substantiate vs toughen up

substantiate

verb
  • To give material form or substance to something; to embody; to record in documents 

  • To verify something by supplying evidence; to authenticate or corroborate 

toughen up

verb
  • To make or become mentally tougher. 

How often have the words substantiate and toughen up occurred in a corpus of books? (source: Google Ngram Viewer )