Welding is a key manufacturing process for many industries and may introduce defects into the welded parts causing significant negative impacts, potentially ruining high-cost pieces. Therefore, a real-time process monitoring method is important to implement for avoiding producing a low-quality weld. Due to high surface temperature and possible contamination of surface by contact transducers, the welding process should be monitored via non-contact transducers. In this paper, airborne acoustic emission (AE) transducers tuned at 60 kHz and non-contact ultrasonic testing (UT) transducers tuned at 500 kHz are implemented for real time weld monitoring. AE is a passive nondestructive evaluation method that listens for the process noise, and provides information about the uniformity of manufacturing process. UT provides more quantitative information about weld defects. One of the most common weld defects as burn-through is investigated. The influences of weld defects on AE signatures (time-driven data) and UT signals (received signal energy, change in peak frequency) are presented. The level of burn-through damage is defined by using single method or combine AE/UT methods.
World events have called for a need for fast, reliable, and more deployable methods of detection of improvised explosive
devices (IEDs) than trained canines and visible detection by X-ray screening technologies. Anodized Aluminum Oxides
(AAOs) are ideal substrates for chemical sensor developments. The nanoporous structure provides small pore-to-pore
distance and large surface areas. These unique qualities allow optical interference in the visible spectrum when the thin
film thickness is in the proper range. By coating the nanowells of the oxide surface first with a thin film of a noble metal
followed by a monolayer of a target-specific chemical, detection of trace amounts of explosive materials becomes
possible. Research has shown that the carboxyl group of 6-mercaptopyridine-3-carboxylic acid (6-MNA) has an
attraction to the nitro groups of 2,4,6-trinitrotoluene (TNT) while the thiol group of 6-MNA creates a self-assembled
monolayer on the substrate. By utilizing these chemical properties together, UV-vis spectrometry can detect a shift in the
visible spectrum on the coated AAO substrate as the 6-MNA structure attracts trace amounts of TNT particles.
A nanostructured sensor based on double wall carbon nanotubes (DWNTs) was fabricated and assessed for hydrogen gas
detection. DWNT networks were used as an active substrate material evaporated with layers of palladium nanoparticles
of three thicknesses 1, 3 and 6 nm. The electrical resistance change of nanosensor with hydrogen gas exposure in
compressed air at room temperature was monitored. The nanostructures were characterized using high resolution
transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Hydrogen concentrations as low as
0.05 vol% (500 ppm) can be detected at room temperature. Sensitivity values as high as 65% and response times of
about 3 seconds were obtained. The results indicate that DWNT- based sensors exhibit comparable performance as that
for SWNT-based high performance hydrogen sensors, but with potential improvement in mechanical and thermal
resistance associated with the double layer structure.
Anodized aluminum oxide (AAO) membranes are fabricated under different anodization potentials in dilute sulfuric
acid. Here we report the growth of AAO under 10, 15, 20, and 25V. These AAO membranes consist of nanopores with
pore-to-pore distance from 35 to 69 nm. When AAO membranes are kept thin (less than ~500 nm), together with the
unreacted aluminum substrate, interference colors are observed. The inference color of the membrane is changed by its
thickness and the pore-to-pore distance, which is controlled by the anodization time and voltage, respectively. By using
thin film interference model to analyze the UV-Vis reflectance spectra, we can extract the thickness of the membrane.
Thus the linear growth of AAO membrane in sulfuric acid with time during the first 15 minutes is validated. Coating
poly (styrene sulfonate) (PSS) sodium salt and poly (allylamine hydrochloride) (PAH) layer by layer over the surface of
AAO membrane consistently shifts the interference colors. The red shift of the UV-Vis reflectance spectrum is correlated
to the number of layers. This color change due to molecular attachment and increasing thickness is a promising method
for chemical sensing.
A nanostructured sensing element based on anodic aluminum oxide (AAO) nanowells was fabricate and assessed for
hydrogen gas sensing. AAO nanowells with an average diameter of 73 nm and depth proportional to the anodization
time were immersed in a surfactant solution and coated with an 8 nm film of palladium nanoparticles. The electrical
resistance change of the nanostructure with hydrogen gas exposure was used as the sensing parameter. The AAO
nanowells-Pd nanostructures were characterized using atomic force microscopy (AFM), field-emission scanning electron
microscopy (FESEM), and contact angle test. Hydrogen concentrations as low as 0.05 vol% (500 ppm) can be detected
at room temperature. Response times as fast as 1.15 seconds were obtained. Compared to current devices and
nanostructures in development, the AAO nanowell-Pd nanostructure is found to be considerably fast without
compromising sensitivity and selectivity.
The employment of hydrogen has shown a lot of promises as an alternative for conventional fuel sources. However, if
not handled properly, hydrogen content as low as 4% can lead to a life-threatening catastrophe. Some sensors for
hydrogen detection have already been built to address this safety issue. Unlike most of the traditional hydrogen sensors,
the sensor developed in this study features high sensitivity, fast response, miniature size, and the ability to detect
hydrogen under room temperature. The sensor template has a special nanoporous structure, coming from self assembled
aluminum oxide after anodization process. Deposition of palladium particles into the nanopores brings superb hydrogen
sensing ability by introducing a granular structure of sensing particles. The sensor prototype has been tested under
controlled atmosphere with varying hydrogen concentrations.
The capability and sensitivity of an electromagnetic (EM) sensor to be used as a non destructive evaluation (NDE) technique to detect and monitor corrosion in structural steels has been evaluated. Three structural carbon steels: AISI 1018, AISI 1045, and Stress Proof, were used for the study. The effect of corrosion on the magnetic properties of the steels was evaluated. Correlation curves and equations relating mass loss due to corrosion at early stages and magnetic property are presented. Based on the results it is established that the EM sensor has the potential to be used as a reliable NDE tool to detect corrosion at early stages based on the variation in magnetic saturation. These results are used to estimate and monitor the degree of damage in terms of mass loss.