Rita Ambu

Investigation of the effect of damage on the strength of notched composite laminates by digital image correlation

In this paper the results of an experimental investigation on the effect of subcritical damage on the residual strength properties of notched composite laminates are presented. A procedure based on the digital image correlation method was applied to laminates subjected to static and fatigue tensile loading. The digital image correlation method (DICM) is a whole-field technique that calculates surface displacements and strains from digital images characterized by a random distribution of intensity grey levels. Graphite/PEEK (polyether ether ketone) and graphite/epoxy laminates with different stacking sequences were analysed and the damage progression near the stress riser was evaluated by means of the strain maps obtained by digital image correlation. It was found that damage developing before final fracture may significantly affect the structural performance of composite laminates. The digital image correlation technique allowed clarification of the beneficial or detrimental role played by the different failure mechanisms on the strain redistribution around the hole and, as a consequence, on the residual strength and fatigue life of notched samples. The findings of the investigation suggest that the DICM is an efficient and reliable tool for full-field monitoring and detailed damage characterization of structural composite elements.

A Method with a Statistical Approach for the Evaluation of Tolerance Chains

In this paper a procedure based on a statistical approach to manufacturing for the analysis of tolerance chains is reported. In particular, the proposed approach can be summarised into two main steps. First, each single technological operation (for example, the drilling of a hole) is simulated by extracting, from a statistical distribution typical of the machine tool, the parameters characteristic of the manufacturing procedure. Then, a simulation is performed, to verify if the real features of the part can simultaneously fit the virtual gage. This method of acceptance/rejection of a part is according to the ISO/ASME standards and is representative of the real functional requirements of the part.

Residual Stress Evaluation in Vitreous Enameled Steel Sheets by Digital Images Analysis of Microstructures

Composite vitreous-enameled steel sheet have become more attractive for structural applications. In this chapter, an investigation on the residual stresses, introduced during the manufacturing of these materials, is reported. The local structure evidences the presence of bubbles in the coating and the interface domain between the substrate and the external layer made of a complex material system where the ceramic and the metal constituents are mixed. This particular local structure can affect the distribution and entity of the residual stresses. Digital images of cross-section micrographs have been processed and used to discretize the material microstructure into a mesh suitable for finite element analysis. The residual stresses have been evaluated on coatings manufactured with different technologies and, in particular, the effect of the presence of bubbles on the stresses has been highlighted.