Nano-indentation instrumented tests are carried out at shallow depths on PAN-based and MPP-based carbon fibres. Indentation moduli are obtained by performing the tests at ten different measured orientations with respect to the fibre axis. They are used to identify the elastic constants of the fibres, assuming a transversely isotropic behaviour, by minimising a cost function between measured and estimated values. Inconstancies between the identified in-plane shear and transverse moduli and reported literature values are pointed out, and some drawbacks of the nano-indentation method are highlighted. An improved method taking into account the buckling mechanisms of crystallites at stake during the indentation process, and visible in the hysteretic behaviour of force-penetration nanoindentation curves, is proposed. It allows to identify values of elastic constants that are in accordance with literature values. These elastic properties of carbon fibres are in turn used to estimate the elastic properties of epoxy matrix composites containing these fibres. Very good agreement is found with experimentally available values of unidirectional ply properties. An excellent correlation between experiments and Finite Element Analyses of the indentation response of carbon fibres is eventually found.

中文翻译：

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纳米压痕法测定碳纤维弹性常数的研究

纳米压痕仪器测试是在 PAN 基和 MPP 基碳纤维上在较浅的深度进行的。压痕模量是通过在十个不同的测量方向相对于纤维轴进行测试来获得的。它们用于通过最小化测量值和估计值之间的成本函数来确定纤维的弹性常数，假设横向各向同性行为。指出了确定的面内剪切和横向模量与文献报道值之间的不一致，并强调了纳米压痕方法的一些缺点。考虑到压痕过程中微晶的屈曲机制，并在力-穿透纳米压痕曲线的滞后行为中可见，提出了一种改进方法。它允许识别符合文献值的弹性常数值。碳纤维的这些弹性特性又被用来估计含有这些纤维的环氧树脂基复合材料的弹性特性。发现与单向帘布层特性的实验可用值非常一致。最终发现实验与碳纤维压痕响应的有限元分析之间存在极好的相关性。