The curvilinear integral method: computer realization and testing 1 (under non-roportional reversed axial force and torque)

Abstract The curvilinear integral method seems to be the first not to search for loading cycles; damage accumulation (and the corresponding fatigue life) is computed in terms not of cycles but of differentials of loading (on differential level). Following the classical mathematical differential-integral method, and considering the mutual change of the loading components, a differential of load change ds during d t has been defined as a short element of a ‘trajectory’ (path in appropriate coordinates). The damage differential on ds is d D . Integrating d D to D , the loading is allowed to be arbitrary: non-cyclic, nonproportional (with different component variations), and random. This feature of universality makes the method applicable to real structures for life prediction. The concept of the curvilinear integral has been published previously; this paper provides additional information and details about the mathematical and computer realization of the method and its first testing using a new program. Experimental data from LBF-Darmstadt Germany on the cast iron material GTS45 have been used, under reversed (alternating) axial and shear stresses: in phase, out of phase and of different frequencies.