Research

Structural mechanics

Keywords: Nonlinear structural mechanics; Geometrically-exact shell and plate models; Absolute tensor notation; Composite laminates for aerospace.

Description: The intrinsic complexity of structural models for aerospace laminates, driven by their anisotropy and inhomogeneity, often leads to the adoption of linear formulation unable to describe mechanical states characterized by the presence of large displacements and strains. This and other considerations motivate the ddevelopment of geometrically nonlinear mechanical models of composite plate and shell structures for the aerospace. The adoption of a geometrically-exact description of the kinematics through the Green-Lagrange strain tensor and the enforcement of equilibrium via Piola-Kirchhoff stress tensors enables the models to express large displacements/strains, enabling a more accurate and reliable prediction of their behavior. In addition to this, the adoption of an absolute tensor notation featuring Christoffel’s symbols boosts the modelling capabilities of the proposed structural formulations. The expression of the so-derived governing equations, in fact, becomes independent of the geometrical nature of the domain to be modeled (which remains identified completely by the Christoffel’s symbols themselves), this feature proving to be particularly suitable for numerical implementation in finite elements codes.

Related journal and conference papers:

  • Lacarbonara W, Pasquali M (2011). A geometrically exact formulation for thin multi-layered laminated composite plates: Theory and experiment. Composite Structures, vol. 93, pp. 1649-1663.

  • Pasquali M, Gaudenzi P (2017). A geometrically exact formulation of thin laminated composite shells. Composite Structures, vol. 180, pp. 542-549.

  • Pasquali M, Lacarbonara W, Marzocca P (2010). Geometrically exact plate models for system identification via Higher-Order Spectra extracted from nonlinear dynamic responses, Workshop on Structural Health Monitoring and Control, Amman, Jordan, from 20-06-2010 to 23-06-2010.

  • Pasquali M, Gaudenzi P (2016). A geometrically exact formulation of thin laminated composite shells, Paper No. SEMC2016-395, 6th International Conference on Structural Engineering Mechanics and Computation, Cape Town, South Africa, from 05-09-2016 to 07-09-2016.

System identification

Keywords: Nonlinear structural identification for the aerospace; HOS; Experimental testing; Structural vibrations.

Description: The capability of accurately detect internal damages and defects featured by aerospace maintenance procedures is key to ensure the necessary level of safety and reliability of composite structural components. Form the modelling point of view, this requires the derivation of structural models which are rich enough to encompass the desired features without becoming cumbersome and hard to handle. A stream of research is thus dedicated to detect (via theoretical, numerical and experimental analyses) damage/defect-related nonlinearities from the vibration characteristics of aerospace structural components and systems to characterize their behaviour as well as to identify deviations from the expected response or the deterioration of their performance. One of the novel aspects of this work is the proposition nonlinearity indices (based on Higher-Order Spectra or HOS) as a scalar measure of the strength of different nonlinearities such as quadratic or cubic nonlinearities appearing in the system response as effect of structural changes. A powerful application of such nonlinearity indices is to obtain reliable reduced-order models of plate nonlinear dynamics. By reducing the partial differential equations of motion by one of the variants of the method of weighted residuals hierarchies of reduced-order models with increasing number of trial functions can be derived. An accurate reduced-order model may be obtained when the computed HOS match the experiment-based HOS within a desired order and tolerance. The virtue of such an approach is that it relies on a geometrically-exact model, and consequently it overcomes the severe limitations associated with ad-hoc mechanical models in which various types of approximations and truncations are enforced at the outset.

Related journal and conference papers:

  • Pasquali M, Lacarbonara W, Marzocca P (2014). Detection of nonlinearities in plates via higher-order spectra: numerical and experimental studies. Journal of Vibrations and Acoustics, vol. 136, 041015.

  • Pasquali M, Lacarbonara W, Marzocca P (2011). System identification of plates using higher-order spectra: numerical and experimental investigations, Paper No. 945175, 52nd AIAA/ASME/ ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Denver, CO, USA, from 04-04-2011 to 07-04-2011.

