Structural damage and life-time estimates by nonlinear FE simulation

Accumulation of structural damage leads to the termination of the life of a structure. For structural-life estimation, a new paradigm is introduced defining final structural failure as the passing of damage evolution over an ultimate damage bound. During the life of the structure, the original safety margin will be reduced by deterioration of structural strength, reflected in the time evolution of the tangential stiffness matrix KT, the most suitable assemblage of structural damage information. The definition of damage indicators Di follows from eigenvalues λi of KT, or from its Cholesky decomposition or its frequency spectrum ωi. Since the condition det KT=0 represents structural failure, these Di are valid throughout a structure's life from birth to failure. Damage generally originates from numerous local material defects, but only their effects on structural stiffness or strength can be identified as structural damage. At the centre of the FE solution process stands the formulation of material damage phenomena in the constitutive relations, and its homogenization up to structural level by multi-scale (multi-level) simulation techniques. The developed concept is illustrated by means of three examples, and then extended to the estimation of structural life duration.