That would be considered duplicate content.
A good way to share your content as Jill mentioned,
is to post the link to your social networks along with a short brief on what the article is about and a snappy title and image, as oppose to copying and pasting the entire thing.
You can also integrate social media comments with your blog,
so when users leave a comment on your facebook or twitter for instance, the comment shows up on your blog,
same applies for when a comment is left on your blog it shows up on your facebook and twitter.
That way your sharing your content in a non-duplicate way an also engaging in social media, how you should be.
You want to drive traffic from social media to your site, that's the whole point. Social media platforms are not a place to just dump your articles.
When used correctly with time, effort and engagement they can be great traffic sources of relevant traffic and potential customers.