PHP str_replace replace spaces with underscores
Try this instead:
$journalName = preg_replace('/\s+/', '_', $journalName);
Explanation: you are most likely seeing whitespace, not just plain spaces (there is a difference).
I'll suggest that you use this as it will check for both single and multiple occurrence of white space (as suggested by Lucas Green).
$journalName = preg_replace('/\s+/', '_', $journalName);
instead of:
$journalName = str_replace(' ', '_', $journalName);