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1.
Kaleem M Satterthwaite JD Watts DC 《Journal of materials science. Materials in medicine》2012,23(3):623-627
Effect of variation in filler particle size, morphology and wet conditioning on the viscoelastic stability of resin-composites
under dynamic loading was investigated. Eight experimental light cured resin-composites were selected. For each of the eight
resin-composites, ten cylindrical specimens (4 × 6 mm), divided into two subgroups (n = 5) were prepared. Group 1 and 2 were loaded dynamically after 1 day of dry storage and 1 week of wet storage, respectively.
A cyclic load between 1 and 50 MPa was applied for both groups at a frequency of 0.25 Hz for 30 min to obtain the ‘dynamic’
creep strain (%). Data was analysed by univariate ANOVA. Unimodal spherical and irregular resin-composites showed a significant
influence of particle size and shape on dynamic creep under dry condition, but not for wet conditions. Irregular filler particles
in both unimodal and multimodal resin-composites were more resistant to dynamic creep under wet conditions and showed higher
stiffness. 相似文献
2.
This work presents a methodology implementing random packing of spheres combined with commercial finite element method (FEM)
software to optimize the material properties, such as Young’s modulus, Poisson’s ratio, and coefficient of thermal expansion
(CTE) of two-phase materials used in electronic packaging. The methodology includes an implementation of a numerical algorithm
of random packing of spheres and a technique for creating conformal FEM mesh of a large aggregate of particles embedded in
a medium. We explored the random packing of spheres with different diameters using particle generation algorithms coded in
MATLAB. The FEM meshes were generated using software MATLAB and TETGEN. After importing the databases of the nodes and elements
into commercial FEM software ANSYS, the composite materials with spherical fillers and the polymer matrix were modeled using
ANSYS. The effective Young’s modulus, Poisson’s ratio, and CTE along different axes were calculated using ANSYS by applying
proper loading and boundary conditions. It was found that the composite material was virtually isotropic. The Young’s modulus
and Poisson’s ratio calculated by FEM models were compared to a number of analytical solutions in the literature. For low
volume fraction of filler content, the FEM results and analytical solutions agree well. However, for high volume fraction
of filler content, there is some discrepancy between FEM and analytical models and also among the analytical models themselves.
The discrepancy is attributed to the multi-body interaction effect of the filler particles when they are getting close. 相似文献
3.
N. J. L. Van Ruth J. F. Vega S. Rastogi J. Martínez-Salazar 《Journal of Materials Science》2006,41(12):3899-3905
Morphology and viscoelastic behaviour during the initial stages of crystallisation of isotactic polypropylene were explored
as a function of time and angular frequency by light microscopy and dynamic oscillatory rheology. Results were evaluated according
to the Krieger-Dougherty and Palierne models for viscoelastic suspensions of spheres. The data obtained from light microscopy
were introduced in the rheological models reproducing quite well the viscoelastic response during crystallisation. The Palierne
model was able to describe the behaviour of the system, though it was not possible to observe all the model’s features due
to a limited angular frequency range. Further, at high filler contents, an ‘equilibrium’ modulus needs to be introduced for
the model to fit the experimental data. The exponent required to model the changes occurring in the ‘equilibrium’ modulus
over time resembles that of chemical gelation more than physical gelation. 相似文献
4.
The linear viscoelastic behavior of “model” hybrid materials based on methyl methacrylate and methacryloxypropyl-grafted nanosilica was investigated. As unique features, the materials under study present an excellent dispersion of silica within the polymer matrix and are almost free of uncross-linked chains. In addition, very progressive changes in network architecture are available, resulting from changes in particle diameter, d, volume fraction of filler, Φ, number of methacryloyl units grafted per surface unit of silica particle, n, and nature of the grafting agent. The influence of these parameters on the characteristics of the mechanically active relaxations α and β was examined. Emphasis was put on the storage modulus, E′, on the loss modulus, E′′, and on their dependence on filler volume fraction. E′′ values were shown to simply account for the reduction of the mechanical energy lost within the material, in connection to the occurrence of polymer molecular motions. Analysis of E′ variations as a function of Φ was based on the theoretical models available in the literature to account for the contribution of the spherical filler particles. In the glassy state, Kerner’s and Christensen and Lo’s models yielded comparable results. In the rubbery state, Guth and Gold’s model was shown to prevail on Kerner’s model. 相似文献
5.
