Simplified Bulk Experiments and Hygrothermal Nonlinear Viscoelasticity

Bulk and shear linear viscoelastic functions were simultaneously determined using confined compression experiments on an epoxy primer, one component of a concrete/fiber-reinforced polymer composite bond line. The results were validated with data from separately conducted bulk creep compliance experiments. The transition region of the bulk modulus was as wide as those of the tensile and shear relaxation moduli. Thermal and hygral expansions were measured and used to calibrate a hybrid nonlinear viscoelastic constitutive model which represented the hygrothermal nonlinear viscoelastic response of the material. This model was a combination of Schaperys (Further Development of a Thermodynamic Constitutive Theory: Stress Formulation, AA {&} ES Report (69–2), 1969a, Purdue University, West Lafayette; Schapery, R.A., On the characterization of nolinear viscoelastic materials, Polym. Eng. Sci. 9 1969b, 295–310.) and Popelars (K., Multiaxial nonlinear viscoelastic characterization and modeling of a structural adhesive, J. Eng. Mater. Technol. Trans. ASME 119, 1997, 205–210.) shear modified free volume model, which was calibrated ramp using torsion and tension experiments at various temperature and humidity levels. Using free volume concepts to accomplish time shifting as a function of strain, temperature and humidity levels did not create the extent of the softening behavior that was observed in the experiments, particularly at high humidity levels. The vertical shifting concepts of Schapery were required to capture the extraordinarily strong hygral effect.     

Measurement and prediction of Young’s modulus of a Pb-free solder

Accurate and reproducible measurements of the Youngs modulus of solders are complicated by the early onset of yielding, microporosity, and variations in cooling rate. In this study, we report measurements of Youngs modulus of an Sn–3.5 wt % Ag solder by two techniques: (a) loading–unloading measurements in tension, and (b) non-destructive resonant ultrasound spectroscopy. Both techniques yielded similar values of Youngs modulus. The modulus decreased with increasing microporosity, in accordance with predicted values. Cooling rate affected the Ag₃Sn intermetallic morphology, but not Youngs modulus since the distribution of the particles was relatively random. This result was confirmed by microstructure-based finite element modeling.     

Mapping co-word structures: A comparison of multidimensional scaling and leximappe

The LEXIMAPPE method and Multidimensional Scaling (MDS) are discussed as methods to visualize (map) characteristics of structures of word-occurrence (co-word) relations. Utilization of MDS is proposed as an alternative mapping method able to circumvent problematic features of LEXIMAPPE maps of the total co-word structure. A comparison of both methods on the same real-life co-word matrix demonstrates topological advantages of an extended MDS-mapping.     

Thermal detection of ESR on spin-polarized hydrogen: Study of surface recombination

We introduce a new method for the detection of electron-spin resonance in spin-polarized atomic hydrogen gas (H). Instead of observing the microwave power absorbed in the ESR transition, we monitor the recombination heat deposited by ESR-induced spin-up atoms (H) onto a liquid-helium coated carbon bolometer. The signal from this sensor reproduces well the ESR absorption lineshape registered by our 128 GHz homodyne spectrometer. Using the recombination detection we have achieved a density detection limit of n=3·10¹⁰ atoms/cm³ for 0.2 nW microwave power incident on the resonant cavity at the temperature T=150 mK. We have studied the decay rate of recombination heat absorbed by the bolometer after an ESR excitation pulse and the dependence of this rate on T, n and nuclear polarization of the H sample. The bolometer signal is found to be related mainly to second-order H + H recombination to ortho-H₂ on the surfaces of the sample cell. From the signals we have determined the rate constant K _bc ^c =3.2(5)·10^–5T cm²/s·K^–1/2 in the interval from T=250 to 425 mK in a field of 4.5 T.     

Development of methods and instruments of the Russian service for determination of the Earth’s orbital parameters

The state and future outlook of research to determine the Earths orbital parameters, i.e., Universal Time and the coordinates of the pole, carried out by the State Time and Frequency Service and in calculations of the Earths orbital parameters are described.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 24–27, January, 2005.     

On some new variational formulations and finite element models in classical elastoplasticity

Summary The paper deals with the systematic development of variational methods and associated finite element schemes for the approximate analysis of elastoplastic continua. The major difference between these novel models and existing ones consists in treating the yield condition as an a posteriori (natural) constraint and not as an a priori (essential) constraint. The advantages of this approach over existing ones are pointed out and discussed from a theoretical and a computational standpoint as well.With 1 Figure     

An effective finite element modeling/analysis approach for dynamic thermoelasticity due to second sound effects

Of interest here are dynamic thermoelastic problems influenced by second sound effects. In this regard, the effect of the so called heat waves on solid continua is investigated employing a unified explicit computational architecture which uses the finite element method. The approach is robust and effective for transient interdisciplinary thermal-structural modeling/analysis. The non-classical relaxation model of Green and Lindsay (1972) involving two relaxation times is employed in the present work. Numerical simulations relevant to thermal shock problems in an elastic half-space are described for stainless steel via two different illustrative test cases.     

