INVESTIGATION OF PARAMETERS AFFECTING THE OPERATING CHARACTERISTICS OF TOGGLE-SWITCHES WITH SILVER-CADMIUM-OXIDE CONTACTS

Experimental and theoretical studies are made of small snap-action switches designed for use in thermostatic controls operating on a.c. at 240 volts r.m.s., 50Hz. The performance of the silver cadmium oxide contacts (Ag. CdO, 85/15%) is evaluated over a range of currents from 1 to 10 amps, for make and break operations. The arc at break is found to be the predominant factor contributing to the erosion of the contacts for the range of currents used. Tests using a high speed camera show that the energy dissipated in the arc between the contacts can be evaluated from equations describing the arc in terms of its voltage, current and length as functions of time. Subsequently work is carried out to develop the relation between arc energy and contact erosion, with specific regard to the distribution of energy between the two contact surfaces and the arc column. This is related to the power dissipation in the two electrode fall regions, and the resulting direction of net material transfer is thought to be influenced by the length achieved by the arc before extinction. Erosion is generally in the form of anodic loss and cathodic gain and the reasons for the directional bias in this type of switch are suggested. Ways of reducing the amount of erosion per operation by changing the switch opening characteristic are discussed and supported with experimental results.PETER J

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

Laser assisted arc welding process for dry hyperbaric deep water application

Hyperbaric Gas Metal Arc Welding (GMAW) is an important technology for repair welding of deep sea pipelines and linking of existing pipeline networks to newer ones through tie-ins and hot-tap welding. With increasing water depth the process becomes susceptible to hydrogen assisted cracking due to the very fast cooling rate of the weld caused by higher habitat gas density and resulting higher thermal diffusivity. Maintaining sufficient heat in the welding zone is vital to avoid a potential cracking tendency especially as moisture pick-up may be difficult to avoid during hyperbaric welding operations. In addition to this, hyperbaric GMAW has a limitation of low heat input because it is operated at a short arc length or dip transfer mode to avoid process instability at high pressure. Also, the short arc length generates weld spatter that may affect weld quality. The research presented in this thesis, investigated the use of an industrial laser in conduction mode for the purpose of providing significant additional heat input to control the weld thermal cycles of GMAW. Advanced GMAW power sources such as the Fronius Cold Metal Transfer (CMT) and EWM ColdArc have also been investigated for reduced weld spatter generation. Studies were conducted to investigate the weld pool thermal cycles and resulting metallurgical phase formation in hyperbaric GMAW at different pressures ranging from 1 bar to 200 bar. This was followed by welding trials at one atmosphere to compare the process characteristics of traditional dip transfer GMAW with some advanced GMAW power sources such as CMT and ColdArc. The main experimental trials to investigate a laser assisted GMAW (CMT) process were performed at one atmosphere condition. A thermal model was developed using Abaqus software to predict the weld metal and heat affected zone thermal cycle in a laser assisted GMAW (CMT) process at one atmosphere and under high ambient pressures. Finally, investigation was carried out to evaluate the benefit of the laser assisted process in lowering diffusible hydrogen content from the weld metal. The hyperbaric GMAW experimental results showed that the weld pool cooling rate increases with pressure due to higher chamber gas density and resulting thermal diffusivity. But this effect is not prominent for thicker plates. Therefore, it was concluded that heat conduction through the steel thickness dominates convective losses to the chamber gas environment. It was also shown that the welding arc shrinks as pressure increases in order to minimise energy loss to the environment. This defined the weld bead profile; although it was found that beyond 100 bar pressure the weld penetration depth remained effectively unchanged. Apart from the hardness of the weld made at 1 bar, there was little difference between those at 18, 100 and 200 bar. However, all of the welds show hardness peaks greater than 350 HV10 recommended for offshore structures. It was observed that CMT produced the lowest weld spatter compared to the traditional GMAW and ColdArc. However, this advantage is constrained to low wire feed speed (3 to 5 m/min) beyond which it becomes relatively unstable. For the laser assisted GMAW (CMT) trials, it was shown that the laser serves as a spatially resolved heat source, reheating the weld bead and reducing the cooling rate. For the laser parameters investigated, over 200% reduction of cooling rate could be achieved when compared with GMAW alone. It was also demonstrated that the additional laser thermal input will extend the weld residence time at high temperature (over 300 °C). This will prolong the weld cooling time such that dissolved hydrogen can diffuse out before it comes to room temperature. The laser was shown to significantly reduce the weld peak hardness from about 420 HV0.5 to values below 350 HV0.5, which will be beneficial for hyperbaric welding. The model prediction of the weld thermal cycles was in good agreement with the experimental results. Therefore, it could be used to predict the weld metal and HAZ cooling rate of a laser assisted GMAW (CMT) process although the model would need to be calibrated for higher pressure data. It was also demonstrated that additional laser heat can reduce the weld hydrogen content to acceptable limits of 5 ml/100 g of weld metal even for high moisture content in the welding environment. In conclusion, the addition of laser heating to GMAW will reduce the weld cooling rate, extend the weld pool cooling time, and expel diffusible weld hydrogen. All of these would be immensely beneficial in terms of improving the quality and reliability of structures fabricated through hyperbaric GMAW

