MySQL / PHP - 重音字符导致返回不可用的数据

Question

Here is my code...

$mysqli = new mysqli(HOST, USER, PASSWORD, DATABASE);
mysql_set_charset('utf8');
$sql = "SELECT product_name FROM my_table";
$result = mysqli_query($mysqli, $sql) or trigger_error(mysql_error());
while($row = mysqli_fetch_assoc($result)) {
   foreach($row  as $key => $value) {
       //here, $value is populated but may contain a bad character
       $value = replaceAccents($value);
       //here, $value is now empty if it contained a bad character
   }
}

I have created all my tables with...

DEFAULT CHARSET=utf8 

...and I have also called...

ALTER DATABASE my_database CHARACTER SET utf8 COLLATE utf8_unicode_ci;

Most data is returned fine from the table, but if any field contains an accented character (e.g., Crème) then an unusable value is returned.

I haven't seen a problem like this - only vaguely similar ones, which have led to the above code / changes being implemented.

What is going wrong and how to fix??

Incidentally, if I do the above sql search in phpmyadmin, the problematic value (containing Crème) displays fine.

For completeness, here is my replaceAccents function...

function replaceAccents($str) {

    $str = iconv('UTF-8', 'ASCII//TRANSLIT//IGNORE', $str);

    return $str;
}