A feasibility study of damage tracking through the diffusive communication of wireless sensors

The objective of this paper is to investigate the feasibility of wireless sensors in the development of an autonomous structural health monitoring system. A collaborative searching algorithm is developed such that massively deployed wireless sensor nodes in a structure conveniently comprise a group and constitute a damage-surveillance perimeter. Wireless sensors in this perimeter spontaneously activate themselves for damage-tracking tasks by networking with neighboring sensors. When the damage-sensitive parameter that is measured by a sensor node exceeds a certain threshold, the process of damage-tracking begins. The proposed damage-tracking algorithm does not require any type of global control. Instead, sensor-networking and a pairwise-comparison algorithm that is implemented at each sensor node allows collaborative decision-making for tracking the changes, such as local strain, in structural properties. The extant autonomous, damage-tracking algorithms have been demonstrated through only numerical simulations for a single-damage case. Here, the study is further expanded to address the problem of simultaneously tracking multiple instances of damage in three-dimensional space by using improved algorithms for sensor networking. An event-based task-executing functionality of individual sensor nodes is successfully implemented and verified using four wireless strain sensors that are mounted on a cantilevered beam structure. Experimental results reveal that the overall capability of wireless sensor nodes is functional enough to enable a wireless-based autonomous structural health monitoring system.     

High pressure rheometer for in situ formation and characterization of methane hydrates

We present a novel setup for a high pressure rheometer operating with concentric cylinders geometry for in situ studies of hydrate formation and rheological characterization. The apparatus uses an external high pressure mixing cell to saturate water-in-oil emulsions with methane gas. The capability of mixing combined with a true rheometer design make this apparatus unique in terms of setup and sample formation. We have used the apparatus to form gas hydrates in situ from water-in-oil emulsions and characterize suspension rheological properties such as yield stress and shear-thinning behavior.     

Catalytic decomposition of N2O over monolithic supported noble metal-transition metal oxides

The decomposition of nitrous oxide to nitrogen and oxygen using a series of monolithic (ceria-alumina washcoated cordierite) supported transition metal (Cu, Fe, Co, Ni, Mn) and noble metal (Ir, Rh) oxide catalysts has been studied using gas chromatography. The effect of combining a transition metal with a noble metal has also been investigated. A synergetic effect was observed between transition metal and noble metal oxides in the presence of a small amount of water for some of the catalysts. The synergy between Fe-Ir and Ni-Ir was also verified under dry conditions. X-ray photoelectron spectroscopic measurements on these catalysts indicate that Fe, Rh and Ir are present predominantly as Fe₂O_3, RhO₂ and IrO₂, while significant amounts of Co and Ni ions may migrate inside the support to form cobalt and nickel aluminate. Only the Fe-Ir catalyst showed a significant interaction between the noble metal and the transition metal. The effect of water, oxygen and carbon monoxide on the catalytic behaviour of the five most active catalysts (Ni-Ir, Ni-Rh, Fe-Ir, Co-Ir, Ir) has also been investigated. Oxygen and water were found to inhibit the catalytic activity, although the extent of oxygen inhibition is limited, presumably due to the presence of ceria in the monolith washcoat support. Conversely, carbon monoxide greatly enhances catalytic activity.     

A novel approach to an advanced tertiary wastewater treatment: Combination of a membrane bioreactor and an oyster-zeolite column

A combination of a microfiltration-membrane bioreactor (MBR) and oyster-zeolite (OZ) packed-bed adsorption column was studied for the first time to evaluate the advanced tertiary treatment of nitrogen and phosphorous. The membrane module was submerged in the bioreactor and aeration was operated intermittently for an optimal wastewater treatment performance. Artificial wastewater with COD_cr of 220 mg/L, total nitrogen (T-N) of 45 mg/L, and total phosphorous (T-P) of 6 mg/L was used in submerged MBR with MLSS of 4,000–5,000 mg/L. The experiments were performed during a 100-day period with periodic membrane washing. The results showed that COD_cr could be effectively removed in the MBR alone with over 96% removal efficiency. However, T-N and T-P removal efficiency was slightly lower than expected with only the MBR. The permeate from MBR was then passed through the OZ column for tertiary nutrient removal. The final effluent analysis confirmed that nutrients can be additionally removed resulting in over 90% and 53% removal efficiencies for T-N and T-P, respectively. The results of this study suggest that the waste oyster shell can be effectively reclaimed as an adsorbent in advanced tertiary wastewater treatment processes in combination with a MBR.     

