Nanoindentation and atomic force microscopy tapping mode techniques have been the common techniques for material characterization at the microscale. Atomic Force Microscopy based Peak Force Quantitative Nanomechanics Mapping (PFQNM) technique was developed in the last decade and it has been used for high lateral resolution and characterization at the nanoscale. Details of the calibration parameters include probe stiffness, real spring constant, tip radius, tapping force, deformation level, synchronous distance, drive3 amplitude sensitivity (DDS3), and deflection sensitivity for heterogeneous polymer matrix carbon fiber composites will be discussed. Trace (loading) and retrace (unloading) force vs. deformation curves are used to extract the nano-scale material properties. Reduced modulus, adhesion, and deformation results are used to examine the interphase zone thickness and properties.Co-polymer epoxy resin bisphenol-A/F type with an amine hardener and 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. Specimens from the subsurface (~400 µm from the surface) and the depth (~ 4mm from the surface) were considered. The polymer matrix composite samples have been exposed to heat and humidity. The AFM samples are 1 mm in thickness and are polished to 0.1 µm. AFM Multimode 8, scanner type J with a maximum scanning window of 125µm × 125µm, is used. An indentation depth of up to ~5nm is used during peak force tapping to avoid any damage to the sample and guarantee repeatable results. Since the Deformation is less than or equal to the tip radius; therefore, the Derjaguin, Muller, Toropov (DMT) equation is applied to the retract curve to calculate the elastic modulus.The effects of heat and humidity on the interphase thickness and modulus of polymer matrix composites will be examined using the stochastic analysis technique. The authors use the Weibull model to examine material properties' statistical distribution. Weibull statistics link the probability of the occurrence of an event where the event refers to the interphase thickness or its modulus in this study. Linear regression, the method of moments, and the maximum likelihood method are common techniques for evaluating the Weibull parameters. These techniques are currently examined to investigate the applicability and suitability for interphase properties data set. The scale parameter and the Weibull modulus (shape parameter) of the distribution characterize the data's scattering. A higher Weibull modulus means a steeper function and a lower dispersion. The Weibull analysis results will show the effects of the local moisture content on the interphase thickness and the reduced modulus.

Stochastic Analysis of the Interphase Thickness and Modulus in Carbon Fiber Reinforced Polymer Matrix Composites

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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