  • Pasquali M, Lacarbonara W, Marzocca P (2011). Advanced system identification of plates using a higher-order spectral approach: theory and experiment, Paper No. DETC2011-47975, 2011 ASME DETC, Washington DC, USA from 28-08-2011 to 31-08-2011.

Impact dynamics

Keywords: High-velocity impact; Ballistic limit; Composite aerospace targets; Principal curvatures.

Description: High-Velocity Impacts (HVI) can occur both in aeronautic and space applications (bird strikes, hail storms, impact of satellites with space debris, etc.) with dramatic consequences. The assessment of the capability of a structure to resist to such events can therefore be crucial. However, such evaluation often requires complex ad-hoc numerical studies which fail to deliver a general procedure to investigate the impact-induced behaviour of a structure. As part of the research stream on waves-based structural monitoring techniques, semi-analytical tools are developed to deliver a fast and accurate prediction of the impact response, ballistic resistance and damage extension of composite aerospace structures resorting to the geometrical and material properties of the projectile-target pair. Such physics-based numerical codes are rooted into the estimation of the different energy contributions associated to the various damage/deformation mechanisms which take place during the impact. Particularly innovative with respect to the associated literature is the capability of the proposed approach to encompass the effects of the curvature in determining the ballistic resistance of the impacted thin-walled components. This enables the developed methodology to feature a higher accuracy with respect to alternative procedures when compared to experimental measures.

Related journal and conference papers:

  • Pasquali M, Terra C, Gaudenzi P (2015). Analytical modelling of high-velocity impacts on thin woven fabric composite targets. Composite Structures, vol. 131, pp. 951-965.

  • Nardi D, Lampani L, Pasquali M, Gaudenzi P (2016). Detection of low-velocity impact-induced delaminations in composite laminates using Auto-Regressive models. Composite structures, vol. 151, pp. 108-113.

  • Gaudenzi P, Nardi D, Chiappetta I, Atek S, Lampani L, Pasquali M, Sarasini F, Tirilló J, Valente T (2015). Sparse sensing detection of impact-induced delaminations in composite laminates. Composite Structures, vol. 133, pp. 1209-1219.

  • Pasquali M, Gaudenzi P (2017). Effects of curvature on high-velocity impact resistance of thin woven fabric composite targets. Composites Structures, vol. 160, pp. 349-365.

  • Pasquali M, Gaudenzi P (2015). High-velocity impacts on aerospace thin composite laminates, Paper no. SMART2015-123, 7th ECCOMAS Thematic Conference on Smart Structures and Materials, Ponta Delgada, Azores, from 03-06-2015 to 06-06-2015.

  • Pasquali M, Gaudenzi P (2016). Numerical prediction of the ballistic limit for thin curved composite panels, Paper No. ICCS19-11916, 19th International Conference on Composite Structures, Porto, Portugal, from 05-09-2016 to 09-09-2016.

  • Pasquali M, Gaudenzi P (2018). Analytical prediction of high-velocity impact resistance of plane and curved thin woven fabric composite targets, 15th European Conference on Spacecraft Structures, materials and Environmental Testing, ESA-ESTEC, Noordwijk, The Netherlands from 28-05-2018 to 1-06-2018.

  • Pasquali M, Gaudenzi P (2019). Analytical prediction of high-velocity impact resistance of plane and curved thin woven fabric composite targets, 25th International Congress of the Italian Association of Aeronautics and Astronautics, Rome, Italy, from 9-09-2019 to 12-09-2019.

Structural health monitoring (SHM)

Keywords: SHM of aerospace structures; NDE techniques; Ultrasounds; PZT transducers; Genetic Algorithms; High-frequency elastic waves.

