Lifetime of semi-ductile materials through the critical plane approach

• Carpinteri-Spagnoli proposal is applicable for the estimation of the position of the critical plane of multiaxial fatigue.
• Aluminium alloy 2017A displays intermediate states between elastic-brittle and elastic-plastic.
• Aluminium alloys have intermediate properties between elastic-brittle and elastic-plastic.

This paper presents the results of fatigue strength estimation depending on the variable orientation of the critical plane for proportional and non-proportional bending and torsion with regard to specimens made of aluminium alloy 2017A. The algorithm applied for the fatigue strength evaluation is based on the Carpinteri–Spagnoli proposal and its subsequent modifications in accordance with the ideas developed by the authors. The objective of this paper is to search for a model which offers the best possible results of fatigue strength estimation for materials with properties which are intermediate between elastic-brittle and elastic–plastic, such as aluminium alloys, and a further insight into them with regard to their fatigue strength.