The structural health monitoring of structures during active use (in service) has long been of interest to the NDE community.
One technique uses passive ultrasound or Acoustic Emission (AE). However, the interpretation of the AE signals
is difficult especially when the operator tries to distinguish between the growth of harmless micro-cracks and the
development of harmful delaminations. This paper focuses on two types of structures, i.e., aluminum plates such as used
in wing structures in aircraft and graphite plates such as encountered in aircraft disc brakes where carbon-carbon composite
The objective in this work is to distinguish the acoustic emissions (AE) caused by delaminations from those associated
with microcracking. The technical approach is to use finite element methods (FEM) to simulate AE from sources represented
by piezoelectric wafers embedded in the composites. In flat panels of graphite and aluminum-alloy AE waveforms
were modeled from transverse cracks and longitudinal delaminations. The results show distinct differences in the
amplitudes, durations and frequency content creating a potential avenue for distinguishing between these two flaw types.
A variety of industrial and everyday non-destructive inspection applications exist where the target material/product is
inaccessible or, contact with the material is prohibited. In such cases, air-coupled ultrasonic techniques play a major role
but commonly significant transmission loss is known to occur. Therefore, it becomes imperative to know the amount of
absolute wave mechanical strain achieved in materials embedded in gaseous medium, for certain applications. Thus, the
overall objective of this work was to establish simulated results and specific experimental verifications of the numerical
modeling, and develop guidelines in the use of matching layers to maximize the wave mechanical strain imparted to
materials. A Laser Doppler Vibrometer was used to obtain the displacements/strains induced in the materials. Coupled
Acoustic Piezoelectric Analysis (CAPA), coupled field finite element method software was used to perform the
simulations. The applications considered in this work include metallic targets inside an enclosed container, food products
and also elastomeric composites such as automotive tires.
The objective of this study is to observe the behavior of the living cells after introducing impact, caused by an aluminum bullet shot out from an air gun, onto them via tungsten/polymer plate and culture liquid. An air gun type of apparatus shoots an aluminum bullet, wherein the shape of the bullet is substantially a sphere (diameter: 5 mm), and wherein the velocity of the bullet is controlled by the amount of air used for shooting. The aluminum bullet shot out from the air gun impacts onto the polymer/tungsten plate, located above the living cells grown on the bottom of the container (i.e., thin semi-transparent polymer membrane), which is located on the surface of a 200 kHz Panametrics transducer. The container is supported by a polymer member to prevent movement from shock caused by the bullet impact. The plate generates an acoustic wave (i.e., shock wave) by the mechanical impact (i.e., bullet impact) which is then converted into an electrical signal by the transducer. The amplitude of the electrical signal is measured and monitored by the digital oscilloscope. The transducer is calibrated by hydrophone with its peripheral equipment including computer software. The output voltage from transducer was monitored by the digital oscilloscope. The injury and recovery of the specimen are evaluated by scanned image microscopes. Furthermore, quantitative data showing the injury and recovery of the specimen can be obtained with the electromagnetic measurement.
The detection of fissile materials is of great interest to the National Homeland Security effort. Significant advantages of a technique using nuclear acoustic resonance (NAR) over the traditional detection methods are that it will not rely on nuclear radiation signatures, will be non-intrusive, and has the potential to identify individual components of composite substances including fractional isotope composition of the material under investigation. Technique uses the unique nuclear acoustic resonance signatures generated when materials are driven by high intensity resonant acoustic waves in the presence of a constant magnetic field. This would cause shifts in the nuclear and electronic spin energy levels of the material. Nuclear energy level shifts induce changes in the unique nuclear magnetic properties of the material which can then be quantified using sensitive instruments. This paper will discuss in detail, the physics and detection principles of NAR and also provide some preliminary results.
This paper describes the study carried out to determine the possibility of healing an AS4/PEEK composite plate that was impacted at a low velocity to create the delaminations. Images of the AS4/PEEK composite plates were obtained prior to the impact, to ensure it is free of any gross defects that could have been imparted during the manufacturing of the composite plate. A drop-weight was used to impact the composite plate at a low velocity and the incident energy of impact was maintained at 2.26 ft-lb. Interior images of the composite plates were obtained after the impact and prior to healing by a C-scan imaging system. The healing process was conducted at controlled temperature and pressure. The healed specimens were imaged again by the C-Scan imaging system. The results obtained by analyzing the images show a reduction in the size of the delaminations.
Understanding the elastic properties of the various types of rubber is important for many commercial and academic applications. A sample set consisting of generic elastomeric compounds was studied using non-destructive non-contact ultrasonic techniques. The longitudinal sound wave velocities in the sample and wave amplitude attenuation in the sample were measured using the Second Wave Inc. Non-Contact Analyzer 1000 (NCA1000). The Contact method was then used to corroborate the results obtained. The preliminary results suggest that the differences in attenuation are driven by polymer type and also to a lesser extent by the loading level of carbon black fillers.
This paper contains a description of an unique wave that was created in a two plate system separated by a layer of water. First, a Lamb wave was created in the upper plate by placing a transducer on a wedge on top of the plate at an appropriate angle and frequency. This wave was created to act like quasi-Rayleigh (surface) waves on both surfaces of the plate. The wave on the bottom surface of the upper plate then leaked through the water into the upper surface of the lower plate. We will show both experimentally and theoretically that the wave on the surfaces of the plates in contact with water leak constructively to create a leaky-wave that can travel great distances.
The cracking and failure in ceramic substrates during the laser drilling process has been acknowledged as a major problem by designers and manufacturers in the electronic component industries. The cracking and failure is due to large localized thermal stresses within the narrow heat-affected zone on the ceramics. Although the knowledge of the stress distribution in the ceramic substrate is important in understanding and solving the cracking/failure problem, it is impossible to measure the stress directly. The physical parameters of the laser drilling process such as temperatures or displacements, which can be directly related to stresses, can however be measured. That is why, in this research, an electronic speckle pattern interferometer (ESPI) system was designed and used to take speckle pattern images of the ceramic surface during the laser drilling process. Using commercial software, the speckle fringe images were image processed to quantify whole-field transient out-of-plane displacement measurements. A deformation history of the ceramic surface during the laser shaping process with millisecond temporal resolution was obtained, restricted only by the camera frame rate, camera resolution and laser power available. A finite difference model was developed to compare the deformation measurements with the predicted strain calculations.
The experimental study and the analysis show that the designed in-situ electronic speckle pattern interferometer system provides an excellent experimental basis for whole- field, transient deformation measurements of ceramic substrates during the laser drilling process.
There is a need to analyze locomotive wheels for flank cracks in a non-destructive manner in order to prevent catastrophic failures. Flaw, shape, and size are desired parameters in establishing the quality of commercial tires. A variety of defects such as voids, inclusions, surface and internal cracks, or the like, must be discerned in order to prevent failure.
This paper exhibits and compares the benefits of a number of different techniques used for flaw detection. Non-destructive evaluation techniques used consist of a magnetic particle, dye penetrant, eddy current, electro-magnetic acoustic transducer (EMAT), and longitudinal and shear wave ultrasonic inspection. The techniques vary in their ability to ascertain the flaw characteristics. Surface, sub-surface, and internal defects were visualized using the various methodologies. Magnetic particle, dye penetrant, and eddy current inspection techniques are viable methods for looking at surface flaws. Depending on the penetration depth, sub- surface flaws were also detectable via these methods. EMAT and ultrasonic transducer methods can be used to find surface, subsurface, and internal flaws based on the configuration utilized.