Failure criteria for weak-axis quasi-orthotropic woven fabric composites

Summary The failure behavior of woven fabric composites in the form of plain weave fiber unidirectional laminae is studied in this paper as defined by their failure stresses in simple tension and compression along the three principal stress directions. Since the transverse weave plane is the strong and isotropic plane of the composite, while the normal to it direction the weak one, the material is approximated as a weak-axis transversely isotropic composite.The elliptic paraboloid failure surface (EPFS) criterion, as introduced by the author [1], was shown to describe satisfactorily this type of interesting modern materials. It was shown that such weak-axis transversely isotropic composites correspond to tension strong composites and their failure surfaces consist of a single-sheet convex surface open to the tension-tension-tension octant of the principal stress space.The main characteristic of such surfaces is that they are oblate along the normal direction to the isotropic plane, in contrast with the typical (EPFS)-criterion for fiber composites, which, all of them, are prolate along the same direction. While the intersection of this (EPFS)-criterion by the (₁,₃) stress plane (₃ is the weak axis) resembles closely the respective intersection for the unidirectional fiber composites the (₁,₂)-isotopic plane intersection, which coincides with the weaving strong plane approaches very closely a circle thus indicating that along this isotropic plane the failure stress is hydrostatic and independent of its orientation inside this plane. This property constitutes a significant and most promising property which makes this type of woven composites very attractive in applications.Experimental evidence of failure of such materials, which is very sparse, as derived from tests in a woven T-300 Carbon-epoxy composite corroborated excellently with the theory based on the (EPFS)-criterion.     

The effect of rapid solidification on the structure, decomposition behavior, electrical and mechanical properties of the Sn–Cd binary alloys

A group of rapidly solidified Sn–Cd alloys has been prepared by a melt-spinning technique. X-ray diffraction, microstructure, and differential thermal analysis have been carried out. Youngs modulus and internal friction have been measured, and the temperature dependence of resistivity has been evaluated. The results show a modification in both the microstructure and decomposition behavior. Also, an interesting connection between Youngs modulus and the axial ratio (c/a) of the unit cell of the -Sn was found in which Youngs modulus increases by increasing the axial ratio (c/a). It was found also that the internal friction increases on increasing the Cd concentration.     

The peeling of flexible laminates

The present work has defined an adhesive fracture energy G _a for the peel testing of flexible laminates. The value of G _a characterises the fracture of the laminate and is considered to be a geometry-independent parameter which reflects (i) the energy to break the interfacial bonding forces and (ii) the energy dissipated locally ahead of the peel front in the plastic or viscoelastic zone. We have shown that in order to determine this true adhesive fracture energy G _a that the following energy terms must be considered: (i) the stored strain-energy in the peeling arm, (ii) the energy dissipated during tensile deformation of the peeling arm, and (iii) the energy dissipated due to bending of the peeling arm. The analysis proposed yields quantitative expressions for these various energy dissipation terms and, in particular, considers the energy dissipated due to bending of the peeling arm. Another important feature of the analysis is the modelling of the region below the peel front as an elastic beam on an elastic foundation; such that the peeling arm does not act as a truly built-in beam and root rotation at the peel front is allowed. The analysis described in the present paper has been employed for four different laminates. The values of the local angle ₀ at the peel front from the theoretical calculations have been shown to be in excellent agreement with the experimentally measured values; a small-scale peel test rig having been built so that the peel test, as a function of applied peel angle , thickness h of peeling arm and rate of test, could be observed and photographed using a stereo-optical microscope. The value of the adhesive fracture energy G _a (i.e the fully corrected value) for each laminate is indeed shown to be a material parameter.     

Flow of power-law fluids in cone-plate viscometer

Summary The flow of a power-law fluid in a cone-plate viscometer has been considered. The first order solutions for velocity and pressure have been obtained. Effects of secondary flow on velocity components, pressure, rate of deformation tensors and apparent viscosity have been studied. Both the primary and secondary flows are influenced by flow behavior index n. In shear thinning fluids, the effects on both the primary and secondary flows are of similar nature, whereas in shear thickening fluids, they are of opposite nature. The net result is that for shear thinning fluids the effects of the primary and secondary flows are additive, whereas in shear thickening fluids they almost balance out each other and the resultant effect is insignificant. The other important observation is in Newtonian fluids the secondary flow makes a significant contribution at high value of Reynolds number, which depends on the radius, velocity, density, and viscosity. In power-law fluids, Reynolds number depends on an additional parameter n. With this change, the effect of secondary flows can be important even at low shear rates. A critical value of n is obtained at which flow is independent of shear rates.     

