Report : D 121 – Workshop on Energy Absorbing Structures and Materials in Railway and Aerospace July 3 , 2006

Crashworthiness studies are in high demand for designing transportation systems. Energy absorption capability in vehicle collisions is an important parameter for the development of passive safety systems dealing with the protection of passengers and cargo departments in the event of an accident. Protective structures, which contribute significantly to the crashworthiness capability of automotive structures, are composed of thin-walled structural elements of various cross-section shapes and sizes. The implementation of the Laboratory of Manufacturing Technology of NTUA to the field of Crashworthiness, over the past 30 years, is sum up in an extensive theoretical and experimental research work related to the axial and oblique loading of thin-walled structural components made of various materials, i.e. metals, polymers, composites and bi-materials, exploring steady-state collapse mechanisms that enable high energy absorption capability for the collided structures. The whole activities are divided into three periods: (a) During the 1 period (1978-1988) the following items were covered: • Static and dynamic axial collapse of thin-walled tubes made of commercial metals, i.e. low-carbon steel and aluminium alloys. Thin shells of various geometries, i.e. cylindrical and square tubes, cylindrical and square frusta, prismatic polygonal tubes were tested under different strain rates ranging between 4×10 3×10 s in the press, drophammer and impactor facilities of the Laboratory. The effect of specimen geometry on the energy absorption capability was investigated by varying the cross-sectional dimensions, wall thickness and length of shell, providing in this manner with a complete map with the failure mechanisms developed for each material and tube geometry. • Establishing safe theoretical design criteria on the mechanics of crumpling. Simplified theoretical models, qualified in the area of the structural plasticity, were developed to describe the crashworthy deformation of the geometries tested. The classical models for cylindrical tubes, i.e. Alexander’s model on the extensible collapse mode and Johnson’s model for the inextensional one, were extended and generalized to fill all design requirements. • Testing of thin-walled rigid polyvinylchloride (PVC) tubes, subjected to axial compressive loading. Except of cylindrical or square tubes, new shapes in the form of top-hat and double-hat cross-sections were also examined. PVC was selected because of its low specific gravity and thermoplastic properties. Furthermore, collapsed PVC tubes immersed in boiling water immediately recover almost all of their initial form and reveal the mechanism governing the plastic collapse, clearly showing the various hinge lines Advanced Passive Safety Network APSN 15 Report: D121 – Workshop on Energy Absorbing Structures and Materials in Railway and Aerospace where severe plastic deformation took place, contributing, in this manner, to the verification of the above-mentioned theoretical models. • Testing under axial loading of metal and PVC cylindrical tubes with geometrical discontinuities in the form of internal axial or external circumferential grooves of constant depth and establishing relevant simplified theoretical analysis. • Testing of steel cylindrical thin-walled tubes, subjected to bending loading as cantilever beams and establishing a relevant theoretical model based on the principles of structural plasticity. The flexural tests were conducted on a specially designed testing machine. (b) During the 2 period (1989-1996), the Laboratory of Manufacturing Technology switched to new research orientations, related mainly to the crashworthy behaviour of composite materials. Apart from significant functional and economic benefits that include amongst others increased strength and toughness features, considerable weight reduction and reduced fuel consumption, composites have been found to provide improved level of structural vehicle crashworthiness characteristics. The research activities were focused on the following items: • Extensive static and dynamic axial loading of thin-walled tubes made of FRP (fiberglass reinforced plastic) composite material, , with similar geometries and loading conditions to those for the conventional materials(metals and polymers) of the preceding period. Thin-walled composite structures, on the contrary to conventional materials, are not deformed plastically when subjected to compressive load, but they collapse at various modes featured by extensive micro-cracking development as the predominant failure mechanism. These failure modes depend on the shell geometry and laminate material properties (fibre content, stacking sequence, etc.). Among the various collapse modes, only the progressive stable crushing mode, which is characterized by a relatively low load uniformity index and high average crushing load, was associated with high absorption of crash energy. • Testing of cylindrical thin-walled tubes, subjected to bending loading as cantilever beams made of same composite material as above, under the same flexural conditions of steel components (see 1 period above). The effect of various end restrains (clamping conditions) on the deformation ability of the beam was also investigated. • Extensive static and dynamic axial loading of sandwich composite structures, typically consisting of FRP laminate faces enclosing polymeric foam, with or without internal reinforcements in the form of tubular inserts or corrugations bonded to both the face plates. Such structures are proved excellent collapsible energy absorbers, which could ensure increased level of crashworthiness in various types of transportation vehicles (e.g. cars, buses, trucks, containers and rail vehicle cabs). • Application of Finite Elements Methods (FEM) to the numerical simulation of the deformation of thin-walled components made of conventional materials (metals and polymeric materials). The “explicit” FE Code LS-DYNA was used to simulate the collapse mechanisms of all geometries tested (see above for 1 period). This fully vectorized, large deformation structural dynamics code has been developed for analyzing transient dynamic response of 3D