An improved portable microwave interferometry system has been automated to permit rapid examination of components with minimal operator attendance. Functionalities include stereo and multiplexed, frequency-modulated at multiple frequencies, producing layered volumetric images of complex ceramic structures. The technique has been used to image composite ceramic armor and ceramic matrix composite components, as well as other complex dielectric materials. The system utilizes EvisiveScan microwave interference scanning technique. Validation tests include artificial and in-service damage of ceramic armor, surrogates and ceramic matrix composite samples. Validation techniques include micro-focus x-ray and computed tomography imaging. The microwave interference scanning technique has demonstrated detection of cracks, interior laminar features and variations in material properties such as density. The image yields depth information through phase angle manipulation, and shows extent of feature and relative dielectric property information. It requires access to only one surface, and no coupling medium. Data are not affected by separation of layers of dielectric material, such as outer over-wrap. Test panels were provided by the US Army Research Laboratory, and the US Army Tank Automotive Research, Development and Engineering Center (TARDEC), who with the US Air Force Research Laboratory have supported this work.

Application of non-contact, scanning, microwave interferometry for inspection of ceramic-based composite armor facilitates detection of defects which may occur in manufacturing or in service. Non-contact, one-side access permits inspection of panels while on the vehicle. The method was applied as a base line inspection and post-damage inspection of composite ceramic armor containing artificial defects, fiduciaries, and actual damage. Detection, sizing, and depth location capabilities were compared using microwave interferometry system and micro-focus digital x-ray imaging. The data demonstrates corroboration of microwave interference scanning detection of cracks and laminar features. The authors present details of the system operation, descriptions of the test samples used, and recent results obtained.

A series of 16-inch square by 2-inch thick, multi-layered ceramic composite armor specimens, some of which had intentional design defects inserted between the layers, were inspected using a 128 element, 10MHz immersion phased array ultrasound system. To overcome some of the issues associated with the acoustic wave propagation in layered media, two digital signal processing methods (Fast Fourier Transform (FFT) and Wiener filtering) were employed. While previous work has been presented on the significant improvement in defect detection associated with these methods, the authors present a detailed and quantitative statistical analysis of these results. This analysis suggests that these intentional defects were a) not detectable when the defect was in a particular configuration, b) readily detectable in all cases for alternate defect position configurations, and c) clearly identifiable in most cases for those configurations. However, even in the configuration where intentional defects were not detected (owing to inherent design issues in the armor structure), significant variation in interfacial quality was observed and quantified, and these results will also be presented.

Inspection of ceramic-based armor has advanced through development of a microwave-based, portable. non-contact NDE system. Recently, this system was miniaturized and made wireless for maximum utility in field applications. The electronic components and functionality of the laboratory system are retained, with alternative means of position input for creation of scan images. Validation of the detection capability was recently demonstrated using specially fabricated surrogates and ballistic impact-damaged specimens. The microwave data results have been compared to data from laboratory-based microwave interferometry systems and digital x-ray imaging. The microwave interference scanning has been shown to reliably detect cracks, laminar features and material property variations. The authors present details of the system operation, descriptions of the test samples used and recent results obtained.

: A series of 16-inch square by 2-inch thick, multi-layered ceramic composite armor specimens, some of which had intentional design defects inserted between the layers, were inspected using a 128 element, 10MHz immersion phased array ultrasound system. To overcome some of the issues associated with the acoustic wave propagation in layered media, two digital signal processing methods (Fast Fourier Transform (FFT) and Wiener filtering) were employed. While previous work has been presented on the significant improvement in defect detection associated with these methods, the authors present a detailed and quantitative statistical analysis of these results. This analysis suggests that these intentional defects were a) not detectable when the defect was in a particular configuration, b) readily detectable in all cases for alternate defect position configurations, and c) clearly identifiable in most cases for those configurations. However, even in the configuration where intentional defects were not detected (owing to inherent design issues in the armor structure), significant variation in interfacial quality was observed and quantified, and these results will also be presented.

A microwave interferometry system has been miniaturized and configured for flexible field use to determine the "status" of composite ceramic armor. The system utilizes Evisive Scan microwave interference scanning technique and has been demonstrated to detect damage on composite ceramic test specimens as well as composite ceramic surrogates with engineered features. The microwave interference scanning technique has demonstrated detection of cracks, interior laminar features and variations in material properties such as density. It requires access to only one surface, and no coupling medium. Data are not affected by separation of layers of dielectric material, such as outer over-wrap. Other methods, including through-transmission x-ray, x-ray Computed Tomography, and destructive examination, have been used to corroborate the microwave data and establish quantitative performance.Test panels used in this work were provided by commercial manufacturers, the US Army Research Laboratory, US Army Tank-Automotive Research, Development and Engineering Center (TARDEC) and by the Ballistics Testing Station through Argonne National Laboratory. This paper will describe the system and present current results. This work is supported by US Army Tank-Automotive Research, Development and Engineering Center (TARDEC) and US Army Research Laboratory.

