Enhanced characterization of tow gaps in fiber steered laminates

Abstract

The thesis aimed to characterize the effects of manufacturing-induced defects, particularly gaps in variable stiffness laminates. The primary focus centered on designing a specimen capable of accurately characterizing gap effects. A refined, element-level specimen design featuring a controlled gauge zone was developed, based on pre-defined requirements to represent common variable stiffness structures accurately. The specimens were manufactured and tested. The experimental work featured Digital Image Correlation, Dye Penetrant Testing, and Optical Microscopy. Experimental observations revealed deformation peaks induced by gaps, along with trends in void formation and ply deformation during curing processes. Furthermore, digital image correlation (DIC) analysis unveiled distinct out-of-plane tendencies associated with gap locations. Discrepancies between finite element method (FEM) results and experimental strain distributions highlighted the need for improved modeling, particularly accounting for ply waviness. The main hypothesis presumes that the effects of gaps are influencing off-axis plies through matrix failures. The hypothesis was not proven true based on insufficient proof.