Mukharbiy Banov

Hypothesis of Local Zones with Dependent Fatigue Damages Accumulation

It is set on results the conducted experiments, that the appearance of multiple of fatigue cracks on specimens and design units with numerous concentrators takes place stochastically dependently. This stochastic relationship, both positive and negative, is observed in some zone, with certain dimensions. Positive cross-correlation relationship supposes that before there the fatigue crack will have been originated, the early the subsequent crack will be found out in direction perpendicular to the applied force. Such sequence of fatigue cracks’ originations assumes a mode as a propagation of the first crack, converting it to the only main spread out one. Such zone can be examined as a separate specimen or desigh element with probabilistic descriptions of endurance, fatigue strenght and other characteristics of reliability, that determines reliability of whole system. A physical proof of such zones existence and the description of reliability characteristics are shown as mathematical models.

The Characteristic Features of Composite Materials Specimen’s Static Fracture Investigated by the Acoustic Emission Method

The work is dedicated to the experimental study of micromechanics process of unidirectional composite materials’ specimens under static loading till its fracture using acoustic emission method compared with the strain-load deformation curve. An attempt is made to identify subtle effects of the failure process of the composite material which is impossible using the traditional methods of the strain measurement. The prospect of applying the method of acoustic emission (AE) for the development and improvement of existing methods of model tense- analysis is shown. The characteristic stages of the damage accumulation for unidirectional composites’ specimens and the effect of training on these processes are shown experimentally. It’s shown that the AE-deformation diagram have three stages in contrast to commonly used load-strain deformation curve with one stage. So it become possible to investigate the physical process of composite unit’s fracture under static load.

Fatigue Cracking and Acoustic Emission Regularities in Metals: Crack Origination and Growth

Specimens of Al-and Ti-alloys and turbine blades of Ni-based alloy were considered in the case of crack origination at the surface, subsurface, and at the inner surface of turbine blades. Aircraft structures such as hydrocylinders of Al-based alloy and landing gear of high-strength-steel were also considered. There was used acoustic emission (AE) monitoring to fix moment of crack occurring and, then, analyzing its growth. Fracture surface features appearance was compared with AE-signals regularities based on fractographic analyses. To indicate the crack origination moment it was introduced α-criterion. This criterion characterized drastically increase in summarized AE-signals appearing in dependence on cyclic loads number. During crack propagation, there was used Elber-portion of opened crack to register AE-signals in cyclic loads. It was demonstrated crack increment in unloading portion of cyclic loads with fatigue striations formation. Two aircraft structures of hydrocylinders and shock strut of landing gear were tested on the special test facilities and AE-monitoring was conducted. Effectiveness of α-criterion using for crack registration in the high-cycle fatigue regime was demonstrated applicably to crack appearance on the internal surface and subsurface. The discovered dependences of summarized AE-signals on number of cycles were compared with fracture surface patterns and briefly discussed.