High-pressure strength of aluminum under quasi-isentropic loading

• Published in: International journal of plasticity Vol. 25; no. 4; pp. 671 - 694
• Main Authors: Vogler, T.J., Ao, T., Asay, J.R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2009; Elsevier
• Subjects: Accounting; Aluminum; Applied sciences; Constitutive behavior; Exact sciences and technology; Fundamental areas of phenomenology (including applications); High-pressure loading; Impactors; Inelasticity (thermoplasticity, viscoplasticity...); Metals. Metallurgy; Physics; Ramps; Shock loading; Solid mechanics; Strength; Stress relaxation; Stress waves; Stresses; Structural and continuum mechanics; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...); Stress waves; Constitutive behavior; High-pressure loading; Constitutive equation; Lagrangian; Stress wave; Prestress; Temperature effect; Thermomechanical properties; Aluminium; Isentropy; Elastic wave; Thermal load; Experimental study; Modeling; Shock wave; High pressure; Mechanical shock
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2008.12.003

Under shock loading, metals typically increase in strength with shock pressure initially but at higher stresses will eventually soften due to thermal effects. Under isentropic loading, thermal effects are minimized, so strength should rise to much higher levels. To date, though, study of strength under isentropic loading has been minimal. Here, we report new experimental results for magnetic ramp loading and impact by layered impactors in which the strength of 6061-T6 aluminum is measured under quasi-isentropic loading to stresses as high as 55 GPa. Strength is inferred from measured velocity histories using Lagrangian analysis of the loading and unloading responses; strength is related to the difference of these two responses. A simplified method to infer strength directly from a single velocity history is also presented. Measured strengths are consistent with shock loading and instability growth results to about 30 GPa but are somewhat higher than shock data for higher stresses. The current results also agree reasonably well with the Steinberg–Guinan strength model. Significant relaxation is observed as the peak stress is reached due to rate dependence and perhaps other mechanisms; accounting for this rate dependence is necessary for a valid comparison with other results.