Numerical and experimental investigation of fiber-reinforced constant and variable stiffness composites for open hole tension with fiber continuity and curvature constraints

Official URL: https://risc01.sabanciuniv.edu/record=b2486297_(Table of contents)

A nascent design methodology is applied to find out the manufacturable optimum fiber angle distributions for the open-hole tension with different geometries and load conditions. Optimized Constant stiffness, Optimized variable stiffness, and Least- Squares and Continuity Constraint (LSC) design approaches are applied for each case studies. Variable stiffness and LSC designs results in better structural performance for all the cases. LSC design resulted in fiber angle distributions that satisfies the maximum curvature limit but with a slight compromise in the objective function. The use of variable stiffness is revealed to be more advantageous over shape optimization methods in constant stiffness composites. The proposed method is applicable to the 3D printing of fiber reinforced composites for small samples while in large-scale the automated fiber placement manufacturing technique could be used. Experimental validation of the discussed method is conducted using an additive manufacturing method integrated. Notched samples are 3D-printed utilizing the pure polyethylene terephthalate glycol as well as chopped carbon fiber reinforced composites. Constant stiffness designs with the print path along the longitudinal (0 ) and transverse (90 ) directions while two different variable stiffness designs based on the potential fluid flow and LSC method are designed, 3-D printed, and tested. The results of the experimental study are well consistent with the numerical study. Thus, this method could be applied for different engineering applications, e.g. aeronautical and automotive structures with and without notches. This thesis presented how greener and stiffer structures could be manufactured combining the LSC design with additive manufacturing technique without material waste and increasing the number of layers.