How can I enable core dump?
I am guessing that you are running the crashing process as root. If that is the case, change the domain from '*' to 'root'. The limit.conf lines that contain the wildcard (a.k.a. '*') does not affect the 'root' account.
/etc/security/limits.conf sets the limits, not the defaults. To actually use it you have to run ulimit -c unlimited in the shell you are using.
As with any shell commands to be run in every shell, this can be put in, for example, ~/.bashrc (per user) or /etc/bash.bashrc (all users).