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Analysis of residual strength of a helicopter tail boom

Reymer P., Leski A.

Journal of KONES

2010

Vol. 17, No. 1

343-349

The aim of this work is to determine the residual strength of a Mi-24 helicopter's tail boom with a structural damage. The idea of this work has come from the fact that these helicopters are operated on a battlefleld and often suffer such damages. It may be crucial to make a quick estimation whether any particular damage can cause a critical failure to the whole structure. The scope of this work covers static loading of the structure during landing. The analysis has been based on a numerical model that makes use of the Finite Element Method. The model has been developed using reverse engineering techniques. Structural discontinuities have been modelled in characteristic sections where stress concentrations occur. Boundary conditions and loads applied have been chosen to simulate normal and hard landings. Two failure criteria have been chosen: one based on the Crack Tip Opening Angle (CTOA) method that enables very efficient verification, and the second concerning the tail boom tip dislocation, taken from the helicopter,s alignment manual. The specific load history has been designed to enable detection of tail boom tip dislocation due to plastic strain in the vicinity of damage tips after the hard landing.

Algorytm numerycznego wyznaczania wytrzymałości resztkowej poszycia statków powietrznych.

Leski A.

Zagadnienia Eksploatacji Maszyn

2005

Vol. 40, nr 2

47-58

W pracy przedstawiono algorytm numerycznej symulacji procesu darcia blach duralowych, na podstawie którego można wyznaczyć wytrzymałość resztkową. Jako kryterium pękania przyjęto kąt rozwarcia szczeliny (crack tip opening angle - CTOA). Implementację numeryczną algorytmu wykonano w postaci procedury dołączanej do komercyjnego programu MSC.Marc. Aplikacja kryterium CTOA w programie MSC.Marc łączy ze sobą zalety pracy z własnym kodem programu z olbrzymimi możliwościami, jakie oferuje pakiet komercyjnego oprogramowania. W artykule przedstawiono przykład zastosowania algorytmu wraz z oryginalną procedurą w języku FORTRAN.

In this paper an algorithm of numerical simulation of ductile tearing in aircraft fuselages subjected to widespread fatigue damage is presented. Using this algorithm the residual strength of a cracked airplane skin can be calculated. The crack tip opening angle was chosen as a crack criterion. The numerical implementation was performed as an additional procedure for commercial finite element software MSC.Marc. The application of the CTOA criterion inside the MSC.Marc code combines both the advantage of own code knowledge and huge possibilities of a commercial software. The algorithm makes use of UFORMS subroutine. Originally this subroutine was designated to modify the definition of a constraint condition. Marc's capability for applying arbitrary homogeneous constraints between nodal displacements was applied to fracture simulation. The accompanied procedure in the FORTRAN language is also enclosed. In the paper an example of using the algorithm is presented.