Paper watermark imaging using electron and low energy x-ray radiography

Historians and librarians are interested in watermarks and mould surface patterns in historic papers, because they represent the “fingerprints” of antique papers. However, these features are usually covered or hidden by printing, writing or other media. Different techniques have been developed to extract the watermarks in the paper while avoiding interference from media on the paper. Beta radiography provides good results, but this method cannot be widely used because of radiation safety regulations and the long exposure times required due to weak isotope sources employed. In this work, two promising methods are compared which can be used to extract digital high-resolution images for paper watermarks and these are electron radiography and low energy X-ray radiography. For electron radiography a “sandwich” of a lead sheet, the paper object, and a film in a dark cassette, is formed and it is exposed at higher X-ray potentials (\u3e 300 kV). The photoelectrons escaping from the lead sheet penetrate the paper and expose the film. After development, the film captures the watermark and mould surface pattern images for the paper being investigated. These images are then digitized using an X-ray film digitizer. The film employed could potentially be replaced by a special type of imaging plate with a very thin protection layer to directly generate digital images using computed radiography (CR). For the second method, a low energy X-ray source is used with the specimen paper placed on a digital detector array (DDA). This method directly generates a low energy digital radiography (DR) image. Both methods provide high quality images without interference from the printing media, and provide the potential to generate a “fingerprint” database for historical papers. There were nevertheless found to be differences in the images obtained using the two methods. The second method, using a low energy X-ray source, has the potential to be integrated in a portable device with a small footprint incorporating user safety requirements. Differences obtained using the two methods are shown and discussed

Surface cracks in metals and their characterization using Rayleigh waves

Over recent years there has been an increasing interest in the initial testing and in-service inspection of many engineering products, particularly in relation to items such as aircraft, oilrigs, pressure vessels and pipelines. (Thompson 1976, Lumb 1977) For this purpose a wide range of nondestructive testing techniques has been developed, for both defect location and sizing. these have included the use of X-rays, electromagnetic induction and dye penetration, with the addition, in recent years, of the increasingly important methods which use ultrasonic waves. There is a wide range of methods of ultrasonic testing which use the different types of elastic waves and display the resulting information in a variety of ways

Using Remote NDE, including External Experts in the Inspection Process, to Enhance Reliability and address Todays NDE Challenges

The paper discusses the challenges for NDE operating in the environment of advanced manufacturing techniques characterized by networking of systems. The information environment is impacting all industrial areas (Industry 4.0) and production of individual components tailored to meet the needs of individual customers. The emerging approach of using remote NDE is seen as a potential technique to increase reliability of NDE inspections by integrating additional specialist in to the decision process by “tele-presence.” This can also help to leverage the scarce resource of senior inspectors and have them engaged with industrial inspections at multiple sites. This distance engagement has the potential to enhance performance of inspections, starting from inspection design through to enhanced data analysis and hence enabling reliability of NDE to be improved

An experimental study on the characteristics of wind-driven surface water film flows by using a multi-transducer ultrasonic pulse-echo technique

An experimental study was conducted to investigate the characteristics of surface water film flows driven by boundary layer winds over a test plate in order to elucidate the underlying physics pertinent to dynamic water runback processes over ice accreting surfaces of aircraft wings. A multi-transducer ultrasonic pulse-echo (MTUPE) technique was developed and applied to achieve non-intrusive measurements of water film thickness as a function of time and space to quantify the transient behaviors of wind-driven surface water filmflows. The effects of key controlling parameters, including freestream velocity of the airflow and flow rate of the water film, on the dynamics of the surface water runback process were examined in great details based on the quantitative MTUPE measurements. While the thickness of the wind-driven surface water film was found to decrease rapidly with the increasing airflow velocity, various surface wave structures were also found to be generated at the air/waterinterface as the surface water runs back. The evolution of the surface wave structures, in the terms of wave shape, frequency and propagation velocity of the surface waves, and instability modes (i.e., well-organized 2-D waves vs. 3-D complex irregular waves), was found to change significantly as the airflow velocity increases. Such temporally synchronized and spatially resolved measurements are believed to be very helpful to elucidate the underlying physics for improved understanding of the dynamics of water runback process pertinent to aircraft icing phenomena

