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A Nonlinear Viscoelastic Model for Ceramics at High TemperaturesHigh-temperature creep behavior of ceramics is characterized by nonlinear time-dependent responses, asymmetric behavior in tension and compression, and nucleation and coalescence of voids leading to creep rupture. Moreover, creep rupture experiments show considerable scatter or randomness in fatigue lives of nominally equal specimens. To capture the nonlinear, asymmetric time-dependent behavior, the standard linear viscoelastic solid model is modified. Nonlinearity and asymmetry are introduced in the volumetric components by using a nonlinear function similar to a hyperbolic sine function but modified to model asymmetry. The nonlinear viscoelastic model is implemented in an ABAQUS user material subroutine. To model the random formation and coalescence of voids, each element is assigned a failure strain sampled from a lognormal distribution. An element is deleted when its volumetric strain exceeds its failure strain. Element deletion has been implemented within ABAQUS. Temporal increases in strains produce a sequential loss of elements (a model for void nucleation and growth), which in turn leads to failure. Nonlinear viscoelastic model parameters are determined from uniaxial tensile and compressive creep experiments on silicon nitride. The model is then used to predict the deformation of four-point bending and ball-on-ring specimens. Simulation is used to predict statistical moments of creep rupture lives. Numerical simulation results compare well with results of experiments of four-point bending specimens. The analytical model is intended to be used to predict the creep rupture lives of ceramic parts in arbitrary stress conditions.
Document ID
20050212110
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Authors
Powers, Lynn M.
(Case Western Reserve Univ. Cleveland, OH, United States)
Panoskaltsis, Vassilis P.
(Case Western Reserve Univ. Cleveland, OH, United States)
Gasparini, Dario A.
(Case Western Reserve Univ. Cleveland, OH, United States)
Choi, Sung R.
(NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
August 23, 2013
Publication Date
May 1, 2002
Subject Category
Nonmetallic Materials
Meeting Information
Meeting: Fifth World Congress on Computational Mechanics
Location: Vienna
Country: Austria
Start Date: July 7, 2002
End Date: July 12, 2002
Funding Number(s)
PROJECT: RTOP 708-31-13
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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