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1.
U. Bianchi 《Rheologica Acta》1971,10(2):213-213
The pressure dependencedT g /dP of glass transition temperatureT g has received considerable interest due to its connection with solid state thermodynamic properties and theories of glass transition. Free volume considerations (1, 2) led to an estimate of the pressure effect onT g , showing thatdT g /dP had to depend on thermal expansion and compressibility changes atT g through the equation: [1] $$\frac{{dT_g }}{{dP}} = \frac{{\Delta \beta }}{{\Delta \alpha }}$$ whereΔβ=β e ?β g andΔα=α e ?α g Later work (3, 4, 5, 6) has shown that eq. [1] is not verified by experimental facts, the ratioΔβ/Δα being much larger than (dT g /dP) exp. Recent analysis of the properties of glasses obtained under different pressures have complicated the situation, showing that the experimental value ofdT g /dP depends, of course, on the polymer usedbut also on the experimental procedure used in its determination. Since it is obvious that in order to measure anyΔT g -value we need to operate on at leasttwo glasses, these should be identical in all properties which could influenceT g except pressure. Any difference in morphology,which could lead to a change in T g at constant pressure, should therefore be avoided in order to get a sound value for the pure pressure effectdT g /dP. To reveal this effect, we have performed (7)dT g /dP determinations on two polymers, polyvinylacetate (PVAC) and polyvinylchloride (PVC), following three different procedures:
- Measurement of the changeΔT g induced by application of a pressure incrementΔP on the liquid polymer (T>T g ). This is the procedure normally used; the liquid is cooled down at a fixed rate of temperature change (～5 °C/day) andT g is dilatometrically recorded at 1 atmosphere. Then the polymer is taken again to the liquid state, pressure ΔP is applied and, at the same rate, the system is cooled down isobarically; the newT g is recorded anddT g /dP calculated.
- Measurement of the change ΔTg induced by application of a pressure increment ΔP on the glassy polymer (T
- Measurement ofΔT g during the heating of a glass along an isochor (5, 8). Here the polymer glass is heated at constant volume, by application of an increasing pressure at increasing temperatures given by(?P/?T) v . By repeating this procedure two times, starting from two different specific volumes of the glass, two values ofT g at different pressures can be recorded anddT g /dP calculated.Table 1 shows the result of this work 相似文献2.Summary The glass transition temperatures (T g ) of asphalt samples of different origins and penetration grades were determined by differential scanning calorimetry (DSC-2). TheT g values of samples originating from two sources decreased with increasing penetration whereas those of samples from a third source were identical at all values of penetration. Substituting theseT g data and values of the universal as well as the optimized constantsC 1 andC 2 in the Williams-Landel-Ferry equation, viscosities were calculated for each of the samples and compared with the corresponding experimental results. The universal values forC 1 andC 2 yielded viscosities which were far removed from the experimental data while the optimized values produced much better results.
Zusammenfassung Die GlasübergangstemperaturenT g von Asphaltproben verschiedener Herkunft und Penetrationsgrade wurden mit einem Differentialkalorimeter (DSC-2) bestimmt. DieT g -Werte von Proben aus zwei Quellen nahmen mit wachsendem Penetrationsgrad ab, wohingegen diese bei Proben aus einer dritten Quelle bei allen Penetrationsgraden gleich blieben. Durch Einsetzen dieserT g -Daten in die Williams-Landel-Ferry-Gleichung wurden sowohl unter Verwendung von universellen als auch von optimierten Werten der KonstantenC 1 undC 2 die Viskositäten der verschiedenen Proben berechnet und mit den experimentell gefundenen Daten verglichen. Die universellen Werte ergaben Viskositäten, die große Unterschiede zu den gemessenen aufwiesen, während man bei Verwendung der optimierten Werte eine weitaus bessere Übereinstimmung erhielt.
