Assessment of both residual stresses and material properties for structural diagnosis “in situ”

The assessments of parameters in inelastic constitutive material models and of residual stresses are at present a research subject of growing importance in several industrial fields either for diagnosis of possibly damaged plants in service or for control of structural component productions. Residual stresses (RS) in metal structures, particularly in hydro- and thermoelectric power plants, are frequently assessed by “quasi-non-destructive” Hole Drilling Tests (HDT), also required by various standards and codes, e.g. [1], and frequently dealt with in related recent literature, e.g. [2]. The research results presented in this congress can be outlined as follows (some details will appear in [3] while a survey of the novel methodological context is available, e.g., in [4]). The RS state to assess is modelled so that the parameters to identify govern it linearly and, hence, inverse analyses can be performed fast “in situ” through a pre-generated matrix, after modelling the HDT by a finite element procedure. Displacements caused by the HDT are measured “full-field” by Digital Image Correlation (DIC) cameras (no longer by strain gauges). Sensitivity analyses are performed in order to optimize the selection of DIC monitored points and the RS modelling. In order to reduce further “damages”, required material properties (usually elastic moduli alone) are assessed by an indentation test (IND) either on the bottom or on the edges of the hole. Inverse analyses by a deterministic approach (a general synthesis in [4]) both on HDT and IND are designed as for interactions between the two tests and are computationally tested for their optimization.