This paper describes nondestructive x-ray characterization techniques which detect macroscopic and microscopic defects, determine the overall crystallographic perfection, and detect any unwanted secondary crystals both on the external surface as well as in the interior of single crystal blades. The method of Asymmetric Crystal Topography for diffraction imaging the surfaces of single crystal turbine blades and the method of White Beam Transmission Topography for diffraction imaging through the thickness of single crystal turbine blades are both discussed and illustrated with representive diffraction images (topographs). It is clear that the images gained from these methods have a capability for providing information about the details of crystalline perfection (or lack thereof) in nickel-based alloy single crystal turbine blades. Such information can provide considerable leverage for the crystal grower to help in adjusting processing variables to enhance quality of a critical product. And the same methods of topography can conceiveably provide tools for evaluating the finished product in a way which has not been available to date.

The characteristics and applicable studies of the x rays scattered and propagating near the most upper surface of the substrate under the total reflection condition are described. Since the peak energy of the x rays gives direct information on the electron density of the surface materials, some experiments have been first conducted to confirm this. Then, an in-situ observation of oxidization processes for evaporated Cu films has been also conducted under a UV irradiation and an acid vapor exposure, revealing that there exist several oxidizing stages in time variations, namely a slight increase in the electron density at the initial stage, subsequently an abrupt decrease, and then steady value suggesting the sealing-off mechanism in the oxidization phenomena.

The goal of this study was to develop a three–dimensional imaging method for studies of deformation in low-density materials during loading, and to implement finite element solutions of the elastic equations based on the images. Specimens of silica–reinforced polysiloxane foam pads, 15 mm in diameter by 1 mm thick, were used for this study. The nominal pore density was 50%, and the pores approximated interconnected spheres. The specimens were imaged with microtomography at ∼16µm resolution. A rotating stage with micrometer driven compression allowed imaging of the foams during deformation with precise registration of the images. A finite element mesh, generated from the image voxels, was used to calculate the mechanical properties of the structure, and the results were compared with conventional mechanical testing. The foam exhibited significant nonlinear behavior with compressive loading. The finite-element calculations from the images, which were in excellent agreement with experimental data, suggested that nonlinear behavior in the load displacement curves arises from buckling of the cell walls during compression and not from any nonlinear properties of the base elastomer. High–resolution microtomography, coupled with efficient finite–element modeling, shows promise for improving our understanding of the deformation behavior of cellular materials.

Lightweight metallic cellular materials have the potential for use in composite structures such as plates, shells, and tubes. In order to evaluate the usefulness of these porous materials, an understanding of their failure mechanisms is essential. We have developed a technique called image-guided failure assessment that allows for the 3-dimensional analysis of fracture initiation and progression on the microscopic level. The technique has already been used to study trabecular bone failure, and the objective of this study was to use the technique to study porous aluminum alloys. Image-guided assessment involves the use of a novel micro-compression device to apply and maintain loads, and the use of micro-computed tomography, providing 68 µm isotropic resolution in this application, to image the specimens. Specimens were compressed and imaged at intervals of increasing strain (0%, 0.8%, 4%, 8%, 16%, and 32% strain). The advantage of using a nondestructive approach to assess failure is that subsequent images of increasing strain can be animated to give visual information regarding fracture initiation and progression. In our tests, damage was seen to accumulate and propagate in local bands rather than being evenly distributed throughout the structure. This implies that local strains may be much larger than the apparent strain. These preliminary results demonstrate the usefulness of image-guided failure assessment in obtaining both visual and mechanical data regarding fracture initiation and progression. The technique is applicable to a multitude of porous materials and might, in the future, become a new standard in the mechanical assessment of these structures.

Crack closure is held to be responsible for very low fatigue crack growth rates in many alloys such as Al-Li 2090 T8E41, and early crack face contact during unloading or prolonged contact during loading seems to reduce the driving “force” for crack extension. High resolution x-ray computed tomography (i.e., microtomography) allows one to image the entire volumes of samples and to quantify opening as a function of applied load over the entire crack surface. Crack closure results are reported for a fatigue crack grown under load ratio R=0.1 in a compact tension sample of Al-Li 2090 T8E41; the crack was free to choose its path unconstrained by side-grooves which are normally used to suppress crack deflection. The inter-relationship between crack path, crack face contact and applied load level are discussed.

