I am using drupal 7 built in search module, when I searched for example
mechanics it will filter out the results successfully but when I used to write only
mechan something like this, it displays no results.
Look at the module Fuzzy Search , this may solve your problem.
This module provides drupal sites with a fuzzy search engine to allow for broader keyword matches including partial or misspelled keywords.
Fuzzy matching is implemented by using ngrams. Each word in a node is split into 3 (default) letter lengths, so 'apple' gets indexed with 3 smaller strings 'app', 'ppl', 'ple'. The effect of this is that as long as your search matches X percentage (administerable in the admin settings) of the word the node will be pulled up in the results.