PSI - Issue 6

R.V. Fedorenko et al. / Procedia Structural Integrity 6 (2017) 244–251 Fedorenko R. et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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carried out. At this moment in CAE system ANSYS and ABAQUS there are not any concrete strength models with progressive damage. Progressive damage means (in terms of the finite elements) consequent eroding of the elements, in that some measure of damage is over than predetermined value. Progressive damage is implemented in LS-DYNA CAE system, but it was not used on the first stage of research because of deficiency of the versatile problem-solving environment. Accordingly, along with CDP model, ABAQUS Drucker-Prager concrete model was used. This model considers different tensile and compressive strength of material. Yield surface can be a function of three stress tensor invariants. Drucker-Prager model allows for assuming several progressive damage and failure criterions – element deletion functions [4]. It is important to note, that this model cannot describe cracking and stiffness degradation, that is very important in concrete modelling. Figure 4 shows SDEG parameter distribution for Drucker-Prager (a) and CDP (b) models.

a

b

Fig. 4. Reinforcement concrete impact results: (a) CDP; (b) Drucker-Prager.

Analysis of results shows that CDP model characterizes concrete behavior under dynamic loads more realistically. However, when it is necessary to model the penetration, simplified concrete models can be used, for example, Drucker-Prager model, but the characterization of concrete behavior is less realistic.

4. Aircraft impact structural analysis

4.1. Loads during the aircraft impact The aircraft impact involves three types of loads [16]: structural loads caused by fuselage failure; loads caused by aircraft solid fragment (in most cases the turbine impact is under the assumption, sometimes - undercarriage); aircraft fuel action loads. The first two load types are the mechanical loads, wherein it is necessary to assess the stability of the NPP structures and operability. As for the third type of loads it poses a problem of aircraft fuel and fuel vapors non-penetration into NPP through the holes and service openings. It can be the cause of the fire or equipment failure. At present, the loads on the brick walls are defined by the Riera formula [17]. In this model it is assumed that the impact direction is normal to the rigid wall. Fuselage is schematized as a rigid-plastic beam with mass per unit length μ ( ξ ) and ultimate load P( ξ ), that are smeared along the length ξ. Dynamic loads are defined by the numerical implementation of the Riera method on the basis of Boeing 720 [18], Boeing 747-400 [19] and Airbus A380 [20] characteristics. Along with the preceding approximate method, full-sized modelling of the passenger aircraft was performed. The online CAD-models and sketches were used as a basis for Airbus A380 geometrical model. Figure 5 (a) shows the finite element model of the aircraft.