Description: Retrofitting ultrasounds-based NDE techniques with the goal of continuous/real-time and automated surveillance of the overall integrity of aerospace composite structures through consideration of working condition updates and structural ageing. Among the proposed approaches, the excitation/acquisition of high-frequency through-the-thickness elastic waves to detect interlayer delaminations constitutes an element of absolute novelty in the associated literature. In particular, the local nature of this NDE procedure allows the development of innovative pzt transducers reduced in size – whose design is optimized resorting to genetic algorithm to enhance their actuation/sensing capabilities – enabling the realization of a net of sensors which proves to be very effective in identifying structural damages in the most critical areas of aerospace structures. The promising nature of these research activities culminates in the initiation of a scientific partnership between the Department of Mechanical and Aerospace Engineering of “La Sapienza” University of Rome and the Engineering Institute of the Los Alamos National Laboratory, which took interest in this stream of research, actively collaborating to the experimental validation of various proposed NDE procedures.

Related journal and conference papers:

  • Pasquali M, Lacarbonara W (2015). Delamination detection in composite laminates using high-frequency P- and S-waves - Part I: Theory and analysis. Composite Structures, vol. 134, pp. 1095-1108.

  • Pasquali M, Lacarbonara W, Farrar CR (2015). Delamination detection in composite laminates using high-frequency P- and S-waves - Part II: Experimental validation. Composite Structures, vol. 134, pp. 1109-1117.

  • Pasquali M, Stull CJ, Farrar CR (2012). Info-gap robustness of an input signal optimization algorithm for damage detection. Mechanical Systems and Signal Processing, vol. 50-51, pp. 1-10.

  • Pasquali M, Lacarbonara W, Stull CJ, Farrar CR (2012). On assessing the robustness of an input signal optimization algorithm for damage detection: the Info-Gap Decision Theory approach,

  • Paper No. CSNDD2012-01003, International Conference on Structural Nonlinear Dynamics and Diagnosis, Marrakech, Morocco, from 30-04-2012 to 02-05-2012.

  • Pasquali M, Lacarbonara W, Farrar CR (2012). A new ultrasonic waves-based SHM procedure for delamination detection in composite structures, Paper no. ICMNMM2012-509, International Conference of Nano, Micro and Macro Composite Structures, Torino, Italy, from 18-06-2012 to 20-06-2012.

  • Pasquali M, Lacarbonara W, Gaudenzi P, Farrar CR (2012). A new ultrasonic waves-based SHM procedure for delamination detection in composite structures, Paper no. ASHMCS2012-154, The 1st International Conference on Advances in Structural Health Management and Composite Structures, Jeonbuk, South Korea, from 29-08-2012 to 31-08-2012.

  • Pasquali M, Lacarbonara W, Farrar CR (2014). A local ultrasonic approach to delamination detection in composite structures, International Design & Engineering Technical Conferences and Computers & Information in Engineering Conference, Buffalo, New York, from 17-08-2014 to 20-08-2014.

Smart structures

Keywords: Multi-physics continua; Piezoelectricity; Complete electro-mechanical coupling; PZT transducers.

Description: Many formulations available in literature fail to deliver a consistent description of the mechanical and electrical behaviour of the structure as they rely on an assumed linear dependence of the electric potential on the transducer’s thickness that is proved not to be adequate to represent the potential electric energy. This leads to the development of nonlinear structural formulations able to fully encompass a complete coupling between the electrical/thermal and the mechanical part of multi-physics transducers, in view of achieving enhanced performances in terms of actuation, sensing and energy harvesting capabilities. The nonlinear nature of the electric potential’s variation across the thickness which typically characterizes the mechanical state of piezoelectric transducers leads, via constitutive equations, to a higher-order description of the structure’s kinematics. The virtual work theorem is then enforced to derive the balance equations. A major element of novelty of such approach is that it allows an easy derivation of ad-hoc multi-physics structural formulations which feature the degree of nonlinearity required to accurately describe the electro-mechanical state experienced by structural components as a consequence of their particular shape and application.

Related journal and conference papers:

  • Pasquali M, Gaudenzi P (2012). A nonlinear formulation of piezoelectric plates. Journal of Intelligent Material Systems and Structures, vol. 23, pp. 1713-1723.

  • Pasquali M, Gaudenzi P (2015). A nonlinear formulation of piezoelectric shells with complete electro-mechanical coupling. Meccanica, vol. 50, pp. 2471-2486, ISSN: 1572-9648.

