Anisotropic polyurethane foam with Poisson'sratio greater than 1

Anisotropic polymer foams have been prepared, which exhibit a Poisson's ratio exceeding 1, and ratios of longitudinal to transverse stiffness exceeding 50. The foams are as much as 20 times stiffer in the longitudinal direction than the foams from which they were derived. The transformation process involved applying to open-cell polyurethane foam an axial strain of 25 to 45%, at a temperature above the softening point, followed by cooling under axial strain. This revised version was published online in November 2006 with corrections to the Cover Date.     

The viscoelastic behavior of β-In3Sn and the nature of the high-temperature background

The damping behavior in torsion of single phase -In₃Sn has been evaluated at room temperature over a broad range of frequencies (10^–4 to 10³ Hz) and as a function of various mechanical and thermal treatments. The results are consistent with a model for the power-law (tan f ^–n), high-temperature-background absorption being effected by diffusional processes on grain and, particularly, on subgrain boundaries. The results are compared/contrasted with those for damping in single-phase -InSn₄ and in the two-phase - eutectic. Failure of the eutectic material to follow a composite model for damping, combined with a thermal aging effect that lowers damping only for certain frequencies, shows that the boundary-based absorption model for the high-temperature background applies, too, to phase boundaries.     

Development of a low-cycle fatigue life curve for 80In15Pb5Ag

The purpose of this study is to develop a methodology to predict the low-cycle (large strain—from 0.1 to 0.35 strain) fatigue life of solders subject to thermal cycling. Solders are commonly used in electronic assemblies. Using thermal fatigue data measured for 80In15Pb5Ag, a low-cycle fatigue curve for 80In15Pb5Ag solder subject to thermal cycling was developed. Specifically a Coffin-Manson relationship was derived for the solder, with a high degree of correlation (see Table I), for four different failure criteria, defined in the body of the paper. This relationship, together with calculated strains in the solder joint, allows the low-cycle fatigue life of the solder joint to be predicted.     

Viscoelastic spectra of Cd0.67Mg0.33 in torsion and bending

In both torsion and bending, the alloy exhibited a viscoelastic relaxation that could be modeled as a Debye peak superimposed on a power-law low-frequency background. In torsion, the relaxed and unrelaxed shear moduli were 9 and 12.2 GPa, respectively, maximum loss tangent was 0.12. In bending, relaxed and unrelaxed Young’s moduli were 15 and 35 GPa, respectively; maximum loss tangent was 0.11. Behavior was linear to at least 125 microstrain. These results are significant in that they represent a unique combination of stiffness and loss in a monolithic material.     

EXPERIMENTS OF THREE-DIMENSIONAL FLOW STRUCTURE IN BRAIDED RIVERS

The braided river is a typical river pattern in nature, but there is a paucity of comprehensive data set describing the three-dimensional flow field in the braided river. A physical model experiment was used to study the flow characteristics in the typical braided river with a mid-bar between two anabranches. In the experiment, two kinds of mid-bar with the ratios of its length to maximal width of 3 and 5 were considered. Moreover, the mid-bar could be moved to adjust the width of two anabranches. The detailed measurements of velocity were conducted using an acoustic Doppler velocimeter over a grid defined throughout the whole braided river region, including the bifurcation, two anabranches and the confluence. In two kinds of mid-bar braided models, a separation zone was observed in the anabranch of the model in which the ratio of length to maximal width of mid-bar is 3, however the separation zone was not found in another model in which the ratio is 5. In addition, the opposite secondary cells were observed at the bend apex of anabranch in two models, and different longitudinal velocity distributions in the entrance region of anabranch account for this opposite flow structure. Finally, turbulent kinetic energy were shown and compared in different situations. The high turbulence occurs at the place with strong shear, especially at the boundary of the separation zone and the high velocity passing flow.     

FLOW STRUCTURE OF PARTLY VEGETATED OPEN-CHANNEL FLOWS WITH EELGRASS

Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegetation in order to manage fluvial processes. Experiments in an open-channel flume with natural vegetation were carried out to study the influence of vegetation on the flows. In a half channel with two different densities of vegetation, the flow velocity, Reynolds stresses, and turbulence intensities were measured using an Acoustic Doppler Velocimeter (ADV). We obtained velocity profiles in the lateral direction, Reynolds stresses in the vertical direction, and the flow transition between the vegetated and non-vegetated zones in different flow regimes. The results show that the streamwise velocity in the vegetated zone with higher density is almost entirely blocked. Reynolds stress distribution distinguishes with two different regions: inside and above the vegetation canopies. The turbulence intensities increase with increasing Reynolds number. The coherent vortices dominate the vertical transport of momentum and are advected clockwise between the vegetated zone and non-vegetated zone by secondary currents (a relatively minor flow superimposed on the primary flow, with significantly different speed and direction), generated by the anisotropy of the turbulence.     

Viscoelastic behaviour in indium alloys: InSn,InBi, InCd and InSnCd

Experimental studies of dynamic and transient viscoelastic response were conducted at 24 °C on the indium alloys InSn, InBi, InCd and InSnCd. The experiments were conducted in torsion using an instrument capable of determining viscoelastic properties over ten decades of time and frequency. The damping, tan , followed a ^–n dependence at higher frequency and was essentially constant at low frequency. Creep at long times followed a power law dependence upon time: t ^m. The damping is attributed to a dislocation-point defect mechanism.     

A nonlinear constitutive relationship for asphalt binders

A nonlinear constitutive relationship was developed for asphalt binders. Two binders, one polymer modified and one unmodified, were tested in shear using creep and recovery loading. Five different stress levels and four loading times were considered, to capture the response of the binders in the linear and nonlinear viscoelastic range. The creep response of the binders was successfully modeled with a nonlinear power law function. The modified superposition principle was unable to predict the recovery phase of the testing data. A nonlinear constitutive relationship composed of a nonlinear viscous part plus a linear viscoelastic part was developed. The constitutive relationships successfully predicted the binders’ response in creep and recovery. The predictions of the constitutive relationships matched accurately the response of the binders subjected to the Multiple Stress Creep and Recovery loading pattern.     

Instrumented Force Platform for Postural Sway Studies

A force platform has been developed, which is capable of measuring postural sway in humans in two orthogonal directions. For each direction, output data consist of total average sway in two frequency bands centered on 0.57 and 2.9 Hz. The device is suitable for use in research or in a clinical setting.     

Noncentrosymmetry in micropolar elasticity

Consequences of noncentrosymmetry in a micropolar elastic solid are considered. A solid which is isotropic with respect to coordinate rotations but not with respect to inversions, has three new elastic constants in addition to the six considered in the fully isotropic micropolar solid. The acentric micropolar solid is predicted to undergo torsional deformation when subjected to tensile load.