Three uniquely different initial microstructure regimes were created in 2.5 cm thick copper targets: an as-received 98 μm
grain size containing ∼1010 dislocations/cm2 (Vickers hardness of 0.89 GPa); an annealed 124 μm grain size containing ∼109
dislocations/cm2 (Vickers hardness of 0.69 GPa); and a 763 μm grain size containing ∼109 dislocations/cm2 (Vickers hardness
of 0.67 GPa). Each of these target plates was impacted by 3.18 mm diameter soda-lime glass spheres at nominal impact velocities
of 2, 4 and 6 km s-1. Grain size was observed to have only a very small or negligible contribution to cratering, while the
dislocation density had a controlling influence on both the target hardness and the cratering process. Residual crater hardness
profiles were correlated with specific microstructure zones extending from the crater wall into the target, and both hardness
profiles and residual microstructures differed for each specific target, and for each different impact velocity. Microbands
coincident with traces of {1 1 1} planes were associated with a zone of residual target hardening and increased with increasing
grain size and impact velocity. No significant melt-related phenomena were observed, and crater-related target flow occurs
by solid-state plastic flow through dynamic recrystallization, forming a narrow, softened zone at the crater wall.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
6.
The paper presents an investigation of the influence of silver particles on the microstructure and mechanical properties of
barium titanate. Barium titanate-silver composites have been prepared by ball milling precursor powder constituents; followed
by drying, sieving and calcination prior to powder compaction. After sintering the green compacts, microstructural analysis
was undertaken involving measurement of grain size, silver particle size, phase composition and phase content. Characterisation
of mechanical strength, toughness, hardness and stiffness was also undertaken. Reaction product phases between silver and
barium titanate could not be detected. The dispersed silver particles were shown to inhibit densification. Silver particles
below 1 μm in size were intragranular and attached to domains. The size of the intergranular silver particles increased with
silver content. An increase in silver content improved whereas strength, hardness and stiffness decreased, while toughness
was unchanged. 相似文献
7.
Xu HH Eichmiller FC Smith DT Schumacher GE Giuseppetti AA Antonucci JM 《Journal of materials science. Materials in medicine》2002,13(9):875-883
The mechanical properties of dental resin composites need to be improved in order to extend their use to high stress-bearing applications such as crown and bridge restorations. Recent studies used single crystal ceramic whiskers to reinforce dental composites. The aim of this study was to investigate the effects of thermal cycling on whisker-reinforced composites. It was hypothesized that the whisker composites would not show a reduction in mechanical properties or the breakdown of whisker–resin interface after thermal cycling. Silicon carbide whiskers were mixed with silica particles, thermally fused, then silanized and incorporated into resin to make flexural specimens. The filler mass fraction ranged from 0% to 70%. The specimens were thermal cycled in 5 °C and 60 °C water baths, and then fractured in three-point bending to measure strength. Nano-indentation was used to measure modulus and hardness. No significant loss in composite strength, modulus and hardness was found after 105 thermal cycles (family confidence coefficient=0.95; Tukey's multiple comparison test). The strength of whisker composite increased with filler level up to 60%, then plateaued when filler level was further increased to 70%; the modulus and hardness increased monotonically with filler level. The strength and modulus of whisker composite at 70% filler level were significantly higher than the non-whisker controls both before and after thermal cycling. SEM revealed no separation at the whisker–matrix interfaces, and observed resin remnants on the pulled-out whiskers, indicating strong whisker–resin bonding even after 105 thermal cycles. In conclusion, novel dental resin composites containing silica-fused whiskers possessed superior strength and modulus compared to non-whisker composites both before and after thermal cycling. The whisker–resin bonding appeared to be resistant to thermal cycling in water, so that no loss in composite strength or stiffness occurred after prolonged thermal cycling. 相似文献
8.
Shakiela Begum Ian P. Jones Chengge Jiao Daniel E. Lynch Jon A. Preece 《Journal of Materials Science》2010,45(14):3697-3706
Poly(1-methylpyrrol-2-yl)squaraine (PMPS) particles have been characterised using SEM. The PMPS particles were used as templates
to prepare bare silica and iron–silica hollow spheres, which were characterised using TEM and SEM. The PMPS particles and
the hollow spheres are not uniformly sized and are agglomerated. The hollow spheres with larger diameters (>900 nm) contain
an internal ‘Russian doll’ structure. The iron–silica hollow spheres are fused to one another, and the hollow spheres have
a heterogeneous wall thickness. The silica and iron–silica hollow spheres both aggregate by size. There are two different
size populations (for the diameter) of the bare silica and iron–silica hollow spheres. The smaller silica spheres have thinner
walls compared to the larger silica hollow spheres. The larger silica hollow spheres and the iron–silica hollow spheres have
similar wall thicknesses. The iron compound in the iron–silica hollow spheres has an oxidation state of 3+ and is crystalline. 相似文献
9.
