Title page for ETD etd-42098-124716


Type of Document Master's Thesis
Author Foster, Glenn C.
Author's Email Address gfoster@vt.edu
URN etd-42098-124716
Title Tensile and Flexure Strength of Unidirectional Fiber-Reinforced Composites: Direct Numerical Simulations and Analytic Models
Degree Master of Science in Engineering Mechanics
Department Engineering Science and Mechanics
Advisory Committee
Advisor Name Title
Curtin, William A. Jr. Committee Chair
Batra, Romesh C. Committee Member
Curtin, William A. Jr. Committee Member
Henneke, Edmund G. II Committee Member
Keywords
  • simulation
  • metal matrix composite
  • load sharing
  • ultimate tensile strength
Date of Defense 1998-02-20
Availability unrestricted
Abstract
A Local Load Sharing (LLS) model recently developed by Curtin

and co-workers for the numerical simulation of tensile

stress-strain behavior in fiber-reinforced composites is used

to predict the tensile strength of metal matrix composites

consisting of a Titanium matrix and unidirectionally aligned

SiC fibers.

This model is extended to include the effects of free

boundary conditions and non-constant load gradients and then

used to predict the strength of a Ti-6Al-4V matrix reinforced

with Sigma SiC fibers under 4-point flexure testing.

The predicted tensile and flexure strengths agree very well

with the values measured by Gundel and Wawner and Ramamurty

et al.

The composite strength of disordered spatial fiber

distributions is investigated and is shown to have a

distribution similar to the corresponding ordered composite,

but with a mean strength that decreases (as compared to the

ordered composite) with increasing Weibull modulus.

A modified Batdorf-type analytic model is developed and

similarly extended to the case of non-uniform loading to

predict the strength of composites under tension and flexure. The

flexure model is found to be inappropriate for application

to the experimental materials, but the tensile model yields

predictions similar to the Local Load Sharing models for the

experimental materials.

The ideas and predictions of the Batdorf-type model, which

is essentially an approximation to the simulation model, are

then compared in more detail to a simulation-based model

developed by Ibnabdeljalil and Curtin to more generally

assess the accuracy of the Batdorf model in predicting

tensile strength and notch strength versus composite size

and fiber Weibull modulus.

The study shows the Batdorf model to be accurate for tensile

strength at high Weibull moduli and to capture general trends

well, but it is not quantitatively accurate over the full

range of material parameters encountered in various fiber

composite systems.

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