# why do microscopic cracks happen?

2 weeks ago i asked a question about " Gas permeation through solid metal? " i have got a very good answer here .but microscopic crack was mentioned in the answer. i searched in Internet but i didnt find any informations .

so if i have aluminum sheet (0.5 mm thickness) and it starts to crack if i bend it 30 mm and if i bend it 1 mm it will return to his original shape .

do i get microscopic cracks if i bend it 1mm ? why do microscopic cracks happen ?

im trying to understand the " microscopic cracks" . Thanks in advance