Session: IMECE Undergraduate Research and Design Exposition

Paper Number: 121100

121100 - Investigation of Pseudo Fiber Length Transformation in 3d Printed Thermoset Composites via Single Fiber Pull-Out Tests 

The lightweight and high-strength properties of fiber-reinforced composites have numerous applications in the aerospace industry. Combining these materials with the versatility of additive manufacturing allows for the creation of highly complex parts with direction-specific mechanical properties. The use of composites can also save 40-80% of weight on aircraft/space vehicles when replacing metallic materials. Our research has shown that short-fiber reinforced parts made using Direct-Ink-Write (DIW) additive manufacturing display 2-3 times greater strength and stiffness than the existing analytical models predict, demonstrating that further research into predicting the mechanical properties of these materials is required.

 

It is our hypothesis that the unexpected mechanical behavior of these materials is due to a pseudo-length transformation in which aligned short fibers at high volume fractions act as if they are longer fibers. This transformation is caused by overlapping load transmittal zones, which create a reinforcement effect that allows the short fibers to exhibit the strengthening capability of longer fibers.  

To test our hypothesis, we will conduct single-fiber pullout tests that will allow us to measure the interface shear strength and coupling between a single fiber and an aligned, fiber-reinforced, additively manufactured composite matrix.  

 

To perform the single-fiber pullout tests, composite test samples were initially fabricated via a DIW printing method. Printing ink was prepared by mixing thermoset resin (EPON 826) with chopped Hexcel fibers. The ink was then extruded via the pressure controlled DIW system. Once the half (50%) height of the composite height is achieved, the printing was paused and a single fiber was placed on top of the specimen. Printing was then continued until the remainder of the sample was fabricated. The cured sample with a single fiber protruding from the printed composite was placed in an Instron tensile testing system and the free end of the single fiber was glued on the test fixture. Tensile load was then applied to quantify the adhesion strength of the fiber. Fiber alignment within the composite was varied by alternating the printing velocity during the DIW process and the effect of fiber alignment on the fiber strength was characterized. Initial single-fiber pullout tests performed on the customized test setup have demonstrated the feasibility of the experiments. Our microscopy results have shown that a single fiber was successfully placed inside the composite test specimen and the Instron system could successfully characterize the fiber pullout strength. The outcome of this research can quantify the effect of fiber alignment on the pseudo fiber length transformation concept and tremendously benefit the fabrication of composite materials with unprecedented mechanical performance.

Presenting Author: Neyton Baltodano Jr University of Miami

Presenting Author Biography: Neyton Baltodano is an undergraduate student at the University of Miami in Coral Gables, Florida.

He is currently in his senior year, majoring in Aerospace Engineering.

His research interests include composite materials and additive manufacturing for aerospace applications.

In addition to being involved in undergraduate research, Neyton is an active member of University of Miami's ASME student section, having served in various positions such chapter President and Vice-President.

Neyton currently holds positions at the University of Miami's College of Engineering, including:
-President of the Pi Tau Sigma Mechanical Engineering Honor Society
-Vice-President of the Engineering Student Council
-College of Engineering Student Ambassador
-College of Engineering Peer Mentor

Upon graduation, Neyton plans on pursuing a PhD. degree in Mechanical or Aerospace engineering.

Authors:

Neyton Baltodano Jr University of Miami
Chris Parisi University of Miami
Emrah Celik University of Miami