A Digital Twin Approach to a Quantitative Microstructure-Property Study of Carbon Fibers through HRTEM Characterization and Multiscale FEA.

Rebekah Sweat,Jin Gyu Park,Richard Liang

doi:10.3390/ma13194231

Abstract

Microstructures of typical carbon fibers (CFs) from polyacrylonitrile (PAN) and pitch-based precursors were studied using a novel digital twin approach with individual carbon fibers for a local crystal scale model. The transmission electron microscopy (TEM) samples were prepared using a focused-ion beam (FIB) for both longitudinal and transverse directions of carbon fibers. Measurements of the crystal size and orientation were estimated from X-ray scattering. TEM imaging of graphitic packing facilitated further comprehension of associations between processing and final material properties, which could enable customization of microstructures for property targets. Then the detailed microstructural information and their X-ray scattering properties were incorporated into the simulation model of an individual carbon fiber. Assuming that graphene properties are the same among different forms of carbon fiber, a reasonable physics-based explanation for such a drastic decrease in strength is the dislocations between the graphitic units. The model reveals critical defects and uncertainty of carbon fiber microstructures, including skin/core alignment differences and propagating fracture before ultimate failure. The models are the first to quantify microstructures at the crystal scale with micromechanics and to estimate tensile and compressive mechanical properties of carbon fiber materials, as well as potentially develop new fundamental understandings for tailoring carbon fiber and composites properties.

Highlights

Carbon fibers (CFs) are widely used as the reinforcement material in high-performance composite applications because of their lightweight nature and high mechanical properties [1]
Defect generation and size are related to crystal size, which can reduce the tensile strength of carbon fibers with an increase in tensile modulus
We present high-resolution transmission electron microscopy (TEM) images of PAN and a pitch-based CF prepared using a focused ion beam (FIB) and compare its wide-angle X-ray scattering results to gain an understanding of both graphitic structure and defect properties at the same time

Summary

Introduction

Carbon fibers (CFs) are widely used as the reinforcement material in high-performance composite applications because of their lightweight nature and high mechanical properties [1]. Carbon fiber properties are driven by the microstructure generated through precursors and processing [2]. The precursor materials, oxidization, stabilization, and carbonization processes are performed for carbon fiber production. Defect generation and size are related to crystal size, which can reduce the tensile strength of carbon fibers with an increase in tensile modulus. This correlation is understood for tensile behavior, the microstructural effect on compression and shear behavior of fibers remains mostly empirical [5]

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