Characterization Inspired Manufacturing of Carbon Fiber Composites Considering Multiscale Response

Abstract

A characterization technique for carbon fiber at its single filament level using a highly precise nano-tensile testing data is presented. Using a continuous stiffness method (CSM), instantaneous moduli of single carbon fibers (~7 micron diameter) are acquired as a function of global deformation by applying small sinusoidal harmonic oscillations to a single carbon fiber being deformed in tension. This provides insight on response of small diameter carbon fibers with unprecedented resolution to precisely evaluate the non-linear stiffening response with increasing tensile strain. Precise estimates of modulus and its dependency on strain for single carbon fibers is essential for optimizing multi-scale response of carbon fiber reinforced composites. The rate of increase of tensile modulus with axial strain amplitude will help form a basis to relate the heterogeneity and microstructure of single carbon fibers with its mechanical properties. Microstructure of carbon fibers is characterized by using Wide Angle X-ray Diffraction and Small Angle X-ray Scattering in addition to electron microscopy (SEM and TEM). The current industry norm for specifying carbon fiber properties is based on tensile testing of a composite of unidirectional tow of fibers optimally aligned and tensioned to obtain the tensile modulus and failure strength. This paper will address the role of tow specimen preparation procedure, resulting microstructure for a manual manufacturing processes employed, and implications to the estimation of translation for predicting the upper bound properties of carbon fiber composites. This part of the study will elucidate the role of characterization to further optimize mechanical properties in a composite form considering the linear density and fiber density of carbon fibers. As an application example, we will consider results associated with the multi-scale response of a pultruded carbon fiber plate considering single fiber mechanical testing, interface/interphase with resin system, alignment and tensioning during manufacturing for an epoxy resin system.