Investigation of Contact Angle Effect for Analyzing Interphase Properties in Carbon Fiber Reinforced Polymer Matrix Composite Materials

Jack Mester, B.S.E. Mechanical EngineeringMentor: Dr. Masoud Yekani Fard

School for Engineering Matter, Transport and Energy

Research Questions: How does probe tip angle affect stress fields on the interphase region of carbon composites in Atomic Force Microscopy (AFM) in Peak Force Quantitative Nanomechanical Mapping mode (PFQNM)?

Introduction:• Carbon fiber reinforced polymer matrix (CFRP) composites provide excellent mechanical properties at a low density• CFRPs are commonplace in automotive, aerospace, and energy generation sectors due to these superior properties• CFRPs gain their high tensile strength from carbon fiber monofilaments that are held together via an epoxy matrix

with relatively low elastic modulus• One of the greatest identifiers of determining a PMCs bulk characteristics is the interphase regions properties• The interphase region is typically a few nanometers to a fraction of a micrometer in radial distance away from the

carbon fiber [2,4]• The interphase region is difficult to characterized due to large variance in topography, width and elastic modulus (2-

230Gpa) [2]• PFQNM is a nondestructive tapping mode of AFM that utilizes a fine tipped (5-15nm) probe to map morphology,

adhesion, storage and elastic modulus [1]• The mechanical properties of the material are derived from indentation depth and probe tip geometry, this data is

fitted to a force depth curve based on assumptions including a perpendicular probe contact angle

References:[1] Brunker Nano Inc. (2019). Retrieved from Brunker AFM Probes: https://www.brukerafmprobes.com/Product.aspx?ProductID=3929[2] T.J. Younga, L. C. (2013). Observations on interphase characterization in polymer composites by nano-scale indentation using AFM and FEA. Composites Part A.[3] Chanzgi Qu, et al. (2017). Morphology and Mechanical Properties of Polyimide Films: The Effects of UV Irradiation on Microscale Surface. MDPI[4] Masoud Yekani Fard, et al. (2020). Time-scale through-thickness interphase in polymer matrix composites including hygrothermal treatment. Polymer Testing.[5] TA Bogetti, et al. (1999). Characterization of nanoscale property variations in polymer composite systems: 2. Numerical modeling. Composites Part A.

Methods:• CFRP samples were

manufactured with varying carbon fiber types and orientations

• CFRP samples were cut and polished with fine grit sandpaper and then diamond lapping film (120 grit - 0.5 micrometers)

• CFRP samples were viewed with optical microscopy to find areas of interest

• PFQNM AFM was conducted on areas of interest

• Mechanical properties and morphology was mapped

• Mechanical properties graphed as a function of radial distance away from the carbon fiber to provide properties to be modeled in FEA

Sample preparation, polishing mounted CFRP sample on rotating PSB (left)

Optical microscopy at 600x of polished CFRP sample (right)

Bruker FTIR AFM (Left)

Topography of carbon fiber monofilament (Bottom-right)

Typical force v displacement curve of PFQNM (Top-right) [3]

Results:• CFRP Interphase thickness was found to have

variable thickness ranging from 87 to 95 nm and variable elastic modulus ranging from 23 to 30 GPa from multiple carbon fiber sites [4]

• Carbon fiber delamination occurred in all samples; however, significant delamination of up to 10% average debonding per fiber was found in 2-year hygrothermal aged samples [4]

Conclusion and Future Goals: • Develop 3D Finite Element Analysis (FEA) Models

of the PFQNM probe tip and CFRP sample in ANSYS

• Will utilize resultant mechanical property and morphology data from AFM experimentation to create a three-phase cylindrical model consisting of isotropic (matrix & interphase) and transversely isotropic (carbon fiber) properties

• Varying probe tip angles will be implemented and resulting stress fields inside the sample will be analyzed and compared to actual force displacement curves from AFM experimentation

• FEA modeling will provide a clear understanding of what the true probe tip angle of interaction is with the sample

• Advanced nanoparticle interphases such as CNT and Buckypaper will be examined and studied using PFQNM and FEA modeling

Preliminary CFRP sample FEA model to be constructed and simulated with probe tip (left)

“ Topography, reduced modulus, section line profiles, and interphase thickness for unaged (a–c), one-year aged (d–f), and two-year aged (g–i) conditions at subsurface (500–800 μm)” [4]