PSI - Issue 14
Ritu. J. Singh et al. / Procedia Structural Integrity 14 (2019) 549–555
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Ritu .J. Singh/ Structural Integrity Procedia 00 (2018) 000–000
yields for anisotropic case whereas for isotropic case complete thickness has plastified at an applied pressure of 310 MPa . The difference in the yield initiation of both isotropic and orthotropic case can be explained on the basis of hills yield curve and von mises curve as shown in Fig.5. It is evident that stress path for internal pressure loading is such that yielding occurs at higher stresses for anisotropic material properties. When the autofrettage pressure is removed i.e. unloading occurs, the elastic region of the cylinder tries to resume the original shape whereas the plastic region has permanent deformation which resists going back to original shape. This leads to development
b
a
100
250
pw1-1 pw1-2 pw1-4 pw1-6
pw1.1 pw1-2 pw1_4 pw1_6 pw1_7
80
200
60
150
40
100
20
50
Residual Mises Stress, MPa
Residual Von Mises Stress (MPa)
0
0
Isotropic material model
Anisotropic material model
0
20
40
60
80
100
0
20
40
60
80
100
Distance from inner surface (%)
Distance from inner surface, %
10 20 30
200
-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0
100
0
pw1.1 pw1-2 pw1_4 pw1_6 pw1_7
-100
pw1-1 pw1-2 pw1-4 pw1-6
Residual Hoop stress (MPa)
Residual Hoop Stress, MPa
-200
Anisotropic material model
Isotropic material model
-300
0
20
40
60
80
100
0
20
40
60
80
100
Distance from inner surface (%)
Distance from inner surface, %
0.0
0
-0.5
-5
-1.0
-10
-1.5
-15
pw1.1 pw1-2 pw1_4 pw1_6 pw1_7
-2.0
-20
-2.5
pw1-1 pw1-2 pw1-4 pw1-6
Residual Radial Stress (MPa)
Residual Radial Stress, MPa
-25
-3.0
Anisotropic material model
Isotropic material model
-3.5
-30
0
20
40
60
80
100
0
20
40
60
80
100
Distance from inner surface (%)
Distance from inner surface, %
Fig. 6. Residual von mises, hoop & radial stress distribution for (a) isotropic (b) anisotropic material properties
of residual stress pattern. The unloading process in the present work is treated elastically. Fig. 6. shows residual stress distribution after autofrettage pressure is removed and elastic unloading is done. It is observed that the residual hoop stress developed is compressive in nature at the inner surface and extends beyond the inner surface depending upon the autofrettage pressure applied. This residual compressive stress generated increases the load carrying capability in the subsequent loading. For the anisotropic material case, residual hoop stress magnitude is maximum 85 MPa compressive compared to 250 MPa of compressive stress
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