2.2 | Critical position
Standard specimen (e.g. round rod test piece) usually has a gauge section where the failure occurs. In contrast, the geometry structure and stress distribution of turbine blades are complicated. Before the CCF tests, the critical position under CCF load must be confirmed. The determination of the critical position is based on the combination of the finite element calculation and external field failure. The stress distribution of the turbine blades under the real flight condition is shown in Figure 2(a). It indicates that the maximum stress is located at the upper part of the first stage serration. Besides, Figure 2(b) shows that the blades break at the upper part of the first stage serration in the actual outer field. Therefore, the critical position should be the upper part of the first serration on the leaf side.