The compressive strength of Kevlar is about 1/8 of its tensile strength. If it is bent to a small radius of curvature it will kink as shown in Figure 20.33. Estimate the smallest diameter rod on which Kevlar 49 ?ber of 12-µm-diameter ?bers can be wound without kinking. The tensile strength is 2.8 GPa, Young's modulus is 125 GPa, Poisson's ratio is 1/3, and the tensile strain to fracture is 2.3%.