Papers by Keyword: Foreign Object Damage (FOD)

Abstract: This paper presents results of experimental fatigue analysis of the compressor blades subjected to high cycle fatigue. The blades used in investigations were preliminary defected to simulate the foreign object damage. The blades during experiment were entered into transverse vibration. In results of investigations, the number of cycles to crack initiation and also the crack growth rate were obtained for the blade subjected to transverse vibrations. Moreover, observations of the beach marks on the blade fractures revealed two main shemes of crack propagation process. In this work, the finite element stress analysis of the blade was also performed. Obtrained numerical results shoved that stress level in the notch vicinity is 3 times higher than the stress in the blade without mechanical defects.

Abstract: The article describes a series of experiments and calculations for verification high-speed deformation behavior and fracture models for the titanium alloy Ti-6Al-4V. Samples made of the micro-and nanocrystalline structure alloy Ti-6Al-4V were ballistically damaged in conditions that meet a ballistic damage of real turbine engine fan blades. It is found that the behavior of the microcrystalline alloy is more accurately described by the Johnson-Cook model. In the case of nanocrystalline material the best fit is achieved by using the Cooper-Symonds model. The achieved models parameters are presented.

Abstract: Foreign object damage of engine blades often occurs when they are working with high rotating speed. Nonlinear finite element models for foreign object damage of blades with different centrifugal prestress were established. And the initializations of stress and displacement field for blade due to centrifugal preload were obtained by the dynamic relaxation method in the beginning of the dynamic analysis of impact. The effect mechanism of centrifugal stress on the foreign object damage of the blade was also investigated based on the impact theory of prestressed Timoshenko beam and the principle of stress wave propagation. The results indicate that the local plastic deformation on the impact location of the blade with centrifugal preload, which is produced at the moment of impact, is decreasing with the increase of preload. Attenuation speed of compressive stress wave, which is produced by the moment of impact on the blade face, is reducing with the augment of preload.

Abstract: The influence of centrifugal prestress on the foreign object damage of engine blades was analyzed by numerical simulation. A nonlinear dynamic model for foreign object damage of blade with centrifugal prestress was established. And the dynamic relaxation method was used to obtain the initial stress and displacement field of blade in the beginning of the dynamic analysis of impact. Numerical simulations of foreign objects impacting on the leading edges of the blades under different centrifugal preloads were carried out. The results indicate that the local plastic deformation on the impact location of blade with centrifugal preload, which is produced at the moment of impact, is decreasing with the increase of the preload. The growth of crack produced on the lead edge of blade is accelerated with the preload increasing.

Abstract: The current study investigates the effect of foreign object damage (FOD) on the pre-existing compressive residual stress field associated with laser shock peening (LSP) and its evolution upon combined LCF/HCF cycling. FOD was introduced onto an aerofoil-shaped specimen that had been previously LSP treated through ballistic impacts at angles of 0° and 45° to the leading edge. It is shown that the FOD notch created by 45° impact was asymmetric in shape and smaller in depth compared to that created at 0° impact. Significant through thickness compression was introduced parallel to the leading edge as a result of the LSP process. The residual strain distribution was mapped around the FOD notch by synchrotron X-ray radiation. The results show predominantly compressive stresses ahead of the notch, being greater for the 0 compared to 45 impact. No significant stress relaxation was observed after a combined (1000 HCF cycles superimposed on 1 LCF cycle) cycle.

Abstract: Friction stir welding (FSW) allows the joining of aluminum alloys in ways previously unattainable offering new manufacturing technology. Friction stir processing (FSP) of cast alloys such as Ni-Al bronze eliminates casting voids and improves the properties to that of wrought material. However, the local heating produced by both FSW and FSP can leave a fusion zone with reduced mechanical properties and a heat-affected zone with tensile residual stresses that can be deleterious to fatigue performance. Controlled plasticity burnishing (CPB) is an established surface treatment technology that has been investigated and described extensively for the improvement of damage tolerance, corrosion fatigue, and stress corrosion cracking performance in a variety of alloys. Mechanical CPB processing in conventional CNC machine tools or with robotic tool positioning is readily adapted to industrial FSW and FSP fabrication of components, either simultaneously or as a post process. CPB was applied to FSP Ni-Al Bronze to produce a depth of compression of 2.5 mm and a maximum subsurface magnitude of –150 ksi. The effect of FSP on the fatigue performance in a saltwater marine environment and in the presence of foreign object damage (FOD) was documented with and without CPB processing. FSP was found to increase the fatigue strength of the Ni-Al Bronze by 70% without affecting the corrosion behavior of neutral salt solution. FSW actually produced a more noble material in the acidic salt solution. CPB after FSP mitigated damage 1 mm deep.

Abstract: The current study compares the residual strain around foreign object damage (FOD), measured using synchrotron diffraction, to the strain predicted by a plastic model with power-law dependence. It is shown that the measured strains are significantly lower than those predicted by the model. This may be explained in part, by the inability of the model to account for damage mechanisms such as micro-cracking and shear band formation.