Presentation of KI-COF,a phenomenological model of variable friction in fretting contact

In this paper, a new phenomenological model, called KI-COF is developed to account for variable coefficient of friction (COF) in space and time. The COF is no longer considered as a global value valid for the whole contact area. A local value is introduced instead, the evolution of which is governed by the local history of the contact and the amount of slip.     

Cell formation using multiple process plans

Cell formation (CF) consists of identifying machine groups and part families. Many CF procedures use a part machine matrix as an input and attempt to obtain a block diagonal form. But perfect block diagonalization of parts and machines is not possible is many cases. In this paper we consider a generalized cellular manufacturing (CM) problem, in which each part can have alternate process plans and each operation can be performed on alternate machines. Under these conditions the CF problem of assigning parts and machines to each manufacturing cell can be considered as a two stage process. The first stage deals with the problem of determining a unique process plan for each part. The second stage determines the part families and machine cells. In this research a model for forming part families and machine cells is presented considering alternate process plans. The objective is to analyze how alternate process plans influence and enhance the CM process giving better flexibility to the designer while designing cells for CM.     

A non-uniform friction distribution model for partial slip fretting contact

In partial slip fretting contact, the coefficient of friction (CoF) is often assumed to be constant along the contact surface. The literature shows that the CoF is related to the relative slip, which varies in the slip region of a partial slip contact. This study develops a methodology to consider the effects of non-uniform CoF distribution in the slip region. Two cases were investigated. In the first case, the axial stress on the substrate (specimen) was absent, while the axial stress was present in the second case. In both cases, the CoF was assumed to be static, kept constant in the stick zone, and varied linearly in the slip region. A closed form solution was developed to determine the stick/slip region size and the equivalent constant CoF for the no-axial stress case, and it was supplemented with finite element analysis. In the second case, where an axial stress was applied on the specimen, the stick/slip region size and the equivalent constant CoF were determined by finite element analysis. The equivalent constant CoF with an axial stress was slightly greater than that without the axial stress due to the larger slip zone size. The stress state in the contact region based on the equivalent constant CoF was comparable to its counterpart from the linearly varying CoF case.     

Impedance spectroscopy study of Nd2NiO4+δ, LSM and platinum electrodes by micro-contact technique

The impedance spectra of Nd₂NiO_4+δ, La_1−xSr_xMnO₃ and platinum pin-shaped electrodes pressed on the surface of an electrolyte pellet (Yttria Stabilized Zirconia) have been recorded as a function of temperature, in air atmosphere, under zero dc conditions. Such an electrode configuration was used to study the characteristics of the air electrode reaction with respect to the nature of the electrode material, the geometry of the electrode–electrolyte contact being the same for all electrodes. The impedance data were analyzed and the results evidence different oxygen reduction mechanisms depending on the nature of the oxide, Mixed Ionic and Electronic Conducting (MIEC) oxide for the nickelate, bad ionic but electronic conductor for the manganite and metallic for the platinum.     

Gas entrainment in an evaporating spray jet

Gas entrainment induced by a spray jet can be significantly affected by the spray evaporation rate. In this study, we have directly measured the air entrainment induced by a liquid nitrogen spray jet into an unbounded and stagnant room air. It is realized that the air entrainment is proportional to the axial gradient of oxygen mass flow in a pure nitrogen spray jet. Hence, the air entrainment can be determined by a combined measurement of local cross-sectional distributions of oxygen concentration, gas temperature and gas velocity along the jet path. These measurements are directly obtained using an in situ oxygen concentration analyzer, a thermocouple system, and a Laser Doppler Velocimeter. In order to evaluate the effect of evaporation rate, direct measurements and numerical simulations of the air entrainment by a cold gaseous jet of nitrogen (at a temperature slightly above that of liquid nitrogen) into room air are also performed. Measurements of the entrainment rate and flow similarity of the gaseous jets without droplets compared very well against those from the single-phase jet theories and numerical simulation, which validates our experimental approach and analysis method. Our experimental results indicate rough flow similarities exist in evaporating spray jets with round nozzles. Although the air entrainment by the liquid nitrogen spray is found significantly increased, as compared to that by the cold gaseous jet of nitrogen from the same nozzle and at the same jetting velocity, the increased ratio is far less than the equivalent momentum ratio of the liquid nitrogen spray to the gas nitrogen jet. This experimental finding suggests that the evaporation of spray markedly weakens the gas entrainment. In this study, a parametric model is also developed to provide a theoretical basis of the data analysis for the cross-section averaged spray evaporation rate within the spray jet region.     

Variable-sweep optimization

A hodograph-vector-control concept is applied to the optimization of variable sweep in maneuvering flight. For a flight-control mode which is basically manual, with only the sweep control adjusted automatically as a function of flight conditions and the conventional flight controls, the hodograph approach leads to sweep commands dependent on Mach number, lift coefficient, and throttle/speed-brake setting. Some computations for an example are presented.     

Integrity assessment for a tubeplate using the linear matching method

A series of numerical procedures have been presented recently for the integrity assessment of structures based upon the Linear Matching Method. A typical example of a holed plate has been used to verify these procedures for the evaluation of plastic and creep behaviours of components. In this paper, a more complex 2D tubeplate at the outlet from a typical AGR heat exchanger is analysed for the shakedown limit, reverse plasticity, ratchet limit and creep relaxation based on the application of the Linear Matching Method for a thorough case study. Both a constant material yield stress and a temperature-dependent yield stress are adopted for the evaluation of the ratchet limit. For the evaluation of accumulated creep strains, flow stresses and elastic follow-up factors with differing dwell times at the steady cyclic state, a monotonic creep computation is performed, where the start-of-dwell stress is the rapid cycle creep solution at the beginning of the dwell period. An estimation of the tubeplate lifetime is then obtained by the evaluation of fatigue and creep endurances.