SI&HM Lecture Series - Feb-May 2021

Seminar 1
Date: 19/02/2021
Speaker: Professor Jan Zeman, Czech Technical Univeristy, Prague. 
Title:  Designing Optimal Reinforcement for High-performance Composite Tubes
Abstract:  Fuelled by their excellent stiffness-to-weight ratio and the availability of mature manufacturing technologies, filament wound carbon fiber reinforced polymers represent ideal materials for thin-walled laminate structures. However, their strong anisotropy reduces structural resistance to wall instabilities under shear and buckling. Increasing laminate thickness degrades weight and structural efficiencies and the application of a dense internal core is often uneconomical and labor-intensive. In this contribution, we introduce a convex linear semidefinite programming formulation for truss topology optimization to design an efficient non-uniform lattice-like internal structure. The internal structure not only reduces the effect of wall instabilities, mirrored in the increase of the fundamental free-vibration eigenfrequency, but also keeps weight low, secures manufacturability using conventional three-dimensional printers, and withstands the loads induced during the production process. We showcase a fully-automatic procedure in detail for the design, prototype manufacturing, and verification of a simply-supported composite machine tool component, including validation with roving hammer tests. The results confirm that the 3D-printed optimized internal structure almost doubles the fundamental free-vibration eigenfrequency, allowing to increase working frequency of the machine tool, even though the ratio between elastic properties of the carbon composite and the ABS polymer used for 3D printing exceeds two orders of magnitude.
Seminar 2
Date: 12/03/2021
Speaker: Dr Hanfei Mei, University of South Carolina, Columbia, USA.
Title: Guided-Wave SHM and NDE of Composite Structures: Modeling and Experiments
Abstract: The extensive use of composites in aerospace structures has posed new challenges for implementing effective structural health monitoring (SHM) and nondestructive evaluation (NDE) techniques due to the general anisotropic behavior and complex damage scenarios in composites. This seminar will address SHM and NDE of composite structures using ultrasonic guided waves. New and efficient simulation methods have been theoretically developed and experimentally validated for the prediction of how guided waves interact with damage in safety-critical composite structures. A semi-analytical finite element (SAFE) approach is presented to calculate guided-wave dispersion curves in composites. A user-friendly software ‘LAMSS COMPOSITES’ is developed to retrieve and display the dispersion curves from the guided wave database. To predict guided wave excitation, the SAFE approach is employed to model 1D and 2D wave propagation. Damping effects on guided wave propagation are also considered. A hybrid global-local (HGL) approach coupling the SAFE guided-wave modeling with an efficient small-size local FEM is developed to model guided wave interaction with damage in composites. A predictive tool WFR-2D-Composites is developed as a general description of wave generation, propagation, interaction with damage. Finally, a novel angle beam NDE methodology has been developed for guided-wave detection and sizing of delamination and actual impact damage in composites.
Seminar 3
Date: 26/03/2021
Speaker: Professor Sotirios Grammatikos, Norwegian University of Science and Technology. 
Title: On the durability and lifetime prediction of fibre-reinforced polymer composites
Abstract: Whilst the design, manufacturing and material constituents of structural fibre-reinforced polymer composites have been largely improved the past years, there are still major issues pertaining to degradation especially in challenging operational conditions such as in the offshore. Coupled environmental aging with service-induced degradation lead to significant deterioration during operation. Moisture, rain & sand erosion, UV radiation, lightning strikes, impact damage as well as thermomechanical fatigue are the major causes of degradation. As the effects of the aforementioned conditions (which in most cases act in combination) are not always fully understood, unexpected behavior during service often results in structural failures. This undoubtedly reduces the reliability of composites as structural elements making investors and stakeholders reticent in long-term investing in lightweight structures. A complete analysis of the drawbacks of composites that hinder them from being fully adopted by the industry and especially the infrastructure sector will be presented along with ideas and solutions to overcome such obstacles pertaining to nanotechnology, modelling tools and advanced non-destructive testing.
Seminar 4:
Date: 09/04/2021
Speaker: Professor Stephen Hallett, University of Bristol. 
Title: Length-scale and other challenges in modelling composites structural failure
Abstract: Length-scale and other challenges in modelling composites structural failure Composites structural or macro-scale failure is often driven by small, meso-scale features. Common industrial practise is to use homogenised or smeared-property models. The macro-scale failure, initiating from the meso-scale features, can however often not be predicted using smeared, homogenised models. Further, the meso-scale features are often a function of the part manufacturing processes. Here, a range of cases demonstrating these points and the modelling strategies for high quality meso-scale analysis will be presented. The talk will end with some recent advances in modelling and multi-scale techniques to reduce the computational burden, with a view to reaching structural scale predictions.
Seminar 5: 
Date: 16/04/2021
Speaker: Dr Mazdak Ghajari, Imperial College London, Dyson School of Design Engineering 
Title: computational modelling of traumatic brain injury
Abstract: Traumatic brain injury (TBI) is the leading cause of death and disability in young adults. It is caused by head exposure to impact and blast loading in road traffic collisions, falls, sporting collisions and military incidents. TBI is a mechanical insult, and understanding it requires interdisciplinary research across medicine and engineering. Here I will present our collaborative work across faculties of engineering and medicine on the development of high-fidelity computational models of TBI biomechanics and their validation against data from live human imaging and preclinical models of TBI. I will show applications of the FEA and SPH models of TBI to the prediction of brain/skull relative motion and post-traumatic pathologies, including diffuse axonal injury, neuroinflammation and chronic traumatic encephalopathy.
Seminar 6: 
Date: 23/04/2021
Speaker: Oscar d’Almeida, Research & Technology Manager at Safran Tech (Safran Corporate Research Center)
Title: SHM and value creation for aeronautics in evolving environment
Abstract: Aeronautic structural components are required to be lifecycle managed under the damage tolerant principle and the safe-life, while the airworthiness is maintained through the process of scheduled inspection, and if needed repair or replacement. In that sense, the scheduled inspection is addressed by non-destructive inspection (NDI) techniques compliant with MSG3 document requirement. However, this current practice can be cost consuming, which is mainly due to the high degree of human interaction, and the fact that the structural components may need to be disassembled because of difficult-to-reach locations. To reduce the inspection cost, aeronautic OEMs and stakeholders are looking deeply to the concept of Structural Health Monitoring (SHM). The basic concept of SHM is to acquire and analyze data from on-board sensors to determine the health of a structure and enable condition-based maintenance. To reach such a goal, SHM has to be viable, reliable and to deal with validation and certification concerns. With society's needs for safer, more efficient and environmentally friendly air transport, there is a need of evolving global approach for SHM with all stakeholders and for the whole lifecycle of equipment and structures. The presentation will discuss how this global approach could help to create value while being compliant with safety and sustainability requirements.
Seminar 7: 
Date: 30/04/2021
Speaker: Professor Santiago Hernandez, the University of Coruna, Spain
Title: Structural design and optimization of hypersonic aircrafts. The STRATOFLY-MR3 vehicle
Abstract: The design of the STRATOFLY vehicle is the main objective of a European Union research project stated in 2018. The mission of the vehicle is to be able to fly 20000 km with no stops in about 3 hours, reacting a maximum wind speed of Mach 8 during the trajectory.The STRATOFLY initiative can be seen as a confirmation of previous European Union efforts on the design of hypersonic vehicles for commercial aviation as LAPCAT-MR2 and more as the MORE&LESS project that deals also with supersonic aircrafts.

