Reinforced Mechanism in Polymer Composites by X-ray Diffraction

利用x射线衍射方法研究了聚合物复合材料中应力传递、应力集中及增强效应的机理。研究了基于纤维与基体界面剥离的断裂机理，以及粘结对增强的影响。首先，在垂直于纤维方向的方向上对高性能聚乙烯纤维单向增强环氧复合材料施加应力。发现外加应力传递到掺入纤维上，这可以很容易地通过赤道x射线衍射峰的衍射峰位移来检测。传递到纤维上的应力可以用晶体应变乘以聚乙烯晶体区域的弹性模量来估计。利用这种“x射线衍射技术”，可以原位、无损地测定掺入纤维的应力，即聚合物复合材料中的增强效应。经铬酸处理后，施加的应力能很好地传递到纤维上，说明纤维与基体的黏附对垂直方向的增强起着重要的作用。此外，发现纤维的表面处理改变了断裂模式。发现混合料在纤维轴方向上的作用可以表示其力学性能，并利用x射线衍射对其进行了澄清。对碳纤维增强复合材料和聚对苯基苯并异恶唑增强复合材料也进行了同样的实验。该技术还将用于研究湿度、时间、温度的影响。

X-ray Diffraction method was utilized to investigate the mechanism of stress transfer, stress concentration, and resulting reinforcement effect in polymer composite. Fracture mechanism based on the debonding at the interface between fiber and matrix, the effect of adhesion on the reinforcement have been also investigated. First, the stress was applied to the high-performance polyethylene fiber uni- directionally reinforced epoxy composite in the direction perpendicular to the fiber direction. The applied stress was found to be transmitted to the incorporated fiber, which could be easily detected as the diffraction peak shift of the equatorial x-ray diffraction peak. The stress transmitted to the fiber can be estimated by multiplying the crystal strain by the elastic modulus of the crystalline regions of polyethylene. By using this "X-ray Diffraction Technique" , the stress on tghe incorporated fiber, that is, the reinforced effect in polymer composite can be determined in situ and non-destructively. When the fiber was treated with chromic acid, the applied stress became well trasmitted to the fiber, which indicated that the adhesion between the fiber and matrix plays an important role for the reinforcement in the perpendicular direction. Further, the fracture mode was found to be changed by the surface treatment of the fiber. The mechanical property was found to be expressed by using the role of mixture in the direction of fiber axis, which was also clarified by utilizing the x-ray diffraction. Same kinds of experiments were also performed for carbon fiber reinforced composite, and poly (p-phenylene benzobisoxazole) reinforced composites. This technique will be also applied to investigate the effect of moisture, time, temperature.