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Facilities for “IN SITU” extracting small metal samples and for testing small punch disks in three different test modalities: guided, free, clamped

pubblicazioni - Articolo

Facilities for “IN SITU” extracting small metal samples and for testing small punch disks in three different test modalities: guided, free, clamped

punch disks in three different test modalities: guided, free, clamped Giuseppe Torsello* 1st International Conference: Determination of Mechanical Properties by Small Punch and other miniature testing technique Ostrava, (Czech Republic), 31 Agosto, 2 Settembre 2010 POSTER SESSION * RSE SpA Owing to factors like: aging, in service loading, radiation etc., material properties of the mechanical components degrade. For such a reason, monitoring of such effects is very important in order to, both estimate the component residual life and to hold the component in safe service beyond its design life as far it is possible. Small Punch Method appears as the best candidate to monitor in situ the material mechanical properties of the most stressed zones in the machines components. The paper shows the high degree of fitness in assessing, both the elastic-plastic and fracture, properties of the steels commonly used in the construction of high / mid and low pressure steam turbine rotors. The work included two parts: an experimental part and an analytical simulation part. In the experimental part of the work a lot of tests were performed: SP tests, monotonic tensile tests, fracture mechanics tests, hardness measurements, and metallographic analyses etc. In the analytical simulation part a lot of numerical simulations were carried out by means of FEA codes for tuning, by using the experimental results, the parameters of the material models in order to be able to predict the material properties. In particular, finite element simulations have been carried out for modelling the material behaviour by an elastic-plastic constitutive law and a micro-mechanical damage model (GTN). Initially, the numerical simulations dealt with the prediction of the experimentally determined LDC curve (Load Displacement Curve). Performing of this step required the material parameters derived from the simulated and experimental monotonic tensile tests on notched specimens (direct analysis). Successively a computational framework has been developed aimed at performing the inverse analysis from which was derived the assessment of the static and fracture properties of the material based on the small punch LDC curve. The agreement between experimental values and numerical predictions is very good.

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