Ideal Linear Behavior Research Articles

Thermal and rheological behaviour of some random aromatic polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological behaviour of seven random Cl-ended aromatic PES/PEES copolymers ( M n ≈ 9500 g mol −1), at various PES/PEES repeating unit ratios, was studied. The glass transition temperatures ( T g), determined by DSC experiments, showed a dependence on copolymer composition significantly different from the ideal linear behaviour expected on the basis of Fox equation. Degradations were carried out in the scanning mode, under flowing nitrogen, in the temperature range 35–650 °C and a single degradation stage was observed for all copolymers. The initial decomposition temperatures ( T i) and the half decomposition temperatures ( T 1/2) were directly determined by TG curves, while the apparent activation energies of degradation ( E a) were obtained by the Kissinger method. In addition, the complex viscosity ( η ∗) of molten copolymers was determined in experimental conditions of linear viscoelasticity. T i, T 1/2, E a, and η ∗ values were depending on copolymer composition, showing a trend similar to that of T g values. The results obtained were discussed and interpreted.

Stiffening effects on the natural frequencies of laminated plates with piezoelectric actuators

Abstract Piezoelectric actuators are usually mounted to the top and bottom surfaces of plates and may induce in-plane extension, bending and localized shear deformations at the structural element. The in-plane stresses may have a significant influence on the mechanical behavior of thin plates as initial and/or residual stresses affect the flexural stiffness and in turn the dynamic and stability characteristics of plates. In this work, the effect of the in-plane piezoelectric induced stresses on the natural frequencies of composite plates is numerically and experimentally investigated. A finite element formulation is presented for the analysis of laminated plates with an arbitrary number of piezoelectric actuators and/or sensors. Von Karman non-linear strain–displacement relations are used and ideal linear behavior is assumed for the piezoelectric actuation. The problem is decomposed into an in-plane problem where the strain field induced by the piezoelectric actuators is computed. The natural frequencies and vibration modes are then computed taking the stress stiffening effects of these piezoelectric stresses into account. A number of different configurations are numerically and experimentally analyzed to verify the proposed theory. The configurations use eight PZT actuators bonded to three layer glass fiber/epoxy plates. The plates are square and clamped along two opposing edges and free along the other two. Good agreement is obtained between the predicted and measured natural frequencies.

Magnetic field intensity study of the 1960 Kilauea lava flow, Hawaii, using the microwave palaeointensity technique

SUMMARY It is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known. In this study, two vertical sections, 16 m apart, have been sampled from the approximately 1 m thick 1960 Kilauea lava flow, Hawaii. Variations are seen in the rock-magnetic and palaeomagnetic properties between and within the two sections, indicating that there are small-scale lateral and vertical variations in the lava flow. The two sections showed dierent responses to microwave palaeointensity analysis. Section H6001 generally gave ideal linear behaviour on plots of natural remanent magnetization (NRM) lost against microwave-induced thermoremanent magnetization (T M RM) gained, whilst the majority of samples from H6002 showed anomalous two-slope behaviour. When all plots were interpreted by taking the best-fitting line through all points, the flow mean intensity for H6001 was 31.6±3.6 mT and that for H6002 was 37.1±6.4 mT, compared with the expected intensity of 36 mT. Additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava, and whether it is best to always interpret NRM lost/T M RM gained plots by taking the line of best fit regardless of shape.

Stiffening effects on the free vibration behavior of composite plates with PZT actuators

The free vibration behavior of thin composite plates with surface bonded piezoelectric patches including stress stiffening effects is investigated. A finite element formulation is presented, based on the Reissner–Mindlin theory and including non-linear strain–displacement relations, to formulate a free vibration eigenvalue problem in the presence of a geometrical stiffness matrix. The case of symmetric laminates and ideal linear behavior is assumed for the piezoelectric actuation. Due to the absence of membrane-bending coupling, in-phase applied voltages produce only inplane-induced piezoelectric stress resultants, which are assumed proportional to the applied voltages. Examples with numerical results for unconstrained plates equipped with piezoelectric actuators show that inplane induced stresses may significantly affect the free vibration behavior.

