Modelling of the low-impulse blast behaviour of fibre–metal laminates based on different aluminium alloys

A parametric study has been undertaken in order to investigate the influence of the properties of the aluminium alloy on the blast response of fibre–metal laminates (FMLs). The finite element (FE) models have been developed and validated using experimental data from tests on FMLs based on a 2024-O aluminium alloy and a woven glass–fibre/polypropylene composite (GFPP). A vectorized user material subroutine (VUMAT) was employed to define Hashin’s 3D rate-dependant damage constitutive model of the GFPP. Using the validated models, a parametric study has been carried out to investigate the blast resistance of FML panels based on the four aluminium alloys, namely 2024-O, 2024-T3, 6061-T6 and 7075-T6. It has been shown that there is an approximation linear relationship between the dimensionless back face displacement and the dimensionless impulse for all aluminium alloys investigated here. It has also shown that the residual displacement of back surface of the FML panels and the internal debonding are dependent on the yield strength of the aluminium alloy

Low-impulse blast behaviour of fibre-metal laminates

This paper presents three dimensional (3D) finite element (FE) models of the low-impulse localised blast loading response of fibre-metal laminates (FMLs) based on an 2024-O aluminium alloy and a woven glass-fibre/polypropylene composite (GFPP). A vectorized user material subroutine (VUMAT) is developed to define the mechanical constitutive behaviour and Hashin’s 3D failure criteria incorporating strain-rate effects in the GFPP. In order to apply localised blast loading, a user subroutine VDLOAD is used to model the pressure distribution over the exposed area of the plate. These subroutines are implemented into the commercial finite element code ABAQUS/Explicit to model the deformation and failure mechanisms in FMLs. The FE models consider FMLs based on various stacking configurations. Both the transient and permanent displacements of the laminates are investigated. Good correlation is obtained between the measured experimental and numerical displacements, the panel deformations and failure modes. By using the validated models, parametric studies can be carried out to optimise the blast resistance of FMLs based on a range of stacking sequences and layer thicknesses

Low- and high-fidelity modeling of sandwich-structured composite response to bird strike, as tools for a digital-twin-assisted damage diagnosis

EU, H2020 Smart, Green and Integrated Transport, Aviation program under the acronym EXTREME (Project reference 636549)

Μελέτη της συμπεριφοράς αεροπορικών κατασκευών σε συνθήκες έκρηξης

The scope of this project is the realization of composite and hybrid sub-aerostructures which exhibit superior blast performance compared to reference composite and hybrid substructures. The scope will be fulfilled with minimum weight penalty. Within the scope of this work is to provide a roadmap for the integration of explicit hardening measures for blast in future aerospace structural components. In the case of blast loading, the proposed methodology for achieving these aims involves vulnerability analysis of the composite and the hybrid substructures (scaled fuselage substructure). The vulnerability analysis will be based on numerical results, obtained by the systematic, analysis of the coupled blast/structural problem. The aims and objectives of the present project can be summarized as follows: • Development of numerical models and their correlation against experimental results. • Development of numerical tools for blast vulnerability analysis of composite and hybrid aeronautic structures. • Blast vulnerability map of composite and hybrid scaled fuselage substructure for different charge locations. • Explicit blast hardening strategies of composite and hybrid aerostructures by design and by novel materials

Structural Analysis of a Composite Passenger Seat for the Case of an Aircraft Emergency Landing

Aviation authorities require, from aircraft seat manufacturers, specific performance metrics that maximize the occupants’ chances of survival in the case of an emergency landing and allow for the safe evacuation of the aircraft cabin. Therefore, aircraft seats must comply with specific requirements with respect to their structural integrity and potential occupant injuries, which are certified through the conduction of costly, full-scale tests. To reduce certification costs, computer-aided methods such as finite element analysis can simulate and predict the responses of different seat configuration concepts and potentially save time and development costs. This work presents one of the major steps of an aircraft seat development, which is the design and study of preliminary design concepts, whose structural and biomechanical response will determine whether the concept seat model is approved for the next steps of development. More specifically, a three-occupant aircraft seat configuration is studied for crash landing load cases and is subjected to modification iterations from a baseline design to a composite one for its structural performance, its weight reduction and the reduction of forces transmitted to the passengers

An Impact Localization Solution Using Embedded Intelligence—Methodology and Experimental Verification via a Resource-Constrained IoT Device

Recent advances both in hardware and software have facilitated the embedded intelligence (EI) research field, and enabled machine learning and decision-making integration in resource-scarce IoT devices and systems, realizing “conscious” and self-explanatory objects (smart objects). In the context of the broad use of WSNs in advanced IoT applications, this is the first work to provide an extreme-edge system, to address structural health monitoring (SHM) on polymethyl methacrylate (PPMA) thin-plate. To the best of our knowledge, state-of-the-art solutions primarily utilize impact positioning methods based on the time of arrival of the stress wave, while in the last decade machine learning data analysis has been performed, by more expensive and resource-abundant equipment than general/development purpose IoT devices, both for the collection and the inference stages of the monitoring system. In contrast to the existing systems, we propose a methodology and a system, implemented by a low-cost device, with the benefit of performing an online and on-device impact localization service from an agnostic perspective, regarding the material and the sensors’ location (as none of those attributes are used). Thus, a design of experiments and the corresponding methodology to build an experimental time-series dataset for impact detection and localization is proposed, using ceramic piezoelectric transducers (PZTs). The system is excited with a steel ball, varying the height from which it is released. Based on TinyML technology for embedding intelligence in low-power devices, we implement and validate random forest and shallow neural network models to localize in real-time (less than 400 ms latency) any occurring impacts on the structure, achieving higher than 90% accuracy

Assessment of pressure waves generated by explosive loading

In the present study the estimation of the blast wave by two types of finite element methods is investigated: Eulerian multi-material modeling and pure Lagrangian. The main goal is to compare and study their ability to predict the clearing effect during blast. Element shape and improvements on the codes are also considered. For the Lagrangian finite element models the load is applied by using an empirical method, deriving from databases, for the time-spatial distribution of the pressure profiles. In the ideal case of the above method the blast load is applied as an equivalent triangular pulse to represent the decay of the incident and reflected pressure. The implementation of this method in LS-DYNA is improved and takes a more realistic approach, assuming an exponential decay of the pressure with time. In the case of the Eulerian models the influence of the shape of elements and its influence on the incident and reflected pressure in three types of simulations, using rectangular, cylindrical and spherical grid of air, were investigated. An analytical method to predict impulse is used to compare with the numerical and experimental results. The Eulerian models provide results closer to the experimental. Specifically, the cylindrical grid of air gives better results in comparison with the other methods

The blast response of composite and fiber-metal laminate materials

The blast behavior of composite materials is a subject of growing importance, generally due to the ever-present threat of subversive activity. The aircraft industry will employ composite materials more frequently in the future as they are lightweight, offer superior fatigue resistance, life cycle cost savings, fuel efficiency and (in some cases) improved impact properties when compared with monolithic metals, such as aluminum alloy. However, little is known about their response to blast loading. This chapter provides a brief introduction to the characteristics of explosions and demonstrates that a careful assessment of the blast loading scenarios for each aircraft design is required, as the loading is complicated by the degree of confinement, geometric variations, and the multiplicity of potential explosion scenarios. Various blast protection paradigms are reported, with the containment strategy being most relevant for aircraft design at present. Recent experimental and numerical investigations concerning the blast behavior of aerospace composites are reported. The response of fiber-reinforced polymers, polymeric sandwich panels, and multilayered fiber-metal laminate structures are discussed in the context of the aerospace environment