Skip to main content

Improving the crashworthiness of composite transportation structures

Periodic Reporting for period 2 - ICONIC (Improving the crashworthiness of composite transportation structures)

Reporting period: 2018-10-01 to 2020-09-30

The European aerospace, automotive, and rail industries are committed to improving their energy efficiency to meet targets set within the EU’s climate, energy and transport policies. This has motivated the increased utilisation of lightweight composite materials in transportation structures in lieu of heavier metallics. In doing so, these industries are mandated to attain or exceed the same level of crash performance achieved with metals but at significantly lower weight. This is a challenging goal and the central aim of ICONIC was to develop a critical mass of research and engineering leaders with a world-leading capability in the design of lightweight aeronautical, automotive and rail transportation composite structures with superior crashworthiness. These challenges were addressed by bringing together 15 early stage researchers (ESRs), recruited from an international talent pool, in an innovative, integrated, multiscale and multidisciplinary research and skills development programme that went beyond the state of the art. The ICONIC research programme, adopted a multiscale approach, ranging from material development and characterisation at the nano- and microscales; high fidelity numerical modelling of composite damage at the micro and mesoscales; through to the structural design and optimisation of representative structures (macrosale) with superior energy-absorption and crashworthiness. The influence of processing parameters on structural performance, ageing, sustainability and life-cycle costs were also addressed within this network.

ICONIC has advanced our understanding of the energy absorbing mechanisms of non-metallic fibre reinforced polymer composites and has provided a number of novel technologies which exploit such mechanisms to deliver maximum crashworthiness. These include (i) the development of new composite materials with high energy absorbing capacity, (ii) new computational tools for the virtual crash testing of structures made from these candidate materials, (iii) improved physical testing methods for the accurate characterisation of these materials to generate basic data required for the computation modelling, and (iv) new design concepts for energy absorbing transportation structures.
ICONIC addressed five primary technical objectives related to the advancement of the state-of-the-art in enhancing the crashworthiness of future lightweight non-metallic transportation structures. The first objective was to develop new composite materials with architectures and constituents appropriate for their design function, whilst delivering superior energy absorbing capability.

For large load-bearing structures, new 3D woven fibre-based preforms were manufactured and shown to have good energy absorbing capacity. Polymers enhanced with graphene oxide nanoparticles, self-reinforced composites, where the reinforcement and the matrix are made of the same material, but with distinct molecular structures, where also developed and their energy absorption characteristics assessed. A thin-ply laminate made from discontinuous tape-based composites hot-pressed with a thermoplastic binder was developed and shown to have good energy absorbing capability.

The means to reliably assess and evaluate these materials for crashworthy structures formed the basis of the second objective. New testing methods were developed to assess the materials’ behaviour under different strain-rates. One approach was based on a dynamic tensile testing machine while another made use of a Split Hopkinson Pressure Bar.

An ability to simulate the complex response of these materials in a crash scenario permits analysts and structural engineers to exploit them in their structural designs without the need of extensive and expensive physical testing. This pursuit formed the third objective. New multiscale modelling methodologies were developed which accounted for intrinsic stochastic variations in the materials. Their behaviour under different loading rates was also captured. A new formulation which is an order of magnitude faster than the finite element method was also extended to capture the response of composites to high impact loading.

The fourth objective concerned the design of energy absorbing structural joints. Previous work had shown that joints in aircraft structures may act as energy absorbers. One project developed a new tension-loaded energy-absorbing joint for a fuselage while another developed a new composite-metallic interlocking joint.

A fifth objective focused on delivering technologies for immediate utilisation by industry partners. One project delivered a new methodology for modelling automotive structural components specifically designed to protect passengers in a crash. Another project used the ‘building block’ approach used in the certification of composite aerostructures, and adapted it for composite automotive structures.

In addition to these technical objectives, each early stage researcher (ESR) was engaged in an individually-tailored training and secondment programme which combined aspects of technical and transferable skills development. Moreover, each researcher was also enrolled on a PhD programme and a number have since graduated.

All ESRs were particularly active in the dissemination of results and associated activities, promoting ICONIC and the EU Horizon 2020 MSCA programme through websites, magazines, newspapers, TV, MSCA events, social media, visiting schools and universities. An ICONIC outreach pack (including two videos) was prepared for distribution and exhibition at conferences, trade fairs, workshops and meetings. A number of journal papers and conference contributions were published.

No gender-related barriers were encountered, in the recruitment, management, training and research programme. Gender equality was promoted in the job advertisements for all ICONIC ESR positions, with female candidates being prioritised when candidates had ex aequo qualifications.
The previous section outlined the substantial innovative developments that were achieved through the contributions of each ESR, where each research programme aimed to progress beyond the state-of-the-art. The further exploitation of lightweight structural materials will facilitate reductions in environmental impact and fibre-reinforced polymers (FRPs) are becoming more ubiquitous due to their superior specific strength and stiffness. The use of FRPs is prevalent in the latest generation of passenger aircraft, high performance automotive vehicles and maritime vessels. As these materials find even wider exploitation in transportation, ensuring a level of crashworthiness which is, at least, commensurate to that of comparable structures made from metallics, which have excellent energy absorption/crashworthiness capability, remains a challenge. The research outcomes of this project have led to the design of new material architectures with enhanced energy absorbing capacity, improved high fidelity computational tools to facilitate better structural designs, and better testing methods at quasi-static and dynamic loading rates.
3D woven textile preform architectures
Different steps in material model development
Dynamic testing set-up
Axial stress: (Left) CUF and (right) refined ABAQUS 3D model
Multiscale computational approach
Mechanical behaviour of satin weave carbon/epoxy laminate in compression at different strain rates
Newly developed fixure
Compact tension test simulation
FE model of pin bearing test
Schematic description of TBDC material and equivalent laminate model
SEM images of nylon 6 nanocomposites
Predicted Unit Cell geometry of 3D woven composite
Modulus and Ultimate Tensile Strength of consolidated laminates with compaction temperature
Fastener-less joint mould-in manufacturing method
Finite element model of compression plate test.