18THINTERNATIONAL CONFERENCE ONCOMPOSITEMATERIALS

1 Introduction

New development of aircraft and helicopter structural designs has included more aspect of composite materials thanks to their technical advantages especially as crash-absorbing element. Previous studies [1-3] have proved that with careful design, composite structure can become an excellent energy absorbing component. Due to this reason many studies [4-6] of composite crashworthiness have been done in the recent years. However, from a numerical point of view, there is still a lake of studies in numerical simulation. Most of the models developed in the last few years [7] are based on global tests characterisations that make the model strongly dependant on global parameters, which do not permit to have predictive models. Some models [8] are based on material characteristics, but often need an a priori knowledge of the crush damage mode developed in the crush front. The challenge today in crashworthiness simulation is then to be able to predict both crush damage modes, their evolution during crushing, and then the energy absorption in any structures from elementary material characterisation data. This paper describes recent progress in modelling of crushing of carbon fiber reinforced plastic CFRP) plates at low velocity. Simulation is based mostly on elementary material mechanical characteristics.

2Experimental Testing

The model presented hereafter is based on numerous physical observations made thanks to experimental studies of composite plates crushing done by the authors [9-10]. Results of these crushing tests enabled to determinate the main mechanical

phenomena involved in the progressive crushing of composite plates, and then the appropriate scale to use in numerical simulation. All the experimental testing was performed using a drop tower machine. Details explanation on the fixture design can be found in [9].

Fig.1. The test fixture, with (on right) and without

(on left) upright.

2.1 Specimen Description

The specimens are 160mm x 60mm flat plates. The full characteristics of specimens used in the experimental study can be found in [10]. At the moment, the progress in modelling works focus more on specimen made from Hexply T700/M21 unidirectional carbon-epoxy prepreg with the thickness of each ply is 0.26mm.

3 Numerical Modelling

The commercial finite element code Abaqus V6.9 Explicit was used to represent the mechanical phenomenon based on a mesoscale modelling approach:

FINITE ELEMENT MODELLING OF CFRP PLATES UNDER CRUSHING

H.A.Israr1, S. Rivallant1*, H. Zeng1, JJ. Barrau1

1Université de Toulouse; INSA, UPS, Mines Albi, ISAE; ICA (Institut Clément Ader); Toulouse, France

* Corresponding author (samuel.rivallant@isae.fr)

Keywords: laminate, CFRP, crashworthiness, energy absorption, cohesive element, numerical modelling,

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simulation: visualization of mixed-mode failure during crash initiation.

However, during the progressive crushing, the simulation model failed to have a stable failure mode of fragmentation as recorded in experiment works. It seems like the fragmentation mode only arises during the initiation till just before the specimen transitioned into a progressive crushing mode. After that, it has a tendency to transform into splaying failure mode.

Fig.8. Visualization of mixed mode failure just

before the progressive crushing.

For the analysis of energy dissipation, force/displacement curves of numerical model and experiment were compared as in the fig.9.

Fig.9. Force/displacement curve.

The maximum forces for both curves are close to each other and occurred almost at the same displacement. Both results also show after exceeding 4.5-5mm of plate displacement, the force did not increase but flattened out as the specimen transitioned into a progressive crushing mode. The big difference in the crushing plateau during the progressive crushing between these two curves was due to the absence of the stable fragmentation mode in the simulation model as discussed earlier.

5 Conclusions

The aim of this study is to propose a simulation model for mixed-mode in plates subjected to crush load, only dependent on the elementary material characteristics of the laminate. However, up to this moment this simulation gives good correlation on the crash initiation. It needs to be improved in order to have a stable fragmentation mode which is more efficient in terms of energy absorption.

t=0.18ms

t=0.5ms

t=0.43ms

t=0.63ms

Acknowledgment:

Numerical simulations have been performed with the computing resources of CALcul en MIdi Pyrénées (CALMIP, Toulouse, France).

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