To validate the increasingly used numerical models for optimization and verification of the designs subjected to bird strike, initial (calibration) tests are a necessity prior to full scale testing. Bird strike calibration tests on rigid targets specifically, give a valuable insight in the complex behaviour of a bird. This paper presents the results of a series of bird strike tests and simulations on three rigid targets (a plate, a wedge and a splitter) to quantify the forces originating from the change of momentum and splitting of the bird. In this study, momentum transfer is the key parameter to compare birds with different masses, materials, speeds, etc., as proposed in the reference works from the 20 th century. The main purpose of this paper is fourfold: (i) to introduce another way to measure momentum transfer on these kinds of structures and therefore get more consistent results, (ii) to show that gelatine generates similar impact forces as real birds, (iii) to point out that apart from the change of direction of the momentum, the deviatoric and/or dissipating constitutive behaviour of the bird also plays an important role and (iv) to show that a simple plate structure can be used to measure the residual energy of the bird remainders after an impact event. In a series of numerical simulations, the performance of a SPH bird with an EOS material model is used to validate the analytical models.

The impact of a bird on a structure can, in the first place, be characterized by the pressure exerted on that structure. In bird strike research, the first step towards bird strike modelling is therefore often the investigation of these impact pressures. During impact, two subsequent regimes can be distinguished: a shock and steady state regime. These regimes are characterized by an initially very high shock pressure and a much lower steady state pressure. How relevant the shock regime is during bird strike however can still be questioned. This paper will reveal some key parameters that influence the shock regime, based on the conclusions of several SPH simulations and an experimental test campaign. A zoom on the numerically obtained shock pressure pulse is made, which shows that the impact pressure and duration correspond very well with the theory.Slight tilting of the projectile however can increase the pressure up to 190% of the analytical value. The elastic energy as a measure for the presence of the shock regime is introduced. This shows that the shock regime is relatively negligible for hemispherical ends. The steady state pressures obtained from the simulations are investigated and finally, the analytical values and numerical results are compared to a series of experimental impact pressure measurements with real and (porous) gelatine birds.

The in-house validation of finite element models for bird strike events is currently done by experimental tests on flat plates. High displacement speeds in these experiments demand a small exposure time of the high speed camera (up to 1/50000 s). In order to acquire images of sufficient quality, a special, highintensity light source has to be used, which is not always possible. The regions with high displacement speeds, therefore, often result in blurry images. In this case, a printed line pattern to estimate the shape of the plate during test provides major advantages over a speckle pattern in terms of reconstruction and optimization of the blurry regions. In this work, a stereo vision technique is developed to reconstructs 3D shape maps using images of impacted plates with printed line patterns. It is shown that two cameras are necessary to calculate accurate shape maps in case of large deflections. The resulting shapes can be used for the validation of numerical simulations.

Manuscript number IE_2016_34Reaction force has always been one of the main characterization parameters for impact events. 8