Rate Effects on the Stress-Strain Behaviour of Eps Geofoam

The rate-dependency of the stress-strain behavior of EPS (Expanded Polystyrene) geofoam with densities of 19.3 and 28.0 kg/m³ was investigated by performing unconventional unconfined compression tests. A set of monotonic loading (ML) tests were performed at different constant values of vertical (axial) strain rate, ε_v. The ε_v value was stepwise changed many times and several sustained loading (SL) tests were performed during otherwise ML at a constant ε_v in other tests. A number of SL tests were performed during global unload and reload cycles to infer the stress-strain relation when ε_v=0. The elastic properties were evaluated by applying minute unload/reload cycles during otherwise ML. The rate-dependent stress-strain behaviour observed in these tests was described by an elasto-viscoplastic model (i.e., a non-linear three-component model), for which the vertical (axial) stress, σ_v, consists of inviscid and viscous components, σ_v^f and σ_v^v, while ε_v consists of elastic and irreversible components, ε_v^e and ε_v^ir. It is shown that the viscous property of EPS geofoam is of Isotach type in that, under the loading conditions where ε_v^ir is always positive, the current σ_v^v value is a unique function of instantaneous ε_v^ir and ε_v^ir, therefore the strength increases with ε_v. This viscous property was quantified based on the test results and incorporated into the model. The rate-dependent stress-strain behaviour, including the creep behaviour, observed in the experiment is simulated very well by the proposed model. In particular, the fact that the creep strain becomes significant when the sustained σ_v value becomes larger than the inviscid yield vertical stress is well simulated.     

Intentional side etching to achieve low-noise GaAs f.e.t.

A very-low-noise 0.5 ?m-gate GaAs f.e.t. is realised by using intentional side etching of an Au/Ti double layer as the Schottky-gate metal. At 12 GHz, the minimum noise figure is 2.1 dB, with 7.6 dB associated gain at a bias of VD = 4 V, ID= 10 mA. Maximum stable gain is 14 dB at VD = 4 V, ID = 30 mA.     

Computational Experience with a Dual Backtrack Algorithm for Identifying Frequencies Likely to Create Intermodulation Problems

This paper describes the results of a computational study using a particular enumeration procedure, called a backtrack algorithm, to find the lowest order of radio-frequency intermodulation. The average lowest order and its standard deviation, the average computer time and its standard deviation, along with other relevent statistics are obtained for a series of randomly generated problems with sets of five to 75 threat or source frequencies. Other parameters, such as the guard band, the maximum number of concurrent threats, and the size of the frequency band on the lowest order of intermodulation are varied during the computations. Statistics for these computer runs, along with those relating to terminating the algorithm when the lowest "acceptable" order is reached, are presented in some detail. Brief conclusions follow a listing of the results.     

Tool wear prediction and economics in machining stepped parts

For analysing economics of machining cylindrical stepped parts, tool life must be predicted. In this paper, tool life tests, to obtain tool life changing cutting speed before the tool reaches tool life criterion under a constant speed, are performed and the tool life is calculated. Using the results of the calculations machining economics of various forms of stepped parts for the constant spindle rpm method and the constant cutting speed method, are analysed.     

FORMATION OF MULLITE FROM GROUND PRODUCT OF A KAOLINITE-ALUMINUM TRIHYDROXIDE MIXTURE BY SOLID PHASE REACTION

The present paper describes the effect of grinding a kaolinite/aiuminum-trihydroxide mixture using a planetary ball mill on the structure of the ground product and the mean thermal expansion coefficients of samples sintered from the unground and ground mixtures. The size reduction of the mixture predominates in the early stage of grinding and the obtained fine particles aggregate subsequently with an increase in grinding time. The crystal structure of the mixture is collapsed easily into a disordered one, of which amount increases with an increase in grinding time. Only mullite phase was detected in the sintered body of the ground products at relatively lower temperature 1523K except for anatase as an inherent impurity, whereas corundum, cristobalite and Al-Si spinel phases besides mullite were formed in the sintered body of the unground mixture. The thermal expansion coefficients of sintered bodies of the 120 minutes-ground mixture are considerably lower than those of the unground mixture by about 10%. Consequently, the planetary milling enables us to improve the uniform mixing state at the atomic scale resulting in direct formation of mullite with high purity at relatively low temperature with a lower thermal expansion coefficient of the sintered body.     

Effect of water on permeation,diffusion, and solution of gases in cellophane

The laminate method for studying the permeability and diffusivity of moistened cellophane to gases is described and the humidity dependence of the transport parameters for H₂, He, and Ne is presented. In the relative humidity region of about 0% to 60%, a small increase in the permeability was observed, which is caused by a comparatively small increase in the diffusivity owing to the plasticizing effect of sorbed water and a decrease in the solubility. On the other hand, an extremely large increase in the permeability observed in the relative humidity region above 60% is mainly based on the diffusion coefficient of gas enhanced by the swelling effect of sorbed water. The presence of a minimum in the solubility–relative humidity curves has been confirmed and is discussed.     

Temperature distribution in Li2O pellets under neutron irradiation

The center temperature of Li₂O pellets under neutron irradiation was measured using an encapsuled pin. The surface temperatures of the pellets and the pellet/cladding heat transfer coefficients were estimated on the basis of the well-known conductivity integral.     

Effects of chromate treatments on environmental stability of lead/tin alloy joints bonded with an ethylene–acrylic acid copolymer. II. Failure mechanism in distilled water

The environmental stability in distilled water and the failure mechanism of cathodically chromated tin, lead, and lead/tin alloy joints bonded with an ethylene–acrylic acid copolymer have been investigated by T-peel tests and ESCA and SEM analyses of the fractured surfaces. The peel strength of chromated lead/tin alloy joints and of both untreated and chromated tin joints is kept unchanged with water immersion, whereas that of untreated lead/tin alloy joints and of both untreated and chromated lead joints decreases rapidly with water immersion. ESCA and SEM observations show that lead/tin alloy surfaces consist of both lead and tin phases and that the tin phase interface deteriorates gradually with water immersion after premature deterioration of the lead phase interface. The stabilization effect of chromate treatments for lead/tin alloy joints is due to retardation of the underfilm corrosion of the tin phase.