Generalised fatigue durability diagrams are considered for a material under multi-axial loading given by a (non-regularly) oscillating function of time. Phenomenological strength conditions under such loading are presented in terms of the normalised equivalent stress functionals both for quasi-ductile rupture and brittle fracture. Examples of the functionals are presented for some known and new durability models including those sensitive to the load sequence. Some complex strength conditions applicable to the durability description at fatigue, creep, dynamic loading and their combinations are presente
