PSI - Issue 23

A.A. Shanyavskiy et al. / Procedia Structural Integrity 23 (2019) 57–62 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

2

58

Nomenclature C ae , b factors, characterizing intensity of damage accumulation in a metal during one cycle of cyclic loads C 00 , p factors determined in tests for the relation between N ae and ε 01 C α , m material factors in the relation between ( N f ) α and ( N ae ) t k , C ε experimentally determined factors N f durability N ae summarized AE signals N̅ ae average value of summarized AE signals

( N ae ) 01 summarized AE signals determined for semi-cycle of loading ( N ae ) t summarized AE signals determined for a specified time interval ( N f ) α the in-tests number of cycles when α -criterion registered t test duration in minutes Δ ε Σ full metals deformation in one cycle of cyclic loads ε 01 material plastic deformation in the semi-cycle of loading σ maximum stress level

Second, inside of the engine, there can be a failure of one of the units because of their in-service critical state. The fragment of a unit can damage the blade with creation of stress concentration and the following fatigue crack origination and propagation. Third, Shanyavskiy (2014) demonstrated that it can be some cases of blades resonance because of designer fault or their possible bad contact between the blade root and disk rime area for the root. This bad state of linked arts directed to intensive friction and formation of fretting debris. Areas with fretting damages are physical and mechanical stress-concentrators. At last, there can be damage of blades edges during manufacturing procedure or repair. During in-service damaged areas by the blade surface can be detected with boroscope-inspection. Nevertheless, in the case of the cooled turbine blade, there can be appeared fatigue crack by the inner surface which cannot be in service visually inspected. It has to be applied acoustic emission (AE) control, which used, for example, knowledge about α -criterion that was introduced by Shanyavskiy and Banov (2014). In the case of a crack origination, AE signals have drastically increased and this event can be estimated by the α -criterion. Another possibility in AE-signals using for material state estimation can be discussed for blade durability diagnostics, if in-service its cyclic loading has a statistically homogeneous case. Systematically performed investigations of AE-signals formation during metals fatigue tests have shown that it can be performed methodology for blade durability diagnostics when some number of in-service cycles was realized. The discussed possibility based on the fundamental knowledge about the nature of AE signals appeared in metals subjected to cyclic loads. All AE signals appeared because of dislocations and disclinations moving during cyclic loading and their accumulation up to critical density takes place at the moment of crack origination. Below methodical features of durability diagnostics based on AE-signals registration are discussed applicable to use them in the repair conditions for turbine blades manufactured from superalloys for GTE. AE signals registered during the fatigue test of metals characterized damages accumulation by the bulk material. There can be damages in metals whose appearance has no relation with origin formation for the future fatigue crack. But we can neglect these groups of signals because the main intensity of AE signals takes place from moved damages whose contributions in crack origination is most of all. Let be considered the process of damages accumulation in metals on the different scale levels that was discussed by Shanyavskiy (2010). Without plastic deformation, fatigue crack cannot be originated in metals. But this process can be seen on the macro-, meso-, and microscale levels. On the macro scale, metals have a macro residual strain 2. Durability diagnostics by the average value of summarized AE signals