Tutorials

Ultrasound is one of the most pervasive nondestructive evaluation (NDE) techniques because of its sensitivity, flexibility, and low cost. The selection of the measurement frequency for a specific application is especially important and is usually based on the relevant length scales. If the goal is defect detection, the defect size guides the frequency choice. However, scattering from the inherent microstructure of most polycrystalline materials will reduce the imaging contrast from true defects. This concept of signal-to-grain-noise is crucial for experiment design. In this tutorial, the interaction of ultrasonic waves with complex microstructures will be detailed. Microstructural parameters such as grain size, grain size distribution, grain morphology, and material texture influence the wave speed and attenuation of the incident coherent wave field. In addition, scattering events give rise to a diffuse (i.e., incoherent) field which is governed by the spatial statistics of the microstructure. The coherent and diffuse fields have separate roles in NDE or materials characterization and these will be outlined. The statistics of a collection of signals will also be examined with respect to specific manufacturing processes including cast and forged samples and those created using metal additive manufacturing. Finally, the role of synthetic microstructures as part of the modeling process will be discussed. The structural performance of metals is governed in large part by the organization of the microstructure and ultrasonic experiments must be clearly understood for these measurements to be truly quantitative.

Predictive health monitoring will require the development of advanced sensing techniques capable of providing quantitative information on the damage state of structural materials. Second harmonic generation techniques can measure absolute, strength- based material parameters which can be coupled with uncertainty models to enable accurate and quantitative life prediction. Starting at the material level, this talk will examine a combination of sensing techniques and physics-based models to characterize damage in metals. These second harmonic techniques are acoustic wave based, so component interrogation can be performed with bulk, surface and guided waves using the same underlying material physics. The talk will consider applications to characterize fatigue damage, thermal embrittlement, irradiation damage and sensitization.

Chipless RFID is a relatively new subset of the RFID field with the first reports of the technology occurring around 2006. Chipless tags are wireless and passive, and can be used for both identification applications and sensing applications, such as the sensing of strain, cracks, corrosion, temperature, material properties, and rotation, to name a few. These capabilities are rooted the structure of the tag (i.e., the resonators, patch antennas, microstrip lines, and environmentally sensitive substrates that make up the tag) and are accessed by interrogating the tag with an electromagnetic wave. In this way, chipless RFID provides a low cost, small form factor, minimally invasive, and extreme environment tolerant sensing solution for NDE applications. This tutorial will provide an overview of chipless RFID system design and implementation, including tag architectures, design techniques, fabrication methods, measurement approaches, response interpretation, and implementation considerations.

Thermography is a well-known nondestructive testing and evaluation (NDT&E) technique that has found success in many areas including civil infrastructure and aerospace, amongst others. Thermography is attractive due to its large-scale inspection potential, advanced established signal processing techniques, and relatively easy-to-interpret results. In recent years, thermography has expanded from the traditional flash lamp excitation to other excitation types including laser, induction, ultrasonic, and more recently, microwave based. When incorporating a microwave excitation, the approach is commonly referred to as Active Microwave Thermography, or AMT. AMT utilizes high frequency electromagnetic energy to induce a thermal response in a material or structure of interest. This thermal response is usually achieved through dielectric absorption within the material and takes place volumetrically (as opposed to solely on the surface such as the case for flash lamp thermography). While the concept of microwave-based heating is well-established, this phenomenon, coupled with thermographic inspection, has only joined the NDT&E world in recent years. To this end, AMT has found success in a variety of infrastructure- and aerospace-related inspections including detection of water ingress, delamination, voids, and flat-bottom holes. AMT has also shown promise as an alternative approach for thermal materials characterization.

This tutorial will begin with the introduction of relevant fundamental concepts from thermodynamics and electromagnetics as it relates to AMT including heating mechanisms and the interaction of materials with high frequency signals. Then, the concept of AMT as a thermographic inspection technique will be introduced, with example applications and practical challenges discussed. The tutorial will conclude with a discussion of the future of the technology and new potential applications. 

The U.S. Department of Homeland Security (DHS) needs to protect all ports of entry into the U.S., including air, land, and sea. The tutorial will focus on the nondestructive evaluation (NDE) security systems used to protect air, land and seaports of entry. The tutorial will include a description of the relevant physics utilized by these NDE security systems. Civil aviation airport security systems use techniques such as x-ray computed tomography and mm-wave imaging to detect prohibited items, e.g., explosives and weapons, in carry-on and checked luggage, and on passengers, respectively. For land and seaports of entry, security systems are deployed or are under development to detect prohibited or restricted items from being brought into the U.S. Prohibited items include dangerous toys, cars that don't protect their occupants in a crash, bush meat, or illegal substances like drugs. Restricted items include firearms, certain fruits and vegetables, animal products, animal by products, highly enriched uranium, plutonium, and radiological dispersal devices. Measurement systems deployed or underdevelopment include x-ray radiography, x-ray backscatter, prompt neutron x-ray photo fission, and muon tomography. The tutorial will include a summary of the problem, the physics of the NDE systems, and how these technologies are applied. 

Shearography is a highly effective NDE technique developed in the mid-1980s for the inspection of aerospace composites in manufacturing. Shearography uses the wave nature of laser light in an imaging interferometry, to detect both surface and subsurface defects in ductile materials ranging from foam insulation to titanium. While laser light does not penetrate the surface, a small, applied stress change passes through the volume of the test part. Defects can produce a small out-of-plane deformation on the surface which have a characteristic appearance in shearography images. Stressing methods include ultrasonic and sonic vibration, heat, pressure, partial vacuum, microwave radiation, and electromagnetic induction. In composites, defects such as disbonds, delamination, fiber bridging and wrinkles, FOD, porosity and impact damage are detectable. Shearography NDE techniques offer non-contact inspection and very high throughput for parts with both flat and complex geometries. Further, shearography inspection systems do not require contour following as required with UT C-Scan. 

This tutorial will introduce the basic concepts of the shearography imaging interferometer, stress loading for defect detection, and examples in generic materials and structures. A range of shearography applications and a discussion of the challenges and successes covering aircraft structures, helicopter blades, composite over-wrapped pressure vessels (COPV), liquid propellant rocket engines, and cryogenic rocket fuel tank insulation, will also be presented.