Relating fracture mechanics and fatigue lifetime prediction

Significance Statement

Cause-and-Effect Interaction concept (CEI) may help understandings of natural phenomena in which the elapsed effects E can affect the forthcoming causes C beyond the moment of observation on expense of the available finite causal potential CU. Fatigue is considered as a phenomenon in which the finite ultimate endurance EU is reducing by the progression of the primary fatigue damage F’(L) in proportion to the applied cyclic load L resulting in shortening of the fatigue life on an interactive manner.

The overall fatigue damage progression F is tackled as a process of Fatigue-Endurance-Interaction (FEI) governed by interactions I(L,F) of cyclic loads L and endurance E during load redistribution among failed and intact huge but finite number of microstructural bonds in materials. The causal energy absorption measurement by work W[I(L,F)] done on observable fatigue damage progression recorded by testing offers a mathematical solution for FEI following from the general finite CEI concept for the problem of fatigue life predictions based on the results of fracture mechanics.  

 Relating fracture mechanics and fatigue lifetime prediction,Advances in Engineering

About the author

Kalman Ziha is professor emeritus of the University of Zagreb, Croatia. He made his studies in naval architecture on the Faculty of Mechanical Engineering and Naval Architecture of the University of Zagreb. His interests are in application of information theory to mechanical and other systems, integral system safety and reliability, multidisciplinary optimization and engineering of materials.

Journal Reference

Materials Science and Engineering: A, Volume 651, 2016, Pages 167–176. 

Kalman Ziha

University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Department of Naval Architecture and Ocean Engineering, Ivana Lucica 5, Zagreb, Croatia.

Abstract

This article presents how to link together the results of fatigue crack growth tests, analytic fracture mechanics and experimental methods of fatigue lifetime predictions. The study at the beginning investigates the effect of mechanical load redistribution among failed and intact micro-structural bonds along fatigue crack growth to final crack at vulnerable locations in materials and structures under cyclic loads.

The microstructural load redistribution model is analytically formulated as a mechanical interaction between fatigue crack growth and fatigue endurance on the macroscopic level. The article in continuation investigates how to link the parameters of fatigue crack growth in fracture mechanics to parameters of fatigue life directly from the work done on crack growth determined by testing.

The article at the end illustrates the application of the analytic procedure for fatigue lifetime prediction that combines fracture mechanics and the load redistribution model for determination of SN curve parameters important in structural analysis and design. In this research the fatigue life time parameters are derived from a single fatigue crack growth experiment instead from normally required sets of fatigue tests for different loading conditions.

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