Microfabrication Technology for Isolated Silicon Sidewall Electrodes and Heaters

This paper presents a novel microfabricationtechnology for highly doped silicon sidewall electrodesparallel to – and isolated from – the microchannel. Thesidewall electrodes can be utilised for both electricaland thermal actuation of sensor systems. Thetechnology is scalable to a wide range of channelgeometries, simplifies the release etch, and allows forfurther integration with other Surface ChannelTechnology-based systems. Furthermore, thefabrication technology is demonstrated through thefabrication of a relative permittivity sensor. The sensormeasures relative permittivity values ranging from 1 to80, within 3% accuracy of full scale, including waterand water-containing mixtures

Velocity-independent thermal conductivity and volumetric heat capacity measurement of binary gas mixtures

In this paper, we present a single hot wire suspended over a V-groove cavity that is used to measure the thermal conductivity ($k$) and volumetric heat capacity ($\rho c_p$) for both pure gases and binary gas mixtures through DC and AC excitation, respectively. The working principle and measurement results are discussed

KINETICS OF MOLTEN METAL CAPILLARY FLOW IN NON-REACTIVE AND REACTIVE SYSTEMS

Wetting and spreading of liquid systems on solid substrates under transient conditions, driven by surface tension and viscous forces along with the interface interactions (e.g., a substrate dissolution or diffusion and/or chemical reaction) is a complex problem, still waiting to be fully understood. In this study we have performed an extensive experimental investigation of liquid aluminum alloy spreading over aluminum substrate along with corroboration with theoretical modeling, performed in separate but coordinate study. Wetting and spreading to be considered take place during a transient formation of the free liquid surface in both sessile drop and wedge-tee mating surfaces’ configurations. The AA3003 is used as a substrate and a novel self-fluxing material called TrilliumTM is considered as the filler metal. In addition, benchmark, non-reactive cases of spreading of water and silicon oil over quartz glass are considered. The study is performed experimentally by a high temperature optical dynamic contact angle measuring system and a standard and high speed visible light camera, as well as with infra read imaging. Benchmark tests of non-reactive systems are conducted under ambient environment’s conditions. Molten metal experiment series featured aluminum and silicone alloys under controlled atmosphere at elevated temperatures. The chamber atmosphere is maintained by the ultra-high purity nitrogen gas purge process with the temperature monitored in real time in situ. Different configurations of the wedge-tee joints are designed to explore different parameters impacting the kinetics of the triple line movement process. Different power law relationships are identified, supporting subsequent theoretical analysis and simulation. Under ambient temperature conditions, the non-reactive liquid wetting and spreading experiments (water and oil systems) were studied to verify the equilibrium triple line location relationships. The kinetics relationship between the dynamic contact angle and the triple line location is identified. Additional simulation and theoretical analysis of the triple line movement is conducted using the commercial computer software platform Comsol in a collaboration with a team from Washington State University within the NSF sponsored Grant #1235759 and # 1234581. The experimental work conducted here has been complemented by a verification of the Comsol phase-field modeling. Both segments of work (experimental and numerical) are parts of the collaborative NSF sponsored project involving the University of Kentucky and Washington State University. The phase field modeling used in this work was developed at the Washington State University and data are corroborated with experimental results obtained within the scope of this Thesis

An investigation into the prognosis of electromagnetic relays.