A combination of two nondestructive techniques, Grazing Incidence X-ray Reflectivity and High Resolution X-ray Diffraction, is used to study (at around 10Å resolution) the composition profile across a 500Å thick film of BaTiO3 grown epitaxially on (100) MgO by MOCVD. Results from both studies indicate diffusion of Mg to about 250Å into the film at film-substrate interface, consistent with the diffuse ferroelectric phase transition observed in this film. The lattice parameter a shows a progressive decrease as we move into the film from the interface, and an anomalously low value in the Mg-free portion of the film.

The pulse structure of synchrotron radiation was used in order to carry out timeresolved x-ray diffraction imaging of high-frequency (up to 0.6 GHz) surface acoustic waves propagating through a single crystal. In x-ray topographs, recorded in the stroboscopic mode, the short wavelength (down to 6 μm) individual wave fronts are clearly visible, providing information on the acoustic scattering processes with participation of lattice defects.

Scanning Acoustic Microscopy has been used to measure and map the Rayleigh wave velocity and the Surface Skimming Longitudinal wave velocities near a crack tip in a sample of Ti-6AI-4V. X-ray diffraction measurements have been performed to map the stress in the same region of the sample. The differences in the contrast between the two acoustic velocity images and their sensitivity to stress are examined. Similarities between x-ray stress images and acoustic velocity images are discussed.

A method to characterize the deformation zone at a crack tip and predict upcoming fracture under load using white light interference microscopy was developed and studied. Cracks were initiated in notched Ti-6A1-4V specimens through fatigue loading. Following crack initiation, specimens were subjected to static loading during in-situ observation of the deformation area ahead of the crack. Nondestructive in-situ observations were performed using white light interference microscopy. Profilometer measurements quantified the area, volume, and shape of the deformation ahead of the crack front. Results showed an exponential relationship between the area and volume of deformation and the stress intensity factor of the cracked alloy. These findings also indicate that it is possible to determine a critical rate of change in deformation versus the stress intensity factor that can predict oncoming catastrophic failure. In addition, crack front deformation zones were measured as a function of time under sustained load, and crack tip deformation zone enlargement over time was observed.

This paper describes the initial phase of the development of a nondestructive, multisensor approach for detecting, quantifying and monitoring degradation of organic coatings applied to aluminum surfaces. Descriptions of the purposes and chemical compositions of layered coatings used on aircraft structures are provided. The discussion then concentrates on ultrasonic thickness measurements. One is the well-established pulse/echo scanning acoustic microscopy and, as a proposed alternative, continuous acoustic waves measurements with a probe in contact to the sample. Advantages and disadvantages of the two methods and their potential as in field applications are discussed.

Dissipated heat has been measured by thermographic technique during fatigue experiments on Ti-6AI-4V. Surface temperature of the specimen was found sensitive to the amount of fatigue damage accumulated in the material. An increased heat dissipation due to fatigue can be related to continuous change in the microstructure (increased dislocation density, stacking faults etc.) of the material. A method based on passive thermography can be proposed to monitor damage accumulation in Ti-6Al-4V due to cyclic loading.

Variation in acoustic nonlinearity has been monitored in real time during fatigue, on four dogbone specimens of Ti-6A1-4V, under low cycle fatigue conditions, from the virgin state all the way to fracture. The results of these experiments show that the acoustic nonlinearity undergoes large changes during the fatigue and follows a similar trend for the material under given fatigue test conditions. Transmission electron microscopic (TEM) examination of the samples with similar composition fatigued to different stages indicates a gradual change in the microstructure and dislocation density, which correlates with the changes in acoustic nonlinearity.

Impedance spectroscopy has been used for the characterization the low-temperature degradation of yttria-stabilized tetragonal zirconia polycrystals in a non-destructive assay. Superficial transformations resulting from annealing in air lead to the appearance of an extra relaxation in the impedance spectra which evolves with degradation extent. It has been demonstrated that in situ electrical characterization cannot be performed because the electrode layers retard the degradation phenomenon. The ideal temperature/time condition to record spectra is also discussed.

