu3O7 fine-grained, high-density superconductors are described. Densification and microstructure are found to be strongly dependent on the choice of the barium precursor. The resulting microstructures are characterized using transmission electron microscopy.

The orthorhombic superconducting phase of YBa2Cu3O7 is shown to be differentiable from its tetragonal precursor by optical microscopy. Individual grains 1 μm in diameter or larger are found to either exhibit the color of the compensator in reflected polarized light (tetragonal material) or to change colors from the compensator (orthorhombic material). By using color differences, retained tetragonal material and the orthorhombic nature of untwinned areas of grains are identified. The advantage to producing better superconducting single crystals and sintered polycrystalline materials is discussed.

Solid state ceramic-ceramic or ceramic-metal bonding is a joining method which promises bond properties equivalent to those of the bulk material, both at ambient and elevated temperatures1. Microstructural features at the interface such as cracks, unbonded areas and intermediate reactions layers, however, can strongly influence the mechanical properties. In addition, mismatch between the coefficient of thermal expansion (CTE) can result in large shear stresses across the interface and affect the properties of the joint.

The effect of MgO and ZrO2 dopants, added separeately or simultaneously, on the grain size, denisity, and toughness of Al2O3 was studied. Small ZrO2 addotoopms (

We present the results of transport and microstructural studies on large single crystal and nearly bulk density polycrystalline samples of (RE)Ba 2 Cu 3 O 7 superconductors. These samples were characterized by x-ray and electron diffraction, optical and scanning electron transmission microscopy, electrical resistance, magnetic susceptibility, and magnetic field and orientation dependent magnetization. Among some of the measurements we will report on are: unique features of the microstrure, superconducting fluctuations above the transition temperature, time dependent susceptibility, and critical currents.

Alumina containing 15 vol% monoclinic ZrO2 dispersed at the grain boundaries exhibited very high room-temperature fracture toughness (∼11 MPa·m1/2) on cooling from 1275°C when microcrack precursors nucleated at T

Fused mullite, pure and with 10 to 25 vol% ZrO2 added, was milled in an attritor and sintered in air at temperatures near 1600°C to a dense fine-grained ceramic. The ZrO2 promoted densification and retarded grain growth of the mullite phase. Transmission electron microscopy showed that compositions containing ZrO2 were substantially free of glass, whereas pure mullite bodies contained a glassy phase. The ZrO2 formed inter granular, isolated particles.