A nonproportional strain-controlled load path consisting of two segments was applied to the cobalt-based alloy Haynes 188 at 650°C. The first segment was purely axial; the axial strain was then held constant while the shear strain was increased during the second segment. The alloy exhibited about a 95-percent reduction in axial stress (298 to 15 MPa) during shear straining. This reduction was due primarily to plastic coupling, but time-dependent stress relaxation also occurred. A rate-independent plasticity model approximated the stress reduction due to plastic coupling reasonably well, but as expected was unable to account for time-dependent stress relaxation. A viscoplasticity model capable of predicting the interaction between stress relaxation and plastic coupling also predicted the plastic coupling reasonably well. The accuracy of the viscoplastic model is shown to depend greatly upon the set of nonunique material parameters, which must be characterized from a sufficiently large range of load histories.

1.
Lissenden, C. J., Walker, M. A., and Lerch, B. A., 2000, “Axial-Torsional Load Effects of Haynes 188 at 650°C,” Multiaxial Fatigue and Deformation: Testing and Prediction, STP 1387, American Society for Testing and Materials, Philadelphia, PA, pp. 99–125.
2.
Arnold
,
S. M.
, and
Saleeb
,
A. F.
,
1994
, “
On the Thermodynamic Framework of Generalized Coupled Thermoelastic-Viscoplastic-Damage Modeling
,”
Int. J. Plast.
,
10
, pp.
263
278
.
3.
Arnold
,
S. M.
,
Saleeb
,
A. F.
, and
Wilt
,
T. E.
,
1995
, “
A Modeling Investigation of Thermal and Strain Induced Recovery and Nonlinear Hardening in Potential Based Models
,”
ASME J. Eng. Mater. Technol.
,
117
, pp.
157
167
.
4.
Wilt, T. E., 1999, private communication.
5.
Bhanu Sankar Rao
,
K.
,
Castelli
,
M. G.
,
Allen
,
G. P.
, and
Ellis
,
J. R.
,
1997
, “
A Critical Assessment of the Mechanistic Aspects in Haynes 188 During Low-Cycle Fatigue in the Range 25°C to 1000°C
,”
Metall. Mater. Trans. A
,
28A
, pp.
347
361
.
6.
Saleeb, A. F., Arnold, S. M., Castelli, M. G., Wilt, T. E., and Graff, W., 2001, “A General Hereditary Multimechanism Based Deformation Model With Application to the Viscoelastoplastic Response of Titanium Alloys,” Int. J. Plast., to appear.
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