Core tips：China’s Institute of Coal Chemistry establishes a new method to evaluate carbon fibre microstructure.
The team led by Zhang Shouchun, a researcher at the Institute of Coal Chemistry, Chinese Academy of Sciences, has made progress in the field of carbon fibre microstructure research, and published a paper titled “Assessing the radial microstructural heterogeneity of polyacrylonitrile (PAN)-based carbon fibres using nanoindentation” in the Journal of Materials Research and Technology.
The paper proposed a new method based on nanoindentation technology to characterise the radial structural heterogeneity of carbon fibres and the orientation of graphite crystallites, providing a new technical approach for the study of carbon fibre microstructure with simple sample preparation, reliability and high efficiency.
ink="https://www.jeccomposites.com/?attachment_id=157073" data-orig-file="https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2.jpeg" data-orig-size="900,417" data-comments-opened="0" data-image-meta="{"aperture":"0","credit":"","camera":"","caption":"","created_timestamp":"0","copyright":"","focal_length":"0","iso":"0","shutter_speed":"0","title":"","orientation":"0"}" data-image-title="China’s Institute of Coal Chemistry" data-image-description="<p>China’s Institute of Coal Chemistry</p>
" data-image-caption="<p>Orientation distribution of graphite crystallites in carbon fibre and its deformation mechanism under compression (source: The Institute of Coal Chemistry, Chinese Academy of Sciences)</p>
" data-medium-file="https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2-300x139.jpeg" data-large-file="https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2.jpeg" src="https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2.jpeg" alt="China's Institute of Coal Chemistry" class="wp-image-157073" srcset="https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2.jpeg 900w, https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2-300x139.jpeg 300w, https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2-768x356.jpeg 768w, https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2-500x232.jpeg 500w, https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2-700x324.jpeg 700w, https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2-600x278.jpeg 600w, https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2-129x60.jpeg 129w, https://www.jeccomposites.com/wp-content/uploads/2025/05/image-2-194x90.jpeg 194w" sizes="(max-width: 900px) 100vw, 900px" style="box-sizing: border-box; height: auto !important; max-width: 100%; vertical-align: bottom; border-style: none;" />Orientation distribution of graphite crystallites in carbon fibre and its deformation mechanism under compression (source: The Institute of Coal Chemistry, Chinese Academy of Sciences)
Challenges in characterising radial heterogeneity of carbon fibre
Carbon fibre is a typical structural heterogeneous material. The microstructural analysis and precise control of the radial heterogeneity of carbon fibre are of great significance for breaking through the technical bottleneck of the next generation of high-strength and high-modulus carbon fibre.
With the advancements in micro-area characterisation technology, the radial heterogeneous structural characteristics of carbon fibre have gradually been revealed, such as selected electron diffraction (SEAD), microbeam X-ray diffraction (microbeam-XRD), etc. However, the sample preparation of such high-resolution analysis technology is extremely difficult. The sample needs to ensure strict dimensional accuracy and surface flatness, and its complex pretreatment process significantly increases the difficulty of the experiment.
In addition, there are few reports on the radial distribution of micromechanical properties of carbon fibre. It is very necessary to find a simple characterisation technology in a different way.
Filling the gap in detection methods
Nanoindentation detection technology is like a “geologist” in the microscopic world. It taps the surface of the material with a nanoprobe and deciphers the hardness and toughness codes hidden between atoms from the tiny dents and ripples.
Nanoindentation technology is a key means of modern micromechanical characterisation and has been widely used in the field of carbon fibre and its composite materials, such as the study of the interface properties of carbon fibre composite materials, the determination of carbon fibre elastic constants, etc. It has the core advantage of nanoscale displacement control accuracy. The research team used nanoindentation technology to systematically evaluate the radial distribution of micromechanical properties (elastic modulus and hardness) of several commercial PAN-based carbon fibres in the axial and transverse directions.
The results show that T300 and T700S grade carbon fibres with lower strength grades exhibit severe radial micromechanical property heterogeneity. In contrast, T800H, T800S and T1000G grade carbon fibres exhibit excellent radial micromechanical uniformity. The ratio R can reflect the orientation of graphite crystallites to a certain extent. The larger R is, the better the orientation of graphite crystallites. It is inferred that the orientation degree of different regions within a single fibre is from high to low: transition layer, cortex, and core layer.
Nanoindentation technology has shown significant advantages in evaluating the radial heterogeneity of carbon fibre, including simple sample preparation, reliable results and high detection efficiency.
This study innovatively proposed a new method for characterising the microstructure of carbon fibre based on nanoindentation technology, which fills the gap in the study of radial distribution of micromechanical properties of carbon fibre.
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