four areas have been undertaken within this project: operational evaluation, diagnostic measurements, information condensation, and damage identification. The developments in each of these four aspects of structural health monitoring have been exercised on a broad range of experimental data. This experimental data has been extracted from structures from several application areas which include aging aircraft, wind energy, aging bridges, offshore structures, structural supports, and mechanical parts. As a result of these advances, Sandia National Laboratories is in a position to perform further advanced development, operational implementation, and technical consulting for a broad class of the nation`s aging infrastructure problems.

Cerium oxide (ceria, CeO2) is frequently used as a standard in applications such as synchrotron and x-ray free electron lasers for calibrating x-ray wavelengths and offers the potential for understanding the high pressure properties and deformation mechanisms in a wide range of similar face centered cubic (fcc) materials. In this study, the pressure dependence of the strength of ceria was investigated up to 38 GPa using angle dispersive x-ray diffraction in a radial geometry in a diamond anvil cell. In this experiment, the difference in the stress along the axis of compression and perpendicular to the direction of compression can be determined, giving a quantity known as the differential stress. It was found that the differential stress (t), a measure of the lower bound for yield strength, initially increases rapidly from 0.35 ± 0.06 GPa to 2.2 ± 0.4 GPa at pressures of 1.8 and 3.8 GPa, respectively. Above 4 GPa, t increases more slowly to 13.8 ± 2.6 GPa at a pressure of 38 GPa. The changes in the preferred orientation (texture) of CeO2 with pressure were also measured, allowing for the determination of active deformation mechanisms using an elasto-viscoplastic self-consistent model (EVPSC). It was found that as pressure increased, the [001] direction had a slight preferred orientation along the axis of compression. Our EVPSC model of experimental fiber (cylindrically symmetric) textures and lattice strains were most consistent with dominant slip activity along {111}⟨11¯0⟩.

Tantalum (Ta) is a metal that has useful properties that make it useful in extreme environments. It is, therefore, important to understand how Ta performs in such extreme conditions by accurately measuring its properties. In this work, the yield strength of tantalum has been measured at pressures up to 276 GPa using axial and radial x-ray diffraction (XRD) methods in diamond anvil cells (DACs). We measured strength using XRD in a radial DAC to 50 GPa, in an axial DAC to 60 GPa using diamonds with standard flat culets, and in a final experiment to 276 GPa using toroidal diamond anvils. The radial XRD data were refined using the Material Analysis Using Diffraction Rietveld software package to extract lattice strain and the yield strength. The axial data were refined using the General Structure Analysis System II and a linewidth method was used to calculate the yield strength. The yield strength measured near ambient pressure was found to be 0.5 GPa and increased with a pressure of up to 50 GPa, where the yield strength plateaued at a value of 2.4 GPa. At pressures above 60 GPa, the strength increased again to a maximum value of 9 GPa at the highest pressure of 276 GPa. The data from the three experiments show good agreement between the methods and previously reported experimental data. This agreement illustrates the value of axial diffraction data for material strength determination and allows for measurements at multi-hundreds of GPa using toroidal DACs.

Uranium ditelluride (UTe$_2$) has attracted recent interest due to its unique superconducting properties, which include the potential for a topological odd-parity superconducting state. Recently, ac-calorimetry measurements under pressure indicate a change in the ground state of UTe$_2$ from superconducting to antiferromagnetic at 1.4 GPa. Here, we investigate the effect of pressure on the crystal structure of UTe$_2$ up to 25 GPa at room temperature using x-ray diffraction. We find that UTe$_2$, which at ambient conditions has an orthorhombic ($Immm$) structure, transforms to a body-centered tetragonal ($I4/mmm$) structure at 5 GPa in a quasi-hydrostatic neon (Ne) pressure transmitting medium. In the absence of a pressure-transmitting medium, this transformation occurs between 5 and 8 GPa. The data were fit with a third-order Birch-Murnaghan equation of state resulting in values of $B_0$=46.0 $\pm$ 0.6 GPa, $B^{\prime}$=9.3 $\pm$ 0.5 (no pressure medium) and $B_0$=42.5 $\pm$ 2.0 GPa, $B^{\prime}$=9.3 (fixed) (neon pressure medium) for the $Immm$ phase. For the $I4/mmm$ phase, $B_0$=78.9 $\pm$ 0.5 GPa and $B^{\prime}$=4.2 $\pm$ 0.1 (no pressure transmitting medium), and $B_0$=70.0 $\pm$ 1.1 GPa and $B^{\prime}$=4.1 $\pm$ 0.2 (neon pressure medium). The high-pressure tetragonal phase is retained after decompression to ambient pressure, with approximately 30% remaining after 2 days. We argue that the observed phase transition into a higher symmetry structure at P~5 GPa (orthorhombic to tetragonal), is accompanied by an increase in the shortest distance between uranium atoms from 3.6 Angstrom (orthorhombic) to 3.9 Angstrom (tetragonal), which suggests localization of the 5f electrons, albeit with a 10.7% decrease in volume.

Accurate knowledge of material properties at extreme pressures and temperatures is very valuable in the fields of planetary science and condensed matter physics, as well as in mechanical and structural engineering applications. Sound speeds and elastic moduli are particularly important properties since they can be used to refine equation of state and strength models. One way to determine the temperature and pressure dependence of sound speeds and elastic moduli is to use the ultrasonic pulse-echo technique on a sample compressed in a hydraulic press, often in situ at a synchrotron X-ray source. X-ray radiography is used to determine the physical dimensions of the sample during compression which is needed for sound speed determination. Additionally, X-ray diffraction is used to determine the sample’s density, which is used to determine the elastic moduli. This talk will present the technique and some results of such measurements using the Paris-Edinburgh hydraulic press at the High Pressure Collaborative Access Team (HPCAT) sector of the Advanced Photon Source.

