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Displaying 76 - 100 of 101

Effect of Flaw State on the Strength of Brittle Coatings on Soft Substrates

October 1, 2001
Author(s)
H W. Kim, Y N. Deng, P Miranda, Antonia Pajares, D H. Kim, H E. Kim, Brian R. Lawn
A study is made of the role of flaw state on the strength properties of brittle ceramic coating layers bonded to soft polycarbonate substrates. We introduce Vickers radial cracks at prescribed loads into the coating undersurfaces prior to bonding to

Role of Flaw Statistics in Contact Fracture of Brittle Coatings

October 1, 2001
Author(s)
P Miranda, Antonia Pajares, F Guiberteau, F Cumbrera, Brian R. Lawn
A flaw statistics analysis is here developed to account for systematic differences between experimentally observed and theoretically predicted critical loads for the initiation of contact-induced radial cracks in brittle coatings on compliant substrates

Brittle Fracture Versus Quasi Plasticity in Ceramics: A Simple Predictive Index

March 1, 2001
Author(s)
Y W. Rhee, H W. Kim, Y N. Deng, Brian R. Lawn
Simple relations for the onset of competing brittle and quasi plastic damage modes in Hertzian contact are presented. The formulations are expressed in terms of well-documented material parameters, elastic modulus, toughness and hardness, enabling a priori

Contact Fracture of Brittle Bilayer Coatings on Soft Substrates

January 1, 2001
Author(s)
P Miranda, Antonia Pajares, F Guiberteau, F Cumbrera, Brian R. Lawn
Contact-induced fracture modes in trilayers consisting of a brittle bilayer coating on a soft substrate was investigated. Experiments are performed on model transparent glass/sapphire/polycarbonate structures bonded with epoxy adhesive, to enable in situ

Damage-Resistant Brittle Coatings

November 1, 2000
Author(s)
Brian R. Lawn, K S. Lee, Herzl Chai, Antonia Pajares, D K. Kim, S Wuttiphan, I M. Peterson, X Z. Hu
A conceptually new approach to the design of brittle coating structures on soft substrates, based on prevention of crack initiation rather than on customary crack containment, is outlined. Concentrated loads produce two competing coating fracture modes

Model for Cyclic Fatigue of Quasi-Plastic Ceramics in Contact with Spheres

September 1, 2000
Author(s)
K -. Lee, Yeon-Gil G. Jung, I M. Peterson, Brian R. Lawn, D H. Kim, S K. Lee
A model of contact damage accumulation from cyclic loading with spheres and ensuing strength degradation in relatively tough, heterogeneous ceramics is developed. The damage takes the form of a quasiplastic zone beneath the contact, consisting of an array

Cracking of Brittle Coatings Adhesively Bonded to Substrates of Unlike Modulus

August 1, 2000
Author(s)
K -. Lee, Y W. Rhee, Douglas H. Blackburn, Brian R. Lawn, H Chai
The role of elastic mismatch in determining critical conditions for indentation fracture in brittle coatings on substrates of unlike modulus is investigated. A model transparent trilayer system, consisting of a glass coating layer bonded to a thick

Contact Damage in Porcelain/Pd-Alloy Bilayers

March 1, 2000
Author(s)
H Zhao, X Z. Hu, M T. Bush, Brian R. Lawn
An analysis is made of contact damage in brittle coatings on metal substrates, using as a case study a dental porcelain coating of thickness between 0.1 and 1 mm fused onto a Pd alloy base, with spherical indenter of radii 2.38 and 3.98 mm. At large

Subcritical Crack Growth: Mechanisms

February 28, 2000
Author(s)
Brian R. Lawn
A brief survey is given of mechanisms of subcritical crack growth in ceramics, for a solicited article in Encyclopedia of Materials: Science and Technology.

Lifetime-Limiting Strength Degradation From Contact Fatigue in Dental Ceramics

February 1, 2000
Author(s)
Yeon-Gil G. Jung, I M. Peterson, D H. Kim, Brian R. Lawn
Indentation damage and associated strength degradation from multi-cycle contacts with spherical indenters in water are evaluated in four dental ceramics, to examine the hypothesis that the lifetimes of dental restorations are limited by the accumulation of

Cyclic Fatigue of Intrinsically Brittle Ceramics in Contact with Spheres

December 1, 1999
Author(s)
D K. Kim, Yeon-Gil G. Jung, I M. Peterson, Brian R. Lawn
Contact damage modes in cyclic loading with spheres are investigated in three relatively brittle ceramics, soda-lime glass, porcelain and fine-grain silicon nitride, in moist environments. Initial damage at small numbers of cycles and low loads consists of

Scratch Damage in Zirconia Ceramics

October 25, 1999
Author(s)
S K. Lee, Rajan Tandon, M Readey, Brian R. Lawn
Scratch damage modes in zirconia-based ceramics, Mg-PSZ, T-TZP and Ce-TZP are investigated. Precursor indentation tests with a tungsten carbide sphere foreshadow the nature of damage: in Mg-PSZ - extensive quasi-plastic deformation in the region outside

Cyclic Contact Fatigue of Brittle Ceramics

May 10, 1999
Author(s)
Brian R. Lawn, Yeon-Gil G. Jung, D H. Kim, S K. Lee, I M. Peterson
Contact damage modes in cyclic loading with spheres are investigated in several ceramics, principally silicon nitride but also some ceramics used for dental restorations. Initial damage to small numbers of cycles and low loads consists of tensile-driven

Contact Fatigue in Silicon Nitride

May 1, 1999
Author(s)
S K. Lee, Brian R. Lawn
A study of contact fatigue in silicon nitride is reported. The contacts are made using WC spheres, principally in cyclic but also in static loading, and mainly in air but also in nitrogen and water. Damage patterns are examined in three silicon nitride

Indentation of Ceramics with Spheres: A Century After Hertz

May 4, 1998
Author(s)
Brian R. Lawn
In this article we review the nature and mechanics of damage induced in ceramics by spherical indenters, from the classical studies of Hertz over a century ago to the present day. Basic descriptions of continuum elastic and elastic-plastic contact stress

Damage Modes in Dental Layer Structures

March 7, 1998
Author(s)
Yeon-Gil G. Jung, S Wuttiphan, I M. Peterson, Brian R. Lawn
A study is made of crack patterns in two model coating/substrate bilayer systems conceived to simulate crown and tooth structures, at opposite extremes of elastic/plastic mismatch: porcelain on glass-infiltrated alumina (soft/hard); and glass-ceramic on

Contact Damage Accumulation in Ti3SiC2

February 3, 1998
Author(s)
I M. Low, S K. Lee, Brian R. Lawn, M W. Barsoum
The evolution of deformation-microfracture damage below Hertzian contacts in a coarse grain Ti3SiC2 is studied. The Hertzian indentation stress-strain response deviates strongly from linearity beyond a well-defined maximum, with pronounced strain-softening