PSI - Issue 20

E.S. Oganyan et al. / Procedia Structural Integrity 20 (2019) 42–47 E.S. Oganyan et al. / Structural Integrity Procedia 00 (2019) 000–000

44

3

According to GOST R 54749 (2011), GOST 22703 (2012), the coupler must ensure endurance of the longitudinal tensile force of at least 2.45 MN (250 tf) and compression force of 3.43 MN (350 tf). Wherein, the largest design stresses should not exceed the yield strength of the material. According to GOST R 57445 (2017), lifetime assessment of a part is made on its basic element, which is selected from among the critical ones. The basis of choice is the operational data of damages, the results of calculations. According to the calculation results of the stress-strain state (SSS) of the automatic coupler, performed by the finite element method in a physically nonlinear formulation associated with metal elastoplastic behavior and geometry due to large deformations and contact interaction of parts, using the software complex MSC.MARC, the most stressed is the contact area of bar with draft key along the cylindrical portion of the opening (fig. 1b). In this area, when tensile force of 2 MN is applied to the coupler, the stresses reach the yield strength of the material σ 0.2 . High stresses (~ 0.8 σ 0.2 ) are also obtained at the place of transition of the bar to the coupler head. It should be noted that during compression and impact of 2.5–3.0 MN, the stresses in these areas reach and exceed σ 0.2 .

a

b

Fig. 1. Jumper of the coupler bar as the critical area for evaluation of its lifetime. (a) operational view of the coupler bar jumper fracture; (b) finite-element model of the coupler bar jumper with the calculation results of the most stressed area.

In the considered case, the coupler bar jumper is chosen as the critical element (area). The calculation of the lifetime for it was carried out taking into account the possibility of occurrence and accumulation of residual deformations in the material. Such loading is defined by the deformation criteria of low-cycle fatigue in the form of equations given by Coffin (1963), Manson (1974), Oganyan and Volokhov (2013), characterizing exhaustion of plastic properties with a destructive number of loading cycles N p :

(1)

m p

p p C N ε −

Δ = ⋅

,

σ

2

(2)

−

1

p Δ ⋅ ε =

+

m p

p C N −

,

E





2

0.2       lim P P

ls         N μ −

1 2 1 σ − 

(3)

p Δ ⋅ ε =

+

−

m p

−

C N

,

 

p

E

N

1

