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61.
62.
The work is devoted to the problem of plane monochromatic longitudinal wave propagation through a homogeneous elastic medium
with a random set of spherical inclusions. The effective field method and quasicrystalline approximation are used for the
calculation of the phase velocity and attenuation factor of the mean (coherent) wave field in the composite. The hypotheses
of the method reduce the diffraction problem for many inclusions to a diffraction problem for one inclusion and, finally,
allow for the derivation of the dispersion equation for the wave vector of the mean wave field in the composite. This dispersion
equation serves for all frequencies of the incident field, properties and volume concentrations of inclusions. The long and
short wave asymptotics of the solution of the dispersion equation are found in closed analytical forms. Numerical solutions
of this equation are constructed in a wide region of frequencies of the incident field that covers long, middle, and short
wave regions of propagating waves. The phase velocities and attenuation factors of the mean wave field are calculated for
various elastic properties, density, and volume concentrations of the inclusions. Comparisons of the predictions of the method
with some experimental data are presented; possible errors of the method are indicated and discussed. 相似文献
63.
Nanocomposite materials consisting of an epoxy matrix and silicate clay particles have been processed and characterized mechanically.
The clay material used was a modified natural montmorillonite. The clay particles consisted of 1 nm thick layers with aspect
ratios in the range of 100–1000. The clay particles were mixed with acetone and sonicated, then mixed with the polymer, deaerated
and cured. The ultimate objective of processing was to produce a polymer/clay nanocomposite with separated (exfoliated) platelets,
dispersed as uniformly as possible. Samples were prepared with clay concentrations of up to 10 wt%. The process used resulted
in limited exfoliation but mostly intercalation, i.e., infusion of polymer between the silicate layers and increase of interlayer
spacing. The characteristics of the nanocomposite were assessed by transmission electron microscopy and x-ray diffraction.
Results from these observations show that the basal spacing of clay platelets increased from an initial pre-processing value
of 1.85 nm to 4.5 nm. Enhancement of mechanical properties was measured by tensile testing of coupons. Stiffness increases
of up to 50% over that of the unfilled epoxy were measured for clay concentrations of 5 wt%. Strength increases were also
measured for low clay concentrations and low strain rate loading. Micromechanics modeling of mechanical behavior is discussed
as a function of clay platelet dispersion. 相似文献
64.
复合材料疲劳Ⅱ型层间裂纹扩展门槛值试验方法研究 总被引:1,自引:0,他引:1
疲劳裂纹扩展门槛值在结构损伤安全设计中具有重要作用,该文提出了复合材料Ⅱ型疲劳裂纹扩展门槛值的试验方法,并实测了两种复合材料的疲劳裂纹扩展门槛值。 相似文献
65.
Mostefa Sayhi Nasreddine Haine Belkacem Belaabed Valérie Vigneras 《Journal of Macromolecular Science: Physics》2015,54(10):1183-1195
Conducting polymer blends were prepared using polyaniline doped with para- toluene sulfonic acid (PTSA-PANI) and a polyester polyol-based polyurethane (PU). The morphological, thermal and dielectric properties of the PTSA-PANI/PU blends in the frequency range of 1–5 GHz (S band) were investigated. It was found that the morphology of the samples was affected by the PTSA-PANI loading, resulting in the formation of agglomerates and pathways when above 10 wt%. The thermal stability of the composites was improved with increased PTSA-PANI loading. The electrical conductivity percolation threshold was obtained at 2.5% of PTSA-PANI loading and the electrical conductivity reached the value of 0.13 S/m at a PTSA-PANI loading of 30 wt%. The obtained results for the PTSA-PANI/PU blends prepared indicate a high potential for their successful use in electrical and electromagnetic applications. 相似文献
66.
Titanium-based metal composites (TMCs) are showing great potential to replace existing traditional materials in aerospace, automotive, and other high temperature engineering applications. This is due to their excellent mechanical, thermal, and physical properties and improved strength to weight ratio. Weight savings in the aerospace industry results in higher efficiency. Carbon nanotubes (CNTs), because of their low density and high Young's modulus, are considered to be an excellent reinforcement for metal matrix composites (MMCs). In the last 20 years extensive research has been carried out to investigate the combination of carbon nanotubes with aluminum, nickel, copper, magnesium, and other metal matrices. The production techniques such as mechanical alloying through powder metallurgy routes and their effects on the mechanical properties of CNT reinforced TMCs are reviewed in this article. The role of the volume fraction of carbon nanotubes and their dispersion into the metal matrix are highlighted. Governing equations to predict the mechanical and tribological properties of CNT reinforced titanium matrix composites are deduced. With the help of this initial prediction of properties, the optimal processing parameters can be optimized. Successful development of CNT reinforced TMCs would result in better wear and mechanical behavior and enhance their ability to withstand high temperature and structural loading environments. 相似文献
67.
A facile blending strategy to fabricate multishape memory polymers (SMPs) with only one sort of phase transition material has been reported. In this work, olefin block copolymer (OBC) and styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS), which are both physically crosslinked, are blended with crystalline paraffin together. Due to the different interactions between polymer matrices and paraffin, the paraffin penetrated in OBC and SEBS exhibit separated melting transitions. It is quite interesting that merely paraffin distributed in OBC also shows two distinct melting transitions with enough OBC content in composites. Therefore, excellent quadruple shape memory effect can be achieved with a maximum of three melting transitions. Furthermore, through adjusting the polymer species and content, the mechanical and rheological properties can be conveniently tuned to a great extent. Compared with the reported strategies, this simple and controllable method sheds light on rapid design of multi‐SMPs using inexpensive raw materials, which greatly paves the way for multi‐SMPs from laboratory to factory.
68.
We demonstrate the ability to determine stress intensity factors in orthotropic materials directly from measured temperatures
away from the crack and using far-field expressions for the stresses. This is advantageous, recognizing that recorded thermoelastic
data can be very unreliable near the tip of a crack. In addition to singular terms that govern in the immediate vicinity of
the crack tip, the present series expressions for the stresses contain higher-order finite terms. Little measured input information
is needed and data acquisition positions can be selected largely at the user's discretion. 相似文献
69.
70.