Several initiatives on the topic of supersonic an hypersonic aircrafts have also started in recent years in Japan and USA, Boeing has proposed the wave raider X-51A able to fly in to Mach 5 and Boom Technologies is also involved in the creation of the XB-1 supersonic jet.A characteristic of many new vehicles under design is the change in the fuselage shape, substituting the traditional barrel like by the so called double bubble geometry in which the cross section is composed by the union of two circles or ovals. This lecture will describe the structural design of the STRATOFLY-MR3 that exploits extensively the idea of multi-bubble configuration and the loops of single and multi-objective formulations worked out aimed to obtain a definition of the vehicle that takes into the account vehicle mass and manufacturing complexity as conflicting objective functions.

Seminar 8: 
Date: 21/05/2021
Speaker: Dr Seth Kessler, Metis Design Corporation (USA). 
Title: Preparing Structural Health Monitoring Systems for Real-Life Applications
Abstract: Damage tolerant design for aircraft traditionally requires periodic tear-down and manual NDT by trained inspectors at fixed flight-hour intervals to determine if flaws have grown to a detectable size. These intervals are set to minimize risk, and ensure multiple NDT opportunities to detect a flaw before it could achieve a critical size. While this approach is extremely safe, its conservatism can be quite costly to the life-cycle costs of the aircraft due to the inspection process and associated time out of service for preventative maintenance. For several decades, researchers have been investigating structural health monitoring (SHM) systems as a cost-effective compliment to manual NDT, leading to condition based maintenance (CBM) where targeted manual inspection would be triggered “as needed” based on frequent automated inspections rather than on a fixed schedule. While SHM sensors, hardware and algorithms have matured sufficiently to be taken seriously in the past few years, several roadblocks still remain before these systems can be introduced into military or commercial service. This presentation will highlight the key factors that need to be addressed before an SHM system can be fielded. First, since the SHM system is permanently installed within the aircraft, hardware and sensors much meet environmental and electrical airworthiness standards. Second, since sensors generally need to be intimately bonded to the structure being inspected, formal installation processes must be defined and mechanical loading and durability requirements must be met. Finally, the detection performance (often referred to as the probability of detection or POD) of the SHM system must able to be quantified not only at the time of installation, but throughout its designed life. Examples of each of these types of qualification tests will be illustrated for piezoelectric guided wave based and carbon nanotube (CNT) potential drop based SHM systems developed at Metis Design Corporation.