Session: 03-05-01 Design, Material Processing, and Applications of Polymer Composites

Paper Number: 95573

95573 - Effects of the CNT Network Size and Interphase on Mode I Fracture of Buckypaper Nanocomposites 

BP is a complex 3D CNT structure with randomly distributed CNTs. The size of the CNT network and interphase can potentially affect the fracture behavior of BP nanocomposite on a larger length scale. For multiwall carbon nanotube BP, the main pore sizes range between 20 - 35 nm (intrabundle) and 65 - 110 nm (inter bundle). Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) have proven nano and sub-micron inhomogeneities in BP membranes. These inhomogeneities affect the macroscale mechanical response of BP membranes due to the local high modulus mismatch among CNT particles, the CNT networks, and the polymer. The geometry (shape and size) and the spatial locations (depth and distance between the networks) of the buried CNT networks are amongst critical parameters for the degree of the mechanical mismatch. Atomic Force Microscopy-based Peak Force Quantitative Nanomechanics Mapping (PFQNM) technique is used to quantify the nano- and micro-properties of CNT networks and interphase. Parameters such as a probe, tip radius, and tapping force are critical in characterizing heterogeneous BP nanocomposites. AFM PFQNM indents the material's surface with small probes under controlled tapping force to detect local stiffness and adhesion of material inhomogeneity at the surface and subsurface with a nanometer resolution.

Co-polymer epoxy resin bisphenol-A/F type with an amine hardener and stitch-bonded biaxial carbon fabric was used to fabricate the composite laminate plates using a hot press molding technique. The symmetric composite laminate plates have a thickness of ~8mm. The AFM samples are 1 mm thick and polished to 0.1 µm. Double Cantilever Beam (DCB) specimens are used for mode I fracture characterization. Digital Image Correlation (DIC) system is used to study the strain field around the crack and monitor the delamination crack. The compliance Calibration technique is used to calculate the initiation and propagation energy release rate. There are no prior statistical studies of nanoscale interphase geometry, mechanical properties, and its length scale correlation to different fracture modes in CNT nanocomposites to the authors' best knowledge. The authors use the Weibull model to examine material properties' statistical distribution. Weibull statistics link the probability of an event such as CNT network size, interphase thickness, or mode I fracture. Linear regression is used to investigate the applicability and suitability for nano- and macro-scale properties data set. The distribution's scale parameter and the Weibull modulus (shape parameter) characterize the data's scattering. A higher Weibull modulus means a steeper function and a lower dispersion.

Presenting Author: Masoud Yekani Fard Arizona State University

Presenting Author Biography: Dr. Masoud Yekani Fard is a faculty with the Mechanical and Aerospace Engineering Program at the School of Matter, Transport and Energy at Arizona State University. His expertise is in the area of mechanics and materials.

Authors:

Masoud Yekani Fard Arizona State University
Rohan Raman Arizona State University
Yesenia Orozco Arizona State University
Aditi Tata Arizona State University