ABSTRACT
The early detection of structural damage generates a wide interest in the civil, mechanical, and aerospace engineering fields. For the purpose of this chapter, damage is defined as changes to the material and/or geometric properties of a structure, which adversely affect its performance. Examples of structural damage are fatigue, crack, corrosion, and loosening of bolted connections among others. When the damage reaches a point where the structure is no longer functional, it is referred to as failure. The purpose of damage assessment is to detect and characterize damage at the earliest possible stage, and to estimate how much time remains before maintenance is required, the structure fails, or the structure is no longer usable. Damage assessment has a tremendous potential for life-safety and/or economic benefits: it reduces the maintenance cost and increases the structure safety and reliability. Damage assessment can be categorized into the following four levels:
Level 1: Detecting the presence of damage in the structure.
Level 2: Determining the geometric location of the damage.
Level 3: Quantifying the severity of the damage.
Level 4: Predicting the remaining lifespan.