This paper gives a short summary of the background, theory and methodology needed to utilize electrical measurements as a non-destructive method for microstructural characterization. Examples are given for all classes of materials. Details are given for how to detect: (1) pore volume in thermal barrier coatings, (2) formation of surface layers due to moisture adsorption in a wide variety of materials, (3) orientation of fibers and whiskers in ceramic matrix and polymer matrix composites, (4) crack detection in metals and (5 ) stacking faults in semiconductors. Many other examples are mentioned. It needs to be emphasized that electrical measurements alone are not sufficient to identify the microstructural features of interest but must always be accompanied by complementary techniques. Proper data collection and data interpretation of properties of a specific set of materials can lead to in-line process monitoring, quality control monitoring, mechanical damage monitoring and environmental degradation monitoring of those materials.

Over the last ten years, the application of high frequency dielectric spectroscopy techniques for the assessment of composite structures has been investigated. Novel approaches to assess non-destructively the evolution during ageing of adhesively bonded carbon fibre reinforced plastic (CFRP) structures and bulk glass fibre reinforced plastic (GRP) structures are presented in this paper and the results are critically assessed.

The applicability and limitations of dielectric measurements, in both frequency and time domain, to the monitoring of water ingress at 30°C and 60°C are examined. The correlation between gravimetric and high frequency dielectric spectroscopy data demonstrates the suitability of the techniques regarding the assessment of water uptake in composites structures and illustrates its potential as a non-destructive evaluation (NDE) technique. The dielectric time domain response (TDR) study of adhesively bonded structures indicates a new way to assess such structures. The approach for frequency domain analysis of bulk GRP using a coaxial probe technique indicates the potential portability of the technique for in-situ measurements.

With the electronic industry being one of the most dynamic, in terms of new technologies, electronic packages have to be designed and optimized for new and ever more demanding applications in relatively short periods of time. This, in turn, indicates a need for effective quantitative testing methodologies. In this paper, a novel hybridized use of nondestructive, noninvasive, remote, full field of view, quantitative opto-electronic holography techniques with computational modeling is presented. The hybridization is illustrated with a representative application, which shows that the combined use of opto-electronic holography techniques and computational modeling provides an effective engineering tool for nondestructive study of electro-mechanical components.

The paper deals with questions concerning the material characterization for steels in the field of engineering and metallurgy. Based on the structure-to-property-relationships, a procedure is proposed to strengthen the systematical development of methods for nondestructive characterization of materials. The state of the nondestructive characterization of metals is reviewed and applications are described in which adequate macroscopic physical properties are measured in order to characterize the materials state and properties nondestructively. The materials characterization of ball bearing steel and cast iron using multiparametrical approaches is discussed in detail.

We have investigated several specimens of ASTM A710 steel containing copper-rich precipitates with variations in the final aging treatment. X-ray diffraction line-broadening and small-angle neutron-scattering experiments revealed the existence of the precipitates and associated coherency strain. We determined the nonlinear ultrasonic parameter β for each specimen by harmonic-generation experiments and measured the ultrasonic longitudinal velocity νL and attenuation αL. Although νL and αL showed no consistent trends, β increased with increasing strain. This correlation is compared to a microstructural model for harmonic generation that includes a contribution from precipitate-pinned dislocations.

Heat generation from a notch during the compression-compression fatigue of a cellular Al alloy has been measured and compared with a model. The measurements indicate that heat is generated because of hysteresis occurring in narrow cyclic plastic zones outside the notch. This process continues until the notch closes. At closure, a brief period of heat generation arises because of friction along the notch faces. A plasticity model based on the Dugdale zone is shown to provide a reasonably accurate characterization of the heat generated, with the proviso that an “ineffective” zone be transposed onto the notch tip. It is found that the temperatures generated are too small to cause fatigue by thermal softening. A fatigue mechanism based on either geometric softening of the cells or crack growth in the cell walls is implied.

In recent years increasing interest in magnetic materials especially amorphous and nano crystalline layers has arised. Due to the magnetostrictive and magnetoresistive properties magnetic materials obtained high importance in sensor, actuator and memory applications. Therefore new methods to characterize magnetic and mechanical properties of magnetic materials are required. Two new microscopic techniques will be presented in this paper.