梯度结构C/C复合材料短梁剪切性能研究

Short Beam Shear Performance of Gradient C/C composite

  • 摘要: 为提升碳/碳(C/C)复合材料的层间剪切性能并抑制其分层失效,本文设计并制备了具有梯度结构的缝合C/C复合材料,采用T700-12K展宽布(Spread Tow Woven, STW)作为芯层承载结构,上下表层区将展宽布(STW)与碳纤维网胎(Non-Woven, NW)以不同层数比例构成混杂单元层,经缝合后形成梯度预制体,通过化学气相渗透(Chemical Vapor Infiltration, CVI)工艺进行致密化。采用Micro-CT、偏光显微镜等手段分析了材料的孔隙结构、热解碳织构及损伤形貌,并通过短梁剪切试验结合数字图像相关(DIC)技术研究了其力学行为。结果表明:网胎的引入显著改变了预制体孔隙分布,S3H2结构形成最优的连通孔隙网络,促进了碳源气向芯层扩散,使芯层热解碳沉积更致密均匀;偏光显微镜观察发现S3H2与S5H2表层网胎区热解碳呈现光滑层(SL)与粗糙层(RL)混合的带状织构,而STWS整体以RL为主。梯度结构能有效引导损伤在表层网胎区扩展,通过裂纹偏转、分叉等机制消耗能量,从而抑制分层。S3H2试样表现出最优的综合性能,其剪切强度(24.3 MPa)和剪切韧性(3.02 kJ/m2)较STWS试样分别提升了17.3%和62.3%。本研究为高性能C/C复合材料的结构设计与增韧机制提供了重要理论依据。

     

    Abstract: To enhance the interlaminar shear property of carbon/carbon (C/C) composites and suppress the delamination failure, a gradient-structured stitched C/C composite was designed and fabricated . T700-12K spread tow woven (STW) was employed as the core layer for structural support. The upper and lower surface layers incorporated hybrid units composed of STW and non-woven (NW) carbon fiber mats in varying layer ratios. The fabrics were stitched together to form gradient preforms that perform densification via chemical vapor infiltration (CVI). Micro-CT and polarized light microscopy analyzed the material's pore structure, pyrolytic carbon texture, and damage morphology. Short-beam shear tests combined with Digital Image Correlation (DIC) examined its mechanical behavior. Results indicate that the introduction of the NW mats significantly alters the pore distribution within the performs. The S3H2 structure forms the optimal connected pore network, promoting diffusion of carbon source gas toward the core layer and resulting in denser and more uniform pyrolytic carbon deposition within the core layer. Polarized light microscopy revealed that pyrolytic carbon in the surface mesh region of S3H2 and S5H2 specimens exhibited a band-shaped texture combining smooth layers (SL) and rough layers (RL), whereas STWS specimens predominantly featured RL. The gradient structure effectively guided damage propagation within the surface mesh region, dissipating energy through mechanisms, such as crack deflection and branching, thereby suppressing delamination. The S3H2 specimen demonstrated optimal comprehensive properties, exhibiting a 17.3% increase in shear strength (24.3 MPa) and a 62.3% improvement in shear toughness (3.02 kJ/m2) compared to the STWS specimen. It provides crucial theoretical foundations for the structural design and toughening mechanisms of high-performance C/C composites.

     

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