Molecular association and solvent effects in the electronic and NMR spectra of the tricyanoterpyridineruthenate(II) complex

Solvent effects on the electronic structure and NMR spectra of the[Ru(terpy)(CN)3] complex(terpy = 2,2′,6′,2″-terpyridine) have beeninvestigated and interpreted using quantum mechanical semiempirical methods.A systematic splitting of the electronic bands in the visible is observed, in addition to theirbathochromic shifts depending on the acceptor number of the solvent. The solvent-inducedsplittings are rationalized in terms of the involvement of several charge—transfertransitions exhibiting distinct participation of the ruthenium (II), terpy, and CN−orbitals. Direct evidence of solvent interaction at the cyanide ligands is observedin the [13C]NMR spectra. The most enhanced solvent effects are at the middle13C-4′ and 1H-4′ atoms of terpy, in complete agreement with the theoreticalcalculations. In D2O, stacking interactions involving the terpy ligands are detectedfrom the [1H]NMR spectra, leading to a bimolecular association constant of90 mol−1-dm3. In acetone—D2O mixed solvents, the spectroscopic changes areindicative of preferential solvation departing from the ideal linear behavior.

Stress Stiffening Effects in Laminated Beams with Piezoelectric Actuators

The effectiveness of using piezoelectric elements to enhance the mechanical performance of laminated structures by inducing favorable in-plane stresses is investigated. A finite element formulation is presented for the analysis of laminated Timoshenko beams with an arbitrary number of piezoelectric actuators and/or sensors placed along the length of the beam. Von Kdrman nonlinear strain-displacement relations are used and ideal linear behavior is assumed for the piezoelectric actuation. It is shown that if the beam is longitudinally restrained at both ends the piezolectric actuators induce in-plane stresses that significantly affect the mechanical behavior of the beam. It is also shown that stress stiffening is more pronounced for slender beams. A configuration with a piezoelectric actuator at the top of a slender beam and a sensor at the bottom is analyzed. It is demonstrated that neglecting the stress stiffening effects may lead to large errors in both the static and dynamic analyses of this widely used configuration for slender beams. Further, the stiffness of the beam can be piezoelectrically tuned to significantly change the natural frequency; this has interesting applications in active vibration and acoustics control or smart structures.

Densities of soybean oil/solvent mixtures

AbstractDensity data for soybean oil/acetone and soybean oil/n‐hexane mixtures were measured at 20, 30 and 40 C using a PAAR DMA digital readout calculating precision density meter over the complete range of concentrations. When plotted as molar volume versus molar concentration the mixtures exhibited near ideal linear behavior. To check whether other oil/solvent mixtures behaved in a similar way, data from published literature were replotted in this form and the near ideal linear behavior was observed.Using the data at 20 C, the excess volumes VE were calculated, from which partial molar volumes for each component were obtained. These showed only slight variation over the composition range, confirming the near ideal behavior of these systems. Therefore, if densities of pure oil and solvent are known, their mixture density can be calculated by linear interpolation with sufficient accuracy for engineering design calculations.

Effect of nonsymmetric damping on trim magnification of rolling re-entry vehicles

demonstrated an ideal linear behavior to failure with reasonably repeatable performance. The short column analysis and experimental tube data given in Table 3 indicate that a suitable analytical procedure exists for predicting the local instability of B/A1 columns. It is important to note that such a capability, coupled with the generally more accurate prediction techniques relative to column buckling and strength, greatly enhances the capability to design and analyze B/A1 tubular structures. The limited data suggest that an empirical knockdown factor of approximately 0.75 be applied to predictions using the analysis procedure to improve correlation between theoretical and test data. More correlation studies are required to demonstrate general application of the procedure over a wider range of specimen diameter to thickness (D/t) ratios.

The Absolute Viscosity of Some Lead-Tin Alloys

Abstract The absolute viscosity of lead, tin and nine of their alloys were measured as a function of temperature between the liquidus and 500°C by an oscillating cup viscometer. The viscosity of pure tin ranged from 0.01780 poise at 235°C to 0.01196 poise at 458°C. The viscosity of pure lead ranged from 0.02578 poise at 334°C to 0.01896 poise at 472°C. Viscosity isotherms, as a function of composition, showed an ideal linear behavior with no anomaly detected at the eutectic composition (26.1 at % Pb). A plot of log φ versus 1/T was linear for all samples. Accuracy of the data is estimated to be about 1%.