Mr. Francesco Rizzo Profile

Francesco Rizzo

at Univ of Bath

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Author

Publications (3)

Proceedings Article | 21 March 2019 Paper

High-velocity impact response on advanced hybrid composite structures

F. Rizzo, T. D’Agostino, F. Pinto, M. Meo

Proceedings Volume 10973, 109730T (2019) https://doi.org/10.1117/12.2522385

KEYWORDS: Composites, Finite element methods, Visualization, Manufacturing, Failure analysis, Resistance, Interfaces, 3D modeling, Calibration, High speed cameras

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The use of composite materials of various types and forms has become a significant engineering solution for manufacturing a range of mechanical, aerospace and automotive structures, leading to a significant increase in payload, weight reduction, speed, fire resistance, manoeuvrability and durability in comparison with traditional structural materials [1, 2]. However, the investigation of their mechanical behaviour under high-velocity impact loads is particularly challenging owing to the generation of simultaneous and multiple failure phenomena with an inevitable detriment of residual in-plane properties [3]. In this paper, experimental tests and finite element methods (FEM) were performed on plates and T-stiffened laminates under transient dynamic loading, aiming at better understanding the damage tolerance, failure phenomena and impact damage of these composites. The 3D explicit model, based on continuum damage approach, was built using a DYNA3D suite on a framework of an orthotropic constitutive behaviour with stress-based and energetic failure criteria. Numerical results were validated using visual and ultrasound (C-scan) evaluation from dynamic tests. Furthermore, based on the results of the experimental campaign and the numerical model, a numerical study on the optimisation of the structure of the laminate was carried out, considering the inclusion of a secondary hybrid layer within the layup sequence. The mechanical characteristics and geometry of this secondary phase were studied in order to find the best configuration to optimise damage tolerance and improve dynamic response to out-of-plane loads. Several examples with different initial conditions were carried out on the new hybrid material to demonstrate the excellent predictive capability of the numerical model and to study the influence of new hybrid characteristics on the impact responses and impact-induced damages. Numerical results of analyse and their trend were then presented, showing a decrease of -22%, -33% and -94% in damaged area, a decrease of -33%,-57%, - 58% in maximum indentation and an increase of +62%, +134% and +156% in rebound velocity of projectile due to the presence of TPU layers with 0.25 mm, 0.5 mm and 1 mm of thickness respectively.

Proceedings Article | 27 March 2018 Paper

Bioinspired pseudo-ductile composite laminates with hierarchical energy absorption mechanism

F. Rizzo, F. Pinto, M. Meo

Proceedings Volume 10593, 105930G (2018) https://doi.org/10.1117/12.2301028

KEYWORDS: Manufacturing, Composites, Carbon, Finite element methods, Absorption, Fiber reinforced polymers

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The large diffusion of Carbon Fibre Reinforced Polymers (CFRP) over the last three decades in multiple industrial sectors is due to their excellent in-plane mechanical properties and their exceptional strength-to-weight-ratio. As the use of CFRP moved from non-structural parts to primary structures however, the intrinsic layered nature of these materials and their consequent weak resistance to out-of-plane solicitations has changed the safety approach used for traditional ductile materials, shifting the design paradigm towards more severe safety margins. This zero-damage manufacturing strategy, necessary to prevent catastrophic failures, led to overdesigned composite parts, preventing the full exploitation of their unique characteristics and limiting their use in harsh environments. Based on this premise, the possibility to manufacture composite laminates able to respond with a pseudo-ductile behaviour when subjected to an out-of-plane load is of crucial importance as it would eliminate the need of overdesigned parts and extend the range of applications available to composite structures. This project is aimed to the design, manufacturing and characterisation of a bioinspired CFRP laminate in which the pseudo-ductility arises from an ordered pattern of discontinuities which are created over the surface of the different layers before the curing reaction. The presence of this carved pattern creates a hierarchical interplay of high-strength carbon fibre segments and elastic soft matrix-rich areas which resembles the interaction between the β-sheets crystalline domains and amorphous helical and β-spiral structures typical of spider silk and other biological structures (e.g. cellulose, hair) which enables a combination of high mechanical strength and elasticity. The effect of different geometrical parameters of the carved pattern such as critical length, shape and dimensions, on the mechanical properties of the laminate have been analysed via Finite Element Analyses in order to identify the optimal configuration of the discontinuities, finding the best trade-off between in-plane and out-of-plane mechanical properties. Samples with different carved patterns were then manufactured and their properties were assessed by subjecting them to three-point-bending test. The internal distribution of damaged areas was assessed via different Non Destructive Techniques and was compared with the behaviour of traditional CFRP. Results showed that the presence of the artificial discontinuities is able to induce pseudoductile behaviour into the CFRP, improving the energy absorption mechanism during out-of-plane solicitations without severely affecting the in-plane properties.

Proceedings Article | 11 April 2017 Paper

Impact resistant smart hybrid laminates

F. Pinto, F. Rizzo, M. Meo

Proceedings Volume 10165, 101650W (2017) https://doi.org/10.1117/12.2259925

KEYWORDS: Composites, Shape memory alloys, Resistance, Infrared cameras, Damage detection, Smart materials, Diffusion, Carbon, Thermography, Metals, Copper, Cameras, Manufacturing

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The large diffusion of structural parts made of carbon fibres reinforced polymers (CFRP) in the aerospace and automotive sectors has highlighted the importance of developing hybrid multifunctional materials characterised by improved mechanical properties and coupled with non-structural features. Indeed, while due to their high specific strength and light weight, composite systems are characterised by very high mechanical properties in the in-plane direction, their intrinsic layered structure makes them very susceptible to low-velocity impacts resulting in Barely Visible Impact Damage (BVID) that can lead to the critical failure of primarily structures. Based on these premises, the development of a multifunctional hybrid system can overcome this drawback by tackling this issue from two different points of view, enhancing the total reliability of light-weight composite parts in order to improve fuel efficiency and optimise the footprint of new generation aero-structures. Indeed, by including an additional metallic phase within the structure of a traditional laminate it is possible to develop a smart multifunctional system in which the hybrid phase acts simultaneously as a reinforcement to enhance the out-of-plane properties of the material and as an intelligent embedded sensor system able to communicate information about the health status of the part and detect impact events or critical loads. This work is focused on the design, manufacturing and testing of a hybrid CFRP (H-CFRP) in which the hybridisation is obtained by including an array of Shape Memory Alloys (SMA) or Copper wires within the laminate. The electrical properties of the hybrid network is exploited to design a smart sensing system which can be interrogated to monitor the load distribution on the part and detect critical solicitations in critical points. The low-power system, controlled by an Arduino microcontroller, is able to monitor the integrity status of the part using each wire as a linear probe to scan complex structures at a certain frequency, measuring the local change in the electrical resistance from which it is possible to build a map of the stress distribution. The position of the metallic network along the laminate’s thickness was determined by analysing the response of different configurations of hybrid samples subjected to Low Velocity Impacts (LVI) in order to optimise the design of the H-CFRP and enhance the energy absorption. Using the same Arduinocontrolled Multiplex the smart wires array was exploited as heat source to scan the sample inner structure and monitoring the variation of the superficial apparent thermal variation with an Infra-Red (IR) Camera, a simulated delaminated area was detected.

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