Unit cell models have been proposed to predict the constitutive law and failure of ductile materials with complex microstructures, such as ferritic nodular cast iron and particulate metal matrix composites (PMMCs). The present contribution aims to extend this modelling approach to the prediction of the constitutive response of nodular cast iron with a mixed ferritic/pearlitic matrix. The finite element method is used within the framework of continuum mechanics to carry out the calculations. The effect of some microstructural features, such as graphite volume fraction and ferrite-pearlite ratio of the matrix, on the mechanical performance is determined. The computational results are compared to results obtained in a previous experimental activity on nodular cast irons.
The knowledge of tensile load in reinforcement tie-rods is of crucial importance to assure structural integrity and safety. This work addresses the problem of identifying this tensile load in structural tie-rods of ancient masonry arches and vaults. The proposed procedure is a nondestructive and non-invasive method. It consists in matching the first six natural frequencies of the tie-rod, acquired by a classical accelerometer, with numerically obtained frequencies. This matching procedure is accomplished by an optimisation algorithm in which the length of the rod, the presence of concentrated masses along it and an elastic foundation at the edges are the optimisation variables. In this way, the main unknown, i.e. the axial load, is determined by a mathematical algorithm that automatically minimises the difference between experimental and numerical results on the basis of the choice of multiple parameter combinations. A 'local zoom technique' is adopted around a parameter set, which gives a minimum, in order to determine the load with good approximation. A deep investigation about the stress state in the tie-rods is also carried out via a nonlinear finite element analysis.
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