Monolithic ceramic tile is used as part of ceramic-composite armor. Rejection of individual tile that contain potential threat-defeat-reducing ―defects‖ must be accomplished in a fast and cost-effective manner. Water-immersion phased-array ultrasound using 10 MHz 128-element transducers sequenced at 32-elements has been demonstrated to quickly scan and detect 25-50 um known inclusion-type defects in individual 25 mm thick SiC tile. Further, use of similar phasedarray transducers and similar transducer-element activation sequences, has shown detection of intentional internal defects in tests of 40 cm square by 50 mm thick, multi-layered composite ceramic-armor specimens. Large changes in acoustic velocities of the various layered materials causes focusing issues of the ultrasonic wave. The use of various digital signal processing methods can be used to overcome some of these issues. The results show that use of phased array ultrasound can reliably be used for defect detection in either monolithic or composite ceramic-armor. The technology and various results are presented.

This chapter contains sections titled: Introduction Plan/Scope of Work Description of the NDE Methods Results Conclusions

This chapter contains sections titled: Introduction Approach Results Conclusion

The projected microwave energy pattern, wave guide geometry, positioning methods and process variables have been optimized for use of a portable, non‐contact, lap‐top computer‐controlled microwave interference scanning system on multi‐layered dielectric materials. The system can be used in situ with one‐sided access and has demonstrated capability of damage detection on composite ceramic armor. Specimens used for validation included specially fabricated surrogates, and ballistic impact‐damaged specimens. Microwave data results were corroborated with high resolution direct‐digital x‐ray imaging. Microwave interference scanning detects cracks, laminar features and material properties variations. This paper presents the details of the system, the optimization steps and discusses results obtained.

Determining when to replace current composite ceramic materials to preserve functionality is an important cost factor in their use. The question posed is, "How to estimate performance ability of the individual composite ceramic s in situ?" Identification of damaged material is important usefulness and replacing only damaged material is an important cost factor. Recently, a portable one-sided microwave scanning technique, that can be used in situ. has been demonstrated to detect damage on actual test specimens. Work has been conducted using as-produced and intentionally impact damaged specimens. Data from the microwave scanning test method have been compared directly to through transmission x-ray examination data for the sample specimens. Each "crack" detected by through-transmission x-ray is also detected by the microwave scanning method. While the visual presentation of the microwave image is not identical to the x-ray image, it is equally unambiguous with respect to detection of features in the specimen. Based upon development work done to date. it should lie possible to achieve microwave scanning rates which would permit inspection of an area of about 4 square feet (2 feet by 2 feet) in 5 minutes or less. It appears that the method is suitable for in-situ monitoring of materials.

In this work, X-ray computed tomographic imaging technology with high spatial resolution has been explored for metrological applications to Si3N4 ceramic turbine wheels. X-ray computed tomography (XCT) was developed for image metrology by utilizing a flat-panel, amorphous silicon (a-Si) detector consisting of a 1024 × 1024 matrix of photodiodes on a 100-μm centers. Modulation transfer functions (MTFs) were developed from a 2-D projection image of a line-pair phantom and from a three-dimensional (3-D) reconstruction of a ceramic hole-phantom. These results suggest that the detector can achieve a resolution of 140 μm at 50% contrast, and a resolution of approximately one pixel (100 μm) at 20% of maximum image contrast. Further, for application of the XCT system to NDE metrology, the Si3N4 ceramic turbine wheel was scanned, and cone-beam XCT reconstruction algorithm was used to allow full-volume data acquisition from the turbine wheel. Special software was developed so that edge detection and complex blade contours could be determined from the XCT data. The point-cloud function that is a 3-D edge function of the XCT reconstruction was used to obtain geometrical information about the scanned object. The blade-tip contour was determined from the point-cloud function with ±100-μm accuracy and within <1 min. The feasibility of using the XCT for dimensional analyses was compared with that of a coordinate-measuring machine.

Knowledge of the distribution of the organic binder materials used in the injection molding of ceramics is important because nonuniformity affects local densification rates and hence mechanical properties. Two noncontacting, noninvasive, nondestructive inspection methods-X-ray computed tomography (CT) and nuclear magnetic resonance tomography-have been applied to a set of Si3N4 specimens with discrete regions of known binder concentration ranging from 2-20 wt%. The results suggest that with current technology, X-ray CT is a more sensitive method, with the capability to detect variations of 1 wt% in binder content.

Low-density inclusions and voids in ceramics present a detection problem to X-ray imaging because of the relatively low contrast of the resulting image. An X-ray imaging technique xeroradiography has been in use for medical applications for detecting calcifications (low-density inclusions) in breast tissue. The method has a “built-in” edge enhancement. We have applied this technique to green and densified Si3N4 specimens and have shown initial improvements over other X-ray methods in the detection of seeded defects.

The manufacture of reliable high performance structural ceramics requires a good understanding of the different steps involved in the process. The presence of nonuniformities in the distribution of the polymeric binder could give rise to local fluctuations of density that could produce failure of the ceramic piece. Specimens prepared from Al2O3 with 15 and 2.5% w/w binder were imaged using NMR techniques in order to measure binder distribution maps. The results show that NMR imaging could be a useful technique to nondestructively evaluate the quality of green-state specimens.

The objective of this work was to assess the potential of acousto-ultrasonic non-destructive evaluation method to characterize the strength of clay-bonded SiC and alumina/mullite based hot gas filter materials. Samples were exposed to high temperature water vapor environments, the stress wave factor (SWF) number was determined by acousto-ultrasound method and the hoop strength was obtained by internal burst testing. The samples were further analysed microstructurally using electron microscopy and x-ray diffraction. Density and porosity were obtained using the Archimedes method. A correlation of hoop strength with averaged SWF was seen. The variation in SWF data and strength along the samples are discussed in terms of density and porosity.