Densified silica fume: particle sizes and dispersion in concrete 总被引:1,自引:1,他引:0
Dry densified silica fume is by far the most common form of silica fume used in current concrete practice; the alternative, slurried silica fume has become unavailable in many places. Densified silica fume as commonly supplied consists of particles of sizes up to several millimeters, which are generally not dispersable into individual silica fume spheres. Densified silica fumes from some sources can be dispersed by moderate ultrasonic treatment into small clusters or chains of spheres; others resist such treatment and mostly remain as large agglomerates. Under conventional concrete mixing, substantial contents of agglomerates almost always remain in the concrete. Thus the assumption that the densification process is somehow ‘reversible’ is not generally warranted. The sizes of undispersed agglomerates remaining in concrete after mixing often exceed the sizes of Portland cement particles, thus limiting any potential benefits attributed to the fine particle filler effect. Large undispersed grains appear to always undergo chemical reaction in concrete, but such reactions may induce ASR damage only under especially unfavorable circumstances. 相似文献
10.
The effect of dispersed paint particles on the mechanical properties of rubber toughened polypropylene composites 总被引:2,自引:0,他引:2
The influence of dispersed paint particles on the mechanical properties of rubber toughened PP was investigated. The matrix was basically a hybrid of PP, rubber and talc. Model systems with spherical glass bead filled matrix were also studied to examine the effect of filler shape and size. Properties like tensile strength, strain at break, impact strength, and fracture toughness were influenced by the dispersed inclusions. Tensile strength at yield decreased linearly according to Piggott and Leinder's equation. Strain at break decreased more drastically with paint particles than glass beads, revealing that irregularly shaped particles offered greater stress concentrations. The tensile strength and strain at break were less influenced by the size of paint particles whereas a slight decrease in the modulus values was observed with decreasing particle size. Impact strength and fracture toughness also decreased with increasing filler fraction. Lack of stress transfer between filler and matrix aided in reduction of impact strength. Decrease in fracture toughness was influenced by volume replacement and constraints posed by fillers. The size of paint particles had little effect on the impact strength and fracture properties at the filler concentration levels used in this investigation. 相似文献
11.
Sergej Diel Otto Huber Holger Saage Paul Steinmann Werner Winter 《Journal of Materials Science》2012,47(15):5635-5645
The quasi-static, static, and cyclic compressive behavior of a novel epoxy matrix cellular composite reinforced with glass
foam granules is investigated. Three different grain-size fractions of the granules are used: 0.5–1, 1–2, and 2–4 mm. The
density of the cellular composite varies between 0.65 and 0.82 g/cm3. The material exhibits high specific compressive strength
and stiffness within the class of cellular materials; these properties can be varied using appropriate size of granules. The
glass foam granules increase the stiffness of the cellular composite compared to neat epoxy foam with the same weight. The
measured elastic properties are in good agreement with results obtained from analytical and numerical homogenization methods.
The fatigue behavior is determined in static tests and in cyclic tests at 1 and 20 Hz on one type of cellular composite. The
fatigue process for cyclic loading is a result of an interaction between static and cyclic damage. The sensitivity to static
damage is found to be higher than to cyclic damage. The damage behavior is investigated by evaluation specimen’s stiffness
and using scanning electron microscopy. 相似文献
12.
