Using a past participle to start a relative clause

I have recently received a comment asking about the structure 'The significant percentage of work accomplished on the computer.'  

This is not a sentence as it does not contain a finite verb, but only the past participle ‘accomplished’. The actual structure is a noun phrase containing a relative clause.  However, the relative clause is not fronted by a relative pronoun, but by the past participle verb 'accomplished'.

The = determiner

(significant) percentage of = phrasal quantifier pre-modifying the main noun

work = main noun

accomplished on the computer = relative clause fronted by a non-finite past participle

The subordinate structure ‘accomplished on the computer’ could have been written ‘which was accomplished’.  Often in English we elide the relative pronoun and auxiliary verb to use the non-finite past participle in relative clause position.

So the whole structure is a noun phrase: the main noun work is pre-modified and also post-modified, but cannot stand on its own as a sentence.  You can test this by inserting it into the noun phrase position of sentences.  For example,

The significant percentage of work accomplished on the computer disproved the theory. (SVO structure with phrase in subject position)

The board approved the significant percentage of work accomplished on the computer. (SVO structure with phrase in object position)

If you wanted the original structure to act as a complete sentence, you would need to amend it so that ‘accomplished’ no longer appears as a non-finite verb:

The significant percentage of work was accomplished.  

(SV- the auxiliary verb ‘was’ + past participle ‘accomplished’ forms a passive verb.)

The significant percentage of work was accomplished.  

(SVC with ‘accomplished acting as an adjective in the complement position)