3D Scan of Hardness Imprints for the Non-destructive In-Situ Structural Assessment of Operated Metal Components

The structural integrity of operated components can be assessed by non-destructive mechanical tests performed in-situ with portable instruments. Particularly promising in this context are small scale hardness tests supplemented by the mapping of the residual imprints left on metal surfaces. The data thus collected represent the input of inverse analysis procedures, which determine the material characteristics and their evolution over time. The reliability of these estimates depends on the accuracy of the geometry scans and on the robustness of the data filtering and interpretation methodologies. The objective of the present work is to evaluate the accuracy of the 3D reconstruction of the residual deformation produced on metals by hardness tests performed at a few hundred N load. The geometry data are acquired by portable optical microscopes with variable focal distance. The imperfections introduced by the imaging system, which may not be optimized for all ambient conditions when used in automatic mode, are analysed. Representative examples of the output produced by the scanning tool are examined, focusing attention on the experimental disturbances typical of onsite applications. Proper orthogonal decomposition and data reduction techniques are applied to the information returned by the instrumentation. The essential features of the collected datasets are extracted and the main noise is removed. The results of this investigation show that the accuracy achievable with the considered equipment and regularization procedures can support the development of reliable diagnostic analyses of metal components in existing structures and infrastructures

Parametric failure analysis of metal-based composites

Metal-based composites can fail as a consequence of the growth and coalescence of micro-voids introduced with the manufacturing process. These detrimental phenomena influence the overall performance of the material to different extents since the macroscopic characteristics depend on both the local constitutive properties and geometry patterns, which promote various stress concentration and strain localization effects. The understanding of the different situations that arise in this context is often assisted by numerical simulations based on the GNT constitutive model, first proposed by Gurson (1977) and then refined by Needleman and Tvergaard (1984). However, exploring the influence of the most relevant material parameters on the composite response can be excessively time consuming. Therefore, traditional simulations based on non-linear finite element methods can be replaced by surrogate analytical approximations, which do not involve large computing costs but exhibit accuracy and sensitivity to the model parameters consistent with the practical applications. Some examples are presented in this contribution

A combined experimental and numerical study of the behaviour of paperboard composites up to failure

Paperboard composites have been subjected to non–conventional inflation experiments using a novel instrumentation inspired by burst strength testers. The purpose is to understand the behaviour up to failure of strongly anisotropic and heterogeneous material samples under the loading condition more commonly experienced for instance by beverage packaging. The information collected by the exploited prototype equipment has been interpreted at the light of validated numerical models of the performed tests

Non-destructive integrity assessment of aging steel components

This contribution addresses the integrity assessment of steel components in operation by introducing a simple non-destructive investigation technique. The proposed methodology is based on superficial (according to ASTM E18 Standards classification) hardness tests, complemented by the mapping of the geometry of the residual imprint. The diagnostic analysis can be performed in situ, potentially in a fully automated way. The informative content of the collected data is verified on the results of previous laboratory studies. The proposed material characterization procedure is applied to determine the evolution over the years of the mechanical properties of an exercised gas pipelin

Surrogate analytical models of damage localization in metal matrix composites

Several parameters entering the constitutive laws of metal matrix composites are not amenable to direct measurement. Their determination is therefore demanded to indirect identification procedures, based on the comparison between the output of some experimental works and the results of the iterative simulation of the performed tests. Largely repetitive numerical analyses can also support the optimized design of composite microstructures, the understanding of the actual stress-transfer mechanisms, and virtual testing. Surrogate analytical models can replace effectively non-linear finite element (FE) computations in parametric studies and identification procedures, reducing execution times and costs without compromising the accuracy of the results. In this context, a frequently used approach consists of the interpolation, by means of radial basis functions (RBFs), of data filtered by proper orthogonal decomposition (POD). This methodology is often used to reproduce the smooth output of different mechanical systems. This work is rather focused on the homogenized response of damaging metal matrix composites subjected to strain localization phenomena, and explores the accuracy achievable in these situations by the POD-RBF approximation of more traditional FE analyses. In all considered cases, the POD-RBF results are accurate, and able to distinguish between apparently similar situations. The approach is flexible, and the performance of the surrogate models can be tailored to the requirements of each application. In particular, various analytical approximations can be introduced to support the design of new microstructures and material couplings, and to understand the role of any material and/or geometry imperfections resulting from the production processes

Non conventional fracture tests of heterogeneous and anisotropicpaperboard composites

Non-conventional experimental procedures have been designed in order to characterize the overall constitutive properties and to follow the evolution of the damaging phenomena leading to fracture of heterogeneous and anisotropic paperboard composites. Specimens are monitored all along the tests, either by digital image correlation or by laser profilometry, in order to recover qualitative and quantitative information about the material deformation in the different considered experimental configurations. The interpretation of the results is supported by the numerical simulation of the tests