In this report, we present results of high-pressure experiments probing the melt line of zirconium (Zr) up to 37 GPa. This investigation has determined that temperature versus laser power curves provide an accurate method to determine melt temperatures. When this information is combined with the onset of diffuse scattering, which is associated with the melt process, we demonstrate the ability to accurately determine the melt boundary. This presents a reliable method for rapid determination of melt boundary and agrees well with other established techniques for such measurements, as reported in previous works on Zr.

Titanium (Ti) is commonly used in industrial applications such as aerospace, automotive and biomedical due to its corrosion resistance and high strength to density ratio. At high pressure(2.9-10.5 GPa), Ti transforms from the hexagonal close packed α phase to the open hexagonal ω phase.[1] The ω phase of Ti is brittle and recoverable at ambient pressure and therefore alters the properties of Ti. It is therefore important to understand this phase transformation of Ti as it is known to be affected by several factors including (i) the pressure medium used, (ii) the presence of impurities, and (iii) the compression rate.[1, 2] So far, Ti has mostly been compressed using 'slow' quasi-static or 'fast' shock compression; only one intermediate compression rate has so far been reported.[3, 4] In 2007, Evans et al. described a method for using a piezoelectric crystal to drive a diamond anvil cell, this is known as a dynamic diamond anvil cell (dDAC).[5] This method allows for controllable compression rates, ramp profiles and pressures. In the decade since, developments in both synchrotron technology (including fast detectors) and dDACs have made it possible to use time resolved X-ray diffraction to investigate phase transformations at significantly higher compression rates than conventional DACs, up to 102 TPa/s.[6, 7] These new developments have been used to further understand the phase transformation of Ti under hydrostatic and non-hydrostatic conditions at critical compression rates between static and shock compression rates. Recent dDAC experiments compressing Ti at compression rates between 2.5 and 3500 GPa/s indicate that at faster compression rates, under non-hydrostatic compression (without a pressure medium), the starting and completion pressure of the α to ω phase transformation in Ti increases.

Polyethylene is a widely used plastic exhibiting a large range of properties that depend on molecular weight, crystallinity, chain branching, and cross-linking. In this study, the sound speeds and elastic properties of a variety of commercially available polyethylene materials were experimentally determined using the pulse-echo ultrasound technique. In situ pressure dependent measurements, including ultrasound time of flight, x-ray diffraction, and x-ray radiography, were performed using a Paris-Edinburgh large volume press at the High Pressure Collaborative Access Team (HPCAT), beamline 16-BM-B at the Advanced Photon Source. Polyethylene sound speed and elastic moduli were found to increase with increasing pressure. The zero pressure orthorhombic phase was found to transform to monoclinic at low pressures of similar to 0.1 GPa.

Zirconium (Zr) has properties conducive to nuclear applications and exhibits complex behavior at high pressure with respect to the effects of impurities, deviatoric stress, kinetics, and grain growth which makes it scientifically interesting. Here, we present experimental results on the 300 K equation of state of ultra-high purity Zr obtained using the diamond-anvil cell coupled with synchrotron-based x-ray diffraction and electrical resistance measurements. Based on quasi-hydrostatic room-temperature compression in helium to pressure P  =  69.4(2) GPa, we constrain the bulk modulus and its pressure derivative of body-centered cubic (bcc) β-Zr to be K  =  224(2) GPa and K′  =  2.6(1) at P  =  37.0(1) GPa. A Monte Carlo approach was developed to accurately quantify the uncertainties in K and K′. In the Monte Carlo simulations, both the unit-cell volume and pressure vary according to their experimental uncertainty. Our high-pressure studies do not indicate additional isostructural volume collapse in the bcc phase of Zr in the 56–58 GPa pressure range.

The isothermal compression of transition metal tantalum (Ta) was studied in a diamond anvil cell by X-ray diffraction utilizing rhenium (Re) and gold (Au) as internal X-ray pressure standards. The Re pressure marker was employed during non-hydrostatic compression to pressures up to 310 GPa while the Au pressure marker was used during quasi-hydrostatic compression in a neon pressure-transmitting medium to 80 GPa. Two ultra-high pressure experiments were conducted on Ta and Re mixtures utilizing focused-ion beam machined toroidal diamond anvils with central flats varying from 8 microns to 16 microns in diameter. The Ta metal was observed to be stable in the body-centered-cubic phase to a volume compression V/V-0 = 0.581. The measured equations of state (EOS) of Ta using two different calibrations of the Re pressure marker are compared with the ambient temperature isotherm derived from shock compression data. We provide a detailed analysis of EOS fit parameters for Ta under quasi-hydrostatic and non-hydrostatic conditions.

Ultrasound Pulse-Echo measurements are widely used to determine highly accurate sound speeds and elastic moduli. The most accurate of these measurements accounts for the effect of the acoustic couplant used between a buffer rod and a sample to promote energy transfer through the interface. However, the data acquisition traditionally required for this correction can be time consuming, lasting tens of minutes. This time consumption limits the usability of this approach for measurements on dynamic systems or where time resolved measurements are desired. This work reports on the development and demonstration of a broadband ultrasound pulse-echo technique which enables the frequency dependent couplant correction to be made with data acquisition times that are 20-30 times faster than the traditional approach. The technique is demonstrated on measurements of samples inside a large volume pressure cell. Such measurements enable the determination of the pressure dependence of sound speeds and thus a material's Third Order Elastic Constants, needed for the design of acoustic wave devices intended for high acceleration environments.