G. J. S. Dawes L. E. Fratila-Apachitei K. Mulia I. Apachitei G.-J. Witkamp J. Duszczyk 《Journal of materials science. Materials in medicine》2009,20(5):1089-1094
Drug delivery systems (DDS) based on poly (lactide-co-glycolide) (PLGA) microspheres and nanospheres have been separately
studied in previous works as a means of delivering bioactive compounds over an extended period of time. In the present study,
two DDS having different sizes of the PLGA spheres were compared in morphology, drug (dexamethasone) loading efficiency and
drug release kinetics in order to investigate their feasibility with regard to production of medical combination devices for
orthopedic applications. The loaded PLGA spheres have been produced by the oil-in-water emulsion/solvent evaporation method
following two different schemes. Their morphology was assessed by scanning electron microscopy and the drug release was monitored
in phosphate buffer saline solution at 37°C for 550 h using high performance liquid chromatography. The synthesis schemes
used produced spheres with two different and reproducible size ranges (20 ± 10 and 1.0 ± 0.4 μm) having a smooth outer surface
and regular shape. The drug loading efficiency of the 1.0 μm spheres was found to be 11% as compared to just 1% for the 20 μm
spheres. Over the 550 h release period, the larger spheres (diameter 20 ± 10 μm) released 90% of the encapsulated dexamethasone
in an approximately linear fashion whilst the relatively small spheres (diameter 1.0 ± 0.4 μm) released only 30% of the initially
loaded dexamethasone, from which 20% within the first 25 h. The changes observed were mainly attributed to the difference
in surface area between the two types of spheres as the surface texture of both systems was visibly similar. As the surface
area per unit volume increases in the synthesis mixture, as is the case for the 1.0 μm spheres formulation, the amount of
polymer-water interfaces increases allowing more dexamethasone to be encapsulated by the emerging polymer spheres. Similarly,
during the release phase, as the surface area per unit volume increases, the rate of inclusion of water into the polymer increases,
permitting faster diffusion of dexamethasone. 相似文献
13.
A. V. Buketov P. D. Stukhlyak V. V. Levyts’kyi M. A. Dolgov I. G. Dobrotvor 《Strength of Materials》2011,43(3):338-346
The effect of the modification of a fine filler with an epoxy oligomer and compositions by ultraviolet irradiation on the
creep of materials filled with basalt and glass cloths under the influence of aggressive media has been studied. It has been
found that to reduce the creep of materials, two-layer epoxy composite “hybrid” materials containing glass and basalt cloths
must be used. In order to improve the performance of composites, an ultraviolet-irradiated epoxy binder containing epoxy-oligomer-modified
fine filler particles must be used as an interlayer. 相似文献
14.
Jinho Kim Seongjin Hwang Wookyung Sung Hyungsun Kim 《Journal of Materials Science》2008,43(12):4009-4015
The green sheet of an alumina filler/glass matrix, which is a glass–ceramic based on an anorthite and diopside composite,
is a low-fired substrate material for microelectronic packaging. In this study, alumina/glass sheets were prepared using a
tape-casting process. The mechanical and dielectric properties of the sintered bodies were examined as a function of the sintering
temperature. The volume of the crystalline phases was considered with the peak area of the XRD intensity for evaluating the
alumina/glass composite. The flexural strength and dielectric properties of the sintered alumina/glass composites were 167.2 ± 13.1 MPa
for the four-point bending test, 5.51 for the dielectric constant and 2,078 MHz for the quality factor, respectively. The
dielectric constant was dependent on the volume of crystalline phases present.
Jinho Kim and Seongjin Hwang equally contributed to the article. 相似文献
15.
Nunes TG Pereira SG Kalachandra S 《Journal of materials science. Materials in medicine》2008,19(5):1881-1889
This study shows how treated filler loading influences the photopolymerization of a dimethacrylate comonomer mixture, regarding,
in particular, shrinkage and inhibition under atmospheric oxygen, present in oral environment. Bis-GMA/TEGDMA (75/25 wt.%)
resins were loaded with hybrid filler (Ba aluminosilicate glass and pyrogenic silica), treated with γ-methacryloxy(propyl)trimethoxysilane,
at 0–50 wt.% and light cured over a total of 30 s (45 mW/cm2). Degree of double-bond conversion (DC), obtained using FTIR, decreased with filler content. 1H MAS spectra (293–340 K) and STRAFI images (293 K) were obtained as a function of irradiation time and filler concentration.
1H signals of unreacted methacrylate groups were more intense for higher loaded resins and resonances from –CH2SiO2(OH) (T2) and –CH2SiO3– (T3) units, also observed by 29Si NMR, were resolved and suggest the presence of T2–resin bonds. 1D images show a reduction on polymerization contraction and reaction inhibition at the composite resin surface
with filler loading. 2D resin images present a highly mobile surface layer, hence with lower DC. 相似文献
16.
17.
