PSI - Issue 14

S.C.S.P. Kumar Krovvidi et al. / Procedia Structural Integrity 14 (2019) 855–863 S.C.S.P. Kumar Krovvidi / Structural Integrity Procedia 00 (2018) 000–000

859

5

Figure 5: von Mises stress due to deflection Table 2: Various parameters involved in estimation of fatigue life of the bellows as per RCC-MR (2007) Parameter From loading or computed In tension   (MPa) = (P m +P b +ΔQ/2) 604 MPa 1   = 2 (1 ) 3 E           0.0026 2   Negligible 3   1 ( 1)      K = 0.0008 (  K =1.31)

4       K (

1 1) 

 K = 1.18 )

= 0.00047

(

3   +

(

)

   



1   +

2   +

4  

=

= 0.00388

= 0.38 %

el

pl

In compression   (MPa) = (P m +P b) - ΔQ/2

266 MPa

2 (1 ) 3

E      

 

1   =

  0.0011 As the linear elastic strain is less than 0.2%, the plastic enhancements in the strain is neglected Total strain range   0.49% Allowable number of cycles (N) 3600 cycles The life of the bellows estimated by the method given in RCC-MR which is based on linear elastic FEA is 3500 cycles. 3.2. Inelastic analysis of the bellows using cyclic stress strain curve method The inelastic strain in the bellows is estimated by elasto-plastic analysis using cyclic stress-strain curve given in Appendix A3 of RCC-MR. The geometry, boundary conditions and the loading are as given in the Fig. 6 . The material properties used during the analysis are given in Table 3. Figure 7 & 8 gives the strain induced in the bellows which is computed through elasto-plastic analysis (based on cyclic stress-strain curve) in tension and in compression. At root, the stain range in the bellows is 0.39%. The life of the bellows based on elasto-plastic analysis using cyclic stress-strain curve as material model using RCC-MR design curve is 7800 cycles.