A scientometric cognitive study of neural network research: Expert mental maps versus bibliometric maps

This paper reports on a quantitative analytical methodology which deals with perceptions of scientific experts regarding the intellectual shape and contents (cognitive structure) of their scientific domain. This study examines the method's utility for studying expert views in general, and, more specifically, its strengths and weaknesses as a tool for improving validation studies of bibliometric maps involving subject experts. The main premise is that expert views are based on their internal knowledge structures (mental schemes) of which relevant features can be captured in quantitative data. This approach allows a rigorous and systematic way of studying mental schemes across subject experts. Spatial representations of their data (mental maps) provide insight in properties underlying those knowledge structures. Data from different experts are reconciled to construct a common mental map which displays a group view. This study includes a test to establish the validity of individual mental maps and common mental maps. The methodology is applied to the views of 14 researchers in the field of neural network research and related areas. Key-findings are: (i) mental maps can provide valid representations of expert mental schemes, (ii) experts sharing the same subject field are more likely to share views, (iii) expert judgements of bibliometric maps are affected by the structure of their own mental schemes, as well as (iv) by their views regarding the utility of those maps, and (v) common mental maps and a bibliometric co-word map based on the same set of items differ significantly, showing a resemblance on main features only.     

Hardness of bi-layer films on a leadframe substrate

The indentation hardness and elastic modulus of leadframe materials that consist of Cu alloy substrate and Ni/Pd bi-layer films of differing thicknesses are characterised using the micro-hardness and nano-indentation tests. The true hardness of the individual substrate and film layers is evaluated based on the empirical relationship between the measured composite hardness and the volume of plastically deformed material of film layers. It is found that the composite hardness determined from the nano-indentation test increases rapidly toward a peak at extremely low indentation depth of less than about 20–30 m for all materials studied, due mainly to the finite value of the indenter tip radius and the rough surface of the specimen on the nano-scale. The composite hardness for the coated specimens decreases with further increasing indentation depth toward the hardness value of the substrate, because of the strong influence of the film/substrate interaction and the indentation size effect. The nano-indentation test in general gives higher true hardness values than those obtained from the micro-hardness test. Nevertheless, the relative hardness values of the substrate and films determined from the two tests are consistent. The hardness of Ni film is about 20 to 50% greater than that of Cu alloy, whereas the hardness of Pd film is 7 to 11 times the Ni film in the nano-indentation test.     

Poly(carbazole-co-acrylamide) electrocoated carbon fibers and their adhesion behavior to an epoxy resin matrix

The surface properties of original high strength and preoxidized high modulus carbon fibers were altered by electrocopolymerizing acryl amide and carbazole and therefore depositing a copolymer coating onto the fibers. Scanning electron microscopy and zeta-potential measurements confirmed the presence of a rough but dense and continuous electrocoating with a basic surface character. Therefore, good adhesion behavior between the electrocoated carbon fibers and an epoxy resin matrix should be expected. The interfacial adhesion was measured using the single fiber pull-out and single fiber indentation test. It was shown that only intermediate adhesion was present between the carbon fibers and the electrocoating, but superior adhesion between the coating and epoxy resin exists. The single fiber model composites always failed at the fiber/electrocoating interface. However, as shown by using the indentation test, the interfacial adhesion between fibers and electrocoating can be significantly improved if preoxidized fibers are used as substrate for electropolymerization. A very high tensile strength for the electrocoating can be expected as derived from the single fiber pull-out tests.     

The neural net of neural network research

In this paper we discuss the limits and potentials of bibliometric mapping based on a specific co-word analysis. The subject area is neural network research. Our approach is a simulation of expert assessment by offering the reader a narrative of the field which can be used as background information when reading the bibliometric maps. The central issue in the applicability of bibliometric maps is whether these maps may supply additional intelligence to users. In other words, whether such a bibliometric tool has an epistemological value, in the sense that it ecriches existing knowledge by supplying unexpected relations between specific pieces of knowledge (synthetic value) or by supplying unexpected problems (creative value). We argue that sophisticated bibliometric mapping techniques are indeed valuable for open new avenues to study science as a self-organizing system in the form of a neural network like structure of which the bibliometric map is a first-order aproximation. In that sense, this paper deals with the neural net of neural network research as our bibliometric techniques in fact mimic a connectionistic approach.     

