There is no infinite fatigue life in metallic materials

TLDR

The shape of the S–N curve beyond 10⁷ cycles and the fatigue limit remain largely unknown, and statistical approaches using the standard deviation of the average fatigue limit are inadequate for reducing rupture risk; however, modern piezoelectric fatigue machines can reliably produce up to 10¹⁰ cycles in under a week. The study aims to explore the fatigue life range between 10⁶ and 10¹⁰ cycles to establish a safer modeling foundation. Accelerated fatigue tests at 20 kHz in the gigacyclic regime were conducted on typical aeronautical and space alloys to investigate their behavior.

Abstract

Generally, the shape of the S – N curve beyond 107 cycles is unknown except in some statistical approaches, and this is also true for the fatigue limit. In the case of a statistical approach, the standard deviation applied to the average fatigue limit is certainly not the best way to reduce the risk of rupture in fatigue. Only the exploration of the life range between 106 and 10 10 cycles will create a safer basis for modelling. Today, some piezoelectric fatigue machines are very reliable, capable of producing 10 10 cycles in less than 1 week. We based our research on accelerated fatigue tests which were performed at 20 kHz in the gigacyclic fatigue regime in order to study several typical alloys from the aeronautical and space industries.