PSI - Issue 16

Volodymyr Panasyuk / Procedia Structural Integrity 16 (2019) 3–10 Volodymyr Panasyuk / Structural Integrity Procedia 00 (2019) 000 – 000

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6. Lifetime of cyclically contacting solids

A book by Datsyshyn and Panasyuk (2018) synthesizes the results by authors and other scientific publications on the problems on surface layers fracture of solids under cyclic contact, in particular, such details as: wheel-rail, rollers, roller bearings, supports of drilling bits, etc. (Fig. 6). Calculation models and methods for calculating the propagation paths of cracks that arise in the contact region between bodies under cyclic contact are formulated.

Fig. 6. Damage of the surface contact zone during rolling: a are the paths (dashed lines) of an edge crack growth in conditions of boundary lubrication, depending on the oil pressure on the crack edges ( q = rp 0 , r – numerical coefficient); b is the pitting cross-section on the surface of contacting bodies.

7. Influence of environments on macrocrack growth rate in cyclically deformed metals

Experimental investigations by Panasyuk et al. (1984) showed that ( v – K І ) diagrams are not invariant when they are plotted beginning from different initial K І values under the deformation of a body in a certain corrosive environment (Fig. 7).

Fig. 7. Dependences of crack growth rate ( v ) in the corrosive environment on SIF value, K I ; indexes (1) – (3) correspond to curves 1 – 3.

These diagrams depend on the physico-chemical situation that appears near the crack tip under the environment influence. Two parameters were chosen to control this situation: metal electrode potential φ and environment hydrogen index pH. Such conditions were taken into consideration: parameters value on the metal surface (pH s and φ s ) and near the crack tip (pH t and φ t ) are not equal. Under these conditions the dependence of crack propagation rate in the cyclically deformed body (Fig. 8) is:

I ( , pH , φ )   t t

I ( , pH , φ )  t t v F K , max

 v F K

,

(9)

where: pH min pH , φ minφ     t t t t .

At the end of the past century methods and special specimens were developed at PhMI for measuring and regulation of parameters pH t and φ t (Fig. 9). It is necessary to ensure pH t = const and φ t =const for plotting invariant ( v – K І )- diagrams. Panasyuk and Dmytrakh (1999) established φ t and pH t conditions under which the crack rate growth is maximum ( v max ) for the metal cyclically deformed in a corrosive environment – min φ t and min pH t . Diagram 5 in Fig. 10 is plotted according to the above mentioned and it is compared with data of other authors which