不同应变速率下纳米橡胶颗粒对环氧树脂的增韧特性与机理分析

Toughening Mechanism of Nano-rubber Particles in Epoxy Resin under Different Strain Rates

为了解释不同应变速率下纳米橡胶颗粒对环氧树脂基体的增韧机理,制备了质量分数为6%的纳米橡胶颗粒/环氧树脂复合材料,分别测试了该材料在3种低应变速率(5×10-4s-1,1×10-1s-1,2.5×10-1s-1)和高应变速率下(90 s-1)的I型平面断裂韧性.结果表明,纳米橡胶颗粒在3种低应变速率下可以显著提高环氧树脂的断裂韧性,提高幅度分别为158%,283%和309%.在高应变速率下,纯环氧树脂的断裂韧性由于动态效应而显著升高,然而纳米橡胶颗粒对环氧基体的增韧效果却不明显,增韧幅度仅为2%.由光学显微镜照片可知,随着应变速率的提高,纳米橡胶颗粒/环氧树脂复合材料断口表面的应力发白区域逐渐较少,甚至在高应变速率(90 s-1)下消失.偏光显微镜照片表明,纯环氧树脂与纳米橡胶颗粒/环氧树脂复合材料的裂纹尖端塑性形变尺寸随着应变速率的升高而减小.通过扫描电子显微镜对断口形貌进行分析可知,不同应变速率下纳米橡胶颗粒在环氧基体中空穴增长程度不同,进而导致纳米橡胶颗粒对环氧基体的增韧效果的不同.

In order to understand the toughening mechanism of nano-rubber partieles toughened epoxy resin,the mode I fracture toughness of 6 wt% nano-rubber particles in epoxy resin was investigated under low strain rates（ 5 × 10- 4s- 1,1 × 10- 1s- 1,2. 5 × 10- 1s- 1） and high strain rate（ 90 s- 1） respectively. The results showed the nano-rubber particles can significantly toughen epoxy by 158%,283% and 309% under low strain rates,respectively. However,compared with toughness obtained under low strain rates of 5 × 10- 4s- 1,1 ×10- 1s- 1and 2. 5 × 10- 1s- 1,at high strain rate of 90 s- 1,the fracture toughness of the unmodified epoxy was significantly increased due to the dynamic effect,however,the toughening effect of nano-rubber particles on epoxy resin was reduced obviously. Optical microscopy images showed whitening zone displayed on fractured nano-rubber particle modified epoxy specimen was obviously reduced as the strain rate increased from 5 ×10- 4s- 1to 2. 5 × 10- 1s- 1and even disappeared under high strain rate of 90 s- 1. Polarized microscopy images displayed that the area of the crack tip deformation zones in both nano-rubber particle modified epoxy and unmodified epoxy was reduced when the strain rate was increased. The SEM observations indicated the strain rate variation alters the extent of plastic void growth and rubber cavitations,and finally leads to different toughening effects.