A bibliometric profile of top-scientists a case study in chemical engineering

We carefully selected a group of chemical engineering scientists internationally recognized as top-scientists in their field. A method has been developed to systematically compare bibliometric characteristics of these top-scientists with an average scientist in chemical engineering. This method also includes citation-analysis of books and proceedings. The results show a very clear bibliometric profile. First, top-scientists references are more numerous and, fourth, they concern more recent literature. Our fifth findings is that the journals used by top-scientists for their publications are representative for the field of chemical engineering as a whole. But they differ in specific aspects significantly from the average journal structure in chemical engineering: the published work of top-scientists is both general as well as more specialistic than the average work in chemical engineering.     

Systematic derivation of contour integration formulae for laplace and elastostatic gradient BIE's

A complete set of contour integrands is derived for the primary BIE's of elastostatics and potential flow. Because of surface-independent properties of vector potentials, these apply to nonplanar surfaces and can be differentiated at the fixed point, producing contour integrands for both the so-called hypersingular and Cauchy singular parts of the gradient BIE. The results are applicable to far field, near field and on surface cases. Numerical examples demonstrate exact agreement with surface quadrature, and contour plots are given showing variation of the hypersingular integrands in on surface cases.     

Cohesive crack models for semi-brittle materials derived from localization of damage coupled to plasticity

Based on discontinuous displacement approximation of the continuum and shear band kinematics, two cohesive crack models are derived within the constitutive framework of coupled damage and plasticity. The models employ the Rankine fracture criterion, and the model parameters are determined from a uniaxial tension test (mode I cracking). Bifurcation analysis is used in order to diagnose critical directions along which the crack will gradually develop and propagate. These directions depend on the actual stress state and are kept fixed after fracture has initiated, whereby a fixed crack model is obtained. A discrete crack strategy is employed at the finite element implementation in the sense that interfaces (that represent the cohesive crack) are introduced along inter-element boundaries. This implementation strategy calls for gradual realignment of the mesh as a key feature of the algorithm. Numerical results from the analysis of mixed mode fracture in a notched concrete plate are presented.     

Review Nonlinearity in piezoelectric ceramics

The paper presents an overview of experimental evidence and present understanding of nonlinear dielectric, elastic and piezoelectric relationships in piezoelectric ceramics. This topic has gained an increasing recognition in recent years due to the use of such materials under extreme operating conditions, for example in electromechanical actuators and high power acoustic transducers. Linear behaviour is generally confined to relatively low levels of applied electric field and stress, under which the dielectric, elastic and piezoelectric relationships are described well by the standard piezoelectric constitutive equations. Nonlinear relationships are observed above certain threshold values of electric field strength and mechanical stress, giving rise to field and stress-dependent dielectric (), elastic (s) and piezoelectric (d) coefficients. Eventually, strong hysteresis and saturation become evident above the coercive field/stress due to ferroelectric/ferroelastic domain switching. The thermodynamic method provides one approach to describing nonlinear behaviour in the intermediate field region, prior to large scale domain switching, by extending the piezoelectric constitutive equations to include nonlinear terms. However, this method seems to fail in its prediction of the amplitude and phase of high frequency harmonic components in the field-induced polarisation and strain waveforms, which arise directly from the nonlinear dielectric and piezoelectric relationships. A better fit to experimental data is given by the empirical Rayleigh relations, which were first developed to describe nonlinear behaviour in soft magnetic materials. This approach also provides an indication of the origins of nonlinearity in piezoelectric ceramics, in terms of ferroelectric domain wall translation (at intermediate field/stress levels) and domain switching (at high field/stress levels). The analogy with magnetic behaviour is also reflected in the use of Preisach-type models, which have been successfully employed to describe the hysteretic path-dependent strain-field relationships in piezoelectric actuators. The relative merits and limitations of the different modelling methods are compared and possible areas of application are identified.An erratum to this article can be found at     

Fracture mechanics of a shaft-loaded blister of thin flexible membrane on rigid substrate

A shaft-loaded blister test has been developed to measure the interfacial energy W of a thin flexible polymeric film adhered to a rigid substrate. A theoretical analysis is given of an axisymmetric debond (blister) in terms of an external applied load P, tensile stretching modulus E and thickness h of the adhering layer. The fracture mechanics model presented considers both elastic and elastoplastic deformations in the thin film. The intrinsic stable interface debonding process provides an attractive alternative to the conventional adhesion measurement techniques.