English: Fracture toughness values for a given material are typically quoted at the asymptotic section of the curve. Early work suggested the differences in fracture toughness were due to plane stress versus plane strain loading, but subsequent work has suggested the difference is due to the relative portions of shear and flat fracture in the different specimen geometries Anderson, T. L. (2005). Fracture Mechanics Fundamentals and Applications (3rd ed.). Taylor & Francis. pg.72-78