  • Pasquali M, Gaudenzi P (2016). A nonlinear piezoelectric shell model: Theoretical and numerical considerations. Journal of Intelligent Material Systems and Structures, vol. 27, pp.724-742.

  • Memmolo V, Elahi H, Eugeni M, Monaco E, Ricci F, Pasquali M, Gaudenzi P (2019). Experimental and Numerical Investigation of PZT Response in Composite Structures with Variable Degradation Levels. Journal of Materials Engineering and Performance, vol 28, pp. 3239-3246.

  • Pasquali M, Gaudenzi P (2012). Numerical effects of piezoelectricity within a 2D beam model: a numerical study, Paper no. ICAST2011-017, 22nd International Conference on Adaptive Structures and Technologies, Corfu, Greece, from 10-10-2011 to 12-10-2011.

  • Pasquali M, Gaudenzi P (2014). A nonlinear formulation of piezoelectric shells with complete electro-mechanical coupling, Paper no. ICAST2014-060, 25th International Conference on Adaptive Structures and Technologies, The Hague, The Netherlands, from 06-10-2014 to 08-10-2014.

Dynamc material characterization

Keywords: Thermo-mechanical stresses; Composite materials; Isocoric heating; Particle beam impacts; Shock waves; Spallation; EOS.

Description: Assessment of the dynamic response of material samples exposed to particle beam impacts. This stream of research sees my participation (in the frame of the collaboration between the Department of Mechanical and Aerospace Engineering of “La Sapienza” University of Rome and the Mechanical Materials and Engineering (MME) Group of CERN’s Engineering Department) as Scientific Secretary of the MultiMat experiment (also known as HRMT-36), a two million euros project partially funded by the European Union’s Horizon 2020 Research and Innovation programme under the Grant Agreement No. 730871. The main goal of the experiment is to derive and extend the constitutive models of the tested materials by benchmarking experimental data - collected online by an extensive acquisition system and by non-destructive post-mortem examination - against numerical simulations. The insight gained in the constitutive behaviour of the analysed materials is envisioned to be used to improve the design and performances of all devices interacting with particle beams. At the same time, such knowledge is of great interest also for space applications, as similar extreme phenomena (like shock waves, changes of phase, spallation, micro jetting, etc…) can also characterize hyper-velocity impacts occurring between space debris and space structures (satellites, space crafts, etc…). The role of Scientific Secretary sees the participation to the experiment design, implementation and data post-processing, the latter being characterized by the supervision of numerous Master and PhD students.

Related journal and conference papers:

  • Pasquali M, Bertarelli A, Accettura C et Al. (2019). Dynamic Response of Advanced Materials Impacted by Particle Beams: The MultiMat Experiment. Journal of Dynamic Behavior of Materials, vol. 5, pp. 266-295.

  • Abada A, Abbrescia M, Abdus Salam SS et Al. (2019). FCC Physics Opportunities: Future Circular Collider Conceptual Design Report Volume 1. European Physical Journal C, vol. 79, 474.

  • Abada A, Abbrescia M, Abdus Salam SS et Al. (2019). FCC-ee: The Lepton Collider: Future Circular Collider Conceptual Design Report Volume 2. European Physical Journal: Special Topics, vol. 228, pp. 261-623.

  • Abada A, Abbrescia M, Abdus Salam SS et Al. (2019). FCC-hh: The Hadron Collider: Future Circular Collider Conceptual Design Report Volume 3. European Physical Journal: Special Topics, vol. 228, pp. 755-1107.

  • Abada A, Abbrescia M, Abdus Salam SS et Al. (2019). HE-LHC: The High-Energy Large Hadron Collider: Future Circular Collider Conceptual Design Report Volume 4. European Physical Journal: Special Topics, vol. 228, pp. 1109-1382.

  • Portelli M, Bertarelli, A, Carra F, Pasquali M, Sammut N, Mollicone P (2019). Numerical and experimental benchmarking of the dynamic response of SiC and TZM specimens in the MultiMat experiment. Mechanics of Materials, vol. 138, 103169.

