Internal Variable Modeling of the Creep of Monolithic Ceramics

1995 ◽  
Author(s):  
Charles S. White ◽  
Radwan M. Hazime
Keyword(s):  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Internal Variable ◽  
Complete Characterization ◽  
Tensile Creep ◽  
Internal Variables ◽  
Variable Model ◽  
The Road ◽  
Monolithic Ceramics

Abstract Ceramics are assuming an important role for use in power generation. One of the road blocks is a complete characterization of the deformation and life of advanced ceramics at elevated temperatures. Substantial high temperature creep testing has been conducted in recent years. Most commonly, Norton’s law for deformation and the Monkman-Grant relationship for failure have been used to correlate test data. In this paper, internal variable modeling is discussed as an alternative to Norton’s Law/Monkman-Grant. Through the use of internal variables, micromodeling of the important mechanisms can be extended to the macroscopic behavior. Also, the effects of simultaneous or competing phenomena can be considered. An example is the growth of lenticular cavities on the two grain boundaries of certain silicon nitrides while the grain boundaries are crystallizing. The results of a preliminary internal variable model for HIPed silicon nitride is presented and compared with tensile creep experiments.

Atomic Scale Characterization of Oxygen Vacancy Segregation at SrTiO3 Grain Boundaries

2000 ◽  
Vol 654 ◽  
Author(s):  
R.F. Klie ◽  
N. D. Browning
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Oxygen Vacancies ◽  
Elevated Temperatures ◽  
Theoretical Models ◽  
Atomic Scale ◽  
Close Proximity ◽  
Scale Characterization

AbstractWe have examined the structure, composition and bonding at an un-doped 58° [001] tilt grain-boundary in SrTiO3 in order to investigate the control that the grain boundary exerts over the bulk properties. Room temperature and in-situ heating experiments show that there is a segregation of oxygen vacancies to the grain boundary that is increased at elevated temperatures and is independent of the cation arrangement. These measurements indicate that the widely observed electronic properties of grain boundaries may be due to an excess of mobile oxygen vacancies that cause a highly doped n-type region in the close proximity ( ≍ 1 unit cell) to the boundary. These results are shown to be consistent with both theoretical models and lower resolution chemical analysis.

Constitutive Equations for the Rate-Dependent Deformation of Metals at Elevated Temperatures

1982 ◽  
Vol 104 (1) ◽  
pp. 12-17 ◽  
Author(s):  
L. Anand
Keyword(s):  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Strain Hardening ◽  
Constitutive Equations ◽  
Elevated Temperatures ◽  
Internal Variable ◽  
Internal Variables ◽  
Homologous Temperature ◽  
Static Recovery ◽  
Rate Dependent

Approximate constitutive equations are proposed for use in the analysis of the rate-dependent deformation of metals at temperatures in excess of a homologous temperature of 0.5. The constitutive equations are formulated within the scope of some recent theories of elastoviscoplasticity with internal variables, but employ only a single scalar internal variable representing an isotropic resistance to plastic flow offered by the internal microstructural state of the material. The special constitutive euqations incorporate strain hardening of the Voce type, and account for the effects of the prior histories of strain rate and temperature undergone by the material. These equations, however, do not represent the important effects of static recovery or of static and dynamic recrystallization.

Characterization of grain boundary phases in Si3N4 sintered using Y-Si-Al-O-N additives

1990 ◽  
Vol 48 (4) ◽  
pp. 1070-1071
Author(s):  
C. Koehler ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Secondary Phases ◽  
Amorphous Phases ◽  
High Temperature Mechanical Properties

The usefulness of silicon nitride as a high temperature ceramic can be limited by the presence of amorphous phases at the grain boundaries. Dense silicon nitride ceramics are produced using pressureless sintering of Si3N4 with Y-Si-Al-O-N additives. When these additives are left as a glassy phase at the grain boundaries and triple grain junctions, the mechanical properties at elevated temperatures are weakened due to these low viscous glasses. Post-sintering heat treatments and close compositional control can be effective in transforming the glass into crystalline phases at the grain boundaries thereby increasing the refractoriness.To optimize high temperature mechanical properties, processing must be controlled not only to fully crystallize the grain boundaries but also to avoid certain unstable secondary phases whose oxidation leads to large molar volume changes which causes possible cracking. Transmisssion electron microscopy and x-ray microanalysis (EDS) are significant methods to characterize the amorphous grain boundary pockets and to identify the crystalline grain boundary phases.

