At a point in a strained material the principal stresses are 60MPa and 40MPa. Find the position of the plane across which the resultant stress is most inclined to the normal and determine the value of this stress.

Answer 1

Google "Mohr's circle".

for example:
http://www.youtube.com/watch?annotation_id=annotation_851576&feature=iv&src_vid=1plaFAWN8rk&v=qqgfKHBpj1k