College - Author 1

College of Engineering

Department - Author 1

Materials Engineering Department

Degree Name - Author 1

BS in Materials Engineering

College - Author 2

College of Engineering

Department - Author 2

Materials Engineering Department

Degree - Author 2

BS in Materials Engineering

Date

6-2023

Primary Advisor

Blair London, College of Engineering, Materials Engineering Department

Abstract/Summary

This project aims to develop a dataset on interlaminar tensile strength comparing unidirectional and woven thermoset matrix carbon fiber composites keeping ply count, matrix material, and fiber diameter constant. The interlaminar tensile strength is an important property relating to the delamination failure mode. Interlaminar tensile strength is determined using the ASTM D6415 testing standard. This test is a modified four-point bend test using a 90° curved beam test specimen. Laminates were produced by laying up pre-impregnated carbon fiber sheets onto a curved beam tooling. The unidirectional laminate was produced with 20 plies in a [0,0,90,0,0]4 layup pattern. The woven fiber laminate was produced with 20 plies of a 2x2 twill weave fabric in the 0° orientation. Both laminates were cured in an autoclave. The laminate panels were machined into the test specimens with a width of 1 inch. The ASTM D6415 tests were performed with a crosshead displacement rate of 2.0 mm/min until there was a drop in load indicating initial delamination. The unidirectional specimens had an average interlaminar tensile strength of 8.72 Ksi. The woven fabric specimens had an average interlaminar tensile strength of 9.52 Ksi. After testing, the specimens were sectioned and imaged using optical microscopy and scanning electron microscopy (SEM). The specimens for SEM were gold sputter coated and imaged under high vacuum mode. Imaging indicated that for unidirectional specimens, delamination started in the matrix then propagated along the ply boundary. Woven specimens appeared to fail in regions of excess matrix material at intersections of fiber orientations. It is recommended for continuing work to use a test fixture that does not need to be offset. It would also be beneficial to have adjustable span lengths for the top and bottom jaws to increase specimen compatibility. Lastly, increasing matrix toughness would increase failure loads where stress concentrations are common in components.

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