With 2 figures and 10 tables 相似文献3.4.《International Journal of Solids and Structures》2007,44(2):530-545An experimental method to determine the complete stress versus deformation relation for a thin adhesive layer loaded in shear is presented. The method is based on a classic specimen geometry; the end-notch flexure specimen. The experiments are evaluated using an inverse method. First, the variation of the energy release rate with respect to the shear deformation at the crack tip is measured during an experiment. Then the traction–deformation relation is derived using an inverse method. The theory is based on the path-independence of the J-integral and considers the effects of a flexible adhesive layer.Quasi-static experiments on three different specimen geometries are performed using a servo-hydraulic testing machine. The experiments give consistent results. This shows that the traction–deformation relation can be taken as independent of the dimensions of the adherends. Thus, the constitutive relation can be considered as a property of the adhesive layer. The deformation process at the crack tip is also monitored during the experiments by the use of a digital camera attached to a microscope. 相似文献5.Herzl Chai 《Experimental Mechanics》1992,32(4):296-303Previous tests have shown that the mode II and mode III fracture energies of adhesive bonds coincide, with the nominal value dictated by post-yield shear deformation in the interlayer. This suggests that the complete mixed-mode fracture behavior may be dellineated by determining the interaction curve in either theG I -G II orG I -G III plane. A DCB-type specimen capable of delivering the entire opening versus shearing toughness spectrum in a single test was used. A brittle and a ductile epoxy resin were evaluated, with the adhesive thickness varying from a few micrometers up to 0.6 mm. Excluding very thin bonds, the mixed-mode fracture curve was approximately bilinear; when the applied energy release rate in shear,G s , was relatively small, the total fracture energy equaledG IC but otherwise, the fracture curve decreased essentially linearly with increasingG S . In the case of the ductile adhesive, the transition in trends occurred whenG S was approximately 55 percent of the shearing fracture energy. When the bond thickness was decreased to a few micrometers, the mixed-mode curve displayed a concave shape, with mode interaction occurring promptly. SEM analysis and analytical considerations suggest that this change in mixed-mode behavior was due to the development of a triaxial state of stress in the interlayer. Based on previous fracture studies of the individual fracture modes in adhesive bonds and laminated composites, the present results should be also applicable to mixed-mode interlaminar fracture of laminated composites.Herzl Chai, formerly associated with Polymers Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899 相似文献6.7.H. van Hoorn 《Rheologica Acta》1971,10(2):208-212Summary The development of vinyl esters of C9–C11 carboxylic acids for internal flexibilization of paint latex polymers has led us to study the effect of structural variations. Flexibility being closely connected with the glass-transition temperature,T g , we have investigated the transition behaviour of a large number of homopolymers and copolymers by dynamic-mechanical methods.The polymers studied were model compounds of uniform structure and a wide variety of copolymers. Of the latter, some were polymers of distillation fractions of the technical vinyl ester mixture, others copolymers of this mixture with a well-defined monomer, e.g. vinyl acetate.As we found a linear dependence ofT g on composition, we have, in the calculations, treated the technical vinyl ester mixture as a single monomer. Inspection of polymerized fractions clearly revealed the effect of the structure of isomeric side groups, the higherT g values being found for the more compact structures. The fact that the differences inT g between polymers made from the various fractions are fairly small implies that their type of branching has led to moderately compact side groups. This has been derived fromT g determinations on model polymers of highly branched vinyl esters of C9 carboxylic acids of known structure.Zusammenfassung Die Entwicklung von Vinylestern auf der Grundlage von C9–C11 Carboxylsäuren für die innere Flexibilisierung von Farblatexpolymeren hat uns veranlaßt, den Effekt struktureller Unterschiede zu studieren. Da die Flexibilität eng mit der GlastemperaturT g zusammenhängt, haben wir das Übergangsverhalten einer großen Zahl Homopolymere und Copolymere mit Hilfe von dynamisch-mechanischen Verfahren untersucht.Die verwendeten Polymere umfaßten sowohl Modellverbindungen einheitlicher Struktur als auch verschiedenartige Copolymeren. Einige der letzteren bestanden aus Polymeren von Destillationsfraktionen des handelsüblichen Vinylestergemisches, andere aus Copolymeren dieses Gemisches mit einem gutdefinierten Monomer, z. B. Vinylacetat.Da wir eine lineare Abhängigkeit der Glastemperatur von der Zusammensetzung feststellten, wurde das handelsübliche Vinylestergemisch bei unseren Berechnungen als ein einfaches Monomer betrachtet. Prüfung der polymerisierten Fraktionen erwies deutlich den Einfluß der Struktur isomerer Seitengruppen, wobei sich die höherenT g -Werte bei den kompakteren Strukturen ergaben. Aus der Tatsache, daß die auf den verschiedenen Fraktionen basierenden Polymeren einen ziemlich kleinen Unterschied inT g aufweisen, läßt sich schließen, daß die Verzweigung bei ihnen zu mäßig kompakten Seitengruppen geführt hat. Dieser Befund beruht auf Messungen der Glastemperatur an Modellpolymeren stark verzweigter Vinylester aus C9 Carboxylsäuren bekannter Struktur.
