In Stack overflow within searching my problems solution I finished my total no of voted ie 40 vote and this is two times but it is still not showing in my badges why ??
That is because you've not used all the 40 votes for the day even once, which is the requirement for Vox Populi.
Used the maximum 40 votes in a day.
Doing the simple math, you've used 38 for today, which means you've used 37 in the past whole week barring today. And that leaves with 31 for the remaining month. You've not used all the 40 votes in a single day, and thus you've not been awarded with the badge.
Do note that you're allowed to vote 40 times in a day as long as you make sure 10 of those votes are on questions before you get the warning about only have a few votes left for the day as mentioned in this answer.