Stress dependence of indentation modulus for carbon fiber in polymer composite

Hongxin Wang,Han Zhang,Daiming Tang,Kenta Goto,Ikumu Watanabe,Hideaki Kitazawa,Masamichi Kawai,Hiroaki Mamiya,Daisuke Fujita

doi:10.1080/14686996.2019.1600202

Hongxin Wang, Han Zhang + Show 7 more

Open Access

https://doi.org/10.1080/14686996.2019.1600202

Copy DOI

Abstract

ABSTRACT Elastic modulus measured through atomic force microscopy (AFM)-based indentation on single carbon fiber (CF) is found with dependence on lateral applied stress. An in situ indentation experiment inside a high-resolution transmission electron microscope was performed to quantitatively understand this phenomenon by observing microstructure change in the indented area. Change of graphitic basal plane misalignment angle during indentation was linked to a continuous change of modulus with the help of finite element simulation. The established relationship between modulus and indentation force was further used to calculate residual stress distribution in CF imbedded in a CF reinforced polymer composite using the AFM indentation technique. The stress-induced formation of nanoscale defects in the CF and their transformation into fracture were directly characterized.

Highlights

Modulus characterization by atomic force microscopy (AFM) provides a new method of mapping residual stress in a material with nanometric resolution [1,2]
The operating principle can be described as: the lateral tensile/compressive stress preexisting in the specimen produces a partial force component that counters/enhances the vertically applied AFM probe force; such reduced/increased vertical force applied on the specimen would make the apparent Young’s modulus sensed by the AFM probe smaller/bigger than when no residual stress is presented; the distribution of such apparent
It has been found that pinpoint indentation modulus of carbon fiber (CF) increased with external tensile tress in the orthogonal direction

Summary

Introduction

Modulus characterization by atomic force microscopy (AFM) provides a new method of mapping residual stress in a material with nanometric resolution [1,2]. Young’s modulus over a preassumed uniform material would reflect local stress distribution This phenomenon of modulus hardening is similar to the superlattice modulus effect observed in metal films and modulus softening effect observed in nuclear graphite, but out of very different mechanism [3,4]. This technique is very attractive as nondestructive stress sensing for carbon fiber (CF)-based composite materials. Though widely used as filler materials for CF reinforced plastic (CFRP), the brittle nature of CF often causes catastrophic fatigue failure of the CFRP structural component [5,6].

Objectives

Results

Conclusion