  • Pasquali M, Bertarelli A, Dallocchio A et Al. (2017). The HRMT-36 Experiment (MultiMat), 1st Workshop of ARIES WP17 PowerMat, Turin, Italy, from 27-11-2017 to 28-11- 2017.

  • Pasquali M (2018). Dynamic testing and characterization of advanced materials in the Multimat experiment at HiRadMat, 1st ARIES annual meeting, Riga, Latvia, from 22-05-2018 to 25-05-2018.

  • Pasquali M (2018). Update on the MultiMat experiment: status, outcome and perspectives, 1st Annual Meeting of the ARIES WP17, Valletta, Malta, from 28-10-2018 to 30-10-2018.

  • Bertarelli A, Accettura C, Berthomé E et Al. (2018). Dynamic testing and characterization of advanced materials in a new experiment at CERN HiRadMat facility, Paper No. IPAC2018-WEPMF071, 9th International particle accelerator Conference, Vancouver, BC, Canada, from 29-04-2018 to 4-05-2018.

  • Carra F, Bertarelli A, Gobbi G at Al. (2019). Mechanical robustness of Hl-LHC Collimator Designs, Paper No. IPAC2019-MOPTS091, 10th International particle accelerator Conference, Melbourne, Australia, from 19-05-2019 to 24-05-2019.

  • Pasquali M, Bertarelli A, Accettura C. et Al. (2019). Dynamic response of advanced materials impacted by particles beams: the Multimat experiment, 24th DYMAT Technical Meeting - Temperature dependence of material behaviour at high strain rate, Stresa, Italy, from 9-09-2019 to 11-09-2019.

  • Markiewicz T, Bong E, Keller L et Al. (2019). Design, construction, and beam tests of a rotatable collimator prototype for high-intensity and high-energy. Physical Review Accelerators and Beams, vol. 22, pp. 123002-1 to 123002-15.

  • Carra F, Bertarelli A, Gobbi G et Al. (2019). Mechanical robustness of HL-LHC collimator designs. In Journal of Physics: Conference Series, vol. 1350, pp. 012083-1 to 012083-8.

  • Furness T, Williamson J, Fletcher S et Al. (2020). In-situ displacement measurement for use in LHC collimators. Proceedings of the 20th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2020, Virtual Conference, from 8/06/2020 to 12/06/2020.

Additive manufacturing

Keywords: 3D metal printing; Selective laser melting; Topology optimization; Design for additive manufacturing, Small satellites.

Description: Investigation of AM-induced evolution of the design process for small satellites, posing particular attention in identifying the optimal design strategies to propose an innovative structural configuration for the CubeSat class of satellites able to minimize the system complexity via parts reduction and the integration of subsystems through an innovative assembly configuration. The study encompasses the optimization of the design of parts and of their supports to reduce print-induced residual stresses and distortions. The research is carried out in the frame of the collaboration between the Department of Mechanical and Aerospace Engineering of “La Sapienza” University of Rome and the Mechanical Materials and Engineering (MME) Group of CERN’s Engineering Department, in which I act in the role of Additive Manufacturing Ambassador. In fact, the reduction of mass via topology optimization enabled by 3D printing technologies is a desirable feature for both aerospace structures, where the need for lightweight components is a well-know requirement, and for particles beam intercepting devices, as mass is proportional to the thermo-mechanical loads associated to radiation exposure. The study also delivers a substantial insight in the design of parts and of their supports to reduce heat-induced residual stresses and distortions that often undermine the effective usability of manufactured components both in the aerospace and in the particle accelerators field.

Related journal and conference papers:

  • Gaudenzi P, Atek S, Cardini V, Eugeni M, Graterol Nisi G, Lampani L, Pasquali M, Pollice L (2018). Revisiting the configuration of small satellites structures in the framework of 3D Additive Manufacturing (2018). Acta Astronautica, vol. 146, pp. 249-258.

  • Graterol Nisi G, Eugeni M, Cardini V et Al. (2018). Realization of smart components with embedded electronics by using fused filament fabrication, 15th European Conference on Spacecraft Structures, materials and Environmental Testing, ESA-ESTEC, Noordwijk, The Netherlands, from 28-05-2018 to 1-06-2018.