Diagnostic analyses based on nondestructive testing of metallic structural components in hydropower plants

Metallic structural components (such as turbines and their shafts, pressure water pipes and penstocks), may exhibit original defects or deteriorations such as strength reductions, residual stresses in welds and elsewhere, cracks. These damages, which may reduce the structural safety margins, are quantified by parameters which can nowadays be estimated by diagnostic procedures based on non-destructive tests and inverse analyses. The procedure briefly described in this communication exhibits the following features: indentation performed “in situ” by an instrumented indenter which provides the “indentation curves” (force versus penetration) in digital form; possible additional data provided by a laser “profilometer” on the imprint geometry; parameter estimates computed through inverse analyses made economical and fast by a novel method consisting of “a-priori” “model reduction” and of an algorithm apt to minimize a suitably defined discrepancy between experimental data and their counterparts computed as functions of the unknown parameters. The resulting parameters calibrate the pre-selected materials models of elasticity, plasticity, fracture, and/or residual stress states. Thus overall nonlinear structural analyses for safety assessments of a structural component by usual computer codes may become reliable and realistic.