A computational and experimental analysis of impact to aircraft structures

摘要

The modelling and analysis of high energy impact on aircraft structures is highly complex. Traditional methods give only a limited understanding of what occurs and it is evident from the continuing problem of uncontained engine failure and other debris impact that a more accurate way of predicting the results of such impacts is needed. Finite element techniques can provide that solution.ududThis work attempts to model accurately impacts to existing aircraft structures. Of particular interest is the behaviour at the ballistic velocity as this is where the problem is most difficult to predict. Initially the model consisted of a simple sheet subject to impact by a cylindrical projectile. This was used to develop the modelling techniques for the more complex model. Issues that arose included the mesh density, the material model and the penalty stiffness factor used. Experimental testing was carried out using a gas fired projectile launcher to validate the finite element model. The geometry of the second model was more complex, a right angled stringer was riveted to a plate using four rivets. Two different approaches were used in modelling here, that of modelling the rivets in 3D and that o f modelling the rivets using 2D approximations. Modelling the rivets in 3D proved to be impractical and o f the 2D approximations the model where the rivets were not allowed to fail proved the most accurate. Experimental testing was again used for validation.ududFinally a new gas powered projectile launcher was designed and built. Improvements over its predecessor included the ability to accommodate a half metre squared test plate, impact this plate anywhere on its surface and tilt the plate through 45°. Also included were modifications to the barrel so that projectiles of any shape or size up to a maximum of 50mm in diameter could be used.