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61.
S. Elkoun C. G'Sell L. Cangemi Y. Meimon 《Journal of Polymer Science.Polymer Physics》2002,40(16):1754-1759
Poly(vinylidene fluoride) (PVDF) was subjected to a creep test performed at constant true stress. The use of an original method to control and adjust, in real time, the stress allowed the assessment of volume changes occurring during the test. The adaptation of Bucknall's model enabled us to excerpt the component related to microstructural modifications from the whole volume strain. Mechanisms inducing volume strain are temperature dependent. Above ?40 °C and below 80 °C, that is, in between both glass transitions of PVDF, a linear increase of volume strain was observed as a result of polymer damage via the crazing phenomenon. In addition, this region is characterized by the presence of two distinct domains that could be attributed to either nucleation and propagation of voids or to an increase of the number of potential sites for nucleation resulting from microstructural modifications taking place during the test. On the contrary, above the secondary glass transition, a regular decrease of volume strain was observed. It was assigned to a material densification as a result of molecular orientation of the amorphous chain segments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1754–1759, 2002 相似文献
62.
M. Ciarletta 《Journal of Mathematical Analysis and Applications》2007,333(1):142-150
A model for coupled elasto-acoustic waves, thermal waves, and waves associated with the voids, in a porous medium is investigated. Due to the use of lighter materials in modern buildings and noise concerns in the environment such models for thermo-poroacoustic waves are of much interest to the building industry. Analysis of such waves is also of interest in acoustic microscopy where the identification of material defects is of paramount importance to industry and medicine. We present a model for acoustic wave propagation in a porous material which also allows for propagation of a thermal wave. The thermodynamics is based on an entropy inequality of A.E. Green, F.R.S. and N. Laws and is presented for a modification of the theory of elastic materials with voids due to J.W. Nunziato and S.C. Cowin. A fully nonlinear acceleration wave analysis is initiated. 相似文献
63.
韧性材料在强动载作用下的损伤演化 总被引:2,自引:1,他引:2
采用细观动力学分析方法在高加载率条件下得到了孔洞的动态增长模型。模型考虑了应变率效率、惯性效应和热效应对孔洞增长的影响,给出了孔洞增长的应力临界值表达式。模型的数值分析表明:初始温度T0对应力临界值Pcrit有较大影响;在高应变率条件下惯性和热效应对韧性孔洞动态增长有明显的影响,惯性表现为对孔洞增长的阻碍作用,而热效应应则表现为对孔洞增长的促进作用,数值分析还表明,在低应变率条件下惯性效应可以忽略 相似文献
64.
Faleh A. Al-Sulaiman Yagoub N. Al-Nassar Esmail M.A. Mokheimer 《Heat and Mass Transfer》2006,42(5):449-461
The need to determine the thermal conductivity of fibers for design purposes of new composite materials and the inherent difficulties
in the direct measurement of the thermal conductivity of fibers motivated the present work due to its importance for energy
conservation purposes. In this work, a correlation formula is developed to predict the thermal conductivities of fiber as
function of the effective thermal conductivity of a fiber-reinforced composite laminates and their constituents which are
easy to measure. The parallel and series thermal models of composite walls have been utilized in developing this correlation
equation. The coefficients of this formula can be given as functions of the voids volume fraction for each fiber to resin
volume ratio considered. The validity of the models is verified through finite element analysis. This model also shows excellent
agreement with the available experimental values. 相似文献
65.
Luo En 《Acta Mechanica Sinica》1993,9(2):142-148
According to the basic idea of dual-complementarity, in a simple and unified way proposed by the author[1], some basic principles in dynamic theory of elastic materials with voids can be established systematically. In this paper,
an important integral relation in terms of convolutions is given, which can be considered as the generalized principle of
virtual work in mechanics. Based on this relation, it is possible not only to obtain the principle of virtual work and the
reciprocal theorem in dynamic theory of elastic materials with voids, but also to derive systematically the complementary
functionals for the eight-field, six-field, four-field and two-field simplified Gurtin-type variational principles. Furthermore,
with this approach, the intrinsic relationship among various principles can be explained clearly.
The project supported by the Foundation of Zhongshan University Advanced Research Center 相似文献
66.
