Nonlinear Elastic Wave Spectroscopy (NEWS) Techniques to Discern Material Damage, Part I: Nonlinear Wave Modulation Spectroscopy (NWMS)

The level of nonlinearity in the elastic response of materials containing structural damage is far greater than in materials with no structural damage. This is the basis for nonlinear wave diagnostics of damage, methods which are remarkably sensitive to the detection and progression of damage in materials. Nonlinear wave modulation spectroscopy (NWMS) is one exemplary method in this class of dynamic nondestructive evaluation techniques. The method focuses on the application of harmonics and sum and difference frequency to discern damage in materials. It consists of exciting a sample with continuous waves of two separate frequencies simultaneously, and inspecting the harmonics of the two waves, and their sum and difference frequencies (sidebands). Undamaged materials are essentially linear in their response to the two waves, while the same material, when damaged, becomes highly nonlinear, manifested by harmonics and sideband generation. We illustrate the method by experiments on uncracked and cracked Plexiglas and sandstone samples, and by applying it to intact and damaged engine components.     

Ionic conductivity of Sm,Gd, Dy and Er-doped ceria

Ceria-based materials are prospective electrolytes for intermediate-temperature solid oxide fuel cells. The ionic conductivities of ceria-doped with Sm, Gd, Dy and Er are investigated as a function of temperature by using a.c. impedance. The results show that conductivity depends on the rare earth dopant, its amount, an appearance of second phase, and the microstructure. With 10 mol% dopant, Sm exhibits higher conductivity than Gd, Dy and Er, respectively. With an increase in Dy content, the total conductivity increases, which is attributed to an increase in grain boundary conductivity. By contrast, an increasing amount of Er from 10 to 20 mol% reduces the conductivity of ceria and results in a separated phase of Er₂O₃ as detected by X-ray diffraction and scanning electron microscopy. In addition, the grain size corresponding to grain boundary density affects the conductivity due to the contributions from the grain interior and grain boundary conductivities.     

Effect of La and K on the microstructure and dielectric properties of Bi0.5Na0.5TiO3-PbTiO3

Small amounts of lanthanum and potassium dopants could modify the microstructure and dielectric properties of 0.90Bi_0.5Na_0.5TiO₃-0.10PbTiO₃ and 0.88Bi_0.5Na_0.5TiO₃-0.12PbTiO₃ solid solutions. La lowered both phase transition temperatures of ferroelectric to antiferroelectric and antiferroelectric to paraelectric. It also decreased the maximum value of relative dielectric permittivity of the composition. In contrast, K shifted the first phase transition to the lower temperature but insignificantly affected the Curie temperature and raised the maximum dielectric permittivity. Furthermore, K influenced the microstructure in the way to enhance the long grains of this solid solution but La inhibited this effect.     

La-, K- and Nb-doped 0.90(Bi0.5Na0.5TiO3)–0.10PbTiO3

Lanthanum, Potassium and Niobium have been selected as cation dopants to modify the relaxor characteristics of 0.90(Bi_0.5Na_0.5TiO₃)–0.10PbTiO₃. The experimental results show that La lowers the phase transition temperatures and decreases the grain size. In contrast, the grain size of K-doped composition tends to increase. Furthermore, the maximum of dielectric permittivity and the Curie temperature increase as compared to those of La-doped material. La can improve the broadness of dielectric permittivity of 0.90(Bi_0.5Na_0.5TiO₃)–0.10PbTiO₃. However, Nb is a better promising dopant for enhancing the relaxor behavior for this composition.     

Melt Processing of YBa2Cu3O7-x

Sintering YBa₂Cu₃O_{7- x} bulk forms at 1050°C followed by annealing at 980°C causes the development of a thick oriented surface layer (Lotgering factor = 0.7). The thickness of the layer depends on the thermal treatment, which is a two-step sintering process. Firing at 1050°C for 2.5 h followed by 30 h at 980°C leads to the development of a 0.1-mm-thick surface layer, with clear indication that longer annealing would result in a thicker film. Some orientation develops during un-axial compaction of the powders. Lotgering orientation factor calculation from X-ray diffraction analysis. SEM, and TEM were used to characterize the microstructure of these samples. T _c was similar to that of conventionally processed high-density samples, between 83 and 87 K. Some thermal treatments resulted in samples that displayed high resistivity above T _c , possibly caused by segregation of Cu to the grain boundaries.     

Characterization of Bi0.5Na0.5TiO3-PbTiO3M Dielectric Materials

Bi_0.5Na_0.5TiO₃ (BNT) modified with Pb showed an increased and broadened dielectric constant and limited grain growth. Pb also lowered the first transition temperature. The phases of BNT were confirmed to be ferroelectric at room temperature which transformed to antiferroelectric above 220°C. When BNT was doped with 10% Pb, the first transition decreased to 140°C and abruptly disappeared in the composition with 17% Pb. The crystal structure of 17%-Pb-doped BNT at room temperature is tetragonal, which differs from the rhombohedral structure at lower Pb contents. Thus, the phase boundary between rhombohedral and tetragonal ferroelectric phase was determined to be between 15% to 17% Pb in this study.     

Nonlinear Elastic Wave Spectroscopy (NEWS) Techniques to Discern Material Damage,Part I: Nonlinear Wave Modulation Spectroscopy (NWMS)

Abstract

The level of nonlinearity in the elastic response of materials containing structural damage is far greater than in materials with no structural damage. This is the basis for nonlinear wave diagnostics of damage, methods which are remarkably sensitive to the detection and progression of damage in materials. Nonlinear wave modulation spectroscopy (NWMS) is one exemplary method in this class of dynamic nondestructive evaluation techniques. The method focuses on the application of harmonics and sum and difference frequency to discern damage in materials. It consists of exciting a sample with continuous waves of two separate frequencies simultaneously, and inspecting the harmonics of the two waves, and their sum and difference frequencies (sidebands). Undamaged materials are essentially linear in their response to the two waves, while the same material, when damaged, becomes highly nonlinear, manifested by harmonics and sideband generation. We illustrate the method by experiments on uncracked and cracked Plexiglas and sandstone samples, and by applying it to intact and damaged engine components.