Paper presented at the Symposium at Leende of De Nederlandse Rheologische Vereniging on 21st and 22nd May 1970. 相似文献8.Paul E.W. Labossiere Martin L. DunnShawn J. Cunningham 《Journal of the mechanics and physics of solids》2002,50(3):405-433Motivated by the existence of a universal singular stress field at bimaterial interface corners, a fair amount of work has been performed to support the use of the corresponding critical stress intensities to correlate fracture initiation. The approach is in the spirit of interface fracture mechanics but applicable to a different class of problems, specifically, when a crack does not previously exist (or cannot be detected, at least economically), and when subsequent crack propagation does not necessarily occur along the interface. Here we further progress toward the development, understanding, and application of the approach, both experimentally and theoretically, for a series of silicon/glass anodically bonded structures. To this end we designed and fabricated two series of silicon/glass anodically bonded bimaterial specimens with different interface corner geometries that commonly arise from different silicon etching technologies. Offset three-point flexure tests were performed that resulted in brittle fracture that initiated at the interface corner. From a rigorous stress analysis at the interface corner, we determined the order of the stress singularities and the angular variation of the stress fields. We computed the corresponding stress intensities via full-field finite element analyses of the silicon/glass specimens loaded in offset three-point flexure. Measured fracture data show that although the failure stress varies significantly with bond size, the corresponding critical stress intensity of the dominant mode is constant, thus providing support for its use as a fracture initiation criterion. In the light of both the stress analysis and the measured fracture data, we discuss the effect of mode mixity (loosely shearing versus opening) and show that it has little influence on the results for the specimens and loading considered in this study. Via an idealized model of a small crack, either interfacial or extending into one of the adherends, we study the effects of geometrical perturbations at the interface corner on the stress state, and discuss implications for fracture analysis and interpretation of fracture data. We also explore the prediction of the crack initiation angle and achieve reasonable success with a simple criterion based on the maximum circumferential stress near the uncracked interface corner. 相似文献9.J.L. Hgberg B.F. Srensen U. Stigh 《International Journal of Solids and Structures》2007,44(25-26):8335-8354Mixed mode testing of adhesive layer is performed with the Mixed mode double Cantilever Beam specimen. During the experiments, the specimens are loaded by transversal and/or shear forces; seven different mode mixities are tested. The J-integral is used to evaluate the energy dissipation in the failure process zone. The constitutive behaviour of the adhesive layer is obtained by a so called inverse method and fitting an existing mixed mode cohesive model, which uses a coupled formulation to describe a mode dependent constitutive behaviour. The cohesive parameters are determined by optimizing the parameters of the cohesive model to the experimental data. A comparison is made with the results of two fitting procedures. It is concluded that the constitutive properties are coupled, i.e. the peel and shear stress depend on both the peel and shear deformations. Moreover, the experiments show that the critical deformation in the peel direction is virtually independent of the mode mixity. 相似文献10.I. Golobic J. Petkovsek M. Baselj A. Papez D. B. R. Kenning 《Heat and Mass Transfer》2009,45(7):857-866Experiments were performed to study the spatio-temporal temperature variation underneath growing bubbles on a thin platinum heating foil in saturated and subcooled nucleate pool boiling of water at atmospheric pressure. The transient wall temperature distributions were recorded with spatial resolution of 40 μm by a high-speed infrared camera at intervals of 1 ms, synchronised with a high-speed video camera to record bubble motion. Examples are presented of the transient distributions of wall temperature, heat flux and heat transfer coefficient underneath bubbles growing with the fast and slow bubble detachment mechanisms in saturated and subcooled pool boiling. Comments are made on the evidence for and against particular mechanisms of heat transfer. 相似文献11.H. Baur 《Rheologica Acta》1989,28(4):333-349Relaxation processes in the glass transition region, especially the recovery of the volume and the physical ageing of polymers, do not follow the common (linear) theory of relaxation. On the contrary, they show a development which depends on the previous history, may be non-monotonous and requires a relaxation time that may have negative values and a pole. These phenomena can be explained if the single relaxation time is replaced by a spectrum of relaxation times and the relaxation times are supposed to be subjected to a feedback via certain structure- and temperature-parameters (as, for instance, in the KAHR-theory).However, the feedback and a pole of the relaxation time arise already for a single internal degree of freedom by themselves, if, in the non-equilibrium thermodynamics, a dynamic and a static temperature are strictly differentiated. In the case of the relaxation of the diffusive translational motion of the molecules in the glass transition region the dynamic temperature is identical with the socalled fictive temperature introduced by Tool.With regard to the relaxation of the volume three different temperature regions must be distinguished: A fluid region at high temperatures where the relaxation is controlled by the free volume and complies with the linear theory at least approximately; a glass-like region at low temperatures where the relaxation is