《Composites Science and Technology》2007,67(7-8):1574-1583
The occurrence and effect of aggregation in PP composites containing seven different precipitated CaCO3 fillers coated with stearic acid are described in this study. The particle size and specific surface area of the filler varied in a relatively wide range, the latter changed between 2 and 12 m2/g. The fillers were characterized by various methods including surface area, particle size and bulk density. PP composites were prepared in an internal mixer in the composition range of 0–0.3 volume fraction filler content and their structure was studied by optical microscopy. The tensile and rheological properties of the composites were related to their structure. The results prove that the unambiguous detection of the presence of aggregation is difficult in particulate filled composites. The coating of CaCO3 fillers with a surfactant changes the behavior of the particles considerably, but does not eliminate aggregation completely. The association of filler particles depends on the relative magnitude of adhesion and separating forces. Although coating decreases the surface free energy of the filler significantly, gravitational forces are much smaller than adhesion between either uncoated or coated fillers thus powder particles always aggregate. Different forces act in suspensions used for the determination of the particle size distribution of the filler; the shape of the distribution may indicate the presence of aggregation. Coated fillers form much looser aggregates with more diffuse interphases, than uncoated particles. Composite stiffness is completely insensitive to changes in structure or interaction, but the direct evaluation of other tensile properties may also lead to erroneous conclusions. Model calculations, oscillatory viscometry, as well as the proper representation of the results allow the unambiguous detection of aggregation. 相似文献
18.
The plastic deformation and fracture of aluminium hydroxide filled polypropylene has been investigated. A transition between
two mechanisms with an increase of the filler volume fraction has been observed. Below a critical filler volume content φcr
≈ 20 vol% (designated region 1) adhesive failure processes and polymer deformation in the neighbourhoods of different particles
occur in an uncorrelated manner. Above this critical value (designated region 2) exfoliation along the surface of the initial
portion of inclusions causes the formation of craze-like deformation zones transverse to the direction of the loading. The
concentration of craze-like zones is essentially determined by the filler content and the level of interphase interaction
which in turn depends on the particle size. In region 1 deformation occurs in a macro heterogeneous way with the formation
and growth of a neck. The elongation to break decreases with an increase in the mean diameter of the filler phase. At φ>φcr
composites, filled with small particles, fail in quasi brittle manner with the formation of a short and narrow neck. In contrast
to the case for a small filler concentration, an increase of the inclusion size leads to an increase in the ultimate elongation
and a tendency to macro homogeneous yielding. An explanation of the observed behaviour is proposed based on a change in adhesive
failure conditions with filler content and size.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
19.
In this study, WC-30Co cemented carbide is welded to carbon steel by the gas tungsten arc welding (GTAW) using Ni-Fe filler
metal and Ni-Fe-C filler metal. The butt joints manifest more embrittling η-phase carbides with Ni-Fe filler metal, while
less even no η-phase carbides with Ni-Fe-C filler metal. The η-phase carbides morphology and formative factors were further
discussed using Backscattered Electron Imaging (BEI) method; Electronic probe microanalysis (EPMA) is used to determine the
distribution of elements Ni, Fe, C, W and Co across the HAZ (Heat Affected Zone) near WC-30Co/welded-seam interface. The hardness
profile is determined using micro-hardness measurements and bend strength value of butt joint with different filler metal
is tested by four-point bend strength test. The hardness profile and bend strength value agree with the information obtained
from microstructure analysis, BEI analysis and X-rays phase analysis very well. The results show: (1) butt joint of WC-30Co/carbon
steel can be obtained using GTA with Ni-Fe-C filler metal; (2) the addition of carbon content to Ni-Fe filler metal leads
to less even none η-phase multi-carbides strongly, and mechanical property of butt joint can be improved. 相似文献
20.
Curvature determination in the bending test of continuous fibre reinforcements 总被引:2,自引:0,他引:2
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Bending deformation is one of the main deformation modes in the forming of continuous fibre reinforcements. It is very specific compared to the classical continuous materials. In most textile material forming simulation models, bending stiffness is neglected, but taking into account it would give a more accurate predication, particularly the shape of wrinkles. In the deformation, fibres constituting the reinforcement can slide to each other, resulting in the bending stiffness of reinforcement is not directly related to its in‐plane tensile modulus as the classical continuous materials. Consequently, it is necessary to determine the bending stiffness by the experimental method. A cantilever bending stiffness test approach was proposed to measure the bending stiffness of continuous fibre reinforcements. A CCD camera was used to take the bending deflection shape. To calculate the curvature of bending deflection curve, uniform quartic B‐spline curve was chosen. A detailed process of curvature calculating of deflection curve was given in this paper. A single bending test gives the bending moment as a function of curvature from zero to the maximum value. Bending tests were conducted to validate the capacity of the proposed approach. A smooth curvature plot along the bending deflection curve was obtained for different types of reinforcements, and the non‐linear bending deformation behaviour can be identified with the proposed bending test method. 相似文献