se détacher

[alan gould]

With regard to clothes/shoes, I would use it if a button or buckle actually came off.  But the dictionary has it as "to come undone."  I would use "défaire" if a shoe were untied or a button unbuttoned and it's probably equivalent to "undone" which is heard without being more specific ("untied, unbuttoned").  Will I hear "se  détacher" regarding clothes when something has not physically separated?  

merci d'avance 

[Florian Chanonat]

Hmm it's better to use "défaire" when you're talking about buckle, shoelace, button...