<?php

   $str = "2017-02-27 13:40:42";

   $first=explode(' ',$str);

   $second=explode('-', $first['0']);

    $three=explode('-', $first['0'])['2'];

    print_r($first);

    echo "<br>";

    print_r($second);

    echo "<br>";

    print_r($three);

?>