Reinforced Mechanism in Polymer Composites by X-ray Diffraction

利用X射线衍射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脱粘的复合材料断裂机理，以及粘结对复合材料增强效果的影响。首先，对高性能聚乙烯纤维单向增强环氧树脂复合材料施加垂直于纤维方向的应力。发现施加的应力被传递到掺入的纤维，这可以容易地检测到作为赤道X射线衍射峰的衍射峰位移。传递到纤维的应力可以通过将晶体应变乘以聚乙烯结晶区的弹性模量来估计。利用这种“X射线衍射技术”，可以原位无损地测定掺入纤维上的应力，即聚合物复合材料的增强效果。经铬酸处理后，纤维与基体之间的粘结力对垂直方向的增强起着重要的作用。此外，断裂模式被发现通过纤维的表面处理而改变。用混合物在纤维轴方向上的作用来表达力学性能，并用X射线衍射进行了验证。对碳纤维增强复合材料和聚苯撑苯并二恶唑增强复合材料也进行了同样的实验。该技术也将被应用于研究水分、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.