Most of those investigations deal with the fact that many 8 and 5 mile an hour bumpers (meaning they shouldn't break under lower impacts) end up shattering at m

Most of those investigations deal with the fact that many 8 and 5 mile an hour bumpers (meaning they shouldn't break under lower impacts) end up shattering at maybe 2mph and cost thousands of dollars to fix -- implying that the manufactuers are engineering them that way on purpose to sell replacement bumpers or that they are no effectively engineering the bumpers to meet the specifications.