Abstract: A survery of the development of fracture mechanics is given on the basis of damage tolerant design of structures.The effects of three dimensional stress state on residual strength,fatigue crack propagation life under cnstant-as well as variable-amplitude loading of aircraft structures and cracking resistance of aircraft materials are analyzed in detail.Some ideas on solving the roblems are proposed and some new results worked out by the author are presented.A brief discussion is made on three dimensional effects upon fatigue and fracture resistance of materials at elevated temperatures and in corrosion environments,durability of airframe,etc.Finally,a list of three dimensional problems is proposed,which must be solved to improve the techniques of damage tolerant design of aircraft structures.

Key words: aircraft structure, damage t olerances design, three dimensional analysis