Research on Flexural Test Methods for Advanced Composite Materials

1)在日本，3点或4点弯曲被规定为JIS（日本工业标准）用于弯曲测试方法。然而，如果将其应用于单向碳纤维增强塑料（CFRP）等具有极端各向异性的先进复合材料，则由于局部断裂而发生失效，2）短厚试件在三点弯曲下的抗弯强度远低于长薄试件在四点弯曲下的抗弯强度。3）针对三点弯曲法和四点弯曲法存在的应力集中问题，研制了两种纯弯曲试件。用它们得到了真实的弯曲断口，其弯曲强度比三点弯曲法和四点弯曲法提高30%~ 50%.对先进复合材料的试验应采用纯弯曲法。

1) In Japan, the 3-point or 4-point bending was prescribed as JIS (Japan Industrial Standard) for the flexural testing methods. However, if it is applied to the advanced composites with extreme anisotropy such as unidirectional carbon-fiber-reinforced plastics (CFRP), the failures take place beneath the loading noses due to the local fractures, without due to the flexural fractures.2) The flexural strengths obtained in short and thick specimens under 3-point bending are much lower than those in long and thin specimens under 4-point bending because of high stress concentration.3) Accordingly, the two kinds of pure bending pigs were developed in order to avoid the stress concentration in the 3- and 4-point bending methods. By using them, the real flexural fractures were obtained the flexural strengths were more than 30%-50% higher than those obtained in the 3- and 4-point bending methods. The pure bending method should be used in testing the advanced composite materials.