Web Pages for Stephen J. Burns

Mechanical properties of materials at extreme stresses and temperatures

Sections are: This Overview Page; Materials Studied; Lecture on Thermodynamics; Jacobian Algebra with a MATLAB Application.

The research group, High Energy Density X, has about 20 active people. It includes graduate students, post docs, LLE researchers, and faculty. The Group HEDX (we use X because physics or science does not fit everyone) is shown in a photo at LLE from fall 2022.

The University of Rochester has been my employer for over 51 years including the years since I retired in September 2016.

Just before retiring, I was interacting with the Laboratory for Laser Energetics. LLE wanted help on X-ray diffraction in-situ of their laser ablated materials that were compressed and shocked by longitudinal planar waves. Danae Polsin, at that time a graduate student, explained to the researchers at LLE and other National Labs that rolled and evaporated metal foils she used in her experiments were not isotropic but these foils had extensive textures as seen in her PhD thesis. The textures were measured using the Philips Materials Research Diffraction Unit. That instrument was the basis for 7 laboratories and some lectures in my course on Diffraction Methods in Materials Science. One of my labs even was measuring texture. She studied textures in rolled foils for her laser ablation experiments and thesis.

My research has always been mechanical properties of materials, so I was well suited to understand the very highly compressed solids found in LLE’s laser ablation compression. Since that start there have been several papers [1-8] on material properties. They are listed below.

I’m quite sure that my use of strain volumes is unique in the world. It was first used in Rochester nearly 50 years ago to avoid assuming the specific volume was held constant in thermodynamic descriptions of stressed solid materials. Energy per unit volume is used when stress is a state variable. Energy balances per unit volume in stressed materials were always well known to have a constant reference volume and this poses a problem see J. W. Gibbs Collected Works, vol. 1, 1948, Yale U. Press. Energy balances in stressed materials contain a constant volume reference state. Use of a liquid avoids this problem.

If the energy balance is from the first law of thermodynamics, energy per unit mass is used, then the specific volume is considered constant if stress variables are used. At very high stresses, as we see at LLE the specific volume is not constant. Laser fusion is thought to be successful when the specific volume for deuterium is compressed to about 1/20 of the solid material’s density. The hypothesis is the atoms will then fuse. Laser fusion has been experimentally demonstrated recently.

The research I’ve pursued has two major directions: first is to include shear at very high stresses in describing solid materials. The assumption that pressure alone is a valid mechanical description of a solid material’s behavior, and that shear stress can be neglected is doubtful. This assumption makes liquids and solids the same. The second objective is to correctly predict the temperature and specific volume of a solid when extensively compressed. Not necessarily isentropically but adiabatically including the heating from irreversible deformation. In my research, reference [8] shows real progress in addressing elastic moduli. Also, I’ve known for some time that all third order Gibbs derivatives of solids in the literature are not right. Finally, since most of my work is on linear elastic materials and I have extensive thermodynamic descriptions of linear thermodynamic systems, several of my papers include the third order Gibbs derivatives [2, 4, 5].

Recently using a very fast IR camera, measurements of the temperature of 2024 aluminum alloys and 4340 steels during tensile testing were made. Some new phenomena were observed, and new thermal properties measured.

Reference papers on recent work by myself with lots of others:

1. Burns, S.J., Thermodynamic Predictions of Thermal Expansivity and Elastic Compliances at High Temperatures and Pressures Applied to Perovskite Crystals. Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science, 2016. 47A(12): p. 5852-5858.

2. Burns, S.J., 77 new thermodynamic identities among crystalline elastic material properties leading to a shear modulus constitutive law in isotropic solids. Journal of Applied Physics, 2018. 124(8).

3. Burns, S.J., Elastic shear modulus constitutive law found from entropy considerations. Journal of Applied Physics, 2018. 124(8).

4. Burns, S.J., Linear dielectric thermodynamics: A new universal law for optical, dielectric constants. Journal of the American Ceramic Society, 2021. 104(5): p. 2087-2101.

5. Burns, S.J., Rygg, J.R., Polsin, D., Henderson, B., Marshall, M., Zhang, S., Hu, S., Collins, G., Planar, longitudinal, compressive waves in solids: Thermodynamics and uniaxial strain restrictions. J. Appl. Phys., 2022. 131: p. 215904-1 215904-11.

6. Polsin, D.N., et al., Measurement of body-centered-cubic aluminum at 475 GPa. Physical Review Letters, 2017. 119(17): p. 175702-4.

7. Polsin, D.N., et al., X-ray diffraction of ramp-compressed aluminum to 475GPa. Physics of Plasmas, 2018. 25(8): p. 10.

8. Burns, S.J. and S.P. Burns, The shear contribution to the equation of state: A universal law for the elastic moduli of solids. International Journal of Solids and Structures, 2023. 279.

Isothermal predictions for copper in red and tantalum in blue are based on reference [8]. These graphs are isotherms with elastic properties. Irreversible heating and adiabatic material conditions are not isothermal. Most materials are neither isentropic nor reversible at such high stresses. VISAR schematic image is from J. S. Wark, et al, Journal Applied Physics 2023, a major review paper.