controlled by the thermal expansivity of the free volume and where, under certain conditions, the statements set up by Davies and Jones are valid; an intermediate region (the glass transition region) where the free volume as well as its coefficient of expansivity are decisive. In that region the effective relaxation time of the volume may have a pole and the dynamic temperature may approach its equilibrium value by discontinuous jumps or in a chaotic manner.Dedicated to Professor Dr. J. Meissner (ETH Zürich) on the occasion of his 60th birthday 相似文献12.A thermo-mechanically-coupled large-deformation theory for amorphous polymers in a temperature range which spans their glass transition 总被引：1，自引：0，他引：1Vikas Srivastava Shawn A. ChesterNicoli M. Ames Lallit Anand 《International Journal of Plasticity》2010Amorphous thermoplastic polymers are important engineering materials; however, their non-linear, strongly temperature- and rate-dependent elastic-viscoplastic behavior is still not very well understood, and is modeled by existing constitutive theories with varying degrees of success. There is no generally agreed upon theory to model the large-deformation, thermo-mechanically-coupled, elastic-viscoplastic response of these materials in a temperature range which spans their glass transition temperature. Such a theory is crucial for the development of a numerical capability for the simulation and design of important polymer processing operations, and also for predicting the relationship between processing methods and the subsequent mechanical properties of polymeric products. In this paper we extend our recently published theory [Anand, L., Ames, N. M., Srivastava, V., Chester, S. A., 2009. A thermo-mechanically-coupled theory for large deformations of amorphous polymers. Part I: formulation. International Journal Plasticity 25, 1474–1494; Ames, N. M., Srivastava, V., Chester, S. A., Anand, L., 2009. A thermo-mechanically coupled theory for large deformations of amorphous polymers. Part II: applications. International Journal of Plasticity 25, 1495–1539] to fill this need. 相似文献13.14.15.A. C. M. Beljaars 《Applied Scientific Research》1976,32(5):509-518The time dependent differential equation for the local wire temperature of a constant temperature anemometer is solved by a perturbation method in case of a harmonically changing heat transfer coefficient. The time dependent power supply to the wire follows from the condition of constant mean temperature imposed by the anemometer circuit. The influence of thin supporting wires, or copper-plated wire ends, is evaluated also. Numerical results are given for a number of cases that are of practical interest.Nomenclature c specific heat - D diameter of the wire - D u diameter of the copper-plated ends of the wire - f D - g I 2 r 0 - I electric current - L length of the wire - P 1/4D 2 c - q 1/4D 2 - r resistance of the wire per unit length at temperature T' - r 0 resistance of the wire per unit length at temperature T - T T' – T - T' local temperature of the wire - T ambient temperature - T w constant mean temperature imposed by the anemometer circuit - T u local difference between the temperature of the supporting wire and the ambient temperature - t time - x axial coordinate with the origin in the middle of the wire - heat transfer coefficient - temperature coefficient of the resistance - small parameter - time constant = cD 2/4D - u time constant of the copper-plated ends cD u 2 /4D u - thermal conductivity of wire material - u thermal conductivity of the copper-plated wire ends - density - circular frequency 相似文献16.Dynamic fracture behavior of a Griffith crack along the interface of an adhesive bonded material under normal loading is studied. The singular integral equations are obtained by employing integral transformation and introducing dislocation density functions. By adopting Gauss-Jacobi integration formula, the problem is reduced to the solution of algebraic equations, and by collocation dots method. their solutions can be obtained Based on the parametric discussions presented in the paper, the following conclusions can be drawn： （1） Mode I dynamic stress intensity factor （DSIF） increases with increasing initial crack length and decreasing visco-elastic layer thickness, revealing distinct size effect; （2） The influence of the visco-elastic adhesive relaxation time on the DSIF should not be ignored. 相似文献17.A small load transducer has been used to obtain force histories arising from the impact of steel spheres with flawed, laminated plates. The modification of the force-time record in the presence of the flaw is used for the detection of these force histories. Tests are reported for both bonded aluminum and glass-epoxy composite plates.Paper was presented at the 1983 SESA Spring Meeting held in Cleveland, OH on May 15–20, 1983. 相似文献18.The mechanical and stress-optical behavior of Bisphenol-A polycarbonate was investigated in the glass-transition region. For this purpose, optical creep experiments were carried out in shear and elongation on a tensile tester specially designed for use on a microscope state. A Kohlrausch Williams Watts equation (KWW) with a temperature-independent parameter could successfully be applied to the curves describing the time-dependent values of the stress-optical coefficient for several temperatures. The temperature dependence of the corresponding retardation time could be established and described by the WLF equation. For variable stresses the time-dependent birefringence is obtained from a generalized linear stress-optical rule as modeled according to linear superposition. The time-temperature superposition principle was applied to all measurements. With the dynamic moduli some deviations were observed at the transition from the rubbery plateau to the relaxation. The strain-optical coefficient was found to decrease with increasing time and strain. The strain dependence was found to be independent of temperature at constant stress. 相似文献19.