Simple go/no-go test for subcritical damage in body armor panels

The development of a simple test for subcritical damage in body armor panels using pressure‐sensitive dye‐indicator film has been performed and demonstrated effective. Measurements have shown that static indicator levels are accurately reproduced in dynamic loading events. Impacts from hard blunt impactors instrumented with an accelerometer and embedded force transducer were studied. Reliable correlations between the indicator film and instrumented impact force are shown for a range of impact energies. Force and acceleration waveforms with corresponding indicator film results are presented for impact events onto damaged and undamaged panels. We find that panel damage can occur at impact levels far below the National Institute of Justice acceptance test standard

High contrast air-coupled acoustic imaging with zero group velocity Lamb modes

The well known zero in the group velocity of the first-order symmetric (S1) plate wave mode has been exploited in air-coupled ultrasonic imaging to obtain significantly higher sensitivity than can be achieved in conventional air-coupled scanning. At the zero group velocity point at the frequency minimum of the S1mode, a broad range of wavenumbers couple into the first-order symmetric mode at nearly a constant frequency, greatly enhancing transmission at that frequency. Coupled energy remains localized near the coupling point because the group velocity is zero. We excite the mode with a broadband, focussing, air-coupled transducer at the frequency of the zero group velocity point in the S1 mode. By exploiting the efficient coupling at the zero group velocity frequency, we have easily imaged a single layer of Scotch tape attached to a 6.4-mm thick Plexiglas plate and 3.2-mm Teflon inserts in a composite laminate

Nonlinear elastic behavior of sub-critically damaged body armor panel

A simple go/no-go test for body armor panels using pressure-sensitive, dye-indicator film (PSF) has been shown to be statistically effective in revealing subcritical damage to body armor panels. Previous measurements have shown that static indicator levels are accurately reproduced in dynamic loading events. Further impact tests on armor worn by a human resuscitation dummy using instrumented masses with an attached accelerometer and embedded force transducer have been performed and analyzed. New impact tests have shown a reliable correlation between PSF indication (as digitized images) and impact force for a wide range of impactor energies and masses. Numerical evaluation of digital PSF images is presented and correlated with impact parameters. Relationships between impactor mass and energy, and corresponding measured force are shown. We will also report on comparisons between ballistic testing performed on panels damaged under various impact conditions and tests performed on undamaged panels

Preface: Review of Progress in Quantitative Nondestructive Evaluation

The 38 th annual Review of Progress in Quantitative NDE was held at the University of Vermont in Burlington, VT, on July 17-22, 2011. This conference, widely regarded as the most prestigious of NDE research conferences, emphasizes the interface between current research results in the development of new measurement techniques (theory with experimental confirmation) and early engineering applications used to enhance the safety in high technology systems. With an attendance of 350 persons - approximately one half coming from overseas and the other half from U.S. academia, industry, and government - over 320 technical papers were presented in both verbal and poster sessions. As is customary for this meeting, papers in essentially all NDE technologies were presented, ranging from fundamental theoretical analyses to practical applications. Attendees included members of the World Federation of NDE Centers, an organization dedicated to broad cooperation in and harmonization of research and education for NDE. Student papers from the 9th Annual Student Poster Competition were incorporated as a part of the Review and are included in these volumes. The Review was organized by the Center for Nondestructive Evaluation at Iowa State University and sponsored by QNDE Programs with welcome assistance from the Air Force Research Laboratory, the Ames Laboratory (DOE) at Iowa State University, the American Society of Nondestructive Testing (ASNT), the Army Research Laboratory, the Federal Aviation Administration (FAA), the National Aeronautics and Space Administration (NASA), and the National Science Foundation (NSF) Industry/University Cooperative Centers

High‐Sensitivity Air‐Coupled Ultrasonic Imaging with the First‐Order Symmetric Lamb Mode at Zero Group Velocity

A new method for high‐sensitivity non‐contact, through‐transmission, air‐coupled imaging of small material property changes or discontinuities in plates is demonstrated. Our approach exploits the excitation of the first‐order symmetric Lamb wave mode at its minimum frequency point of zero group velocity. Because this Lamb wave resonance couples energy extremely efficiently with the air and does not propagate energy in the plane of the plate, it is the dominant mode of transmission of an airborne focussed‐beam broadband impulse through the plate. We take advantage of the sensitivity of this mode by performing C‐scans at the frequency of the group‐velocity zero to image spatial discontinuities and property changes. Our results show that images measured at this frequency are more sensitive and more consistent than those measured elsewhere in the plate‐wave spectrum

Air-coupled acoustic imaging with zero-group-velocity Lamb modes

A Lamb wave resonance has been found that allows unusually efficient transmission of airborne sound waves through plates. This occurs at the zero-group-velocity point at the frequency minimum of the first-order symmetric (S1 ) Lamb mode. At this frequency, plane waves with a range of incident angles can couple between the air and the Lamb mode in the solid plate, dominating the spectrum of transmitted focused sound beams by 10 dB or more. We use this frequency for C-scan imaging, and demonstrate the detection of both a 3.2-mm-diameter buried flaw and a subwavelength thickness changes of .005l ~1%!

Human Factors Considerations in the Assessment of Nondestructive Evaluation (NDE) Reliability

The overall performance level for an NDE operation is dependent on the NDE material, equipment, processes (methodology) and human skills applied to the operation. It is important to understand and consider human factors elements and contributions to NDE applications in the improvement of applications, in the design and validation of new applications, in automating portions of task performance, and in the development of modeling tools for the prediction of task performance for existing and new applications

Towards Intelligent Databases

This article is a presentation of the objectives and techniques of deductive databases. The deductive approach to databases aims at extending with intensional definitions other database paradigms that describe applications extensionaUy. We first show how constructive specifications can be expressed with deduction rules, and how normative conditions can be defined using integrity constraints. We outline the principles of bottom-up and top-down query answering procedures and present the techniques used for integrity checking. We then argue that it is often desirable to manage with a database system not only database applications, but also specifications of system components. We present such meta-level specifications and discuss their advantages over conventional approaches

Forward Modeling of Transducer Misalignment Effects in Ultrasonic Leaky Wave Measurements

Ultrasonic measurements performed with a pair of acoustic transducers in pitch-catch mode are of common use in the NDE field. In particular, for nearfield leaky wave (LW) measurements which are directed at precise determination of material properties of layered elastic structure in immersion. In LW measurements, the acoustic transducer beams are aligned at angles so as to phase match to one or several of the structure’s leaky (Rayleigh or Lamb) waves. The amplitude and phase of the scattered acoustic energy collected, and converted to an electrical voltage, by the phase-sensitive receiving transducer depends not only on the properties of the structure but also on the parameters of the transducers used, in particular, their apertures and alignment angles. Transducer alignment issues are especially important for transducers that radiate or receive over a narrow angular range