Catalytic effect of 2,2′‐diallyl bisphenol A on thermal curing of cyanate esters

Cyanate esters are a class of thermal resistant polymers widely used as thermal resistant and electrical insulating materials for electric devices and structural composite applications. In this article, the effect of 2,2′‐diallyl bisphenol A (DBA) on catalyzing the thermal curing of cyanate ester resins was studied. The curing behavior, thermal resistance, and thermal mechanical properties of these DBA catalyzed cyanate ester resins were characterized. The results show that DBA is especially suitable for catalyzing the polymerization of the novolac cyanate ester resin (HF‐5), as it acts as both the curing catalyst through depressing the exothermic peak temperature (T_exo) by nearly 100°C and the toughening agent of the novolac cyanate ester resin by slightly reducing the elastic modulus at the glassy state. The thermogravimetric analysis and dynamic mechanical thermal analysis show that the 5 wt % DBA‐catalyzed novolac cyanate ester resin exhibits good thermal resistance with T_d⁵ of 410°C and the char yield at 900°C of 58% and can retain its mechanical strength up to 250°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1775–1786, 2006     

Curing behavior and thermal mechanical properties of cyanate ester blends

Cyanate esters are a class of important thermally resistant polymers. To tailor their processability and thermomechanical properties, a series of cyanate ester blends based on a trifunctional novolac cyanate ester (HF‐5), a difunctional bisphenol E cyanate ester (HF‐9), and a reactive catalyst [2,2′‐diallyl bisphenol A (DBA)] were formulated. The effect of the blend composition on the rheology and curing behavior of these cyanate ester blends and the corresponding thermal and mechanical properties of the cured cyanate ester blends was studied. The results showed that HF‐5 contributed to good mechanical property retention at high temperatures because of its trifunctionality, whereas HF‐9 imparted processability by reducing the viscosity and extending the pot life of the formulated cyanate ester blends at the processing temperature. On the basis of the results, an optimal cyanate ester blend suitable for resin transfer molding was determined: the HF‐5/HF‐9/DBA weight ratio of 80 : 15 : 5 exhibited good processability and thermomechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4284–4290, 2006     

Effect of environmental and metallurgical factors on hydrogen induced cracking of HSLA steels

Hydrogen induced cracking (HIC) resistance of two high strength low alloy (HSLA) steel plates equivalent to API X70 grade was evaluated in various test solutions with different H₂S partial pressures and pH values. Results showed that H₂S partial pressure is the key parameter affecting HIC resistance. Hydrogen permeation rate was affected by both H₂S partial pressure and pH of test solutions, whereas the apparent hydrogen diffusivity was determined mainly by pH value in case of H₂S partial pressure less than 0.1 atm. HIC in the steels primarily nucleated at inclusions and/or clusters containing the Al and Ca oxides. HIC resistance was determined by diffusible hydrogen amount with different microstructures.     

Impact tests on steel–concrete–steel sandwich beams with lightweight concrete core

This paper studies the impact performance of Steel–Concrete–Steel (SCS) sandwich beams consisting of a lightweight concrete core sandwiched between two face plates that are connected by J-hook connectors. Impact tests were carried out by dropping free weights on to sandwich beams to investigate their structural response against impact loads. Test results revealed that the proposed J-hook connectors provide an effective means to interlock the top and bottom steel face plates, preventing them from separation during impact. The use of fibres in concrete core and J-hook connectors for composite action enhances the overall structural integrity of the sandwich beams when compared with those without such enhancement. An elastic–plastic analysis method is developed to predict the force-indentation relationship of sandwich sections subjected to local impact. Dynamic analysis based on the local force-indentation relationship is carried out to predict the impact force and global response behavior of the sandwich beams. The predicted results are compared with those obtained from the tests to validate their accuracy so that they can be used to evaluate the performance of sandwich beams under low velocity hard impact.     

Stiffness modeling of a soft finger

This paper presents the design and stiffness modeling of a new 3 DOF soft finger mechanism using a spring as a backbone. The mechanism consists of a spring and 3 cylinders, which behave like joints. To control each joint, wires of different length are penetrated into the cylinders which have small holes in their cross-sectional areas, and each joint can be controlled by pulling each wire. Also, the stiffness modeling is conducted to measure the softness of the finger mechanism as well as to estimate the actuator size. First, the forward kinematics is solved by using the geometry of mechanism, and length of wires and Jacobian are obtained. In order to evaluate the efficiency of the proposed mechanism, the position control, the flexibility and safety, and the stiffness model are verified through experimental work.