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41.
A theoretical model for the evaluation of the elastic modulus in particulate composites has been developed. The method takes into account the existence of a mesophase between main phases, which constitutes an important parameter influencing the behaviour of a composite material. This layer between the matrix and filler develops different physico-chemical properties from those of the constituent phases and variable ones along its thickness. The effect of the progressive variation of the elastic modulus of the mesophase on the modulus of the composite was estimated by applying various simple laws of variation. Convenient laws of variation were introduced, varying from a simple one, assuming a linear law, to a more refined one using a parabolic law. Experimental results with particulates, based on iron-filled epoxy composites, compared satisfactorily with other models. However, the model based on a parabolic law was superior to all others on physical grounds.List of symbols
E
elastic modulus
-
v
Poisson's ratio
-
volume fraction
-
r
radius
-
V
volume
-
K
bulk modulus
-
r
thickness of mesophase
-
parameter which depends on the sudden changes of the heat capacity for the filled and unfilled polymer C
p
f
and C
p
0
相似文献
42.
A thermoviscoelastic analysis of a three-phase composite cylinder is presented in this work. The solutions of the heat conduction and thermoelastic problem for three dissimilar media are derived based on the method of analytic continuation associated with the alternation technique. A rapidly convergent series solution for both the temperature and stress field, which is expressed in terms of an explicit general term of the corresponding homogeneous potential, is obtained in an elegant form. The hereditary integral in conjunction with the Kelvin–Maxwell model is applied to simulate the thermoviscoelastic properties while a thermorheologically simple material is considered. According to the correspondence principle, the Laplace transformed thermoviscoelastic solution is directly determined from the corresponding thermoelastic one. The real time solution can then be solved numerically by taking inverse Laplace transform. Finally, some typical examples of interfacial stresses are discussed. 相似文献
43.
Nicola Bellomo Nils Calander Eugen Mamontov Magnus Willander 《Comptes Rendus Mecanique》2003,331(7):461-467
44.
F. Lanza di Scalea 《Experimental Mechanics》1998,38(4):233-241
The measurement of the coefficients of thermal expansion (CTEs) of composite materials using electrical resistance strain
gages is addressed. Analytical expressions for the CTEs of an orthotropic lamina are derived, accounting for the effects of
transverse sensitivity and possible misalignment of the gages. Experiments are performed for the characterization of the thermal
expansion behavior of a fiber-glass-reinforced epoxy unidirectional lamina using an invar specimen as reference material.
Preliminary training cycles are performed for the determination of an optimal heating rate for the measurements, which ensures
thermal equilibrium conditions. Three measurement cycles yield the principal CTEs of the lamina α1, α2 and α12 with repeatability within ±0.34×10−6, ±0.85×10−6 and ±2.8×10−6/°C, respectively. It is noted that inhomogeneity of the specimen and variation in thermomechanical properties of the gages
can cause a noticeable spead in the measurements. 相似文献
45.
正交异性光弹性应力分离的边界元法 总被引:1,自引:0,他引:1
本文对平面正交各向异性复合材料模型引入正应力线性和及边界上正应力线性和流的概念,提出从应力相容方程出发.用边界元法计算正交异性光弹性模型内任一点的正应力线性和位的方法,再与正交异性光弹性法中所给出的应力同的关系结合,即可进行正交异性光弹性应力的分离.最后,对边界元方法的精度进行了讨论. 相似文献
46.
Vladimir Kobelev 《Meccanica》2006,41(6):653-660
Failure of a composite is a complex process accompanied by irreversible changes in the microstructure of the material. Microscopic
mechanisms are known of the accumulation of damage and failure of the type of localized and multiple ruptures of the fibers
delamination along interphase boundaries, and also mechanisms associated with fracture of fibers. In this work, we propose
a mathematical model of the local mechanism of failure of a composite material randomly reinforced with a system of short
fibers. We implement the Cosserat moment model of crack tip for filament material, reinforced with whiskers or in fiber- reinforced
polycrystalline materials. It is assumed that the angular distribution of the fibers is isotropic and the elastic characteristics
of the fibers are considerably higher than the elastic constants of the matrix. We implement the homogenization procedure
for the effective Cosserat constants similarly to the effective elastic constants. The singular solution in the vicinity of
the crack tip in the Cosserat moment model is found. Using this solution, we examine the bending stresses in the filaments
due to effective moment stresses in the material. The constructed model describes the phenomenon of fracture of the fibers
occurring during crack propagation in those composites. The following assumptions are used as the main hypotheses for the
micromechanical model. The matrix contains a nucleation crack. When the load is increased the crack grows and its boundary
comes into contact with the reinforcing fibers. A further increase of the stress causes bending of the fiber. When~the fiber
curvature reaches a specific critical value, the fiber ruptures. If the stress at infinity is given, the fibers no longer
delay the development of failure during crack propagation The degree of bending distortion of the fiber in the vicinity of
the boundary of the crack is determined by the moment model of the material. The necessity to take into account the moment
stresses in the failure theory of the reinforced material was stressed in [Muki and Sternberg (1965) Zeitschrift f angew Math
und Phys 16:611–615; Garajeu and Soos (2003) Math Mech Solids 8(2):189–218; Ostoja-Starzewski et al (1999) Mech Res Commun
26:387–396]. The moment Cosserat stresses were accounted also for inhomogeneous biomechanical materials by Buechner and Lakes
(2003) Bio Mech Model Mechanobiol 1: 295–301. We should also mention the important methodological studies [Sternberg and Muki
(1967) J Solids Struct 1:69–95; Atkinson and Leppington (1977) Int J Solids Struct 13: 1103–1122] concerned with the moment
stresses in homogeneous fracture mechanics. 相似文献
47.
