why alias names defined in .bashrc file are not working?

Did you source your .bashrc file after you changed it? Try:

. ~/.bashrc

Then your shell should see the changes. Alternatively, you can terminate and restart your shell.

p.s.

When you run from a script, load this first ref

shopt -s expand_aliases

Maybe you are trying to define your aliases in your .bashrc that are already global.

Usually your aliases in .bashrc are defined before the /etc/bashrc call. Try to define them after.

Here an example of your .bashrc:

# Source global definitions
if [ -f /etc/bashrc ]; then
        . /etc/bashrc
fi

# User specific aliases and functions
alias c='clear'
alias l='ls -lt'
alias h='history'
alias d='ls -lt |grep "^d"'

export ORACLE_HOME=/ora11gr2/app/oracle/product/11.2.0/db2
export ORACLE_LIB=/ora11gr2/app/oracle/product/11.2.0/db2/lib
export PATH=$ORACLE_HOME/bin:/usr/vac/bin:/usr/vacpp/bin:.    
export LD_LIBRARY_PATH=$ORACLE_HOME/lib:.

Just in case any MacOS users come looking for this answer, I tried this on my MacBook and even restarting the Terminal would not load the new alias definitions. The only way I could get it to work was to source ~/.bashrc every time. I then tried moving my alias definitions to ~/.bash_profile and this is what did the trick.