Dr. Livia Maria Serio Profile

Dr. Livia Maria Serio

at Politecnico di Bari

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Publications (3)

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Proceedings Article | 14 May 2018 Presentation + Paper

Thermographic signal analysis of friction stir welded AA 5754 H111 joints

Davide Palumbo, Rosa De Finis, Livia Serio, Umberto Galietti, Luigi A. C. De Filippis

Proceedings Volume 10661, 106610Y (2018) https://doi.org/10.1117/12.2304984

KEYWORDS: Signal processing, Signal analysis, Aluminum, Statistical analysis, Thermography, Infrared detectors, Infrared cameras, Infrared imaging

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Aluminium alloys present some criticalities in terms of fatigue life characterisation due to the absence of a point representing the ‘fatigue limit’, the topic becomes complicated when the material is welded. In this case, the fatigue characterisation lies on design specifications which have to clearly explain the guidelines for the performing the tests and for evaluating the failures, in order to design tailored welded joints. However, the fatigue of welded joints is a difficult subject since the welding process makes the material different, introducing residual tensions, defect, etc. Also, the standard test methods provide only the estimation of the strength at fixed loading cycles but no information on the damage processes occurring in the material. Prompted by these issues researchers deal with the study of other approaches to achieve not only information on fatigue resistance but also damage information. In particular, the thermography can be used for thermal signal analysis of dissipative heat sources involved in fatigue of material undergoing cyclic test. In this paper, this approach is adopted to study the fatigue behavior of friction stir welded joints of AA5754-H111 during specific loading conditions. The component of the temperature related to intrinsic dissipations is assessed and the fatigue strength is evaluated together with a graphical study of the location of damaged areas.

Proceedings Article | 14 May 2018 Presentation + Paper

Capability of infrared thermography for studying the friction stir welding process

Livia M. Serio, Rosa De Finis, Luigi A. C. De Filippis

Proceedings Volume 10661, 106610Z (2018) https://doi.org/10.1117/12.2304991

KEYWORDS: Infrared cameras, Thermography, Aluminum, Nondestructive evaluation, Defect detection

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The Friction Stir Welding (FSW) is an innovative solid-state welding method based on frictional and stirring phenomena, discovered and patented by TWI Ltd in 1991, providing high quality components for aerospace, marine and automotive industrial fields. In this process, a rotating non-consumable tool that plunges into the work piece and moves forward produces the heat necessary to weld the parts together. The much lower temperatures compared with those achieved in traditional welding processes by melting, determine the following main advantages of FSW: minimal mechanical distortion, excellent surface finish, absence of splash, no crack formation and porosity after welding, thanks to the low input of total heat. This work deals with the use of thermographic techniques for monitoring the friction stir welding process applied on AA 5754-H111 plates, in order to evaluate the quality of the produced joints in terms of presence of defects and Mechanical strength. The adopted experimental approach was addressed to study and optimizing the FSW process by analyzing the thermographic sequences and extracting several indexes related to the heating involved in the process. Such the indexes, the maximum temperature, the heating and cooling rate of the material, correlated to the frictional power input and the presence of defects respectively, have been investigated for different process parameters (the travel and rotation tool speeds) configurations. The results of the research have been quantitatively supported and characterized by destructive and non-destructive techniques.

Proceedings Article | 14 May 2018 Presentation + Paper

Potentialities of thermal signal analysis approach for a rapid mechanical characterisation of high diffusivity materials

Rosa De Finis, Davide Palumbo, Livia Maria Serio, Luigi Alberto Ciro De Filippis

Proceedings Volume 10661, 106610J (2018) https://doi.org/10.1117/12.2304983

KEYWORDS: Aluminum, Thermal effects, Signal analysis, Thermography, Smoothing, Data processing

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One of the most important advantages of using high-diffusivity alloys like aluminium, in industry, is to reduce the weight without renouncing to high strength components. To accelerate the time of the mechanical characterisation, frequently experimental methods based on temperature measurements are adopted, even if in this case, these methods could involve in wrong estimations. In particular, the study of energy dissipations could produce some assessment errors of fatigue limit due to the fact that the fraction of the detected energy dissipated could be lower if compared to the effective energy intrinsically dissipated in the material due to damage. Furthermore, the fatigue life assessment of Aluminium alloys is problematic due to a non-distinct ‘knee’ in the S-N curve. To take into account these issues and to estimate the fatigue strength in rapid and accurate way, in this work, a method providing a specific thermal signal analysis is presented applied to an aluminium alloy 5754 H-111. Firstly, the well-known methods based on direct temperature measurements for estimating fatigue strength of metals, were applied on an aluminium alloy 5754 H111 in order to demonstrate their problematic application for high-diffusivity materials. Furtherly, a specific thermal signal analysis was adopted for extracting first and second order temperature variations as better parameter for fatigue strength assessment. This work questions the use of direct temperature evaluation in high diffusivity materials and fully replaces it in favor of an approach based on in-depth analysis of thermal signal by using thermoelastic and dissipative temperature variations.

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