No abstract

No abstract

Nonrandom porous mullite ceramics with controlled pore geometry have been fabricated using a lost mold process, where the molds were fabricated using the fused deposition process from CAD data. The pore geometry of molds was varied to achieve different pore sizes and shapes. These porous ceramic structures were then tested under uniaxial compression to evaluate their strength degradation for different pore volumes created by varying pore sizes and shapes. The finite element method (FEM) has been used to understand the effect of these porosity parameters based on stress concentrations along pore boundaries. Strength degradation of porous ceramics was found to be related to the increase in stress concentration along the pore boundaries in three-dimensional nonrandom porous ceramics.

A numerical framework for the coupled thermo-mechanical analysis of crack growth in structures loaded by an applied heat flux is outlined. Using a thermo-mechanical cohesive zone model (TM-CZM), load transfer behavior is coupled to heat conduction across an interface and the corresponding interface crack. Nonlinear effects occur due to the coupling between the mechanical and thermal problem introduced by the conductance-separation response between crack faces as well as through the temperature dependence of material constants of the CZM. The description of the load transfer behavior uses a traction-separation law with an internal residual property variable that characterizes the extent of damage caused by mechanical loading. The description of thermal transport includes a representation of the breakdown of interface conductance with increase in material separation. The current state of interface failure, the presence of gas entrapped in the crack, the radiative heat transfer across the crack and a contact conductance between crack faces determine the cohesive zone conductance. The TM-CZM is implemented into a finite element code and applied in the study of interface crack growth between an oxidation protection coating on a thermal protection material.

No abstract