solids and structures, employing, as an explicit code, the central-difference method in order to solve the equation of motion and possessing simultaneously many advantages that are critical for efficient and accurate analyses of crashes. The collapse procedure was successfully simulated within a reasonable amount of CPU time and the obtained numerical results were found to be in good agreement with actual experimental data from small-scale models. Advanced Passive Safety Network APSN 16 Report: D121 – Workshop on Energy Absorbing Structures and Materials in Railway and Aerospace (c) During the 3 period (1997), the research activities of the Laboratory of Manufacturing Technology were concentrated on the following topics: • Extension of the axial loading (static and dynamic) to thin-walled structural components made of other types of composite materials (CFRP and aramid laminates in which the reinforcing fibre layers were in the form of woven fabric impregnated in epoxy resin). • Edgewise and flatwise loading of sandwich panels and bending of single strips. • Development of a new testing devise to characterize the splaying ability of a composite material under flexural conditions (curling test). • Extensive application of simulation techniques (FEM) to the analysis of the crashworthy behaviour of any structural type tested (thin-walled composite and thick-walled sandwich structures) under any loading conditions (axial collapse, bending, side impact, etc.) From theoretical and experimental research activities point of view, the Laboratory of Manufacturing Technology participates into a great number of research projects mainly with industrial international cooperation, qualified in the area of the structural plasticity pertaining to the crashworthy deformation of thin-wall structures of metals, polymers, composites and for the application in the automotive, rail and air craft industry. Some of them are listed below: • “Predictive techniques for the analysis and design of composite materials and structures to withstand impulsive loading” (BRITE R I1B-0215-C(GDF) (Partners: Claudius Dornier, DSM, ΒΑeSEMA, Univ. of Gent) • “Hybrid composite structures for crashworthy bodyshells, containers and safe transportation structuresHYCOTRANS” (BRITE/EURAM BE 963027, ERBBRPRCT96-0257) (Partners: Advanced Railway Research Centre Sheffield, Costaferroviaria Spa, D’ Appolonia, Ifor Williams Trailers, APME, CETMA, Institut für Kunstofftechnik RWTH Aachen, University of Perugia). • “Design of advanced composite production processes for the systematic manufacture of very large monocoque hybrid composite sandwich structures for the transportation sectorHYCOPROD” (GROWTH/G3RD-CT-1999-00060) (Partners: Advanced Railway Centre Sheffield, Costaferroviaria Spa, ΒΟΧ Modul, Ifor Williams Trailers, Hübner, Irizar, Ιnstitut für Kunstofftechnik RWTH Aachen, D’ Appolonia, TNO, Ashland, ATRI, Composit AB, ΑΡΜΕ, Ahlstrom, Fibrocom, Sicomp). • “Crashworthiness of helicopter on water: Design of structures using advanced simulation toolsCAST” (GROWTH/G4RD-CT-2000-0178) (Partners: Agusta, GKN Westland Helicopters, Eurocopter Deutschland, Israel Aircraft Industry, WSKJ PZLSwidnik, CIRA, DLR, ESI S.A., SNLR, ΟΝΕRA, Cranfield University, Megalog SARL, Politecnico di Milano). Recently, in the frames of common research activities with the Telecom Laboratory of NTUA, a more effective use of simulation results concerning crashworthiness applications is attempted by developing a Grid computing system. Grid computing is increasingly being viewed as the next phase of distributed computing since it enables organizations to share computing and information resources across department and organizational boundaries in a secure, highly efficient manner. On APSN, the grid Advanced Passive Safety Network APSN 17 Report: D121 – Workshop on Energy Absorbing Structures and Materials in Railway and Aerospace infrastructure will be used in order to complete computer intensive calculations such as Finite Element Method (FEM) applications (e.g. LS-Dyna) in a rapid and efficient way addressing security, performance and reliability issues. The grid infrastructure is based on the GRIA Middleware which has been designed and developed in the framework of the GRIA (Grid Resources for Industrial Applications) IST project. GRIA is Grid middleware which enables commercial use of the Grid in a secure, interoperable and flexible manner. The GRIA middleware primarily focuses on industrial users with a need to share computational resources on a commercial or collaborative basis. Moreover, GRIA makes use of business models, processes and semantics to allow resource owners and users to discover each other and negotiate terms for access to high-value resources, by implementing an overall business process to find, procure and utilize resources capable of carrying out high-value, expert-assisted computations. One of the important facts of GRIA is the ability to combine Services from different providers in order to create applications using a simple and easy-to-use Application Programming Interface (API). From the architectural point of view, GRIA provides a package of Web Services that together enable a service provider to provide access to shared remote computation and data storage, subject to a well-defined business process. The Resource Allocation Service allows remote users to request and be granted (or denied) allocations of computation and data storage capacity at the service provider site. The Data Storage Service allows remote users to upload and download data files to the service provider. The Job Execution Service allows remote users to start, monitor or kill computational jobs, executed by the service provider. Session 1: Energy Absorption Materials for Non-Road Safety Energy Absorption Mechanism in Braiding Pultrusion Process Composite Rods E. C. Chirwa **,1 , Hiroshi Saito * , Ryuji Inai *, **,2 , Hiroyuki Hamada * * Division of advanced fibro science, Kyoto Institute of Technology, Kyoto, Japan. ** Automotive Engineering, Faculty of Technology, Bolton Institute, Deane Road, Bolton BL3 5AB, UK. 1 Bolton Automotive & Aerospace Research Group, Dept. of Engineering and safety, University of Bolton. 2 Visiting scholar to Bolton Automotive & Aerospace Research Group, The University of Bolton.