Final answer:
The statement is true; the blade root does connect to the hub. An appropriate failure theory for a maximum strain at failure of 2% with Sut and Suc of 200 MPa is the strain energy theory, specifically the von Mises criterion.
Step-by-step explanation:
The statement about the blade root being the circular blade section that connects to the hub is true. An acceptable failure theory to use given a maximum strain at failure of 2% with Sut (tensile strength) and Suc (compressive strength) of 200 MPa could be the strain energy theory also known as the von Mises criteria, or the distortion energy theory. These theories are typically used for ductile materials under multidirectional stress states, where yielding is the failure mode.
The von Mises criterion is particularly suitable when the material yields at the same stress value in tension and compression, which is the case when Sut and Suc are equal. However, to determine if the material will fail under a given stress condition, the actual stress state at the blade root must be compared to the failure theory. It's important to note that while the statement is technically true, the application of an acceptable failure theory requires further stress analysis.