Electrical contacts provide a well-proven solution to switching various loads in a wide variety of applications, such as power distribution, control applications, automotive and telecommunications. However, electrical contacts are known for limited reliability due to degradation effects upon the switching contacts due to arcing and fretting. Essentially, the life of the device may be determined by the limited life of the contacts. Failure to trip, spurious tripping and contact welding can, in critical applications such as control systems for avionics and nuclear power application, cause significant costs due to downtime, as well as safety implications. Prognostics provides a way to assess the remaining useful life (RUL) of a component based on its current state of health and its anticipated future usage and operating conditions. In this thesis, the effects of contact wear on a set of electromagnetic relays used in an avionic power controller is examined, and how contact resistance combined with a prognostic approach, can be used to ascertain the RUL of the device. Two methodologies are presented, firstly a Physics based Model (PbM) of the degradation using the predicted material loss due to arc damage. Secondly a computationally efficient technique using posterior degradation data to form a state space model in real time via a Sliding Window Recursive Least Squares (SWRLS) algorithm. Health monitoring using the presented techniques can provide knowledge of impending failure in high reliability applications where the risks associated with loss-of-functionality are too high to endure. The future states of the systems has been estimated based on a Particle and Kalman-filter projection of the models via a Bayesian framework. Performance of the prognostication health management algorithm during the contacts life has been quantified using performance evaluation metrics. Model predictions have been correlated with experimental data. Prognostic metrics including Prognostic Horizon (PH), alpha-Lamda (α-λ), and Relative Accuracy have been used to assess the performance of the damage proxies and a comparison of the two models made

Phase separation and self-assembly in vitrimers: hierarchical morphology of molten and semi-crystalline polyethylene/dioxaborolane maleimide systems

Vitrimers - a class of polymer networks which are covalently crosslinked and insoluble like thermosets, but flow when heated like thermoplastics - contain dynamic links and/or crosslinks that undergo an associative exchange reaction. These dynamic crosslinks enable vitrimers to have interesting mechanical/rheological behavior, self-healing, adhesive, and shape memory properties. We demonstrate that vitrimers can self-assemble into complex meso- and nanostructures when crosslinks and backbone monomers strongly interact. Vitrimers featuring polyethylene (PE) as the backbone and dioxaborolane maleimide as the crosslinkable moiety were studied in both the molten and semi-crystalline states. We observed that PE vitrimers macroscopically phase separated into dioxaborolane maleimide rich and poor regions, and characterized the extent of phase separation by optical transmission measurements. This phase separation can explain the relatively low insoluble fractions and overall crystallinities of PE vitrimers. Using synchrotron-sourced small-angle X-ray scattering (SAXS), we discovered that PE vitrimers and their linear precursors micro-phase separated into hierarchical nanostructures. Fitting of the SAXS patterns to a scattering model strongly suggests that the nanostructures - which persist in both the melt and amorphous fraction of the semi-crystalline state - may be described as dioxaborolane maleimide rich aggregates packed in a mass fractal arrangement. These findings of hierarchical meso- and nanostructures point out that incompatibility effects between network components and resulting self-assembly must be considered for understanding behavior and the rational design of vitrimer materials

Fundamental study of underfill void formation in flip chip assembly

Flip Chip in Package (FCIP) has been developed to achieve the assembly process with area array interconnects. Particularly, a high I/O count coupled with finer pitch area array interconnects structured FCIP can be achieved using no-flow underfill assembly process. Using the assembly process, a high, stable yield assembly process recently reported with eutectic lead-tin solder interconnections, 150 µm pitch, and I/O counts in excess of 3000. The assembly process reported created a large number of voids among solder interconnects in FCIP. The voids formed among solder interconnections can propagate, grow, and produce defects such as solder joint cracking and solder bridging. Moreover, these voids can severely reduce reliability performance. Indeed, many studies were conducted to examine the void formation in FCIP. Based on the studies, flip chip geometric design, process conditions, and material formulation have been considered as the potential causes of void formation. However, the present research won't be able to identify the mechanism of void formation, causing a lot of voids in assembly process without consideration of chemical reaction in the assembly process with a fine-pitch, high I/O density FCIP. Therefore, this research will present process technology necessary to achieve high yields in FCIP assemblies using no-flow underfills and investigate the underlying problem of underfill void formation in these assemblies. The plausible causes of void formation will be investigated using experimental techniques. The techniques will identify the primary source of the void formation. Besides, theoretical models will be established to predict the number of voids and to explain the growth behavior of voids in the FCIP. The established theoretical models will be verified by experiments. These models will validate with respect to the relationship between process parameters to achieve a high yield and to minimize voids in FCIP assemblies using no-flow underfill materials regarding process as well as material stand points. Eventually, this research provides design guideline achieving a high, stable yield and void-free assembly process.Ph.D.Committee Chair: Baldwin, Daniel; Committee Member: Colton, Jonathan; Committee Member: Ghiaasiaan, Mostafa; Committee Member: Moon, Jack; Committee Member: Tummala, Ra