U–6Nb shear stress relaxation in compression waves (IJP 585-AV)

• Published in: International journal of plasticity 2009-04, Vol.25 (4), p.635-648
• Main Authors: Hayes, D.B., Gray, G.T., Hixson, R.S., Hall, C.A., Byers, M.E., Vorthman, J.E.
• Format: Article
• Language: English
• Subjects: A. Acoustics; A. Shock wave; A. Stress relaxation; A. Twinning; B. Rate-dependent material; Cold rolling; Computer simulation; Density; Dislocations; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Inelasticity (thermoplasticity, viscoplasticity...); Physics; Ramps; Shear stress; Solid mechanics; Stress relaxation; Structural and continuum mechanics; Twinning; Uranium base alloys; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...)
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2008.12.005

When uranium alloyed with 6-wt% niobium (U–6Nb) is rapidly compressed in uniaxial strain experiments, shear stress is observed to relax with a characteristic time of 30 ± 7 ns. In shock wave experiments, this relaxation inhibits the development of an elastic precursor commonly seen in other materials. When U–6Nb is cold-rolled to pre-twin and significantly increase the density of dislocations in the material, stress relaxation effects are diminished suggesting that twinning causes relaxation in the un-worked material. Separate ramp wave compression experiments produce effects that agree with those observed in shock-loading experiments. A phenomenological model is introduced that allows accurate simulation of all experiments. Estimates of residual shear stress after relaxation are obtained.