摘要
梯度功能材料，是指在材料设计制造过程中，使构成材料的要素沿着厚度方向由一侧到另一侧呈梯度连续变化，并使材料的性能与功能呈现连续变化的一种新型材料。
本文首次运用水泥基梯度功能材料的概念，分析了分散相在水泥基材料中的作用及其作用机理，探讨了分散相梯度分布对水泥基复合材料物理力学性能以及功能特性的影响。在没有专门的水泥基梯度材料成型设备的情况下，采用组分梯度变化，通过分层布料和机械振动成型的方法，通过合理的控制，基本上保证了组分的相对梯度变化，分层越多，梯度分布连续性越好。
研究工作主要有三个方面：(1)碳纤维的分散工艺；(2)碳纤维梯度分布对水泥基材料电、热性能的影响；(3)骨料和玻璃纤维线性、抛物线性梯度分布对水泥基材料力学性能影响。
研究结果表明：(1)采用甲基纤维素和超细硅粉复合掺拌的分散办法，使纤维充分分散，导电效果比较理想，为纤维分散提供了一条优良的途径；(2)碳纤维混凝土中，导电网络形成后，纤维含量继续增加对电阻率的影响不大。本试验结果表明当含量在0.3～0.8％之间时，导电率迅速上升，当0.8％含量以后，上升速度变缓。碳纤维的掺入对砂浆混凝土的热膨胀能够起到一定的抑制作用。碳纤维梯度分布，使得在纤维用量最少的情况下实现了导电发热功能，并有效地改善了内部温差和温度应力，缓解了应力集中。通电后迅速发热，随着时间的延长升温速度变缓(电阻增大)，最终达到发热和散热的平衡而使温度恒定；(3)不同性能骨料的梯度分布可带来比其均匀分布优越的力学性能。骨料梯度分布时富熟料侧分布于受拉区，承受较大应力，使得总体强度上升，尤其抗弯强度的变化幅度较大。抛物线梯度不如线性梯度增强效果好，线性梯度变化比均匀分布试件抗折强度提高了16％，抛物线梯度提高了8％；玻璃纤维的高抗拉强度及较高的弹性模量，提高了纤维混凝土复合材料的拉伸强度和弹性模量。纤维梯度分布，增强纤维较多的分布于受拉区，纤维的分布更符合材料(构件)的受力方式。在承受最大弯拉应力部位，梯度分布的纤维含量比均匀分布高，因此梯度分布比均匀分布对抗弯强度的提高更明显。抛物线梯度分布组28天抗弯强度比均匀试件提高达18％，而线性梯度提高6％。
不同性能与功能的分散相梯度分布，使水泥基材料的物理力学性能得到了明显改善并可以实现在同一制品上的复合功能，这为水泥基梯度功能材料的设计与进一步发展奠定了基础，同时展示了水泥基梯度复合功能材料良好的研究价值和应用前景。
Functionally Graded Materials (FGM) is that the components and the structure of the material are gradient distribution from one side of the material (product) to the omer. So far, FGM has been widely used in modern Industries.
In this paper, the concept of FGM is firstly applied in cement-based materials to study the effect of dispersion phase gradient distribution in cement-based materials on physicomechanical property and functions after the effect of dispersion phase and its mechanism in cement-based materials were analyzed. Without special forming equipment, the gradient distribution of components and the designed properties of the material can be achieved by the component graded change, layering formation and mechanical vibration. And the study shows that more layers of the structure, smoother transition from one layer to another.
Three aspects are studied: (1) The methods of carbon fibers (CF) dispersion; (2) The effect of CF gradient distribution on thermal and electric properties; (3) the effect of aggregates and glass fibers (GF) with linear and parabolic component gradient variation on mechanical property.
The test results indicate that the properties and functions of the cement-based FGM can be obviously improved by the gradient distribution of different disperse phases. Namely:
(1) The CF can be dispersed by methyl cellulose and superfine silica fume used together and the electrical resistivity is low. So it provides a good way for CF dispersion;
(2) The results on CF cement-based FGM include four aspects. Firstly, the electrical resistivity is influenced little by CF content increase after the conductive circuit formation. The results in this paper show that the conductivity increases quickly when CF weight percentage is 0.3-0.8% and turns to low after 0.8%; Secondly, it indicates that thermal expansion is restrained by CF obviously. Furthermore, electric-thermal property can be realized and thermal stress can be reduced in CF cement-based FGM in which the discontinuous carbon fibers are gradient distribution. Lastly, the test results show that the increase of the temperature of the carbon fiber reinforced cement-based FGM is quick when the electric circuit passes through it, and the heat quantity of the matrix decreases (the electric
resistance of the matrix increases) as the temperature of the matrix increase and the temperature of the matrix may tend to a constant value at last when the heat generating quantity of thg matrix equal to the heat radiating quantity of the matrix.
(3) Compared with that of the homogeneous distribution of the high strength aggregates and the activation aggregates, the higher strength of the gradient distribution of the disperse phase of the cement-based FGM are achieved, especially the bending strength. It is because the clinker is distributed much more in tensile area which bears more stress. For example, with linear and parabolic component gradient variation of aggregates, linear component gradient variation of aggregates reinforces higher than parabolic variation. Linear component gradient variation of aggregates improves 16% of aggregates homogeneous distribution on bending strength; parabolic component gradient variation does 8%. GF is widely used as composite reinforcement due to low cast and excellent properties such as high tensile strength and high elastic modulus. When the reinforced glass fibers (GF) gradient distribution, the same reinforced role can be achieved in the lower volume of the reinforced fibers, because the distribution of the r
einforced fibers is coincident with the stress distribution of the specimen. For example, with linear and parabolic component gradient variation of GF, parabolic component gradient variation of GF reinforces higher than linear variation. Parabolic component gradient variation of GF improves 18% of GF homogeneous distribution on bending strength; linear component gradient variation only does 6%.
In conclusion, different properties (or functions) of the dispersion phase improve cement-based FGM and t
引文
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