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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.
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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