buckle down vs get down to business

buckle down

verb
  • To put forth the needed effort; to focus; become serious; apply oneself (e.g. to work or study). 

get down to business

verb
  • To commit oneself to a task or activity that is employment-related or that requires serious effort or concentration. 

How often have the words buckle down and get down to business occurred in a corpus of books? (source: Google Ngram Viewer )