A Review of Prognostics and Health Management Applications in Nuclear Power Plants

The US operating fleet of light water reactors (LWRs) is currently undergoing life extensions from the original 40-year license to 60 years of operation. In the US, 74 reactors have been approved for the first round license extension, and 19 additional applications are currently under review. Safe and economic operation of these plants beyond 60 years is now being considered in anticipation of a second round of license extensions to 80 years of operation.Greater situational awareness of key systems, structures, and components (SSCs) can provide the technical basis for extending the life of SSCs beyond the original design life and supports improvements in both safety and economics by supporting optimized maintenance planning and power uprates. These issues are not specific to the aging LWRs; future reactors (including Generation III+ LWRs, advanced reactors, small modular reactors, and fast reactors) can benefit from the same situational awareness. In fact, many SMR and advanced reactor designs have increased operating cycles (typically four years up to forty years), which reduce the opportunities for inspection and maintenance at frequent, scheduled outages. Understanding of the current condition of key equipment and the expected evolution of degradation during the next operating cycle allows for targeted inspection and maintenance activities. This article reviews the state of the art and the state of practice of prognostics and health management (PHM) for nuclear power systems. Key research needs and technical gaps are highlighted that must be addressed in order to fully realize the benefits of PHM in nuclear facilities

Performance Evaluation of the FBG Sensing Device and Comparison with Piezoelectric Sensors for Acoustic Emission Detection

In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. As the most mature technique in fiber-optic field, Fiber Bragg Grating (FBG) sensors have emerged as a reliable, in situ and nondestructive tool for monitoring and diagnostics in large-scale structure. Main objectives of this work are to evaluate and compare the acoustic emission (AE) sensing characteristics simultaneously with FBG sensor array and piezoelectric (PZ) sensors. The pencil-lead-break (PLB) test, ball dropping test and the excitation from the PZ transducer are treated as the AE source which conducted on the platy and blocky structure respectively for acoustic wave. The source repeatability will be verified to choose the source with more stable performance. A commercial 4-channel FBG AE detection device was used to compare with the PZ sensor on the amplitude and frequency response which can indicate the sensitivity of the sensors. The low sensitivity and low sampling rate are the main issue for the engineering application of the FBG sensors. Besides, the sensitivity and directional dependence of the FBG sensor have been discussed. It shows that the encapsulation method of the FBG sensor will impact both of them significantly

Analysis of critically refracted longitudinal waves

Fabrication processes, such as, welding, forging, and rolling can induce residual stresses in metals that will impact product performance and phenomena such as cracking and corrosion. To better manage residual stress tools are needed to map their distribution. The critically refracted ultrasonic longitudinal (LCR) wave is one such approach that has been used for residual stress characterization. It has been shown to be sensitive to stress and less sensitive to the effects of the texture of the material. Although the LCR wave is increasingly widely applied, the factors that influence the formation of the LCR beam are seldom discussed. This paper reports a numerical model used to investigate the transducers\u27 parameters that can contribute to the directionality of the LCR wave and hence enable performance optimization when used for industrial applications. An orthogonal test method is used to study the transducer parameters which influence the LCR wave beams. This method provides a design tool that can be used to study and optimize multiple parameter experiments and it can identify which parameter or parameters are of most significance. The simulation of the sound field in a 2-D water-steel model is obtained using a Spatial Fourier Analysis method. The effects of incident angle, standoff, the aperture and the center frequency of the transducer were studied. Results show that the aperture of the transducer, the center frequency and the incident angle are the most important factors in controlling the directivity of the resulting LCR wave fields