What you mean by 'application get crashed'?
Normally the JBoss should run in most cases without any optimization!
What configuration do you deploy?
Please scan through the posts in the Performance Tuning forum (http://community.jboss.org/en/jbossas/performance), it contains many helpful tuning suggestions.
If that does not help, please provide more details.
And there is no need to shout (large, bold text).