Bending and Torsion Fatigue-Testing Machine Developed for Multiaxial Non-Proportional Loading

Fumio Ogawa,Takahiro Morishita,Stefano Bressan,Takamoto Itoh,Yusuke Shimizu

doi:10.3390/met9101115

Abstract

A new fatigue-testing machine was developed to perform high-cycle multiaxial fatigue tests at 50 Hz, in order to reduce testing time. The developed machine can combine bending and torsion loading and perform fatigue tests at a high frequency, under proportional and non-proportional loading conditions, where the principal stress direction changes during a cycle. The proportional loading is cyclic bending loading, and the non-proportional loading is cyclic, combining bending and reversed torsion loading. In this study, the effectiveness of the testing machine was verified by conducting tests under these loading conditions, using specimens of type 490A hot-rolled steel and type 304 stainless steel. The fatigue life linked to bending loading obtained using the new testing machine was slightly extended compared with that obtained using the conventional fatigue-testing machine. The fatigue life derived as a result of a combination of bending and torsion was comparable to that obtained using the conventional fatigue-testing machine, although a fatigue limit reduction of 100 MPa was observed compared to the former study. The feasibility of tests using the developed multiaxial fatigue-testing machine was confirmed.

Highlights

Machines and structures, such as vehicles, ships, and bridges, experience multiaxial fatigue loads, which leads to shortened fatigue life
Limited data exist on fatigue properties in high-cycle regions under non-proportional multiaxial fatigue; performing fatigue tests in high-cycle regions is time-consuming, and currently, only a small number of testing machines are suitable for non-proportional multiaxial fatigue in high-cycle regions
In the low-cycle region, fatigue endurance was extended under non-proportional loading compared with proportional loading, because additional hardening led to decreasing strain value, which dominated fatigue life under non-proportional loading

Summary

Introduction

Machines and structures, such as vehicles, ships, and bridges, experience multiaxial fatigue loads, which leads to shortened fatigue life. Many components are subjected to non-proportional multiaxial loading, in which the principal directions of stress and strain change during a cycle, further reducing fatigue life [1,2,3,4,5,6,7]. Regarding high-cycle multiaxial fatigue, Itoh et al performed stress-controlled tension–torsion multiaxial fatigue tests for structural rolled steel type SS400 [8]. In the low-cycle region, fatigue endurance was extended under non-proportional loading compared with proportional loading, because additional hardening led to decreasing strain value, which dominated fatigue life under non-proportional loading. The fatigue limit at 107 cycles was decreased under non-proportional loading [8].

Objectives

Results

Conclusion