Experiences in the Use of Guided Ultrasonic Waves to Scan Structures

The use of guided ultrasonic waves to rapidly interrogate large structures is a topic that is currently receiving considerable attention. The purpose of this paper, and the companion paper by Alers [1], is to briefly review some past experience that may not be readily available to current researchers since many of the results were not presented in archival publications. The work described in this paper was conducted in the context of exploring applications of electromagnetic-acoustic transducers (EMATs) [2,3] as a part of the NDE effort at the Rockwell International Science Center in the period 1970–1980. In addition to the author, others playing key roles in various parts of this effort included G. A. Alers, R. K. Elsley, C. M. Fortunko, M.W. Mahoney and C. F. Vasile. The companion paper by Alers includes subsequent developments at the private company, Magnasonics, Inc. as well as more recent work at the National Institute of Standards and Technology. Although EMAT’s were used in all of this work as the sensors to excite and detect the guided ultrasonic modes, the basic ideas apply to the use of guided modes excited by any kind of sensor to scan structures

Ultrasonic Measurement of Formability in Thin Ferritic Steel Sheet

The formability of rolled sheet metal is strongly influenced by the texture of the polycrystalline metal. For steel sheet, it is desirable to have high drawability to make automobile body parts, etc. In addition, material homogeneity is desired; that is, material cut from different parts of a rolled sheet should have the same plastic deformation when subjected to deep drawing

Experimental Validation of Models Applicable to the Ultrasonic Inspection of Nuclear Components

Achieving reliable inspection of nuclear reactor components requires the development and proper field implementation, of a variety of ultrasonic techniques. Because of advances in ultrasonic technology and concerns with ever changing potential failure modes of aging reactors, new inspection techniques are constantly undergoing development and validation. The cost of a purely experimental approach to this process can be excessive due to sample fabrication, measurement and data interpretation, and destructive analysis. Consequently, research efforts have been aimed at the development and application of models which will help reduce those costs by providing theoretical guidance [1,2]. Reported here are the results of an experimental program which was undertaken with the goal of determining the accuracy of the models in predicting inspection results. Two models were considered. The first predicts the evolution of ultrasonic field patterns as a beam propagates from a transducer and into a component. The second predicts the ultrasonic inspection response of a branched crack, which is an idealization of an intergranular stress corrosion crack (IGSCC)

Measurement of Thermal Stress in Railroad Rails Using Ultrasonic SH Waves

The use of welded joints in railroad tracks has led to problems of rail buckling brought about by the development of large compressive stresses during hot days. On cold days, tensile stresses can actually fracture the rail. In order to prevent this source of derailments, it is desirable to develop an easily used instrument to measure the level of stress in an arbitrary section of track in the field. Ultrasonic birefringence, acoustic emission and certain magnetic phenomena have all been used to attack this problem but they all suffer from the necessity for calibrating the sensor under stress-free conditions in order to correct for metallurgical structure variations. A new ultrasonic technique based on using surface skimming shear horizontal ultrasonic waves generated and detected by EMATs was investigated here because it rigorously eliminates the effects of metallurgical texture as well as unreliable coupling of the transducer to the part. Tests on sections of rail mounted in a 200,000 pound testing machine at the University of New Mexico demonstrated that the theory for the basic phenomenon is correct and that the stress level can be measured in spite of the presence of considerable texture in the rail microstructure

Refining Automated Ultrasonic Inspections with Simulation Models

Computer models of ultrasonic beams can be used to accurately predict fields radiated from transducers [1,2]. Given these fields and reciprocity relations [3] the responses from reflectors of known shape can be calculated. Often scan sensitivity for an inspection is quantified relative to the response from a flat bottomed hole (FBH). Because the FBH is a simple known shape, a computer simulation with an ultrasonic measurement model [4] can be used to model and refine the inspection

Type discrimination of Various Welding Defects Created During Production and In-Service Use

Verification of the quality of welded structures, both post-production and in-service, has long been a concern of the engineering, materials and nondestructive communities. Nondestructive techniques have been developed and refined to address this verification problem. Each technique has inherent limitations, however, that in certain situations preclude its use or severely restrict the type of information that may be obtained particularly concerning the flaw type. Of these techniques, x-ray investigation is probably the most versatile in determining flaw type and size at present. The equipment required for x-ray examination, however, place constraints on its use, particularly for in-service structures, from the standpoint of accessibility and personnel safety.</p

A Comparison of Laser Ultrasonics and EMAT Texture Measurements in Aluminum Alloys

Ultrasonic techniques, which measure elastic anisotropy, have been used to study texture and plastic anisotropy of sheet materials. Ultrasonic velocity measurements can determine the orientation distribution coefficients (ODCs) W400, W420, and W440 which are used to describe crystallographic orientation distributions [1]. For steel sheets, strong correlations have been observed between ultrasonic velocity and the formability parameters r̄ and Δr [3]. The results for aluminum show a relationship between the ODC W440 and the degree of earing [2–3].</p

Entropically Driven Formation of Hierarchically Ordered Nanocomposites

Using theoretical models, we undertake the first investigation into the rich behavior that emerges when binary particle mixtures are blended with microphase-separating copolymers. We isolate an example of coupled self-assembly in such materials, where the system undergoes a nanoscale ordering of the particles along with a phase transformation in the copolymer matrix. Furthermore, the self-assembly is driven by entropic effects involving all the different components. The results reveal that entropy can be exploited to create highly ordered nanocomposites with potentially unique electronic and photonic properties. © 2002 The American Physical Society

Binary hard sphere mixtures in block copolymer melts

We perform a self-consistent-field/density-functional-theory hybrid analysis for a system of diblock copolymers mixed with polydisperse, hard, spherical particles of various chemical species. We apply this theory to study the equilibrium morphologies of two different binary sphere/diblock melts. First, we examine the case where the particles have two different sizes, but both types are preferentially wetted by one of the copolymer blocks. We find that the single-particle distributions for the two species do not track one another and that the particles show a degree of entropically generated separation based on size, due to confinement within the diblock matrix. Second, we study the case where the particles are all the same size, but are of two different chemical species. We find that, as expected, the particle distributions reveal a degree of enthalpically driven separation, due to the spheres’ preferential affinities for different blocks of the copolymer. © 2002 The American Physical Society

Self-assembly of a binary mixture of particles and diblock copolymers

Using theoretical models, we undertake the first investigation into the synergy and rich phase behavior that emerges when binary particle mixtures are blended with microphase-separating copolymers. We isolate an example of spontaneous hierarchical self-assembly in such hybrid materials, where the system exhibits both nanoscopic ordering of the particles and macroscopic phase transformation in the copolymer matrix. Furthermore, the self-assembly is driven by entropic effects involving all the different components. The results reveal that entropy can be exploited to create highly ordered nanocomposites with potentially unique electronic and photonic properties. © 2003 The Royal Society of Chemistry