Serviceable limits of a crack type foreign object damaged blade considering high cycle fatigue

To develop a method of determining serviceable limits of foreign object damage (FOD) in aeroengine titanium fan/compressor blades, researches of serviceable limits in typical blades were firstly conducted, then stress ratio related contour maps of FOD crack non-propagation were established based on the principle of crack growth threshold, the suitability of two crack non-propagation criteria was compared according to the TC4 titanium material fatigue durability limit strength at different stress ratios, finally, serviceable limits of tearing/crack type foreign object damages in a typical fan blade were determined by this method. The results show that, in the present maintenance books, serviceable limit requirements are different for different types of FOD and different blade regions, the main limited size of FOD serviceable limits is damage depth, the depth limitation is generally less than 1mm. The tearing/crack type FOD serviceable limits of the typical fan blade determined by the contour maps of crack non-propagation are within the range of 0.020-0.525mm, the serviceable limit distribution along the blade span can be divided into three regions: the serviceable limit in the blade root area is about 0.08mm, the serviceable limit in the blade middle area is about 0.3mm, and the serviceable limit in the blade tip area is about 0.5mm, the closer to blade root means the smaller serviceable limit.