These notes consist of drafts of the lectures delivered to the students of the University of Pisa, Department of Mechanical Engineering, in spring semester of academic year 1991/92.
As time allotted for lecturing was limited to 12 teaching hours, the author had to solve the fundamental question: should these lectures be:
A: - a systematic presentation of a theory which allows to describe gradual material deterioration and structures collapse,
B: - a projection of author's contribution to a specific branch of fracture mechanics onto existing attempts of describing extremely complex physical phenomenon?
Both approaches have their pros and cons. From educational point of view the solution labeled A seems to be more appropriate, but B offers to the students a chance to look at "the kitchen" of problem solving, and demonstrates the power of damage mechanics used as a tool to solve important problems of structure's durability.
The reason that author has chosen the solution B came by very simple reason: the complete theory of damage does not exits, and, perhaps, may not exist at all. The variety of materials used in engineering practice, and very complex loading conditions preclude the existence of such an universal theory, which could cover phenomena like creep, fatigue, stress assisted corrosion, thermal loading for metals, ceramics, or multitude of composites (long or short fiber reinforced polymers, laminates, etc.).
Additionally, looking critically at author's (and his co-workers') contribution allows to point out existing problems, and bring students' attention to numerous unsolved ones.
Finally, author's involvement in the subject since late 60-ties allows him to build a continuous path from very early stages of damage mechanics development until the present maze of different theories and problems solved, and unsolved, as well. It is author's hope, that the students may continue along this path in a future.