陶瓷纤维增强SiO2气凝胶复合材料面内拉伸非均匀全场应变测量与分析

通过设计圆弧边缘夹持方案和狗骨形拉伸试样，开展了陶瓷纤维增强SiO₂气凝胶复合材料室温环境中的面内拉伸性能试验，采用数字图像相关方法对陶瓷纤维增强SiO₂气凝胶复合材料表面的全场变形进行测量和分析，并结合获得的非均匀应变分布情况进一步讨论其力学行为特征和变形断裂机制。结果表明:纤维增强增韧机制使陶瓷纤维增强SiO₂气凝胶复合材料的面内拉伸行为表现出一定的非线性及韧性特征；在一定载荷水平下，陶瓷纤维增强SiO₂气凝胶复合材料表面应变分布呈显著的非均匀特征，与内部随机的纤维排布及各处传力情况不同相关，可选择较大计算区域进行平均化处理来减弱对测试中应变度量的影响；在加载和断裂过程中陶瓷纤维增强SiO₂气凝胶复合材料表面存在局部应变集中现象，并随着裂纹扩展而发生演变，面内拉伸载荷下的宏观断口呈锯齿状特征，主要由剪应力主导的基体断裂、法向针刺对纤维铺层的约束等原因所致。本文研究结果为隔热复合材料的强韧化性能提高指明了方向。 

Measurement and analysis of in-plane tensile non-uniform full-field strain of ceramic fiber reinforced SiO2 aerogel composites

By designing the circular arc edge griping scheme and dog bone type tensile specimen, the in-plane tensile property tests of ceramic fiber reinforced SiO₂ aerogel composites at room temperature were conducted. The full field deformation of ceramic fiber reinforced SiO₂ aerogel composites surface was measured and analyzed based on digital image correlation method. The non-uniform strain distribution results were obtained and discussed. The mechanical behavior characteristics and deformation and fracture mechanisms were further discussed. The results show that the in-plane tensile behavior of the ceramic fiber reinforced SiO₂ aerogel composites exhibits some nonlinear and ductile characteristics due to fiber reinforced and toughened mechanisms. Under certain load level, the strain distribution on the ceramic fiber reinforced SiO₂ aerogel composites surface shows significantly non-uniform. This is related to the internal random fiber arrangements and the different force transferring situations. In the mechanical tests, larger calculation areas can be selected for averaging treatment to reduce the non-uniform influence on the strain measurement. In the process of loading and fracture, the local strain concentration phenomenon exists on the ceramic fiber reinforced SiO₂ aerogel composites surface and evolves with the crack propagation. The fracture appearance under the in-plane tensile load has a serrated feature. It is mainly caused by the matrix fracture dominated by shear stress and the constraint effect of normal needling on the fiber layers. Results can point out the direction to improve the strengthening and toughening of thermal insulation composites.