A novel methodology for the assessment of the residual elastic properties in damaged composite components

Significance Statement

The use of composite materials is rapidly increasing in many industrial applications due to their flexibility in shaping and high specific stiffness and strength. However, one limitation to the use of these innovative materials is represented by their damage complexity. Composite materials can fail owing to different interacting failure modes which induce a progressive and rapid degradation of the mechanical properties which can be hardly monitored. Methodologies able to monitor the damage evolution and allowing for predicting the residual structural integrity would extend furthermore the diffusion of composite materials in structural applications.

Presently, non-destructive tests (NDTs) have been adopted to assess the damage level of in-service composites and for quality control in manufacturing processes. Examples of NDTs include shearography, acoustic emission and ultrasonic based methods. These methods are mainly used to locate defects and determine their size and orientation, but do not permit a direct evaluation of the local residual properties, thus limiting the use of composite materials for critical structural applications.

A team of researcher from Politecnico di Torino, Italy, proposes an effective methodology to quantitatively assess the residual properties of damaged laminates. The macro energetic variable, the detecting Damage Index (DId), computed after non-destructive low energy impacts is used for assessing the residual mechanical properties of damaged composites. The proposed methodology is described and experimentally validated in a research paper published in the Journal Composite Structures: Part B.

A structural composite laminate for automotive application (composite made of epoxy resin reinforced by eight twill-2×2 carbon fabrics) is used for the experimental validation of the proposed methodology. A first set of impact tests is carried out to identify the threshold energy , defined as the impact energy that induces a negligible damage to the composite material (i.e., less than 5% reduction of the elastic properties). An impact below  can be considered as non-destructive for the laminate and therefore can be used for assessing the damage level through the DId. The correlation between the DId and the residual mechanical properties (Young’s and shear moduli) is experimentally verified. Undamaged plates are subjected to two subsequent impacts: after the first damaging impact, a second non-destructive impact at  is performed to assess the DId in the damaged area. A good correlation is found between the DId and the residual elastic properties of the impacted laminates, confirming that the DId can be effectively used for the prediction of the residual elastic properties. The proposed methodology is finally successfully validated on damaged laminates.

The innovative methodology proposed by the Authors is proved to be effective in the prediction of the residual elastic properties. Non-destructive impacts are used to assess the damage degree of composite materials and the residual mechanical properties. The proposed methodology can be adopted in many practical applications and represents an effective way for guiding the maintenance strategy in structural composite components subject to damage during service.

About The Author

Andrea Tridello is a Research Assistant of the Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin (Italy). He received his PhD in Mechanics from Politecnico di Torino in 2016 with a thesis titled A novel experimental approach for the assessment of size effect in VHCF. He earned his MSc Degree in Mechanical Engineering from Politecnico di Torino in 2012.

His research activities can be broadly divided into two main topics: a) Very-High-Cycle Fatigue (VHCF) of metallic materials and materials used for Additive Manufacturing; b) Impact and fatigue damage of composite laminates.

About The Author

Alessio D’ANDREA is a Fellow of the Fabrication Methods & Subcontracting section at CERN, Geneva (Switzerland). He received his Master’s degree in Mechanical Engineering from Politecnico di Torino in 2015, cum laude, with a thesis titled A methodology for the assessment of residual properties in damaged components made of composite materials. After, he worked as Quality Engineer of bevel gears at Avio Aero, a General Electric Aviation business.

His activity is to manage the manufacturing of Mechanical components for different CERN’s projects, in the framework of the LHC Injectors Upgrade (LIU) and High Luminosity Large Hadron Collider (HL-LHC) Projects. At the moment, he works on 3 main projects: a) FINEMET; an upgrade of the Proton Synchrotron Booster (PSB), b) Coax lines ID345 200MHz; new radio frequency lines, an upgrade of the Super Proton Synchrotron (SPS) and c) MCBRB 2M D2;a new corrector prototype for the Large Hadron Collider (LHC).

About The Author

Davide S. Paolino is an Associate Professor of the Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin (Italy). He received his PhD in Machine Design and Construction from Politecnico di Torino in 2007. He earned his MSc Degree cum laude in Mechanical Engineering from Politecnico di Torino in 2002.

His research activities can be broadly divided into three main topics: a) Statistical modeling of fatigue and reliability data and design and analysis of experiments for different applications (automotive, mechanical, biomedical); b) Very-High-Cycle Fatigue (VHCF) of metallic materials; c)Impact and fatigue damage of composite laminates.

About The Author

Giovanni Belingardi was born in Torino in 1951, he got his Master degree in Mechanical Engineering at the Politecnico di Torino in 1975.

From 1977 to 1983 he joined the Technical Department of FIAT Auto. Then he came back to Politecnico di Torino and joined the Mechanical Engineering Department as Assistant Professor. Here he developed his academic carrier up to his present position of full Professor.

His present research activity is mainly devoted to structural design and experimental testing in automotive engineering, with particular attention to lightweight design of the car body and to passive safety of vehicle occupants and pedestrians.

He is author of more than 280 papers published in international scientific journals and in proceedings of national and international conferences.

He has recently been and at present is the scientific coordinator of the Operative Units of the Mechanical and Aerospace Engineering Department for a number of projects of the framework programs of the European Union, of the National and Regional Governments. Research cooperation with industrial partners has been effective as well.

He is the responsible for International cooperation of Politecnico di Torino within the frame of the Automotive Engineering, with particular attention toward Canada, US, Brazil, Poland and Serbia. Quite frequent visits of those countries give him a special insight of their situation and needs and allowed him to construct a wide net of partnership.

Reference

Andrea Tridello, Alessio D’Andrea, Davide S. Paolino, and Giovanni Belingardi. A novel methodology for the assessment of the residual elastic properties in damaged composite components. Composite Structures, volume 161 (2017), pages 435–440

Department of Mechanical and Aerospace Engineering, Politecnico di Torino, 10129 Turin, Italy.

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