Robert Lipton 《Journal of the mechanics and physics of solids》2005,53(11):2471-2481
Composites made from two linear isotropic elastic materials are subjected to a uniform hydrostatic stress. It is assumed that only the volume fraction of each elastic material is known. Lower bounds on all rth moments of the hydrostatic stress field inside each phase are obtained for r?2. A lower bound on the maximum value of the hydrostatic stress field is also obtained. These bounds are given by explicit formulas depending on the volume fractions of the constituent materials and their elastic moduli. All of these bounds are shown to be the best possible as they are attained by the hydrostatic stress field inside the Hashin-Shtrikman coated sphere assemblage. The bounds provide a new opportunity for the assessment of load transfer between macroscopic and microscopic scales for statistically defined microstructures. 相似文献
48.
复合软模板法可控制备红毛丹状AlOOH/Al2O3纳米材料 总被引:1,自引:0,他引:1
以Al(NO3)3为铝源,尿素为均相沉淀剂, 在聚乙二醇400(PEG4000)-DL-天冬氨酸形成的复合软模板体系中, 通过简单的常压回流方式成功合成出形貌和尺寸较为均一的红毛丹状γ-AlOOH纳米结构, 继而考察了反应物和添加剂用量对前驱体形貌和尺寸的影响, 并对γ-AlOOH纳米结构可能的形成机理进行了探讨. 实验结果表明, 所合成的红毛丹状γ-AlOOH具有球中球的核壳结构, 统计得内球直径约为400 nm, 外壳外径约为600 nm, 密集状态的壳层厚度约为15 nm, 毛刺状凸出物长度可达60 nm以上. 前驱体样品经600℃煅烧5 h后即转变为具有良好形貌继承性的γ-Al2O3, Brunauer-Emmett-Teller (BET) N2-吸附实验表明其比表面积高达299.97 m2·g-1. 相似文献
49.
石墨烯/聚苯胺复合材料的制备及其电化学性能 总被引:1,自引:0,他引:1
以苯胺和氧化石墨烯(GO)为原料, 采用电化学方法制备了石墨烯/聚苯胺(GP)复合材料. 利用X射线衍射(XRD)、扫描电镜(SEM)、拉曼(Raman)光谱、X射线光电子能谱分析(XPS)对其结构、微观形貌进行了表征,并对复合材料电化学性能进行了测试. 结果表明, 复合材料保持了石墨烯的基本形貌, 聚苯胺颗粒均匀地分散在石墨烯表面, 复合材料在500 mA·g-1的电流密度下比电容达到352 F·g-1, 1000 mA·g-1下比电容为315 F·g-1, 经过1000 次的充放电循环后容量保持率达到90%, 远大于石墨烯和聚苯胺单体的比电容. 复合材料放电效率高, 电解质离子易于在电极中扩散和迁移. 相似文献
50.
负载纳米银复合微球制备及其催化性能 总被引:1,自引:0,他引:1
以具有温度和pH双重敏感性能的N-异丙基丙烯酰胺(NIPAM)共聚丙烯酸(AA) P(NIPAM-co-AA)高分子微凝胶为模板, 以乙醇为还原剂, 原位还原得到负载纳米银的微米尺度Ag/P(NIPAM-co-AA)复合微凝胶材料. 通过扫描电子显微镜(SEM)、X射线衍射(XRD)仪和紫外-可见(UV-Vis)分光光度计等对复合材料的形貌、组成和催化性能进行表征. 研究结果表明, Ag/P(NIPAM-co-AA)复合微球具有均一的表面结构, 微凝胶的限域作用显著提高了纳米银的分散性和稳定性. 另外, Ag/P(NIPAM-co-AA)复合微球对对硝基苯酚(4-NP)的还原具有较好的催化活性, 且其催化活性与微凝胶网络结构的溶胀、收缩行为有一定关系, 即模板微凝胶的温敏特性可以实现对对硝基苯酚催化反应活性的调控作用. 相似文献