Abstract
Very-High-Cycle-Fatigue regime for metals was considered and mechanisms of the subsurface crack origination were introduced. In many metals first step of crack origination takes place with specific area formation because of material pressing and rotation that directed to transition in any volume to material ultrahigh- plasticity with nano-structure appearing. Then by the border of the nano-structure takes place volume rotation and fracture surface creates with spherical particles which usually named Fine-Granular-Area. In another case there takes place First-Smooth-Facet occurring in area of origin due to whirls appearing by the one of the slip systems under discussed the same stress-state conditions. Around Fine-Granular-Area or First- Smooth-Facet there plastic zone appeared and, then, subsurface cracking develops by the same manner as for through cracks. In was discussed quantum-mechanical nature of fatigue crack growth in accordance with Yang’s modulus quantization for low level of deformations. New simply equation was considered for describing subsurface cracking in metals out of Fine-Granular-Area or Fist-Smooth-Facet.
Highlights
Fatigue crack growth for metals subsurface cracking in VHCF regime has been investigated in many cases [1,2,3,4,5]
In many cases studied of steels [10] and superalloy [8] subsurface cracking, there were very clear registered fatigue striations on the fracture surface which has been formed before crack evidence on the specimen surface
Following by this consideration was clear that subsurface fatigue cracking performs not in vacuum but in low level pressure of rest cases existing in metals which are enough for environment influence consideration on this process
Summary
Fatigue crack growth for metals subsurface cracking in VHCF regime has been investigated in many cases [1,2,3,4,5]. The problem of subsurface crack initiation and propagation has been briefly discussed in the case of titanium alloy VT3-1 [11] Following by this consideration was clear that subsurface fatigue cracking performs not in vacuum but in low level pressure of rest cases existing in metals which are enough for environment influence consideration on this process. Investigating of crack initiation processes, occurring and developing in chemically clean metals because of different types of defects formation, such as, for instance, pore’s, microcracks and etc., the theory of strength suggested that there inside of the defect volume has to be vacuum state It contradicted with physics of phase transformation [12]. Will be discussed process of subsurface fatigue crack propagation in steels in gigacycle or Ultra-High-Cycle-Fatigue (UHCF) regime based on the introduced above criteria
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