Nana Cao Xinbo Wang Lingyong Song Zhi Cheng Zhang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5800-5810
A polymerizable cationic quaternary ammonium surfactant (CQAS) based on 2‐(dimethylamino)ethyl methacrylate (DMAEMA) was successfully synthesized via quaternization reaction. The product was characterized by FTIR and 1H NMR spectroscopy, and its critical micelle concentration (CMC) was obtained by surface tension measurement. The surfmer acted well as comonomer and surfactant to stabilize monomer droplets during miniemulsion polymerization. To identify whether this system undergoes miniemulsion nucleation mechanism, surface tension, particle size, and Ndroplet/Nparticle of the system were also measured. The effect of concentration and counter‐ion of the surfmer, and pH value of the system were systematically investigated by kinetic analysis and dynamic light scattering (DLS). The resulting nanopore microspheres were observed by transmission electron micrograph (TEM) and field emission scanning electron micrograph (FESEM) and showed the nanopore morphology with reasonable stability. Another cationic surfactant cetyltrimethylammonium bromide (CTAB) was used for comparative studies. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5800–5810, 2007 相似文献
67.
The evolution of defects in a material under irradiation is studied at low doses (∼5 dpa or less) using rate equations. It
is shown that as a function of temperature at a critical valueT
c a transition occurs in the behaviour of the solutions of the rate equations. BelowT
c the voids show incubation effects. An expression is derived for the critical dislocation density at which the void growth
starts. This is related to the trapped vacancy fraction ε in vacancy dislocation loops. AboveT
c the incubation effects are shown to be related to the gas production rate which becomes the rate controlling parameter in
determining the evolution of the defects. A gas-bubble to void transition occurs at a critical void radius and expressions
are derived for the critical void size and dose at which the transition appears. It is shown that closely related to this
is the incubation dose for interstitial loops. Finally, these features are corroborated by actual numerical integration of
the rate equations. 相似文献
68.
Laurent Farge Stéphane Andre Andrzej Pawlak Sarah C. Irvine Adrian‐Marie Philippe 《Journal of Polymer Science.Polymer Physics》2013,51(10):826-841
In this work, we used two techniques to study the deformation‐induced whitening phenomenon that occurs when certain semicrystalline polymers (SCPs) are subjected to tensile drawing: (1) IPLST (Incoherent Polarized Steady Light Transport) was used for characterizing the light scatterers and in particular for determining their size. (2) SRXTM (Synchrotron Radiation X‐Ray Tomographic Microscopy) was used to visualize the internal structure of the deformed SCPs. In particular, with this technique the possible presence of micrometric cavities can be detected. In the early whitening stage of a cavitating polypropylene (PP), the IPLST technique was found to show that the size of the light scatterers is larger than 1 μm. At the same time, the SRXTM measurements showed that no void larger than 1 μm was present in the material. The micrometric light scatterers responsible for the whitening phenomenon may thus not be simple cavities. In fact, this experimental study suggests that they correspond to areas where smaller objects (possibly nanovoids) are highly confined. At the scale of visible wavelengths, these regions could scatter visible light like individual entities of micrometric size. The study also showed that the size of cavities observable using SRXTM for a very deformed PP is dependent on the initial dimensions of the spherulites. Results previously obtained for a non‐cavitating high density polyethylene are also briefly presented in this article to confirm the theory that deformation‐induced‐whitening phenomenon may have various origins for such complex microstructuring. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys., 2013 相似文献
69.
T. Quatravaux S. Elkoun C. G'Sell L. Cangemi Y. Meimon 《Journal of Polymer Science.Polymer Physics》2002,40(22):2516-2522
Damage to poly(vinylidene fluoride) was studied under uniaxial tension testing at different temperatures and strain rates. A satisfactory accuracy was reached with an original procedure for the assessment of the principal strains and volume strain. The semicrystalline polymer exhibited an increase in the volume strain with the true axial strain caused by material damage. This damage depended on the temperature and strain rate and was related to the whitening phenomenon generally observed. The use of the general ideas of Bucknall's model, based on the decomposition of the whole volume strain into three components, allowed the extraction of the component of the volume strain corresponding to microstructural mechanisms of plastic deformation other than shearing. Therefore, nucleation and growth stages of cavitation were revealed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2516–2522, 2002 相似文献
70.
I. E. Zanin K. B. Aleinikova M. M. Afanasiev M. Yu. Antipin 《Journal of Structural Chemistry》2004,45(5):844-848
The structure of Zn3P2 (P 42/nmc, a = b = 8. 0785 Å, c = 11. 3966 Å) was solved and refined to R = 3. 2% in a precision X-ray diffraction experiment (λ-MoK
a, graphite monochromator on a primary beam, 27,496 reflections) . Interatomic distances and bond angles have been determined. The fcc lattice of the structure is built from phosphorus atoms, and the zinc atoms occupy 3/4 of all tetrahedral voids; the structure is described by two equivalent models where 1/4 occupied (by zinc atoms) and 1/4 vacant voids change places. The zinc atoms that occupy the voids following the diamond principle do not change places.Original Russian Text Copyright © 2004 by I. E. Zanin, K. B. Aleinikova, M. M. Afanasiev, and M. Yu. Antipin__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 889–892, September–October, 2004. 相似文献