scholarly journals A Study on Hybrid Sensor Technology in Winter Road Assessment

Safety ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 17
Author(s):  
Aleksander Pedersen ◽  
Tanita F. Brustad
Keyword(s):  
Visual Analysis ◽  
Complete Characterization ◽  
Sensor Technology ◽  
Road Maintenance ◽  
Worst Case ◽  
The Road ◽  
Road Users ◽  
Heavy Haul ◽  
Winter Road

Road conditions during the winter months in Nordic countries can be highly unstable. Slippery roads combined with heavy haul traffic and ordinary road users can create dangerous, even lethal, situations if road maintenance is unsuccessful. Accidents and critical road conditions may lead to blocked roads, putting strain on a limited number of main roads in many regions, and may in the worst case isolate areas entirely. Using sensors in winter road assessment has been a popular topic for over 20 years. However, with today’s developments connected to smaller and cheaper sensors, new opportunities are presenting themselves. In this study, we performed preliminary experiments on a variety of sensors, both commercial and experimental, to evaluate their benefits in possible hybrid sensor technology, which can give a more complete characterization of the road surface than what is possible from just one sensor. From the collected data and visual analysis of the results, the idea of a hybrid sensor seems promising when considering the differences in the tested sensors and how they may complement each other.

High-resolution electron microscopy of nanostructured materials

1995 ◽  
Vol 53 ◽  
pp. 172-173
Author(s):  
M. José-Yacamán
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundaries ◽  
Nanostructured Materials ◽  
High Resolution Electron Microscopy ◽  
Hrem Image ◽  
Small Particles ◽  
Resolution Electron ◽  
Nanophase Materials

Electron microscopy is a fundamental tool in materials characterization. In the case of nanostructured materials we are looking for features with a size in the nanometer range. Therefore often the conventional TEM techniques are not enough for characterization of nanophases. High Resolution Electron Microscopy (HREM), is a key technique in order to characterize those materials with a resolution of ~ 1.7A. High resolution studies of metallic nanostructured materials has been also reported in the literature. It is concluded that boundaries in nanophase materials are similar in structure to the regular grain boundaries. That work therefore did not confirm the early hipothesis on the field that grain boundaries in nanostructured materials have a special behavior. We will show in this paper that by a combination of HREM image processing, and image calculations, it is possible to prove that small particles and coalesced grains have a significant surface roughness, as well as large internal strain.

Characterization of Serrated Grain Boundaries in Ni-Based Alloy 690

2014 ◽  
Vol 52 (9) ◽  
pp. 695-704
Author(s):  
Yun Soo Lim ◽  
Dong Jim Kim ◽  
Seong Sik Hwang
Keyword(s):  
Grain Boundaries ◽  
Alloy 690

Experimental Characterization of Mechanical Behavior of Cord-Rubber Composites

1982 ◽  
Vol 10 (1) ◽  
pp. 37-54 ◽  
Author(s):  
M. Kumar ◽  
C. W. Bert
Keyword(s):  
Response Characteristic ◽  
Cord Compression ◽  
Complete Characterization ◽  
Strain Response ◽  
Strain Gages ◽  
Experimental Characterization ◽  
Rubber Composites ◽  
Stress Strain ◽  
Strain Data

Abstract Unidirectional cord-rubber specimens in the form of tensile coupons and sandwich beams were used. Using specimens with the cords oriented at 0°, 45°, and 90° to the loading direction and appropriate data reduction, we were able to obtain complete characterization for the in-plane stress-strain response of single-ply, unidirectional cord-rubber composites. All strains were measured by means of liquid mercury strain gages, for which the nonlinear strain response characteristic was obtained by calibration. Stress-strain data were obtained for the cases of both cord tension and cord compression. Materials investigated were aramid-rubber, polyester-rubber, and steel-rubber.

Characterization of CMOS Structures (0.6 µm process) Submitted to HBM and COM ESD Stress Tests

1997 ◽  
Author(s):  
G. Meneghesso ◽  
E. Zanoni ◽  
P. Colombo ◽  
M. Brambilla ◽  
R. Annunziata ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Electrostatic Discharge ◽  
Stress Test ◽  
Complete Characterization ◽  
Stress Tests ◽  
Test Procedures ◽  
Emission Microscopy ◽  
Fast Rise ◽  
Scanning Electron

Abstract In this work, we present new results concerning electrostatic discharge (ESD) robustness of 0.6 μm CMOS structures. Devices have been tested according to both HBM and socketed CDM (sCDM) ESD test procedures. Test structures have been submitted to a complete characterization consisting in: 1) measurement of the tum-on time of the protection structures submitted to pulses with very fast rise times; 2) ESD stress test with the HBM and sCDM models; 3) failure analysis based on emission microscopy (EMMI) and Scanning Electron Microscopy (SEM).

Sign in / Sign up

Export Citation Format

Share Document