Design of Low Cost Carbon Fiber Composites via Examining the Micromechanical Stress Distributions in A42 Bean-Shaped versus T650 Circular Fibers

Imad Hanhan,Michael D Sangid

doi:10.3390/jcs5110294

Abstract

Recent advancements have led to new polyacrylonitrile carbon fiber precursors which reduce production costs, yet lead to bean-shaped cross-sections. While these bean-shaped fibers have comparable stiffness and ultimate strength values to typical carbon fibers, their unique morphology results in varying in-plane orientations and different microstructural stress distributions under loading, which are not well understood and can limit failure strength under complex loading scenarios. Therefore, this work used finite element simulations to compare longitudinal stress distributions in A42 (bean-shaped) and T650 (circular) carbon fiber composite microstructures. Specifically, a microscopy image of an A42/P6300 microstructure was processed to instantiate a 3D model, while a Monte Carlo approach (which accounts for size and in-plane orientation distributions) was used to create statistically equivalent A42/P6300 and T650/P6300 microstructures. First, the results showed that the measured in-plane orientations of the A42 carbon fibers for the analyzed specimen had an orderly distribution with peaks at |ϕ|=0∘,180∘. Additionally, the results showed that under 1.5% elongation, the A42/P6300 microstructure reached simulated failure at approximately 2108 MPa, while the T650/P6300 microstructure did not reach failure. A single fiber model showed that this was due to the curvature of A42 fibers which was 3.18 μm−1 higher at the inner corner, yielding a matrix stress that was 7 MPa higher compared to the T650/P6300 microstructure. Overall, this analysis is valuable to engineers designing new components using lower cost carbon fiber composites, based on the micromechanical stress distributions and unique packing abilities resulting from the A42 fiber morphologies.

Highlights

IntroductionAdoption of polymer matrix carbon fiber composite materials in high volume applications (such as automotive applications) is not widespread and the rate of adoption has been slow
Adoption of polymer matrix carbon fiber composite materials in high volume applications is not widespread and the rate of adoption has been slow
A Matlab algorithm which isolated the boundary pixels of each fiber cross-section was used to compute this vector for each fiber in the segmented and post-processed scanning electron microscopy (SEM) image of the A42/P6300 composite, in order to compute the distribution of the in-plane orientations

Summary

Introduction

Adoption of polymer matrix carbon fiber composite materials in high volume applications (such as automotive applications) is not widespread and the rate of adoption has been slow. This is partly because of their higher costs compared to traditional materials ( the cost of the carbon fibers). The PAN precursor is made from crude oil, which is refined and filtered (into dope), and coagulated in a specialized coagulation bath [2]. This precursor undergoes stabilization in air by applying tension to the precursor at a temperature between 200 and 300 ◦C for about 2 h [1]. The most expensive part of this process is the cost of the precursor fiber, which makes up 53% of the total cost of the carbon fiber, followed by the carbonization step, which makes up 24% of the total cost of the carbon fiber [3]

Methods

Results

Conclusion