A measure of the equivalent shear stress amplitude from a prismatic hull in the principal coordinate system

A measure is proposed in this paper in order to assess the equivalent shear stress amplitude for high-cycle multiaxial tests. It is obtained from a prismatic hull oriented along the principal load axes while it encloses the stress path. Harmonic and non-harmonic load examples are presented for illustrating this definition. Moreover, a comparison with various definitions is presented from two same amplitude stress loads. On these examples, the definitions based on the elliptic and prismatic hulls are too safe and this could have a significant impact on the cost of design.