Low cycle fatigue behavior of additively manufactured Ti-6Al-4V under non-proportional and proportional loading

Stefano Bressan,Filippo Berto,Fumio Ogawa,Takamoto Itoh

doi:10.3221/igf-esis.48.03

Abstract

Experimental tests were conducted on additive manufactured Ti-6Al-4V titanium alloy to investigate the mechanical and crack properties under multiaxial cyclic loading. Selective Laser Sintering technique (SLS) was employed to fabricate four types of cylindrical hollow specimens. The typology of each specimen is defined by the orientation of the layers and by the application of a stress-relieving heat treatment after the production process. Stress-strain cyclic curves of the materials were obtained to investigate the material cyclic plastic behavior, that resulted independent of specimen variety. Strain-controlled multiaxial low cycle fatigue tests under proportional and non-proportional loading paths were carried out on the specimens. Not heat-treated specimens exhibited a higher low cycle fatigue resistance both for proportional and non-proportional loading. Drastic initial softening was detected in the majority of the tests. Additional hardening was detected in part of non-proportional tests, which is atypical for this alloy. The mutual influence of applied load and microstructural characteristics on fatigue life are finally discussed.

Highlights

I n the recent years, additive manufacturing (AM) or 3D printing fabrication technique has been increasingly applied for the production of a wide variety of mechanical components
Proportional and non-proportional low cycle fatigue tests have been conducted on four types of additively manufactured Ti-6Al-4V specimens
The specimen type is defined by the layer orientation post process stressrelieving heat treatment

Summary

INTRODUCTION

I n the recent years, additive manufacturing (AM) or 3D printing fabrication technique has been increasingly applied for the production of a wide variety of mechanical components. Uniaxial fatigue properties have been widely investigated and the number of cycles to failure resulted dependent on the additive manufacturing technique and the post process treatments [10,11,12,13,14,15]. Four types of specimens characterized by a different orientation of the layers and by the presence or absence of a post process stress-relieving heat treatment have been analyzed. The types of specimens are four, depending on the layer orientation and the post process heat treatment performed. The layer orientation seems having a minor influence on failure life compared to the heat-treatment case, similar to the trends of the static mechanical properties. Given that the crack initiation process was not investigated, it is impossible to determine whether the crack initiated from such external defects

Findings

DISCUSSION

CONCLUSIONS