Ultrasonic fatigue experiments with biaxial cruciform specimens

Pedro R Da Costa,Diogo Montalvão,Manuel Freitas,Luis Reis,T Palin-Luc,F Morel,A Carpinteri

doi:10.1051/matecconf/201930018004

Abstract

Fatigue studies of materials in simple or complex loading systems for any given lifetime is object of continuous research. This is due to the advancements on mechanical and structural components, as well as for new and innovative materials, which implies the knowledge of a materials response to all dynamic loads. The fatigue failure regime beyond what was once considered to be the fatigue limit (infinite life) is characterized between 107 and 109, known as Very High Cycle Fatigue regime. Due to the time consuming and wide energy consumption of conventional fatigue testing for such regime, fatigue tests under ultrasonic actuators are being used, capable of applying the dynamic loads at around 20 kHz. Nowadays, several variants of ultrasonic fatigue tests were already proposed and tested but it is still a somewhat limited fatigue test if compared to the conventional servo-hydraulic fatigue testing machines of general use. In this study, biaxial in plane stresses are induced in specially designed cruciform specimens with ultrasonic fatigue testing resonant principals. Two geometries were numerically analysed, manufactured and experimentally tested, the in-phase tension-tension (T-T) specimen and the out-of-phase compression-tension (C-T) specimen. All specific designed geometries go under a thorough numerical and several experiments analysis for their validation. The specimens showing a correct and as intended behaviour are led to failure.

Highlights

Many of every day mechanical devices and structures have many components subjected to dynamic and cyclic loadings, as cars, airplanes, trains, hydraulic machines and so on
Many of the mentioned components can reach in their life time higher than 107 cycles due to the high frequency of dynamic loads and/or long life in service
All specimens were painted black in one side for better measurement of the temperature by a thermal camera

Summary

Introduction

Many of every day mechanical devices and structures have many components subjected to dynamic and cyclic loadings, as cars, airplanes, trains, hydraulic machines and so on. To ensure the safety and reliability of the users and the machine every material employed to such components should be carefully chosen in accordance to the applied forces and life cycle. The study of the materials resistance and behaviour to fatigue damage will ensure a higher safety and a correct projection of key components in such mechanical devices and structures. Many of the mentioned components can reach in their life time higher than 107 cycles due to the high frequency of dynamic loads and/or long life in service. Many researchers as Bathias and Sonsino have determined that no real fatigue limit is ever present [1, 2]

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Results

Conclusion