D.P. Papapostolou

Crashworthy characteristics of axially statically compressed thin-walled square CFRP composite tubes: experimental

In this paper the results of experimental works pertaining to the crash behaviour, collapse modes and crashworthiness characteristics of carbon fibre reinforced plastic (CFRP) tubes that were subjected to static axial compressive loading are presented in detail. The tested specimens were featured by a material combination of carbon fibres in the form of reinforcing woven fabric in thermosetting epoxy resin, and they were cut at various lengths from three CFRP tubes of the same square cross-section but different thickness, laminate stacking sequence and fibre volume content. CFRP tubes were compressed in a hydraulic press of 1000 kN loading capacity at very low-strain rate typical for static testing. The influence of the most important specimen geometric features such as the tube axial length, aspect ratio and wall thickness on the compressive response and collapse modes of the tested tubes is thoroughly analysed. In addition, the effect of the laminate material properties such as the fibre volume content and stacking sequence on the energy absorbing capability of the thin-wall tubes is also examined. Particular attention is paid on the analysis of the mechanics of the tube axial collapse modes from macroscopic and microscopic point of view, emphasizing on the mechanisms related to the crash energy absorption during the compression of the composite tubes.

On the compression of hybrid sandwich composite panels reinforced with internal tube inserts: experimental

Edgewise and flatwise compression was performed on hybrid sandwich composite specimens with internal tube reinforcements, in order to evaluate the load-carrying capacity and energy absorption capability of such composite structures and provide data related to panel design for crashworthiness applications. Extensive experimental data were recorded on the compressive properties of the tested hybrid composite panels and the failure modes were examined.

Axial collapse of hybrid square sandwich composite tubular components with corrugated core: numerical modelling

The present paper is dealing with the implementation of the explicit FE Code LS-DYNA to the simulation of the crash behaviour and energy absorption characteristics of thick-walled square tubular crashworthy components made of hybrid sandwich material with corrugated core subjected to axial compressive loading. The obtained numerical results are compared with actual experimental data from small-scale models in terms of deformation modes, energy absorption capability, load/deflection history and crush zone characteristics, showing very good agreement.

Experimental investigation of the collapse modes and the main crushing characteristics of composite sandwich panels subjected to flexural loading

The flexural properties, collapse modes and crushing characteristics of various types of composite sandwich panels – that were candidate materials for the manufacture of the front-end bumper of transportation vehicles – were investigated in a series of three-point bending tests that were performed in accordance with the American Society for Testing and Materials International Standard D790. The tested hybrid composites were constructed trying four types of polymer foam core (more specifically polymethacrylimide foam, cross-linked and linear polyvinyl chloride foam and polyurethane foam) and two types of fibreglass reinforced polyester faceplate laminates made of glass fibre reinforcements impregnated in modified acrylic resin, in eight different material combinations. Two modes of collapse were recorded in the series of flexural tests: the first was foam core shear failure and the second was local indentation collapse mode. The influence of the most important material properties of the faceplate laminates and foam core and the sandwich construction geometry on the flexural response and the crushing characteristics of the tested sandwich panels such as the peak load, crash energy absorption and collapse modes is extensively analysed. Particular attention is paid to the analysis of the mechanics of progressive deformation and crumpling of the sandwich panels in each of the collapse modes emphasising the mechanisms related to the crash energy absorption during the bending of the sandwich panels.

Experimental investigation of strain rate effects on the crushing characteristics of composite sandwich panels

In the present work, the influence of strain rate on the collapse modes, the crushing mechanisms and the energy absorption characteristics of four types of composite sandwich panels was investigated in a series of impact and static in-plane tests. The tested sandwich specimens were formed combining two types of glass fibre reinforced plastic (FRP) faceplate laminates with three types of polymer foam core (poly-methacryl-imide (PMI) foam and two grades of cross-linked poly-vinyl chloride (PVC) foam) in four different material combinations. Three modes of collapse were observed in the series of impact and static compression tests, but only one of them – which was observed only at higher strain rates – was a stable mode featuring progressive end-crushing of the sandwich panel and significant crash energy absorption. The analysis of the test results showed that the increase of the strain rate influenced significantly the mode of collapse of the tested sandwich panels and some of their energy absorption characteristics such as the critical load for failure initiation and the peak collapse load. Apart from the strain rate effects, the analysis of the test works focused on the mechanics of progressive deformation and crushing related to each mode of collapse and the influence of significant parameters of the sandwich panel construction – such as the properties of the foam core and the faceplates – on the overall crushing response and the energy absorption characteristics.

Finite element modelling of the crushing response of composite sandwich panels with FRP tubular reinforcements

Abstract The crushing response and the crash energy absorption characteristics of composite sandwich panels with internal fibre reinforced plastic (FRP) tubular reinforcements were investigated in the numerical simulation works described here using the LS-DYNA3D finite element code. Several models were developed in order to simulate a series of compressive tests performed at the National Technical University of Athens using composite sandwich panels with glass FRP faceplates and syntactic foam core that were internally reinforced with FRP tubes, and, moreover, to examine how the construction parameters of the sandwich panels influence the main crushing characteristics, i.e. the crash energy absorption and the peak compressive load. The sandwich construction parameters whose influence was investigated were the properties of some of the constituent materials (more specifically the foam core and the reinforcing FRP tubes) and the geometric characteristics of the internal reinforcements such as the thickness of the FRP tubes. The agreement between the finite element calculations and the experimental results was excellent concerning the load—displacement curve and the main crushing characteristics of the tested hybrid composite materials, as well as the overall crushing response of the sandwich panels in compressive loading, as a result of several refinements that were applied to the finite element models.