Financing: Ministry of Science, Education and Sports Republic of Croatia; Croatia Airlines

 

Keywords: aeronautical structures, damage mechanics, damage variables, finite element method, composite structures, sandwich structures, explicit integration, Abaqus/Explicit, Coupled Euler Lagrangian, equation of state (EOS)

 

Within this project, in collaboration with Croatia Airlines as an industrial partner, the prototype of the system for the numerical assessment of damage in aircraft structures has been developed. The procedure includes: CAD database of critical elements in aircraft structure; the establishing of procedure to determine structural damage as well as normal operation of movable parts after impact with foreign objects and ground equipment; validation of the procedure through the comparison with Structural Repair Manual (SRM).

 

Bird impact damage in the certain parts of the structure (e.g. ailerons, flaps, slats) has been analysed in accordance with the FAR 25.571. Materials used in the structural components are mostly CFRP, sandwich structures and aluminium alloys 2024 and 7075. Stress field has been determined by the finite elements method using transient dynamic analysis within the program Abaqus/Explicit. By the user subroutine VUMAT, constitutive equations have been defined for characteristic behaviour of sandwich materials. Failure is determined using damage parameters, shear failure criterion and Hashin’s failure criteria. Bird impactor has been modelled using coupled Eulerian – Lagrangian analysis (CEL) where Eulerian material flows through the finite element mesh and impacts the target material that is modelled with Lagrangian approach. Bird material model has been defined by the equation of state (EOS). Contact forces are transferred from impactor to the structures by means of penalty general contact algorithm. In order to increase the numerical efficiency, substructuring has been implemented (not inherently present within Abaqus/Explicit) using C# programme coupled with Python scripts. Aerodynamic loading has been determined by programme Fluent, and appropriate Fortran subroutines have been developed in order to transfer data, by means of user subroutine VDLOAD, into the Abaqus/Explicit input file.

 

Furthermore, flight mechanics has been applied as to determine the bird velocity vector, depending on the airplane position and ailerons/flaps/slats deployment angle. By storing modelled detailed structural parts in the data base and by knowing precise impact location, structural response and information on damage can be determined rapidly, particularly in the internal structural parts.

 

Within these activities, Project Laboratory for Numerical Modelling of Damage in Aeronautical Structures has been established at FMENA with the task of verifying the methodology and continuing its further development.

 

Collaborators: Prof. Dr. Sc. Ivica Smojver (head and principal investigator); Prof. Dr. Sc. Milan Vrdoljak; Prof. Dr. Sc. Tanja Jurcevic Lulic; Darko Ivancevic, MAE; Dario Mihaljevic, Grad. AE; Miso Klaric, Grad. ME (Croatia Airlines); Davor Bujan, Grad. ME (Croatia Airlines); Mirko Hrvoje, Grad. ME (Croatia Airlines)