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Displaying 26 - 50 of 66

Surfaces Formed by Subcritical Crack Growth in Silicate Glasses

October 16, 2008
Author(s)
J -. Guin, Sheldon M. Wiederhorn
The topology of surfaces formed by subcritical crack growth was investigated by the method of mapping using atomic force microscopy. The objective of the study was to determine how well the upper and lower surfaces matched after they have been formed by a

The Influence of Ceramic Interphases on the Creep Behavior of Silicon Nitride

October 16, 2008
Author(s)
Sheldon M. Wiederhorn
In this paper we discuss the role played by the intergranular phases in the creep of silicon nitride, which is completely controlled by the amount and effective viscosity of the intergranular phases. After briefly reviewing the structure and creep behavior

Finite element analysis of a crack tip in silicate glass: No evidence for a plastic zone

May 15, 2008
Author(s)
Theo Fett, G Rizzi, D Creek, Susanne Wagner, J.P. Guinn, JM Lopez-Cepero, Sheldon M. Wiederhorn
Recently, the claim was made that cracks in silicate glasses propagate by the nucleation, growth, and coalescence of cavities at crack tips, which is the same way as in metals but at a much smaller scale. This hypothesis for crack growth is based in part

Do Plastic Zones Form at Crack Tips in Silicate Glasses?

December 13, 2007
Author(s)
Jose Lopez-Cepero, Sheldon M. Wiederhorn, Theo Fett, Jean-Pierre Guin
In a number of recent studies, the claim has been made that silicate glasses fracture by the formation, growth and coalescence of cavities, in the same way that metals do but at a much smaller scale. Evidence for cavity formation comes from the examination

Standard Measurement Methods for Materials Properties: Plasticity

January 2, 2006
Author(s)
Richard J. Fields, Sheldon M. Wiederhorn
Plasticity, or permanent deformation, is one of the most useful mechanical properties of materials. It permits forming of parts, and provides a significant degree of safety in use. The ability to specify plastic properties measured by the standard methods

Interpretation of Effects at the Static Fatigue Limit of Soda-Lime-Silicate Glass

December 1, 2005
Author(s)
Theo Fett, J -. Guin, Sheldon M. Wiederhorn
Crack growth behavior in soda-lime-silicate glass in the vicinity of the static fatigue limit, and observations of the crack shape obtained by atomic force microscopy are rationalized are rationalized by a fracture mechanics model of the crack tip, in

Stresses in Ion Exchange Layers of Soda-Lime-Silicate Glass

June 1, 2005
Author(s)
Theo Fett, J -. Guin, Sheldon M. Wiederhorn
This paper presents a new method to determine both the magnitude and the sign of the surface stresses that develop as a consequence of sodium/hydrogen ion exchange in soda-lime-silicate glass immersed in water. At 90 degrees C very thin layers that develop

Crack-Tip Structure in Soda-Lime-Silicate Glass

March 1, 2005
Author(s)
J -. Guin, Sheldon M. Wiederhorn, Theo Fett
The topology of crack tips in soda-lime-silicate glass was investigated using atomic force microscopy. Studies were conducted on cracks that were propagated in water and then subjected to stress intensity factors either at or below the crack growth

Influence of Grain Size on the Tensile Creep Behavior of Ytterbium-Containing Silicon Nitride

March 1, 2004
Author(s)
Sheldon M. Wiederhorn, A R D Lopez, William E. Luecke, Michael J. Hoffmann, B Hockey, J French, D C. Yoon
The effect of grain size on the tensile creep of silicon nitride is investigated on two materials, one containing 5 % by volume Yb2O3, the other containing 5 % by volume Yb203 and 0.5 % by mass Al2O3. Annealing of the alumina-free silicon nitride increased

Dynamical Adhesion Force of Cells on Biomaterial Substrates

February 1, 2004
Author(s)
Y N. Deng, Carl Simon Jr., P M. McGuiggan, Sheldon M. Wiederhorn, Brian R. Lawn
The adhesion of cells to synthetic biomaterial implant surfaces is an essential step for tissue growth in bone repair. Such adhesion can mandate whether the tissue will accept or reject the implanted biomaterials. In this study, the adhesion forces between

Near the Static Fatigue Limit in Glass

May 1, 2003
Author(s)
Sheldon M. Wiederhorn, A Dretzke, J Rodel
The atomic force microscope is used to explore the nature of fracture surfaces in soda lime silicate glass formed near or below the apparent crack growth threshold. Conventional theory suggests that cracks in glass will blunt when subjected to stresses

Structure of Sapphire Bicrystal Boundaries Produced by Liquid-Phase Sintering

April 1, 2003
Author(s)
B Hockey, Sheldon M. Wiederhorn, J Blendell, Jong S. Lee, M K. Kang
Vitreous bonded aluminum oxide bicrystals were formed by growing oriented sapphire through polycrystalline tapes of anorthite-bonded aluminum oxide. The structure and composition of the bicrystal grain boundaries depended on the crystallographic

Crack Growth Threshold in Soda Lime Silicate Glass: Role of Hold-Time

February 1, 2003
Author(s)
J -. Guin, Sheldon M. Wiederhorn
Atomic force microscopy was used to examine the shapes of cracks and residual features left behind on the fracture surface after holding cracks at a stress intensity factor below the fatigue threshold for soda lime silicate glass. After propagating a crack

Crack Growth in Soda-Lime Silicate Glass Near the Static Fatigue Limit

September 1, 2002
Author(s)
Sheldon M. Wiederhorn, A Dretzke, J Rodel
The atomic force microscope (AFM) was used to explore the nature of features formed on the surfaces of cracks in soda-lime-silicate glass that were held at stress intensity factors below the crack growth threshold. All studies were conducted in water

Crack Growth in Sapphire

January 1, 2002
Author(s)
Sheldon M. Wiederhorn, Ralph Krause
Crack growth was studied in sapphire on both the m-plane and the r-plane (rhombohedral twin plane). Crack growth on the m-plane fit a power law function of stress intensity factor and an Arrhenius function of temperature. Crack growth on r-plane double

Non-Cavitational Tensile Creep in Lu-Doped Silicon Nitride

January 1, 2002
Author(s)
F Lofaj, Sheldon M. Wiederhorn, Gabrielle G. Long, B Hockey, P R. Jemian, L Browder, April Andreas
The tensile creep behavior of a Lu-based silicon nitride, SN 281, was studied in the temperature range 1400 C to 1550 C with test periods of up to 10 000 h. Strain rates were 3 to 5 orders of magnitude less than those for Yb-based grades of silicon nitride