Modeling Angle Beam Ultrasonic Testing Using Multi-Gaussian Beams

This paper proposes a new approach to modeling angle beam ultrasonic testing that can predict pulse-echo signals, in an absolute and computationally efficient manner, from various reflectors in steel welded joints. This approach relies on a model of the entire ultrasonic measurement process, a model which requires one to solve three subsidiary problems; 1) determination of a system efficiency factor, 2) evaluation of the ultrasonic beam field around the flaw, and 3) calculation of the scattering from the reflector. Here, solutions are offered for each of those three subsidiary problems. To solve the first problem we employ the specular reflection from the cylindrical part of a STB-A1 (Standard Test Block in compliance with Japanese Industrial Standards Z 2347) (equivalently IIW (International Institute of Welding) type 1) standard block to determine the system efficiency factor. To solve the second problem, we calculate the ultrasonic wave field at the flaw with a highly efficient multi-Gaussian beam model. For the third problem, we treat the scattering from a reflector by high frequency approximations. We explicitly give the solutions to all three of these subsidiary problems for counter bore, crack, and side-drilled hole reflectors. Experimental results that validate this approach are also given.     

Characterization of Bonding Quality in a Multilayer Structure Using Segment Adaptive Filtering

Ultrasonic testing is widely used in detection of disbonds in multilayer structures such as solid fuel rocket motors, which consist of steel, rubber laminate, and solid fuel. However, only a small fraction of ultrasonic waves can transmit through the steel–rubber interface because of their large difference in acoustical impedance. Very little ultrasound is reflected back by the weak bond interface within the rubber laminate or from the interface between the rubber and solid fuel. Consequently, the interface bond degradation can only produce a very slight variation in the received ultrasonic echo sequences, which are too weak to be detected effectively. In this paper, ultrasonic pulse reflection from the interfaces is considered to evaluate the interface bond condition. A multilayer model with spring boundary condition is used to describe the weak bond, and ultrasonic reflection response is obtained for the structure in the immersion mode. After analysis of the ultrasonic echo sequences of the steel–rubber structure, the segment adaptive filtering method is used to separate the simulated echo sequences and to obtain the interface signals. With the separated interface signals, the weak bond of all the interfaces, including the one within the rubber laminate, can be detected. The procedure has been applied to signals measured from the steel–rubber samples, and the amplitude and envelope of various interface signals agree well with those from the corresponding simulated signal. The disbond and weak bond can be detected and evaluated by the amplitude of corresponding signal of interfaces.     

Modeling nonlinear thermo-elastic response for glassy polycarbonate using ultrasonic results under compression in a confined cell

We develop a nonlinear thermo-elastic model for polycarbonate (PC) using ultrasonic longitudinal and shear waves applied on a sample under confined compression. The model is a thermodynamically consistent model developed based on data obtained from a modified pressure-volume-temperature measurement system that also provides the longitudinal and shear wave moduli (Masubuchi et al., 1998. Materials Science Research International 4(3), 223-226). The heat capacity data was obtained by using a differential scanning calorimeter. The resulting model reproduces the ultrasonic behavior of the PC over the temperature range of 35 °C to 150 °C and under pressures from 0 to 70 MPa. Since the response at constant pressure is close to linear below the glass transition temperature of 147 °C, one may extend the use of the model to temperatures below 35 °C, possibly covering most of the range of use for most applications.     

Using a Single Transducer Ultrasonic Imaging Method to Eliminate the Effect of Thickness Variation in the Images of Ceramic and Composite Plates

This article describes a single transducer ultrasonic imaging method based on ultrasonic velocity measurement that eliminates the effect of thickness variation in the images of ceramic and composite plate samples. The method is based on using a reflector located behind the sample and acquiring echoes off the sample and reflector surfaces in two scans. As a result of being thickness-independent, the method isolates ultrasonic variations due to material microstructure. Its use can result in significant cost savings because the ultrasonic image can be interpreted correctly without the need for precision thickness machining during nondestructive evaluation stages of material development. Velocity images obtained using the thickness-independent methodology are compared with apparent velocity maps and c-scan echo peak amplitude images for monolithic ceramic (silicon nitride), metal matrix composite and polymer matrix composite materials having thickness and microstructural variations. It was found that the thickness-independent ultrasonic images reveal and quantify correctly areas of global microstructural (pore and fiber volume fraction) variation due to the elimination of thickness effects. A major goal achieved in this study was to move the thickness-independent imaging technology out of the lab prototype environment and into the commercial arena so that it would be available to users worldwide. The method has been implemented on commercially-available ultra-sonic can systems manufactured by Sonix, Inc. via a formal technology transfer agreement between NASA and Sonix.     

Mathematical Modeling of Thin Layer Drying of Papaya Seeds in a Tunnel Dryer Using Particle Swarm Optimization Method

The processing of papaya generates a significant amount of solid wastes. The seeds represent a significant amount and a source of untapped products. Papaya seeds have useful compounds, which can be obtained from its extracts or oils and can be a very effective biosorbent. For good results in the compounds achievement and the pretreatment, it is essential the appropriated choice of the drying conditions. This article proposes the study of the drying of papaya seeds in a tunnel dryer at three drying temperatures (40, 70, and 100°C) and three air drying velocities (1.0, 1.5, and 2.0 m · s^?1). Empirical and semi-empirical models were proposed to adjust the kinetic parameter as a function of the drying conditions. The particle swarm optimization method was used, obtaining, as a result, an exponential model with good prediction quality and with few parameters to be adjusted.     

Testing and modelling of creep crack growth in compact tension specimens from a P91 weld at 650 °C

Creep crack growth tests were performed, at 650 °C, on compact tension (CT) specimens machined from the parent material and from the weld region of a P91 weldment. Parent material tests were performed on a number of different CT specimen designs in order to investigate the effects of side grooves on the shape of the crack front. Tests of CT specimens machined from the weld region were performed with the initial cracks located within the heat-affected zone (HAZ) along the interface with the parent material (i.e. the type IV position). All of the specimens were prepared with initial cracks created by wire spark erosion. Good correlations between creep crack growth rates and C^∗ were obtained for both the parent and type IV test results. The results indicate that the crack growth rates in the weld specimens are about four times higher than those of the parent material specimens, at the same C^∗. Microstructural investigations of the fracture surfaces using SEM and hardness measurements have shown that the exact location of the initial crack within the weldment has a large effect on the crack growth rate, at various loading levels. The results of Finite Element (FE) analyses of the parent material specimen tests, using a creep continuum damage material model, compared favourably with those obtained from the experiments.