Constitutive modelling of damage and plasticity in metal matrix composites. Ph.D. Thesis

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1994

OSTI ID:264018

Boyd, J G

A general method for deriving constitutive equations for damage and plasticity in metal and ceramic matrix composites has been presented. The discussion is intended to introduce constitutive modeling to beginning graduate students. The method consists of identifying the independent variables, known as state variables, that determine the free energy. An explicit expression for the free energy is then written, and the rate of change of the state variables is given as a function of the thermodynamic forces and the state variables. The state variables include the reversible strain, the temperature, and a set of internal variables that account for the free energy of crystalline defects. The plastic eigenstresses were modelled by isotropic and kinematic hardening internal variables in the free energy. The thermal eigenstresses were not modelled as internal variables, but as contributions to the entropy. The fictitious eigenstresses due to microcracks were modelled by an internal variable that results in a negative contribution to both the elastic modulus and the plastic hardening modulus amd a positive contribution to the surface free energy. It was shown that in composite materials, the damage variable and the plastic hardening variables are not independent. A micropolar model was presented to predict the evolution of damage and plasticity in large-fiber, inhomogeneous composites. the choice of phenomenological constitutive equations was supported by a microthermodynamics derivation of the constitutive equations.

• Research Organization: Texas Univ., Galveston, TX (United States)
• OSTI ID: 264018
• Report Number(s): N--96-23698; NIPS--96-08065
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CERAMICS
EIGENVECTORS
FRACTURE MECHANICS
FREE ENERGY
ISOTROPY
MATHEMATICAL MODELS
MATRIX MATERIALS
METALS
PLASTICITY
SURFACE ENERGY
THERMAL STRESSES
THERMODYNAMICS