Abstract In this work, a cyclic indentation test is employed for the in-situ characterisation of the local mechanical properties of a PR520 epoxy resin matrix in a 3D carbon fiber composite. Since the evolution of indentation response with time is studied, the cyclic loading allows to characterise both the elastic and the time dependent, viscoelastic, mechanical response of the material simultaneously. The 3D carbon fiber composite used in this study contains a number of large resin pockets between fiber bundles (mesoscopic scale) with a characteristic dimension ranging from several hundred of micrometers to several millimeters. The mechanical behaviour of the polymer matrix is investigated on the external surface and in volume of the composite and compared with the neat polymer. The instantaneous elastic modulus from reloading, the energy ratio and the residual depth are determined from the cyclic material response and compared through a Student t-test based statistical analysis. Results show that there is at least 95% of probability that the neat and in-situ polymer matrix material belong to different populations. However, this difference is rather small (between 1 and 2.5%) and almost constant with cycles. Moreover, a difference between composite core and surface was measured.

中文翻译：

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通过循环压痕测试原位表征 3D 碳纤维复合材料中聚合物基体的局部机械性能

摘要 在这项工作中，采用循环压痕试验对 3D 碳纤维复合材料中 PR520 环氧树脂基体的局部机械性能进行了原位表征。由于研究了压痕响应随时间的演变，循环载荷允许同时表征材料的弹性和时间相关、粘弹性、机械响应。本研究中使用的 3D 碳纤维复合材料在纤维束（细观尺度）之间包含许多大的树脂袋，其特征尺寸从几百微米到几毫米不等。在复合材料的外表面和体积上研究聚合物基体的机械性能，并与纯聚合物进行比较。重新加载的瞬时弹性模量，能量比和残余深度由循环材料响应确定，并通过基于学生 t 检验的统计分析进行比较。结果表明，纯聚合物基质材料和原位聚合物基质材料至少有 95% 的概率属于不同的群体。然而，这种差异相当小（在 1% 和 2.5% 之间）并且几乎随周期变化而恒定。此外，还测量了复合芯和表面之间的差异。