Damage tolerance analysis of compressor blade

In this paper, we apply damage tolerance analysis to a certain compressor blade by finite element and fracture mechanics methods. The blade is analysed by using the isoparametric finite element with 20 nodes, its stress and displacement fields are determined, and the critical position where the crack probably initiates is located. Then the value of J-integral with different crack sizes in the critical position are computed using the 3-D J-integral program. On the basis of the fracture toughness of blade material, J_c, the blade extension limit, δ_c, and the deviation of natural frequency, Δf_c, the failure criterion of the blade is discussed and the critical crack size, a_c, is determined. Then according to the crack growth rate obtained from the testing, the residual life of the blade with different crack sizes is evaluated. The maximum allowable crack size, a₀, is determined using the condition that the crack would not grow to critical crack size during double overhaul periods. This value can be used to design the structure of compressor blade or to establish the criterion to judge whether a compressor blade with a crack can be used. In this way the safety and reliability of airplanes is maintained and the costs are reduced. So the damage tolerance analysis of compressor blades is practical and economical.